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125 results on '"M. Unverzagt"'

1. Helicity dependent cross sections for the photoproduction of π0π± pairs from quasi-free nucleons

Author

D. Ghosal, V. Sokhoyan, A. Fix, S. Lutterer, S. Abt, P. Achenbach, F. Afzal, Z. Ahmed, J.R.M. Annand, M. Bashkanov, R. Beck, M. Biroth, N. Borisov, A. Braghieri, W.J. Briscoe, F. Cividini, C. Collicot, S. Costanza, A. Denig, M. Dieterle, A.S. Dolzhikov, E.J. Downie, P. Drexler, S. Fegan, S. Gardner, D.I. Glazier, I. Gorodnov, W. Gradl, M. Günther, D. Gurevich, L. Heijkenskjöld, D. Hornidge, G.M. Huber, N. Jermann, A. Käser, V.L. Kashevarov, M. Korolija, B. Krusche, A. Lazarev, K. Livingston, I.J.D. MacGregor, D.M. Manley, P.P. Martel, Ch. Meier, R. Miskimen, M. Mocanu, E. Mornacchi, C. Mullen, A. Neganov, A. Neiser, M. Ostrick, P. Otte, D. Paudyal, P. Pedroni, A. Powell, G. Reicherz, T. Rostomyan, K. Spieker, O. Steffen, I.I. Strakovsky, A. Thiel, M. Thiel, A. Thomas, M. Unverzagt, Yu.A. Usov, S. Wagner, N.K. Walford, D.P. Watts, D. Werthmüller, J. Wettig, L. Witthauer, M. Wolfes, and N. Zachariou

Subjects
Physics, QC1-999
Abstract

Photoproduction of π0π±-pairs from quasifree nucleons bound in the deuteron has been investigated to study the helicity dependence of this reaction. Measurements with a liquid deuterium target were used to extract the unpolarized cross sections for reactions on protons and neutrons. A deuterated, longitudinally polarized solid-butanol target, together with a circularly polarized photon beam, determined the double polarization observable E. From these results the spin-dependent cross sections σ1/2 and σ3/2, corresponding to the anti-parallel and parallel spin configurations of the beam photon and target nucleon, have been derived. The measurements were performed at the Mainz MAMI accelerator with tagged, circularly-polarized photon beams produced via bremsstrahlung from longitudinally polarized electron beams. The reaction products were detected with an almost 4π solid-angle covering calorimeter composed of the Crystal Ball and TAPS detectors, supplemented by plastic scintillation detectors for charged particle identification. The results are sensitive to sequential decays of nucleon resonances via intermediate states and also to the decay of nucleon resonances by emission of charged ρ mesons, and are compared to recent model results.

Published
2023
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2. Measurement of the beam-helicity asymmetry in photoproduction of π0η pairs on carbon, aluminum, and lead

Author

V. Sokhoyan, S. Prakhov, A. Fix, S. Abt, P. Achenbach, P. Adlarson, F. Afzal, P. Aguar-Bartolomé, Z. Ahmed, K. Altangerel, J.R.M. Annand, H.J. Arends, K. Bantawa, M. Bashkanov, R. Beck, M. Biroth, N.S. Borisov, A. Braghieri, W.J. Briscoe, S. Cherepnya, F. Cividini, C. Collicott, S. Costanza, A. Denig, M. Dieterle, E.J. Downie, P. Drexler, M.I. Ferretti Bondy, L.V. Fil'kov, S. Gardner, S. Garni, D.I. Glazier, I. Gorodnov, W. Gradl, M. Günther, G.M. Gurevich, L. Heijkenskjöld, D. Hornidge, G.M. Huber, A. Käser, V.L. Kashevarov, S. Kay, I. Keshelashvili, R. Kondratiev, M. Korolija, B. Krusche, A. Lazarev, K. Livingston, S. Lutterer, I.J.D. MacGregor, R. Macrae, D.M. Manley, P.P. Martel, J.C. McGeorge, D.G. Middleton, R. Miskimen, E. Mornacchi, C. Mullen, A. Mushkarenkov, A. Neganov, A. Neiser, M. Oberle, M. Ostrick, P.B. Otte, D. Paudyal, P. Pedroni, A. Powell, E. Rickert, G. Ron, T. Rostomyan, A. Sarty, C. Sfienti, K. Spieker, O. Steffen, I.I. Strakovsky, B. Strandberg, Th. Strub, I. Supek, A. Thiel, M. Thiel, A. Thomas, M. Unverzagt, Yu.A. Usov, S. Wagner, N.K. Walford, D.P. Watts, D. Werthmüller, J. Wettig, L. Witthauer, M. Wolfes, and N. Zachariou

Subjects
Physics, QC1-999
Abstract

The beam-helicity asymmetry was measured, for the first time, in photoproduction of π0η pairs on carbon, aluminum, and lead, with the A2 experimental setup at MAMI. The results are compared to an earlier measurement on a free proton and to the corresponding theoretical calculations. The Mainz model is used to predict the beam-helicity asymmetry for the nuclear targets. The present results indicate that the photoproduction mechanism for π0η pairs on nuclei is similar to photoproduction on a free nucleon. This process is dominated by the D33 partial wave with the ηΔ(1232) intermediate state.

Published
2020
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3. First measurement of helicity-dependent cross sections in π0η photoproduction from quasi-free nucleons

Author

A. Käser, M. Dieterle, L. Witthauer, S. Abt, P. Achenbach, P. Adlarson, F. Afzal, Z. Ahmed, J. Ahrens, J.R.M. Annand, H.J. Arends, M. Bashkanov, R. Beck, M. Biroth, N.S. Borisov, A. Braghieri, W.J. Briscoe, F. Cividini, C. Collicott, S. Costanza, A. Denig, E.J. Downie, P. Drexler, A. Fix, S. Garni, D.I. Glazier, I. Gorodnov, W. Gradl, M. Günther, G.M. Gurevich, L. Heijkenskjöld, D. Hornidge, G.M. Huber, V.L. Kashevarov, S. Kay, I. Keshelashvili, R. Kondratiev, M. Korolija, B. Krusche, A.B. Lazarev, V. Lisin, K. Livingston, S. Lutterer, I.J.D. MacGregor, D.M. Manley, P.P. Martel, V. Metag, W. Meyer, R. Miskimen, E. Mornacchi, A. Mushkarenkov, A.B. Neganov, A. Neiser, M. Oberle, M. Ostrick, P.B. Otte, D. Paudyal, P. Pedroni, A. Polonski, S.N. Prakhov, G. Reicherz, G. Ron, T. Rostomyan, A. Sarty, C. Sfienti, V. Sokhoyan, K. Spieker, O. Steffen, I.I. Strakovsky, Th. Strub, I. Supek, A. Thiel, M. Thiel, A. Thomas, M. Unverzagt, Yu.A. Usov, S. Wagner, N.K. Walford, D.P. Watts, D. Werthmüller, J. Wettig, M. Wolfes, and L. Zana

Subjects
Physics, QC1-999
Abstract

The helicity-dependent cross sections for the photoproduction of π0η pairs have been measured for the first time. The experiment was performed at the tagged photon facility of the Mainz MAMI accelerator with the combined Crystal Ball – TAPS calorimeter. The experiment used a polarized deuterated butanol target and a circularly polarized photon beam. This arrangement allowed the σ1/2 (photon and target spin antiparallel) and σ3/2 (parallel spins) components to be measured for quasi-free production of π0η pairs off protons and neutrons. The main finding is that the two helicity components contribute identically, within uncertainties, for both participant protons and neutrons. The absolute couplings for protons and neutrons are also identical. This means that nucleon resonances contributing to this reaction in the investigated energy range have almost equal electromagnetic helicity couplings, A1/2n,p and A3/2n,p. Identical couplings for protons and neutrons are typical for Δ resonances and identical A1/2 and A3/2 components are only possible for J≥3/2 states, which constrains possible contributions of nucleon resonances.

Published
2018
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4. First measurement of the polarization observable E and helicity-dependent cross sections in single π0 photoproduction from quasi-free nucleons

Author

M. Dieterle, L. Witthauer, F. Cividini, S. Abt, P. Achenbach, P. Adlarson, F. Afzal, Z. Ahmed, C.S. Akondi, J.R.M. Annand, H.J. Arends, M. Bashkanov, R. Beck, M. Biroth, N.S. Borisov, A. Braghieri, W.J. Briscoe, S. Costanza, C. Collicott, A. Denig, E.J. Downie, P. Drexler, M.I. Ferretti-Bondy, S. Gardner, S. Garni, D.I. Glazier, D. Glowa, W. Gradl, M. Günther, G.M. Gurevich, D. Hamilton, D. Hornidge, G.M. Huber, A. Käser, V.L. Kashevarov, S. Kay, I. Keshelashvili, R. Kondratiev, M. Korolija, B. Krusche, A.B. Lazarev, J.M. Linturi, V. Lisin, K. Livingston, S. Lutterer, I.J.D. MacGregor, J. Mancell, D.M. Manley, P.P. Martel, V. Metag, W. Meyer, R. Miskimen, E. Mornacchi, A. Mushkarenkov, A.B. Neganov, A. Neiser, M. Oberle, M. Ostrick, P.B. Otte, D. Paudyal, P. Pedroni, A. Polonski, S.N. Prakhov, A. Rajabi, G. Reicherz, G. Ron, T. Rostomyan, A. Sarty, C. Sfienti, M.H. Sikora, V. Sokhoyan, K. Spieker, O. Steffen, I.I. Strakovsky, Th. Strub, I. Supek, A. Thiel, M. Thiel, A. Thomas, M. Unverzagt, Yu.A. Usov, S. Wagner, N.K. Walford, D.P. Watts, D. Werthmüller, J. Wettig, M. Wolfes, and L. Zana

Subjects
Physics, QC1-999
Abstract

The double-polarization observable E and the helicity-dependent cross sections σ1/2 and σ3/2 have been measured for the first time for single π0 photoproduction from protons and neutrons bound in the deuteron at the electron accelerator facility MAMI in Mainz, Germany. The experiment used a circularly polarized photon beam and a longitudinally polarized deuterated butanol target. The reaction products, recoil nucleons and decay photons from the π0 meson were detected with the Crystal Ball and TAPS electromagnetic calorimeters. Effects from nuclear Fermi motion were removed by a kinematic reconstruction of the π0N final state. A comparison to data measured with a free proton target showed that the absolute scale of the cross sections is significantly modified by nuclear final-state interaction (FSI) effects. However, there is no significant effect on the asymmetry E since the σ1/2 and σ3/2 components appear to be influenced in a similar way. Thus, the best approximation of the two helicity-dependent cross sections for the free neutron is obtained by combining the asymmetry E measured with quasi-free neutrons and the unpolarized cross section corrected for FSI effects under the assumption that the FSI effects are similar for neutrons and protons.

Published
2017
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5. Threshold π0 photoproduction on transverse polarised protons at MAMI

Author

S. Schumann, P.B. Otte, C.S. Akondi, J.R.M. Annand, H.-J. Arends, R. Beck, A.M. Bernstein, N. Borisov, A. Braghieri, W.J. Briscoe, S. Cherepnya, C. Collicott, S. Costanza, E.J. Downie, M. Dieterle, C. Fernández-Ramírez, A. Fix, L.V. Fil'kov, S. Garni, D.I. Glazier, W. Gradl, G. Gurevich, P. Hall-Barrientos, D. Hamilton, D. Hornidge, D. Howdle, G.M. Huber, V.L. Kashevarov, I. Keshelashvili, R. Kondratiev, M. Korolija, B. Krusche, A. Lazarev, V. Lisin, K. Livingston, I.J.D. MacGregor, J. Mancel, D.M. Manley, P.P. Martel, E.F. McNicoll, W. Meyer, D. Middleton, R. Miskimen, A. Mushkarenkov, B.M.K. Nefkens, A. Neganov, A. Nikolaev, M. Oberle, M. Ostrick, H. Ortega, P. Ott, B. Oussena, D. Paudyal, P. Pedroni, A. Polonski, V.V. Polyanski, S. Prakhov, G. Reicherz, T. Rostomyan, A. Sarty, M.H. Sikora, V. Sokhoyan, O. Steffen, I.I. Strakovsky, Th. Strub, I. Supek, L. Tiator, A. Thomas, M. Unverzagt, Yu.A. Usov, D.P. Watts, D. Werthmüller, L. Witthauer, and M. Wolfes

Subjects
Threshold π0 photoproduction, Target asymmetry, Electromagnetic multipoles, Physics, QC1-999
Abstract

Polarisation-dependent differential cross sections σT associated with the target asymmetry T have been measured for the reaction γp→→pπ0 with transverse target polarisation from π0 threshold to photon energies of 190 MeV. The data were obtained using a frozen-spin butanol target with the Crystal Ball / TAPS detector set-up and the Glasgow photon tagging system at the Mainz Microtron MAMI. Results for σT have been used in combination with our previous measurements of the unpolarised cross section σ0 and the beam asymmetry Σ for a model-independent determination of S- and P-wave multipoles in the π0 threshold region, which includes for the first time a direct determination of the imaginary part of the E0+ multipole.

Published
2015
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6. The isospin structure of photoproduction of πη pairs from the nucleon in the threshold region

Author

A. Käser, J. Ahrens, J.R.M. Annand, H.J. Arends, K. Bantawa, P.A. Bartolome, R. Beck, V. Bekrenev, H. Berghäuser, A. Braghieri, D. Branford, W.J. Briscoe, J. Brudvik, S. Cherepnya, S. Costanza, B. Demissie, M. Dieterle, E.J. Downie, P. Drexler, L.V. Fil'kov, A. Fix, D.I. Glazier, D. Hamilton, E. Heid, D. Hornidge, D. Howdle, G.M. Huber, O. Jahn, I. Jaegle, T.C. Jude, V.L. Kashevarov, I. Keshelashvili, R. Kondratiev, M. Korolija, S.P. Kruglov, B. Krusche, V. Lisin, K. Livingston, I.J.D. MacGregor, Y. Maghrbi, J. Mancell, D.M. Manley, Z. Marinides, J.C. McGeorge, E. McNicoll, D. Mekterovic, V. Metag, S. Micanovic, D.G. Middleton, A. Mushkarenkov, A. Nikolaev, R. Novotny, M. Oberle, M. Ostrick, P. Otte, B. Oussena, P. Pedroni, F. Pheron, A. Polonski, S.N. Prakhov, J. Robinson, G. Rosner, T. Rostomyan, S. Schumann, M.H. Sikora, D.I. Sober, A. Starostin, I. Supek, M. Thiel, A. Thomas, M. Unverzagt, D.P. Watts, D. Werthmüller, and L. Witthauer

Subjects
Physics, QC1-999
Abstract

Photoproduction of πη-pairs from nucleons has been investigated from threshold up to incident photon energies of ≈ 1.4 GeV. The quasi-free reactions γp→pπ0η, γn→nπ0η, γp→nπ+η, and γn→pπ−η were for the first time measured from nucleons bound in the deuteron. The corresponding reactions from a free-proton target were also studied to investigate final-state interaction effects (for neutral pions the free-proton results could be compared to previous measurements; the γp→nπ+η reaction was measured for the first time). For the π0η final state coherent production via the γd→dπ0η reaction was also investigated. The experiments were performed at the tagged photon beam of the Mainz MAMI accelerator using an almost 4π coverage electromagnetic calorimeter composed of the Crystal Ball and TAPS detectors. The total cross sections for the four different final states obey the relation σ(pπ0η)≈σ(nπ0η)≈2σ(pπ−η)≈2σ(nπ+η) as expected for a dominant contribution from a Δ⋆→ηΔ(1232)→πηN reaction chain, which is also supported by the shapes of the invariant-mass distributions of nucleon–meson and π–η pairs. The experimental results are compared to the predictions from an isobar reaction model.

Published
2015
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7. Single $$\pi ^0$$ production off neutrons bound in deuteron with linearly polarized photons

Author

M. Günther, D. P. Watts, M. Bashkanov, R. A. Miskimen, S. Abt, C. S. Akondi, N. Jermann, Yu. A. Usov, O. Steffen, I. J. D. MacGregor, P. Pedroni, N. K. Walford, Nicholas Zachariou, Concettina Sfienti, S. N. Prakhov, D. Ghosal, S. Wagner, G. Reicherz, A. Powell, V. L. Kashevarov, A. Braghieri, Z. Ahmed, Th. Strub, Patrick Achenbach, Susanna Costanza, Andy Thomas, I. I. Strakovsky, M. Ostrick, M. Mocanu, Michaela Thiel, I. Supek, B. Krusche, J. Wettig, Lena Heijkenskjöld, J. R. M. Annand, R. Beck, K. Livingston, V. V. Kulikov, S. Lutterer, S. Fegan, S. Gardner, N. S. Borisov, I. Gorodnov, Ron L. Workman, C. Mullen, S. Kay, D. M. Manley, M. Korolija, A. B. Neganov, V. Sokhoyan, D. Hornidge, A. Thiel, A. G. Denig, M. Dieterle, K. Spieker, P. P. Martel, F. Afzal, Durga Paudyal, A. Kaeser, E. J. Downie, A. Lazarev, Lilian Witthauer, E. Mornacchi, W. Gradl, C. Meier, M. Wolfes, D. Werthmüller, M. Biroth, G. Gurevic, C. Collicott, P. B. Otte, P. Drexler, M. A. Martemianov, W. J. Briscoe, M. Unverzagt, T. Rostomyan, F. Cividini, Guy Ron, G. M. Huber, M. Oberle, D. I. Glazier, and M. I. Ferretti-Bondy

Subjects
Physics, Nuclear and High Energy Physics, Particle physics, Photon, Nuclear Theory, 010308 nuclear & particles physics, media_common.quotation_subject, Hadron, 01 natural sciences, Asymmetry, High Energy Physics - Experiment, High Energy Physics - Phenomenology, Pion, Isospin, 0103 physical sciences, Production (computer science), Center of mass, Nuclear Experiment, 010306 general physics, Crystal Ball, media_common
Abstract

The quasifree $\overrightarrow{\gamma} d\to\pi^0n(p)$ photon beam asymmetry, $\Sigma$, has been measured at photon energies, $E_\gamma$, from 390 to 610 MeV, corresponding to center of mass energy from 1.271 to 1.424 GeV, for the first time. The data were collected in the A2 hall of the MAMI electron beam facility with the Crystal Ball and TAPS calorimeters covering pion center-of-mass angles from 49 to 148$^\circ$. In this kinematic region, polarization observables are sensitive to contributions from the $\Delta (1232)$ and $N(1440)$ resonances. The extracted values of $\Sigma$ have been compared to predictions based on partial-wave analyses (PWAs) of the existing pion photoproduction database. Our comparison includes the SAID, MAID, and Bonn-Gatchina analyses; while a revised SAID fit, including the new $\Sigma$ measurements, has also been performed. In addition, isospin symmetry is examined as a way to predict $\pi^0n$ photoproduction observables, based on fits to published data in the channels $\pi^0p$, $\pi^+n$, and $\pi^-p$., Comment: 11 pages, 9 figures, 5 tables; fixed 2 glitches

Published
2021

8. Extracting the spin polarizabilities of the proton by measurement of Compton double-polarization observables

Author

Susanna Costanza, A. G. Denig, V. L. Kashevarov, V. Metag, C. Sfienti, W. Gradl, G. M. Huber, M. Oberle, D. Werthmüller, J. Wettig, M. Biroth, F. Afzal, P. B. Otte, V. Lisin, A. Polonski, V. Sokhoyan, A. B. Lazarev, Anthony W. Thomas, D. I. Glazier, K. Livingston, S. Lutterer, K. Spieker, J. Mancell, S. Gardner, N. S. Borisov, A. Käser, D. Hornidge, C. Collicott, A. Braghieri, A. B. Neganov, Th. Strub, A. Rajabi, D. P. Watts, Patrick Achenbach, J. R. M. Annand, H. J. Arends, P. Drexler, M. Ostrick, R. Kondratiev, Michaela Thiel, Lena Heijkenskjöld, M. I. Ferretti-Bondy, D. Glowa, M. Bashkanov, R. A. Miskimen, M. Korolija, S. N. Prakhov, Yu. A. Usov, O. Steffen, A. Thiel, G. M. Gurevich, David Manley, P. Pedroni, Lorenzo Zana, P. P. Martel, S. Garni, A. Neiser, I. Keshelashvili, David Hamilton, W. Meyer, B. Krusche, J. Linturi, M. Dieterle, Lilian Witthauer, S. Kay, S. Günther, S. Wagner, G. Reicherz, S. Abt, C. S. Akondi, A. J. Sarty, Reinhard Beck, I. Supek, I. Gorodnov, M. H. Sikora, Roderick M. Macrae, W. J. Briscoe, A. N. Mushkarenkov, T. Rostomyan, Guy Ron, E. J. Downie, M. Unverzagt, F. Cividini, P. Adlarson, Z. Ahmed, I. I. Strakovsky, C. Mullen, Durga Paudyal, M. Wolfes, A. Powell, N. K. Walford, E. Mornacchi, and I. J. D. MacGregor

Subjects
Nuclear reaction, Physics, Chiral perturbation theory, Proton, 010308 nuclear & particles physics, Resonance, 16. Peace & justice, 01 natural sciences, Baryon, 0103 physical sciences, Proton spin crisis, Atomic physics, 010306 general physics, Microtron, Spin-½
Abstract

The Compton double-polarization observable \ud Σ\ud 2\ud z\ud has been measured for the first time in the \ud Δ\ud (\ud 1232\ud )\ud resonance region using a circularly polarized photon beam incident on a longitudinally polarized proton target at the Mainz Microtron. This paper reports these results, together with the model-dependent extraction of four proton spin polarizabilities from fits to additional asymmetry data using either a dispersion relation calculation or a baryon chiral perturbation theory calculations with the weighted average of these two fits resulting in \ud γ\ud E\ud 1\ud E\ud 1\ud =\ud −\ud 2.87\ud ±\ud 0.52\ud ,\ud \ud γ\ud M\ud 1\ud M\ud 1\ud =\ud 2.70\ud ±\ud 0.43\ud ,\ud \ud γ\ud E\ud 1\ud M\ud 2\ud =\ud −\ud 0.85\ud ±\ud 0.72\ud , and \ud γ\ud M\ud 1\ud E\ud 2\ud =\ud 2.04\ud ±\ud 0.43\ud , in units of \ud 10\ud −\ud 4\ud fm\ud 4\ud .

Published
2020

9. Cross section for γn→π0n measured at the Mainz A2 experiment

Author

K. Livingston, S. Lutterer, S. Gardner, N. S. Borisov, M. Unverzagt, V. V. Kulikov, H. J. Arends, A. B. Lazarev, A. Neiser, Alfred Švarc, F. Cividini, A. Braghieri, F. Afzal, D. G. Middleton, B. Oussena, C. Collicott, D. P. Watts, K. Spieker, K. Bantawa, M. Bashkanov, R. A. Miskimen, M. Ostrick, S. Kay, C. Sfienti, V. E. Tarasov, Patrick Achenbach, Yu. A. Usov, G. M. Huber, A. E. Kudryavtsev, A. Käser, O. Steffen, P. Aguar-Bartolomé, V. L. Kashevarov, A. G. Denig, E. J. Downie, N. K. Walford, J. Wettig, E. Mornacchi, A. Thiel, J. Stahov, S. Fegan, Durga Paudyal, J. C. McGeorge, Nicholas Zachariou, V. Sokhoyan, I. J. D. MacGregor, M. I. Ferretti Bondy, M. A. Martemianov, D. Gurevich, D. Hornidge, D. Ghosal, S. Wagner, M. Wolfes, Anthony W. Thomas, D. I. Glazier, Guy Ron, Z. Ahmed, Susanna Costanza, Michaela Thiel, W. J. Briscoe, A. Powell, M. Günther, L. Tiator, I. I. Strakovsky, A. N. Mushkarenkov, S. A. Bulychjov, D. M. Manley, Lena Heijkenskjöld, P. P. Martel, R. Omerović, M. Korolija, R. Beck, C. Mullen, J. R. M. Annand, D. Werthmüller, M. Biroth, M. Hadžimehmedović, P. B. Otte, A. B. Neganov, P. Pedroni, W. Gradl, S. N. Prakhov, B. Krusche, P. Drexler, H. Osmanović, T. Rostomyan, I. Supek, I. Gorodnov, Ron L. Workman, Roderick M. Macrae, S. Abt, C. S. Akondi, and A. J. Sarty

Subjects
Physics, 010308 nuclear & particles physics, Nuclear Theory, 7. Clean energy, 01 natural sciences, Resonance (particle physics), Nuclear physics, Cross section (physics), Pion, Amplitude, Deuterium, Reaction dynamics, 0103 physical sciences, Neutron, Nuclear Experiment, 010306 general physics, Microtron
Abstract

The γ n → π 0 n differential cross section evaluated for 27 energy bins span the photon-energy range 290–813 MeV ( W = 1.195 –1.553 GeV) and the pion c.m. polar production angles, ranging from 18 ∘ to 162 ∘ , making use of model-dependent nuclear corrections to extract π 0 production data on the neutron from measurements on the deuteron target. Additionally, the total photoabsorption cross section was measured. The tagged photon beam produced by the 883 MeV electron beam of the Mainz Microtron MAMI was used for the π 0 -meson production. Our accumulation of 3.6 × 10 6 γ n → π 0 n events allowed a detailed study of the reaction dynamics. Our data are in reasonable agreement with previous A2 measurements and extend them to lower energies. The data are compared with predictions of previous said, maid, and BnGa partial-wave analyses and to the latest said fit MA19 that included our data. Selected photon-decay amplitudes N ∗ → γ n at the resonance poles are determined for the first time.

Published
2019

10. Experimental study of the $ \gamma p \rightarrow K^{0}\Sigma^{+}$, $ \gamma n \rightarrow K^{0} \Lambda$, and $ \gamma n \rightarrow K^{0} \Sigma^{0}$ reactions at the Mainz Microtron

Author

Anthony W. Thomas, D. I. Glazier, A. Mushkarenkov, M. Biroth, B. Krusche, H. J. Arends, I. Gorodnov, S. Abt, C. S. Akondi, E. J. Downie, Th. Strub, R. Beck, M. Unverzagt, A. J. Sarty, V. L. Kashevarov, M. Bashkanov, F. Cividini, D. G. Middleton, D. Gurevich, M. Wolfes, David Manley, Yu. A. Usov, O. Steffen, M. Ostrick, A. B. Neganov, Concettina Sfienti, Jrm Annand, W. Gradl, E. Mornacchi, M. Käser, S. Kay, C. Mullen, J. C. McGeorge, Igor Strakovsky, Lena Heijkenskjöld, P. Aguar-Bartolomé, I. J. D. MacGregor, A. Powell, A. Braghieri, J. Wettig, N. K. Walford, A. Thiel, M. Günther, M. I. Ferretti Bondy, A. Denig, P. P. Martel, M. Oberle, S. Costanza, S. N. Prakhov, S. Wagner, G. Ron, A. Lazarev, M. Thiel, D. Hornidge, M. Korolija, I. Supek, Lilian Witthauer, D. Werthmüller, A. Neiser, K. Spieker, W. J. Briscoe, F. Afzal, K. Livingston, S. Lutterer, S. Gardner, M. Dieterle, N. S. Borisov, P. Drexler, P. B. Otte, P. Pedroni, V. Sokhoyan, T. Rostomyan, B. Oussena, C. Collicott, D. P. Watts, K. Bantawa, Z. Ahmed, Patrick Achenbach, R. Miskimen, D. Paudyal, and G. M. Huber

Subjects
Physics, Nuclear and High Energy Physics, Particle physics, Hadron, Sigma, Nuclear fusion, Lambda, Nuclear Experiment, Legendre polynomials, Microtron
Abstract

This work measured $d\sigma/d\Omega$ for neutral kaon photoproduction reactions from threshold up to a c.m.\ energy of 1855MeV, focussing specifically on the $\gamma p\rightarrow K^0\Sigma^+$, $\gamma n\rightarrow K^0\Lambda$, and $\gamma n\rightarrow K^0 \Sigma^0$ reactions. Our results for $\gamma n\rightarrow K^0 \Sigma^0$ are the first-ever measurements for that reaction. These data will provide insight into the properties of $N^*$ resonances and, in particular, will lead to an improved knowledge about those states that couple only weakly to the $\pi N$ channel. Integrated cross sections were extracted by fitting the differential cross sections for each reaction as a series of Legendre polynomials and our results are compared with prior experimental results and theoretical predictions., Comment: 16 pages, 13 figures, 7 tables

Published
2019

11. Measurement of the beam-helicity asymmetry in photoproduction of π0η pairs on carbon, aluminum, and lead

Author

R. A. Miskimen, A. G. Denig, Durga Paudyal, M. Wolfes, I. Keshelashvili, Yu. A. Usov, O. Steffen, K. Spieker, P. Pedroni, Susanna Costanza, P. Aguar-Bartolomé, Concettina Sfienti, A. N. Mushkarenkov, M. Ostrick, D. G. Middleton, M. Günther, S. Garni, A. Powell, I. Supek, A. Käser, R. Beck, I. Gorodnov, M. Unverzagt, V. L. Kashevarov, F. Cividini, Roderick M. Macrae, L. V. Fil'kov, P. Adlarson, M. Oberle, S. Abt, E. J. Downie, Patrick Achenbach, D. P. Watts, S. Cherepnya, A. J. Sarty, K. Bantawa, G. M. Huber, Z. Ahmed, S. Kay, I. I. Strakovsky, T. Rostomyan, K. Livingston, S. Lutterer, B. Strandberg, S. Gardner, N. S. Borisov, C. Mullen, Guy Ron, D. I. Glazier, S. Wagner, H. J. Arends, W. J. Briscoe, A. B. Lazarev, Michaela Thiel, A. Neiser, A. Fix, A. Braghieri, Th. Strub, P. Drexler, F. Afzal, A. B. Neganov, Nicholas Zachariou, W. Gradl, J. Wettig, J. C. McGeorge, V. Sokhoyan, P. P. Martel, J. R. M. Annand, D. Hornidge, E. Mornacchi, I. J. D. MacGregor, M. Korolija, David Manley, N. K. Walford, B. Krusche, K. Altangerel, E. Rickert, M. Biroth, P. B. Otte, R. Kondratiev, G. M. Gurevich, S. N. Prakhov, Lilian Witthauer, M. Dieterle, Lena Heijkenskjöld, M. I. Ferretti Bondy, Andy Thomas, A. Thiel, D. Werthmüller, C. Collicott, and M. Bashkanov

Subjects
Nuclear and High Energy Physics, Proton, media_common.quotation_subject, Nuclear Theory, chemistry.chemical_element, 7. Clean energy, 01 natural sciences, Asymmetry, Nuclear physics, Aluminium, 0103 physical sciences, Intermediate state, Nuclear Experiment, 010306 general physics, QC, media_common, Physics, 010308 nuclear & particles physics, Helicity, lcsh:QC1-999, 3. Good health, chemistry, High Energy Physics::Experiment, Nucleon, Carbon, lcsh:Physics, Beam (structure)
Abstract

The beam-helicity asymmetry was measured, for the first time, in photoproduction of $\pi^{0}\eta$ pairs on carbon, aluminum, and lead, with the A2 experimental setup at MAMI. The results are compared to an earlier measurement on a free proton and to the corresponding theoretical calculations. The Mainz model is used to predict the beam-helicity asymmetry for the nuclear targets. The present results indicate that the photoproduction mechanism for $\pi^{0}\eta$ pairs on nuclei is similar to photoproduction on a free nucleon. This process is dominated by the $D_{33}$ partial wave with the $\eta\Delta(1232)$ intermediate state., Comment: Accepted for publication in Physics Letters B (2020)

Published
2020

12. Measurement of the decay η′→π0π0η at MAMI

Author

Z. Ahmed, David Manley, K. Livingston, S. Gardner, David Hamilton, N. S. Borisov, I. Supek, I. Keshelashvili, H. J. Arends, Ron L. Workman, T. Rostomyan, A. G. Denig, Michaela Thiel, Durga Paudyal, J. C. McGeorge, S. Wagner, M. Ostrick, M. Wolfes, A. B. Lazarev, Lorenzo Zana, B. Oussena, C. Collicott, K. Spieker, A. B. Neganov, M. Korolija, P. P. Martel, D. P. Watts, A. Braghieri, Th. Strub, P. Ott, J. R. M. Annand, R. Kondratiev, D. G. Middleton, C. S. Akondi, G. M. Gurevich, D. Hornidge, S. Kay, C. Sfienti, A. J. Sarty, I. J. D. MacGregor, A. Käser, V. L. Kashevarov, B. Krusche, A. Neiser, W. Gradl, Lilian Witthauer, Yu. A. Usov, O. Steffen, S. N. Prakhov, R. Miskimen, Andy Thomas, A. Thiel, P. Pedroni, A. Polonski, Igor Strakovsky, Susanna Costanza, J. Linturi, Reinhard Beck, M. Dieterle, M. I. Ferretti Bondy, D. Glowa, Guy Ron, S. Garni, L. Tiator, W. J. Briscoe, P. B. Otte, D. I. Glazier, J. Wettig, V. Sokhoyan, F. Afzal, G. M. Huber, M. Oberle, M. Unverzagt, A. Rajabi, F. Cividini, P. Adlarson, A. N. Mushkarenkov, E. J. Downie, and D. Werthmüller

Subjects
Cusp (singularity), Physics, Meson, 010308 nuclear & particles physics, Resolution (electron density), Magnitude (mathematics), Scattering length, 01 natural sciences, Nuclear physics, 0103 physical sciences, 010306 general physics, Microtron, Parametrization, Sign (mathematics)
Abstract

An experimental study of the η′→π0π0η→6γ decay has been conducted with the best up-to-date statistical accuracy, by measuring η′ mesons produced in the γp→η′p reaction with the A2 tagged-photon facility at the Mainz Microtron, MAMI. The results obtained for the standard parametrization of the η′→π0π0η matrix element are consistent with the most recent results for η′→ππη decays, but have smaller uncertainties. The available statistics and experimental resolution allowed, for the first time, an observation of a structure below the π+π- mass threshold, the magnitude and sign of which, checked within the framework of the nonrelativistic effective-field theory, demonstrated good agreement with the cusp that was predicted based on the ππ scattering length combination, a0-a2, extracted from K→3π decays.

Published
2018

13. High-statistics measurement of the η→3π0 decay at the Mainz Microtron

Author

D. Paudyal, E. Mornacchi, V. L. Kashevarov, Lena Heijkenskjöld, I. J. D. MacGregor, J. Ahrens, Igor Strakovsky, R. Kondratiev, R. Miskimen, C. B. Hamill, M. Oberle, M. Biroth, F. Afzal, A. Käser, A. Lazarev, D. I. Glazier, G. M. Gurevich, I. Supek, C. Sfienti, F. Cividini, M. Bashkanov, P. Drexler, M. Dieterle, L. Zana, I. Gorodnov, A. Mushkarenkov, M. I. Ferretti Bondy, N. K. Walford, A. Thiel, Patrick Achenbach, S. Cherepnya, Yu. A. Usov, O. Steffen, I. Keshelashvili, E. J. Downie, S. Kay, Reinhard Beck, A. Braghieri, D. Hornidge, J. R. M. Annand, P. Aguar-Bartolomé, David Manley, V. Lisin, A. Fix, A. Denig, A. Polonski, P. Pedroni, M. Wolfes, A. B. Neganov, D. Werthmüller, S. Costanza, A. Neiser, M. Unverzagt, S. Abt, S. Wagner, Th. Strub, D. G. Middleton, W. J. Briscoe, S. N. Prakhov, Z. Ahmed, G. Ron, A. Thomas, G. M. Huber, P. Adlarson, Lilian Witthauer, A. J. Sarty, P. B. Otte, C. Collicott, D. P. Watts, J. C. McGeorge, K. Bantawa, P. P. Martel, M. Korolija, B. Krusche, K. Livingston, S. Lutterer, V. Sokhoyan, B. Strandberg, S. Gardner, N. S. Borisov, T. Rostomyan, H. J. Arends, L. V. Fil'kov, W. Gradl, J. Wettig, M. Thiel, M. Ostrick, S. Garni, and K. Spieker

Subjects
Cusp (singularity), Physics, Meson, 010308 nuclear & particles physics, Dalitz plot, 01 natural sciences, 7. Clean energy, Moment (mathematics), Nonlinear system, Quadratic equation, 0103 physical sciences, Statistics, High Energy Physics::Experiment, Nuclear Experiment, 010306 general physics, Microtron, Parametrization
Abstract

The largest, at the moment, statistics of 7×106η→3π0 decays, based on 6.2×107η mesons produced in the γp→ηp reaction, has been accumulated by the A2 Collaboration at the Mainz Microtron, MAMI. It allowed a detailed study of the η→3π0 dynamics beyond its conventional parametrization with just the quadratic slope parameter α and enabled, for the first time, a measurement of the second-order term and a better understanding of the cusp structure in the neutral decay. The present data are also compared to recent theoretical calculations that predict a nonlinear dependence along the quadratic distance from the Dalitz-plot center.

Published
2018

14. Experimental study of the γp→π0ηp reaction with the A2 setup at the Mainz Microtron

Author

C. B. Hamill, K. Livingston, S. Lutterer, S. Garni, W. Gradl, B. Strandberg, S. Gardner, N. S. Borisov, N. K. Walford, D. Paudyal, A. Polonski, C. Sfienti, B. Krusche, E. J. Downie, A. Lazarev, K. Spieker, S. Wagner, M. Günther, M. Biroth, P. Pedroni, M. Bashkanov, D. Werthmüller, S. Abt, M. Dieterle, M. Ostrick, M. Oberle, C. Collicott, D. P. Watts, L. Zana, M. I. Ferretti Bondy, J. Wettig, Yu. A. Usov, M. Unverzagt, O. Steffen, A. Thomas, R. Kondratiev, K. Bantawa, Z. Ahmed, F. Cividini, David Manley, A. Fix, A. J. Sarty, V. L. Kashevarov, Lena Heijkenskjöld, G. M. Huber, P. Adlarson, S. Kay, M. Thiel, P. Aguar-Bartolomé, I. Gorodnov, S. N. Prakhov, P. Drexler, A. Braghieri, D. Hornidge, G. Ron, V. Sokhoyan, V. Lisin, F. Afzal, T. Rostomyan, Th. Strub, H. J. Arends, Reinhard Beck, D. G. Middleton, E. Mornacchi, Lilian Witthauer, J. Ahrens, Patrick Achenbach, R. Miskimen, Igor Strakovsky, L. V. Fil'kov, W. J. Briscoe, I. J. D. MacGregor, I. Supek, A. B. Neganov, G. M. Gurevich, J. R. M. Annand, D. I. Glazier, A. Thiel, A. Denig, A. Mushkarenkov, S. Costanza, A. Neiser, J. C. McGeorge, M. Wolfes, P. B. Otte, A. Käser, P. P. Martel, M. Korolija, I. Keshelashvili, and S. Cherepnya

Subjects
Physics, Particle physics, Basis (linear algebra), 010308 nuclear & particles physics, Observable, 7. Clean energy, 01 natural sciences, Reaction dynamics, 0103 physical sciences, Photon polarization, Range (statistics), Photon beam, Nuclear Experiment, 010306 general physics, Microtron, Energy (signal processing)
Abstract

The data available from the A2 Collaboration at MAMI were analyzed to select the γp→π0ηp reaction on an event-by-event basis, which allows for partial-wave analyses of three-body final states to obtain more reliable results, compared to fits to measured distributions. These data provide the world's best statistical accuracy in the energy range from threshold to Eγ=1.45 GeV, allowing a finer energy binning in the measurement of all observables needed for understanding the reaction dynamics. The results obtained for the measured observables are compared to existing models, and the impact from the new data is checked by the fit with the revised Mainz model.

Published
2018

15. First measurement of helicity-dependent cross sections in π0η photoproduction from quasi-free nucleons

Author

J. Wettig, A. Käser, M. Bashkanov, S. Costanza, M. Dieterle, R. Miskimen, S. Wagner, M. Thiel, G. Reicherz, P. Adlarson, F. Cividini, Yu. A. Usov, O. Steffen, R. Kondratiev, H. J. Arends, B. Krusche, V. L. Kashevarov, Lena Heijkenskjöld, P. P. Martel, M. Korolija, M. Unverzagt, E. Mornacchi, I. Supek, F. Afzal, A. Lazarev, S. Abt, C. Collicott, D. P. Watts, G. M. Huber, M. Ostrick, I. J. D. MacGregor, S. N. Prakhov, G. Ron, J. Ahrens, G. M. Gurevich, A. B. Neganov, A. Thiel, M. Günther, P. B. Otte, D. Paudyal, L. Zana, N. K. Walford, W. Gradl, E. J. Downie, Lilian Witthauer, K. Livingston, S. Lutterer, M. Biroth, W. Meyer, C. Sfienti, A. Braghieri, V. Sokhoyan, N. S. Borisov, D. Hornidge, Igor Strakovsky, V. Lisin, T. Rostomyan, A. J. Sarty, D. Werthmüller, Reinhard Beck, David Manley, A. Fix, Th. Strub, S. Kay, D. I. Glazier, A. Mushkarenkov, A. Polonski, A. Thomas, I. Gorodnov, W. J. Briscoe, M. Wolfes, M. Oberle, P. Drexler, P. Pedroni, Volker Metag, Z. Ahmed, Patrick Achenbach, J. R. M. Annand, A. Denig, A. Neiser, S. Garni, K. Spieker, and I. Keshelashvili

Subjects
Nuclear and High Energy Physics, Photon, Nuclear Theory, FOS: Physical sciences, 7. Clean energy, 01 natural sciences, Nuclear physics, Pion, 0103 physical sciences, Neutron, ddc:530, Nuclear Experiment (nucl-ex), 010306 general physics, Nuclear Experiment, Spin-½, Physics, 010308 nuclear & particles physics, Helicity, lcsh:QC1-999, 3. Good health, Deuterium, Nucleon, lcsh:Physics, Crystal Ball, reaction gamma-p, polarization, eta, mesons, mami, Pi(0)-pairs, photon, proton, pairs
Abstract

The helicity-dependent cross sections for the photoproduction of $\pi^0\eta$ pairs have been measured for the first time. The experiment was performed at the tagged photon facility of the Mainz MAMI accelerator with the combined Crystal Ball - TAPS calorimeter. The experiment used a polarized deuterated butanol target and a circularly polarized photon beam. This arrangement allowed the $\sigma_{1/2}$ (photon and target spin antiparallel) and $\sigma_{3/2}$ (parallel spins) components to be measured for quasi-free production of $\pi^0\eta$ pairs off protons and neutrons. The main finding is that the two helicity components contribute identically, within uncertainties, for both participant protons and neutrons. The absolute couplings for protons and neutrons are also identical. This means that nucleon resonances contributing to this reaction in the investigated energy range have almost equal electromagnetic helicity couplings, $A_{1/2}^{n,p}$ and $A_{3/2}^{n,p}$. Identical couplings for protons and neutrons are typical for $\Delta$ resonances and identical $A_{1/2}$ and $A_{3/2}$ components are only possible for $J\geq 3/2$ states, which constrains possible contributions of nucleon resonances., Comment: accepted for publication in Phys. Lett. B

Published
2018

16. Photoproduction of π 0 mesons off protons and neutrons in the second and third nucleon resonance regions

Author

S. Kay, D. Gurevich, V. Metag, M. Wolfes, M. Bashkanov, H. J. Arends, Igor Strakovsky, S. N. Prakhov, G. Ron, B. Krusche, Lilian Witthauer, A. B. Neganov, M. Dieterle, M. Günther, R. Kondratiev, L. V. Fil'kov, S. Cherepnya, J. Ahrens, R. Miskimen, Yu. A. Usov, V. Sokhoyan, O. Steffen, F. Afzal, S. Wagner, I. Gorodnov, M. Oberle, D. I. Glazier, P. Drexler, F. Cividini, T. Rostomyan, M. Ostrick, M. Unverzagt, C. Sfienti, A. Thiel, G. M. Huber, K. Livingston, S. Lutterer, David Manley, A. Mushkarenkov, A. Lazarev, N. S. Borisov, A. Braghieri, D. Hornidge, J. R. M. Annand, V. Lisin, K. Spieker, J. C. McGeorge, N. K. Walford, A. Denig, S. Costanza, A. Neiser, D. Paudyal, A. Polonski, I. Keshelashvili, S. Abt, Th. Strub, I. Supek, D. G. Middleton, A. Thomas, A. J. Sarty, V. L. Kashevarov, Lena Heijkenskjöld, S. Garni, B. Oussena, P. Pedroni, L. Zana, C. Collicott, D. P. Watts, Z. Ahmed, E. J. Downie, D. Werthmüller, Reinhard Beck, W. J. Briscoe, P. P. Martel, M. Korolija, A. Käser, P. B. Otte, W. Gradl, P. Aguar Bartolomé, J. Wettig, M. Thiel, M. Biroth, E. Mornacchi, and I. J. D. MacGregor

Subjects
Physics, Nuclear reaction, Proton, Meson, 010308 nuclear & particles physics, Hadron, Nuclear Theory, 7. Clean energy, 01 natural sciences, 3. Good health, Nuclear physics, Pion, Isospin, 0103 physical sciences, tagged photon spectrometer, polarization observable E, cross-sections, pion-photoproduction, baryon resonances, deuteron, MAMI, asymmetry, microtron, threshold, Neutron, ddc:530, 010306 general physics, Nucleon, Nuclear Experiment
Abstract

Photoproduction of mesons off quasi-free nucleons bound in the deuteron allows to study the electromagnetic excitation spectrum of the neutron and the isospin structure of the excitation of nucleon resonances. The database for such reactions is much more sparse than for free proton targets. Single $\pi^0$ photoproduction off quasi-free nucleons from the deuteron was experimentally studied. Nuclear effects were investigated by a comparison of the results for free protons and quasi-free protons and used as a correction for the quasi-free neutron data. The experiment was performed at the tagged photon beam of the Mainz MAMI accelerator for photon energies between 0.45~GeV and 1.4~GeV, using an almost $4\pi$ electromagnetic calorimeter composed of the Crystal Ball and TAPS detectors. A complete kinematic reconstruction of the final state removed the effects of Fermi motion. Reaction model predictions and PWA for $\gamma n\rightarrow n\pi^{0}$, based on fits to data for the other isospin channels, disagreed between themselves and no model provided a good description of the new data. The results demonstrate clearly the importance of a measurement of the fully neutral final state for the isospin decomposition of the cross section. Model refits, for example from the Bonn-Gatchina analysis, show that the new and the previous data for the other three isospin channels can be simultaneously described when the contributions of several partial waves are modified. The results are also relevant for the suppression of the higher resonance bumps in total photoabsorption on nuclei, which are not well understood., Comment: excepted for publication in Phys. Rev. C

Published
2018

17. Threshold π0 photoproduction on transverse polarised protons at MAMI

Author

V. Sokhoyan, S. Costanza, B. Krusche, H. J. Arends, G. M. Huber, T. Rostomyan, Lothar Tiator, V. L. Kashevarov, M. H. Sikora, M. Ostrick, L. V. Fil'kov, P. Hall-Barrientos, S. N. Prakhov, C. S. Akondi, W. Gradl, A. Polonski, S. Garni, D. I. Glazier, A. J. Sarty, A. Braghieri, D. Hornidge, B. Oussena, C. Collicott, E. J. Downie, A. Thomas, A. Mushkarenkov, V. Lisin, E. F. McNicoll, D. P. Watts, K. Livingston, Durga Paudyal, I. Keshelashvili, David Hamilton, R. Miskimen, Lilian Witthauer, N. S. Borisov, W. Meyer, M. Wolfes, P. Pedroni, V. V. Polyanski, R. Kondratiev, J. Mancel, G. Reicherz, Igor Strakovsky, A. B. Neganov, César Fernández-Ramírez, A. B. Lazarev, A. Nikolaev, G. M. Gurevich, B. M. K. Nefkens, D. G. Middleton, Th. Strub, H. Ortega, M. Dieterle, Reinhard Beck, Yu. A. Usov, O. Steffen, J. R. M. Annand, W. J. Briscoe, S. Cherepnya, P. Ott, I. J. D. MacGregor, David Manley, A. Fix, D. Werthmüller, P. P. Martel, Aron M. Bernstein, I. Supek, M. Oberle, M. Unverzagt, D. Howdle, M. Korolija, S. Schumann, and P. B. Otte

Subjects
Physics, Nuclear and High Energy Physics, Photon, Chiral perturbation theory, Scattering, media_common.quotation_subject, Asymmetry, Nuclear physics, Cross section (physics), Transverse plane, Atomic physics, Nuclear Experiment, Multipole expansion, Microtron, media_common
Abstract

Polarisation-dependent differential cross sections σ T associated with the target asymmetry T have been measured for the reaction γ p → → p π 0 with transverse target polarisation from π 0 threshold to photon energies of 190 MeV. The data were obtained using a frozen-spin butanol target with the Crystal Ball / TAPS detector set-up and the Glasgow photon tagging system at the Mainz Microtron MAMI. Results for σ T have been used in combination with our previous measurements of the unpolarised cross section σ 0 and the beam asymmetry Σ for a model-independent determination of S- and P-wave multipoles in the π 0 threshold region, which includes for the first time a direct determination of the imaginary part of the E 0 + multipole.

Published
2015

18. Study of η and η′ Photoproduction at MAMI

Author

H. J. Arends, T. Rostomyan, F. Afzal, S. Garni, P. Pedroni, A. Rajabi, Reinhard Beck, S. Costanza, M. Oberle, K. Spieker, B. Oussena, E. McNicol, A. Thomas, G. M. Huber, C. Collicott, J. C. McGeorge, D. P. Watts, D. I. Glazier, M. Unverzagt, K. Livingston, B. Strandberg, S. Gardner, A. Mushkarenkov, R. Kondratiev, Concettina Sfienti, R. Miskimen, A. Thiel, J. R. M. Annand, V. V. Polyanski, J. Wettig, G. M. Gurevich, S. Schumann, M. F. Taragin, Th. Strub, Michaela Thiel, V. L. Kashevarov, F. Cividini, B. Krusche, V. Sokhoyan, A. Neiser, L. Tiator, Igor Strakovsky, W. J. Briscoe, A. Braghieri, D. Hornidge, David Manley, V. Lisin, David Hamilton, A. Fix, D. Glowa, J. Mancell, M. Ostrick, P. B. Otte, M. Dieterle, O. Steffen, J. Linturi, W. Gradl, D. G. Middleton, I. Keshelashvili, S. N. Prakhov, P. Ott, P. P. Martel, S. Kay, M. Korolija, Ron L. Workman, Roderick M. Macrae, L. V. Fil'kov, L. Zana, G. Rosner, A. Käser, D. Howdle, C. S. Akondi, Lilian Witthauer, D. M. Schott, A. J. Sarty, S. Wagner, I. Supek, G. Reicherz, M. I. Ferretti Bondy, Z. Ahmed, P. Adlarson, E. J. Downie, D. Werthmüller, C. Mullen, A. G. Denig, Durga Paudyal, M. Wolfes, R. F. B. Codling, E. Mornacchi, I. J. D. MacGregor, and J. Robinson

Subjects
Cusp (singularity), Physics, Particle physics, Photon, Proton, 010308 nuclear & particles physics, General Physics and Astronomy, 01 natural sciences, Nuclear physics, Cross section (physics), Excited state, 0103 physical sciences, Isobar, 010306 general physics, Microtron, Crystal Ball
Abstract

The reactions γp→ηp and γp→η′p are measured from their thresholds up to the center-of-mass energy W=1.96 GeV with the tagged-photon facilities at the Mainz Microtron, MAMI. Differential cross sections are obtained with unprecedented statistical accuracy, providing fine energy binning and full production-angle coverage. A strong cusp is observed in the total cross section for η photoproduction at the energies in the vicinity of the η′ threshold, W=1896 MeV (Eγ=1447 MeV). Within the framework of a revised ηMAID isobar model, the cusp, in connection with a steep rise of the η′ total cross section from its threshold, can only be explained by a strong coupling of the poorly known N(1895)1/2− state to both ηp and η′p. Including the new high-accuracy results in the ηMAID fit to available η and η′ photoproduction data allows the determination of the N(1895)1/2− properties.

Published
2017

19. First measurement of the polarization observable E and helicity-dependent cross sections in single π 0 photoproduction from quasi-free nucleons

Author

David Hamilton, T. Rostomyan, M. Bashkanov, W. Meyer, D. I. Glazier, P. B. Otte, R. Miskimen, L. Zana, Concettina Sfienti, Yu. A. Usov, O. Steffen, V. L. Kashevarov, I. Supek, A. G. Denig, P. P. Martel, V. Lisin, Durga Paudyal, K. Livingston, Reinhard Beck, Susanna Costanza, A. Polonski, M. H. Sikora, A. B. Lazarev, S. Lutterer, A. Käser, M. Wolfes, F. Afzal, R. Kondratiev, S. N. Prakhov, A. Braghieri, S. Gardner, S. Kay, Michaela Thiel, Guy Ron, Th. Strub, F. Cividini, N. S. Borisov, A. Rajabi, C. Collicott, S. Abt, W. J. Briscoe, G. M. Gurevich, D. P. Watts, Z. Ahmed, Andy Thomas, A. Thiel, E. J. Downie, E. Mornacchi, D. M. Manley, M. Korolija, G. M. Huber, H. J. Arends, D. Glowa, C. S. Akondi, Patrick Achenbach, S. Wagner, G. Reicherz, B. Krusche, A. J. Sarty, I. Keshelashvili, I. J. D. MacGregor, Igor Strakovsky, D. Werthmüller, J. R. M. Annand, M. Unverzagt, V. Sokhoyan, J. Wettig, J. Linturi, K. Spieker, M. Dieterle, M. Ostrick, J. Mancell, P. Pedroni, S. Garni, M. Biroth, N. K. Walford, P. Adlarson, P. Drexler, M. Oberle, Volker Metag, A. N. Mushkarenkov, A. Neiser, M. I. Ferretti-Bondy, D. Hornidge, Lilian Witthauer, A. B. Neganov, W. Gradl, and M. Günther

Subjects
Nuclear and High Energy Physics, Photon, Meson, Proton, Nuclear Theory, 01 natural sciences, 7. Clean energy, Nuclear physics, Recoil, 0103 physical sciences, Neutron, ddc:530, 010306 general physics, Nuclear Experiment, Physics, 010308 nuclear & particles physics, lcsh:QC1-999, 3. Good health, Nuclear cross section, Atomic physics, Nucleon, i-circle-dot, meson photoproduction, eta-photoproduction, baryon resonances, deuteron, neutrons, protons, asymmetry, photon, pairs, Crystal Ball, lcsh:Physics
Abstract

The double-polarization observable $E$ and the helicity-dependent cross sections $\sigma_{1/2}$ and $\sigma_{3/2}$ have been measured for the first time for single $\pi^{0}$ photoproduction from protons and neutrons bound in the deuteron at the electron accelerator facility MAMI in Mainz, Germany. The experiment used a circularly polarized photon beam and a longitudinally polarized deuterated butanol target. The reaction products, recoil nucleons and decay photons from the $\pi^0$ meson were detected with the Crystal Ball and TAPS electromagnetic calorimeters. Effects from nuclear Fermi motion were removed by a kinematic reconstruction of the $\pi^{0}N$ final state. A comparison to data measured with a free proton target showed that the absolute scale of the cross sections is significantly modified by nuclear final-state interaction (FSI) effects. However, there is no significant effect on the asymmetry $E$ since the $\sigma_{1/2}$ and $\sigma_{3/2}$ components appear to be influenced in a similar way. Thus, the best approximation of the two helicity-dependent cross sections for the free neutron is obtained by combining the asymmetry $E$ measured with quasi-free neutrons and the unpolarized cross section corrected for FSI effects under the assumption that the FSI effects are similar for neutrons and protons., Comment: accepted for publication in Phys. Lett. B

Published
2017

20. Helicity-dependent cross sections and double-polarization observable E in η photoproduction from quasifree protons and neutrons

Author

H. J. Arends, V. Metag, S. Kay, David Manley, S. Garni, R. Kondratiev, J. R. M. Annand, K. Spieker, G. M. Huber, David Hamilton, K. Livingston, S. Lutterer, P. Pedroni, S. Gardner, A. Denig, N. S. Borisov, M. Biroth, F. Afzal, M. Oberle, W. Meyer, S. Wagner, C. Sfienti, F. Cividini, R. Miskimen, M. Unverzagt, G. Reicherz, A. Neiser, Igor Strakovsky, G. M. Gurevich, Z. Ahmed, Th. Strub, A. Rajabi, E. Mornacchi, D. I. Glazier, W. Gradl, I. Supek, Patrick Achenbach, I. J. D. MacGregor, M. Bashkanov, M. Günther, V. L. Kashevarov, A. Mushkarenkov, N. K. Walford, I. Keshelashvili, J. Wettig, M. Dieterle, P. Drexler, M. I. Ferretti-Bondy, M. Thiel, Yu. A. Usov, J. Mancell, O. Steffen, D. Paudyal, D. Glowa, A. Käser, P. B. Otte, Reinhard Beck, P. P. Martel, M. Korolija, W. J. Briscoe, A. Lazarev, L. Zana, V. Sokhoyan, T. Rostomyan, M. H. Sikora, C. Collicott, D. P. Watts, S. Abt, C. S. Akondi, A. B. Neganov, J. Linturi, A. J. Sarty, A. Polonski, M. Wolfes, B. Krusche, M. Ostrick, A. Thomas, A. Thiel, S. N. Prakhov, G. Ron, S. Costanza, Lilian Witthauer, A. Braghieri, D. Hornidge, V. Lisin, E. J. Downie, and D. Werthmüller

Subjects
Physics, Excitation function, Photon, 010308 nuclear & particles physics, Nuclear Theory, Bremsstrahlung, Polarization (waves), 01 natural sciences, Helicity, Nuclear physics, 0103 physical sciences, Neutron, Atomic physics, Nuclear Experiment, 010306 general physics, Nucleon, Crystal Ball
Abstract

Precise helicity-dependent cross sections and the double-polarization observable E were measured for η photoproduction from quasifree protons and neutrons bound in the deuteron. The η→2γ and η→3π0→6γ decay modes were used to optimize the statistical quality of the data and to estimate systematic uncertainties. The measurement used the A2 detector setup at the tagged photon beam of the electron accelerator MAMI in Mainz. A longitudinally polarized deuterated butanol target was used in combination with a circularly polarized photon beam from bremsstrahlung of a longitudinally polarized electron beam. The reaction products were detected with the electromagnetic calorimeters Crystal Ball and TAPS, which covered 98% of the full solid angle. The results show that the narrow structure observed earlier in the unpolarized excitation function of η photoproduction off the neutron appears only in reactions with antiparallel photon and nucleon spin (σ1/2). It is absent for reactions with parallel spin orientation (σ3/2) and thus very probably related to partial waves with total spin 1/2. The behavior of the angular distributions of the helicity-dependent cross sections was analyzed by fitting them withLegendre polynomials. The results are in good agreement with a model from the Bonn-Gatchina group, which uses an interference of P11 and S11 partial waves to explain the narrow structure.

Published
2017

21. Measurement of the ω→π0e+e− and η→e+e−γ Dalitz decays with the A2 setup at the Mainz Microtron

Author

S. N. Prakhov, Lilian Witthauer, P. Pedroni, Andy Thomas, J. Wettig, S. Garni, E. J. Downie, I. Keshelashvili, K. Spieker, E. F. McNicoll, J. Robinson, P. Drexler, V. Sokhoyan, T. Rostomyan, Michaela Thiel, A. Polonski, Z. Ahmed, R. Kondratiev, G. Rosner, D. M. Manley, G. M. Gurevich, S. Wagner, C. Mullen, C. Collicott, A. Rajabi, D. P. Watts, Lorenzo Zana, A. G. Denig, G. M. Huber, V. L. Kashevarov, Durga Paudyal, M. I. Ferretti Bondy, K. Bantawa, N. K. Walford, E. Mornacchi, V. Metag, Guy Ron, C. Sfienti, M. H. Sikora, Igor Strakovsky, W. J. Briscoe, I. J. D. MacGregor, M. Wolfes, P. P. Martel, A. N. Mushkarenkov, Roderick M. Macrae, I. V. Danilkin, J. C. McGeorge, D. Glowa, M. Unverzagt, V. Lisin, M. Ostrick, A. Neiser, D. I. Glazier, F. Cividini, K. Livingston, T. C. Jude, I. Supek, B. Strandberg, M. Korolija, S. Gardner, S. Kay, N. S. Borisov, P. Adlarson, A. B. Neganov, B. Krusche, R. A. Miskimen, P. Aguar-Bartolomé, H. J. Arends, A. Thiel, P. Ott, W. Gradl, David Hamilton, L. V. Fil'kov, H. Berghäuser, A. Käser, Yu. A. Usov, J. Linturi, D. Werthmüller, M. Dieterle, O. Steffen, A. B. Lazarev, A. Braghieri, Th. Strub, M. Biroth, D. G. Middleton, P. B. Otte, A. Nikolaev, J. R. M. Annand, F. Afzal, S. Cherepnya, D. Hornidge, M. Oberle, Susanna Costanza, and R. Beck

Subjects
Physics, 010308 nuclear & particles physics, business.industry, Scattering, Form factor (quantum field theory), Value (computer science), 01 natural sciences, Nuclear physics, Optics, 0103 physical sciences, 010306 general physics, business, Microtron, Crystal Ball
Abstract

The Dalitz decays η→e+e-γ and ω→π0e+e- have been measured in the γp→ηp and γp→ωp reactions, respectively, with the A2 tagged-photon facility at the Mainz Microtron. The value obtained for the slope parameter of the electromagnetic transition form factor of η, Λη-2=(1.97±0.11tot)GeV-2, is in good agreement with previous measurements of the η→e+e-γ and η→μ+μ-γ decays. The uncertainty obtained in the value of Λη-2 is lower than in previous results based on the η→e+e-γ decay. The value obtained for the ω slope parameter, Λωπ0-2=(1.99±0.21tot)GeV-2, is somewhat lower than previous measurements based on ω→π0μ+μ-, but the results for the ω transition form factor are in better agreement with theoretical calculations, compared to earlier experiments.

Published
2017

22. Measurement of the π0→e+e−γ Dalitz decay at the Mainz Microtron

Author

N. K. Walford, E. Mornacchi, C. Collicott, K. Spieker, K. Livingston, T. C. Jude, B. Strandberg, S. Gardner, N. S. Borisov, H. J. Arends, S. Cherepnya, D. P. Watts, V. Metag, E. J. Downie, M. I. Ferretti Bondy, K. Bantawa, C. Sfienti, H. Berghäuser, J. Robinson, J. Wettig, P. Pedroni, D. Hornidge, P. B. Otte, G. M. Huber, G. Rosner, R. A. Miskimen, V. Sokhoyan, Igor Strakovsky, M. Unverzagt, S. Garni, C. S. Akondi, A. Käser, S. Kay, J. Linturi, M. Ostrick, M. Dieterle, I. Keshelashvili, Yu. A. Usov, P. Drexler, P. Aguar-Bartolomé, O. Steffen, P. Adlarson, Michaela Thiel, V. L. Kashevarov, D. I. Glazier, M. Biroth, F. Cividini, A. Thiel, M. Oberle, R. Kondratiev, G. M. Gurevich, Guy Ron, Z. Ahmed, V. Lisin, D. M. Manley, D. Werthmüller, F. Afzal, E. F. McNicoll, S. Wagner, V. V. Kulikov, A. B. Neganov, Susanna Costanza, A. Rajabi, P. Ott, B. Krusche, M. A. Martemianov, C. Mullen, W. J. Briscoe, A. N. Mushkarenkov, A. Nikolaev, J. C. McGeorge, W. Gradl, P. P. Martel, Lilian Witthauer, A. G. Denig, M. Korolija, R. Beck, Lorenzo Zana, D. Glowa, Durga Paudyal, L. V. Fil'kov, M. Wolfes, A. B. Lazarev, I. Supek, A. Braghieri, A. Neiser, Th. Strub, D. G. Middleton, I. J. D. MacGregor, T. Rostomyan, J. R. M. Annand, A. Polonski, S. N. Prakhov, David Hamilton, Andy Thomas, M. H. Sikora, and Roderick M. Macrae

Subjects
Nuclear physics, Physics, Particle physics, Meson, 010308 nuclear & particles physics, 0103 physical sciences, Form factor (quantum field theory), 010306 general physics, 01 natural sciences, Microtron, Dark photon
Abstract

The Dalitz decay π0→e+e−γ has been measured in the γp→π0p reaction with the A2 tagged-photon facility at the Mainz Microtron, MAMI. The value obtained for the slope parameter of the π0 electromagnetic transition form factor, aπ=0.030±0.010tot, is in agreement with existing measurements of this decay and with recent theoretical calculations. The uncertainty obtained in the value of aπ is lower than in previous results based on the π0→e+e−γ decay.

Published
2017

23. Determination of the scalar polarizabilities of the proton using beam asymmetry $\Sigma_{3}$ Σ 3 in Compton scattering

Author

A. Käser, C. S. Akondi, Michaela Thiel, D. Hornidge, I. J. D. MacGregor, P. Ott, A. J. Sarty, D. M. Manley, R. Kondratiev, G. M. Gurevich, B. Krusche, M. Korolija, J. Ahrens, Durga Paudyal, M. Unverzagt, N. Krupina, M. Wolfes, M. Ostrick, P. P. Martel, Judith A. McGovern, S. N. Prakhov, F. Cividini, T. Rostomyan, J. Wettig, H. Ortega Spina, D. I. Glazier, D. Werthmüller, V. Sokhoyan, Lilian Witthauer, B. Oussena, A. Polonski, C. Collicott, A. Rajabi, A. G. Denig, I. Supek, V. Lensky, D. P. Watts, V. L. Kashevarov, I. Keshelashvili, Roderick M. Macrae, S. Schumann, M. Oberle, Andy Thomas, P. B. Otte, I. I. Strakovsky, S. Wagner, D. Glowa, V. Polyansky, E. Mornacchi, W. J. Briscoe, A. N. Mushkarenkov, M. Ferretti, J. Linturi, F. Afzal, P. Pedroni, M. Dieterle, W. Gradl, V. Lisin, A. Braghieri, Th. Strub, E. J. Downie, D. G. Middleton, G. M. Huber, S. Garni, R. A. Miskimen, K. Livingston, O. Steffen, B. Strandberg, S. Gardner, H. J. Arends, David Hamilton, Lorenzo Zana, A. Neiser, J. R. M. Annand, Susanna Costanza, and R. Beck

Subjects
Physics, Nuclear and High Energy Physics, 010308 nuclear & particles physics, media_common.quotation_subject, Nuclear Theory, Scalar (physics), Compton scattering, Sigma, 01 natural sciences, Asymmetry, Nuclear physics, Dipole, Pion, 0103 physical sciences, Nuclear Experiment, 010306 general physics, Nucleon, Microtron, media_common
Abstract

The scalar dipole polarizabilities, $\alpha_{E1}$ and $\beta_{M1}$, are fundamental properties related to the internal dynamics of the nucleon. The currently accepted values of the proton polarizabilities were determined by fitting to unpolarized proton Compton scattering cross section data. The measurement of the beam asymmetry $\Sigma_{3}$ in a certain kinematical range provides an alternative approach to the extraction of the scalar polarizabilities. At the Mainz Microtron (MAMI) the beam asymmetry was measured for Compton scattering below pion photoproduction threshold for the first time. The results are compared with model calculations and the influence of the experimental data on the extraction of the scalar polarizabilities is determined.

Published
2017

24. K+Λ and K+Σ0 photoproduction with fine center-of-mass energy resolution

Author

S. Schumann, P. B. Otte, W. J. Briscoe, P. Pedroni, K. Livingston, V. L. Kashevarov, Z. Marinides, T. C. Jude, D. M. Manley, M. Korolija, G. Rosner, A. Starostin, Yasser Maghrbi, B. Demissie, S. Cherepnya, I. Keshelashvili, B. Krusche, Jason Brudvik, J. R. M. Annand, J. Robinson, F. Pheron, Terry Mart, E. F. McNicoll, V. Lisin, D. P. Watts, B. M.K. Nefkens, K. Bantawa, D. Werthmüller, O. Jahn, M. Ostrick, B. Oussena, A. Polonski, A. V. Sarantsev, I. Supek, F. Zehr, A. Nikolaev, D. Hornidge, V. S. Bekrenev, S. P. Kruglov, M. Thiel, I. M. Suarez, L. V. Fil'kov, J. C. McGeorge, I. I. Strakovsky, P. Aguar-Bartolomé, H. Berghäuser, M. Oberle, M. H. Sikora, R. Gregor, Lilian Witthauer, A. Koulbardis, S. N. Prakhov, D. I. Sober, I. Jaegle, R. Kondratiev, R. Beck, V. A. Nikonov, Anthony W. Thomas, D. I. Glazier, T. Rostomyan, D. Branford, H. J. Arends, D. G. Middleton, M. Unverzagt, A. Braghieri, E. J. Downie, L. K. Akasoy, A. N. Mushkarenkov, E. Heid, M. Dieterle, M. Martinez, and I. J. D. MacGregor

Subjects
Physics, Nuclear and High Energy Physics, Photon, Meson, Resolution (electron density), 7. Clean energy, Calorimeter, Nuclear physics, High Energy Physics::Experiment, Center of mass, Atomic physics, Nucleon, Excitation, Crystal Ball
Abstract

Measurements of γp→K+Λγp→K+Λ and γp→K+Σ0γp→K+Σ0 cross-sections have been obtained with the photon tagging facility and the Crystal Ball calorimeter at MAMI-C. The measurement uses a novel K+K+ meson identification technique in which the weak decay products are characterized using the energy and timing characteristics of the energy deposit in the calorimeter, a method that has the potential to be applied at many other facilities. The fine center-of-mass energy (W) resolution and statistical accuracy of the new data results in a significant impact on partial wave analyses aiming to better establish the excitation spectrum of the nucleon. The new analyses disfavor a strong role for quark–diquark dynamics in the nucleon.

Published
2014

25. First measurement of the helicity dependence of 3He photoreactions in the Δ(1232) resonance region

Author

David Hamilton, L.V. Filʼkov, A. Polonski, D. G. Middleton, M. Thiel, M. Oberle, B. Oussena, Werner Heil, A. Braghieri, J. R. M. Annand, D. P. Watts, F. Rigamonti, T. Rostomyan, D. I. Sober, B. Krusche, V. S. Bekrenev, V. Lisin, H. Berghäuser, K. Livingston, T. C. Jude, P. Pedroni, A. Starostin, O. Jahn, A. Nikolaev, Susanna Costanza, H. J. Arends, D. I. Glazier, A. Fix, P. Aguar Bartolomé, M. Romaniuk, G. Giardina, B. M. K. Nefkens, J. C. McGeorge, R. Beck, J. Krimmer, S. Cherepnya, F. Pheron, D. Werthmüller, I. Keshelashvili, D. Hornidge, J. Mancell, M. Ostrick, A. Kulbardis, I. Jaegle, R. Kondratiev, I. Supek, J. Ahrens, I. J. D. MacGregor, Volker Metag, E. Heid, H. Ortega, S. Schumann, P. B. Otte, D. Howdle, P. Drexler, S. N. Prakhov, Andy Thomas, M. Unverzagt, W. J. Briscoe, S. P. Kruglov, G. Rosner, A. N. Mushkarenkov, V. L. Kashevarov, D. M. Manley, and M. Korolija

Subjects
Physics, Nuclear reaction, Nuclear and High Energy Physics, Photon, 010308 nuclear & particles physics, Nuclear Theory, Nucleon spin structure, Photon energy, 01 natural sciences, Resonance (particle physics), Helicity, Nuclear physics, 0103 physical sciences, Neutron, Nuclear Experiment, 010306 general physics, Crystal Ball
Abstract

The first measurement of the helicity dependence of the total inclusive 3He photo-absorption cross section and of the partial cross sections for several reaction channels was carried out at MAMI (Mainz) in the photon energy range between 150 and 500 MeV. The experiment used the large acceptance Crystal Ball spectrometer, complemented by charged particle and vertex detectors, a circularly polarised tagged photon beam and a longitudinally polarised high-pressure 3He gas target. The results obtained give information on the GDH integral on 3He and on the neutron and allow an investigation of the modifications of nucleon properties inside 3He.

Published
2013

26. Measurement of the beam-helicity asymmetry I⊙ in the photoproduction of π0-pairs off the proton and off the neutron

Author

A. Polonski, I. Keshelashvili, M. Thiel, T. Rostomyan, Yasser Maghrbi, F. Zehr, Volker Metag, R. Beck, E. Heid, S. P. Kruglov, J. Mancell, G. M. Huber, D. I. Sober, E. J. Downie, D. M. Manley, M. Korolija, I. Supek, E. F. McNicoll, B. Demissie, J. R. M. Annand, P. A. Bartolome, S. Schumann, R. W. Novotny, M. H. Sikora, S. N. Prakhov, P. Pedroni, M. Ostrick, S. Cherepnya, D. P. Watts, D. I. Glazier, Sasa Micanovic, K. Bantawa, A. Käser, D. Howdle, Lilian Witthauer, V. S. Bekrenev, Z. Marinides, A. Starostin, D. Werthmüller, M. Martinez, M. Oberle, V. L. Kashevarov, Andy Thomas, G. Rosner, I. J. D. MacGregor, W. J. Briscoe, A. N. Mushkarenkov, Jason Brudvik, A. Nikolaev, A. Kulbardis, M. Unverzagt, B. M. K. Nefkens, P. Drexler, D. Hornidge, B. Krusche, M. Dieterle, J. Robinson, F. Pheron, D. G. Middleton, L.V. Filʼkov, V. Lisin, B. Oussena, O. Jahn, J. C. McGeorge, K. Livingston, T. C. Jude, D. Branford, I. Jaegle, R. Kondratiev, J. Ahrens, A. Braghieri, H. J. Arends, A. Fix, H. Berghäuser, and D. Mekterovic

Subjects
Physics, Nuclear and High Energy Physics, Proton, Meson, 010308 nuclear & particles physics, Nuclear Theory, Hadron, 01 natural sciences, 7. Clean energy, Helicity, Charged particle, Nuclear physics, Pion, 0103 physical sciences, High Energy Physics::Experiment, Neutron, Atomic physics, Nuclear Experiment, 010306 general physics, Crystal Ball
Abstract

Beam-helicity asymmetries have been measured at the MAMI accelerator in Mainz for the photoproduction of neutral pion pairs in the reactions γ → p → p π 0 π 0 and γ → d → ( n ) p π 0 π 0 , γ → d → ( p ) n π 0 π 0 off free protons and off quasi-free nucleons bound in the deuteron for incident photon energies up to 1.4 GeV. Circularly polarized photons were produced from bremsstrahlung of longitudinally polarized electrons and tagged with the Glasgow magnetic spectrometer. Decay photons from the π 0 mesons, recoil protons, and recoil neutrons were detected in the 4π covering electromagnetic calorimeter composed of the Crystal Ball and TAPS detectors. After kinematic reconstruction of the final state, excellent agreement was found between the results for free and quasi-free protons. This demonstrates that the free-nucleon behavior of such observables can be extracted from measurements with quasi-free nucleons, which is the only possibility for the neutron. Contrary to expectations, the measured asymmetries are very similar for reactions off protons and neutrons. The results are compared to the predictions from the Two-Pion MAID reaction model and (for the proton) also to the Bonn–Gatchina coupled channel analysis.

Published
2013

27. TandFasymmetries inπ0photoproduction on the proton

Author

A. Nikolaev, I. J. D. MacGregor, G. Reicherz, P. Ott, D. Hornidge, J. R. M. Annand, B. Oussena, S. Cherepnya, D. I. Glazier, Reinhard Beck, P. Pedroni, A. B. Lazarev, V. L. Kashevarov, I. I. Strakovsky, E. F. McNicoll, M. Dieterle, T. Rostomyan, D. M. Manley, S. Garni, M. Korolija, L. V. Fil'kov, L. Tiator, D. G. Middleton, D. Howdle, C. Collicott, K. Livingston, I. Keshelashvili, D. P. Watts, W. Gradl, M. Oberle, N. S. Borisov, A. Braghieri, Th. Strub, M. Wolfes, A. J. Sarty, I. Supek, H. J. Arends, S. N. Prakhov, S. Schumann, M. Ostrick, David Hamilton, P. B. Otte, A. Fix, Andy Thomas, R. A. Miskimen, V. Lisin, W. Meyer, B. Krusche, H. Ortega, A. B. Neganov, G. M. Huber, Yu. A. Usov, O. Steffen, P. Hall Barrientos, W. J. Briscoe, A. N. Mushkarenkov, M. Unverzagt, E. J. Downie, R. Kondratiev, G. M. Gurevich, V. V. Polyanski, A. Polonski, Lilian Witthauer, D. Werthmüller, P. P. Martel, J. Mancel, and S. Costanza

Subjects
Physics, Particle physics, Photon, 010308 nuclear & particles physics, media_common.quotation_subject, Bremsstrahlung, Photon energy, 01 natural sciences, Asymmetry, Resonance (particle physics), Baryon, Nuclear physics, 0103 physical sciences, Physics::Accelerator Physics, Nuclear Experiment, 010306 general physics, Microtron, Crystal Ball, media_common
Abstract

The γp→π0p reaction was studied at laboratory photon energies from 425 to 1445 MeV with a transversely polarized target and a longitudinally polarized beam. The beam-target asymmetry F was measured for the first time and new high precision data for the target asymmetry T were obtained. The experiment was performed at the photon tagging facility of the Mainz Microtron (MAMI) using the Crystal Ball and TAPS photon spectrometers. The polarized cross sections were expanded in terms of associated Legendre functions and compared to recent predictions from several partial-wave analyses. The impact of the new data on our understanding of the underlying partial-wave amplitudes and baryon resonance contributions is discussed.

Published
2016

28. Photoproduction of $\eta$ $\pi$ pairs off nucleons and deuterons

Author

M. Ostrick, B. Oussena, D. P. Watts, K. Livingston, T. C. Jude, J. R. M. Annand, K. Bantawa, D. Hornidge, H. J. Arends, J. C. McGeorge, Michaela Thiel, W. J. Briscoe, A. N. Mushkarenkov, D. M. Manley, M. Korolija, T. Rostomyan, I. Supek, A. Starostin, S. Schumann, A. Fix, P. A. Bartolome, J. Robinson, D. Mekterovic, Susanna Costanza, A. Braghieri, Th. Strub, M. H. Sikora, D. G. Middleton, R. W. Novotny, P. B. Otte, E. J. Downie, G. M. Huber, V. Metag, R. Beck, M. Dieterle, J. Mancell, D. I. Sober, V. L. Kashevarov, M. Unverzagt, V. Lisin, I. Jaegle, D. Howdle, F. Pheron, B. Krusche, J. Ahrens, R. Kondratiev, D. Werthmueller, F. Mueller, A. Kaeser, D. I. Glazier, Lilian Witthauer, I. J. D. MacGregor, L. V. Fil'kov, S. N. Prakhov, E. F. McNicoll, David Hamilton, A. Nikolaev, A. Polonski, N. K. Walford, Andy Thomas, M. Oberle, P. Drexler, S. Cherepnya, I. Keshelashvili, P. Pedroni, Sasa Micanovic, S. Garni, Z. Marinides, and Yasser Maghrbi

Subjects
Physics, Nuclear and High Energy Physics, Photon, Proton, 010308 nuclear & particles physics, Nuclear Theory, FOS: Physical sciences, 01 natural sciences, 7. Clean energy, Nuclear physics, Deuterium, REACTION GAMMA-P, TAGGED PHOTON SPECTROMETER, I-CIRCLE-DOT, MESON PHOTOPRODUCTION, HIGH-STATISTICS, PROTON, THRESHOLD, MAMI, POLARIZATION, PI(0)-PAIRS, 0103 physical sciences, Pi, Neutron, High Energy Physics::Experiment, ddc:530, Decay chain, Nuclear Experiment (nucl-ex), 010306 general physics, Nucleon, Nuclear Experiment, Crystal Ball
Abstract

Quasi-free photoproduction of $\pi\eta$-pairs has been investigated from threshold up to incident photon energies of 1.4 GeV, respectively up to photon-nucleon invariant masses up to 1.9 GeV. Total cross sections, angular distributions, invariant-mass distributions of the $\pi\eta$ and meson-nucleon pairs, and beam-helicity asymmetries have been measured for the reactions $\gamma p\rightarrow p\pi^0\eta$, $\gamma n\rightarrow n\pi^0\eta$, $\gamma p\rightarrow n\pi^+\eta$, and $\gamma n\rightarrow p\pi^-\eta$ from nucleons bound inside the deuteron. For the $\gamma p$ initial state data for free protons have also been analyzed. Finally, the total cross sections for quasi-free production of $\pi^0\eta$ pairs from nucleons bound in $^3$He nuclei have been investigated in view of final state interaction (FSI) effects. The experiments were performed at the tagged photon beam facility of the Mainz MAMI accelerator using an almost $4\pi$ covering electromagnetic calorimeter composed of the Crystal Ball and TAPS detectors. The shapes of all differential cross section data and the asymmetries are very similar for protons and neutrons and agree with the conjecture that the reactions are dominated by the sequential $\Delta^{\star}3/2^-\rightarrow\eta\Delta(1232)\rightarrow\pi\eta N$ decay chain, mainly with $\Delta(1700)3/2^-$ and $\Delta(1940)3/2^-$. The ratios of the magnitude of the total cross sections also agree with this assumption. However, the absolute magnitudes of the cross sections are reduced by FSI effects with respect to free proton data., Comment: accepted for publication in Eur. Phys. J. A

Published
2016

29. Meson Decays with Crystal Ball at MAMI

Author

M. Unverzagt

Subjects
Nuclear physics, Physics, Nuclear and High Energy Physics, Particle physics, Field (physics), Meson, High Energy Physics::Experiment, Nuclear Experiment, Atomic and Molecular Physics, and Optics, Crystal Ball
Abstract

The Crystal Ball at MAMI setup offers excellent possibilities to study decays of light mesons like η , η ′ , and ω . Here, recent results on η and ω decays are presented. Furthermore, future perspectives in this field at MAMI are described.

Published
2012

30. Determination of the η-transition form factor in the γp→pη→pγe+e− reaction

Author

Jason Brudvik, V. Metag, Yasser Maghrbi, L.V. Filʼkov, B. Krusche, A. Starostin, E. F. McNicoll, P. Aguar Bartolomé, J. Robinson, B. Demissie, M. Martinez-Fabregate, F. Pheron, D. Werthmüller, V. Lisin, P. Pedroni, S. Schumann, R. W. Novotny, S. Cherepnya, D. P. Watts, O. Jahn, I. Zamboni, D. I. Sober, C. M. Tarbert, H. J. Arends, Michaela Thiel, V. L. Kashevarov, R. Kondratiev, I. M. Suarez, D. Mekterovic, P. Drexler, Sasa Micanovic, M. Ostrick, M. Kotulla, K. Bantawa, G. Rosner, L. K. Akasoy, T. Rostomyan, V. S. Bekrenev, D. M. Manley, M. Korolija, I. Supek, A. N. Mushkarenkov, Anthony W. Thomas, D. I. Glazier, D. Hornidge, A. Koulbardis, A. Knezevic, R.O. Owens, K. Livingston, S. N. Prakhov, E. J. Downie, F. Zehr, I. J. D. MacGregor, W. J. Briscoe, B. Lemmer, S. P. Kruglov, T.C. Jude, J. C. McGeorge, R. Beck, M. Unverzagt, A. Fix, H. Berghäuser, A. Nikolaev, A. Polonski, B. M. K. Nefkens, J. R. M. Annand, E. Heid, M. Dieterle, D. Branford, and A. Braghieri

Subjects
Physics, Nuclear and High Energy Physics, Mass distribution, 010308 nuclear & particles physics, Point particle, Branching fraction, Form factor (quantum field theory), Particle accelerator, 01 natural sciences, law.invention, Nuclear physics, law, 0103 physical sciences, High Energy Physics::Experiment, Invariant mass, Nuclear Experiment, 010306 general physics, Order of magnitude, Crystal Ball
Abstract

The Dalitz decay η→γe+e− has been measured using the combined Crystal Ball and TAPS photon detector setup at the electron accelerator MAMI-C. Compared to the most recent transition form-factor measurement in the e+e− channel, statistics have been improved by one order of magnitude. The e+e− invariant mass distribution shows a deviation from the QED prediction for a point-like particle, which can be described by a form-factor. Using the usual monopole transition form-factor parameterization, F(m2)=(1−m2/Λ2)−1, a value of Λ−2=(1.92±0.35(stat)±0.13(syst)) GeV−2 has been determined. This value is in good agreement with a recent measurement of the η Dalitz decay in the μ+μ− channel and with recent form-factor calculations. An improved value of the branching ratio BR(η→γe+e−)=(6.6±0.4(stat)±0.4(syst))⋅10−3 has been determined.

Published
2011

31. First measurement of the circular beam asymmetry in the γ→p→π0ηp reaction

Author

M. Kotulla, M. H. Sikora, A. Koulbardis, E. J. Downie, I.I. Stakovsky, D. G. Middleton, P. Aguar-Bartolomé, D. Branford, Yasser Maghrbi, C. M. Tarbert, T. Rostomyan, M. Ostrick, A. Nikolaev, L. K. Akasoy, W. J. Briscoe, A. N. Mushkarenkov, B. M. K. Nefkens, D. Werthmüller, A. Braghieri, F. Zehr, M. Martinez-Fabregate, R. F. B. Codling, J. D. Kellie, D. Mekterovic, S. P. Kruglov, R. Beck, D. I. Glazier, I. Jaegle, R. Kondratiev, R. Gregor, I. Zamboni, B. Demissie, B. Oussena, D. P. Watts, I. M. Suarez, K. Bantawa, V. S. Bekrenev, I. Keshelashvili, D. I. Sober, V. Metag, J. Robinson, F. Pheron, M. Unverzagt, I. J. D. MacGregor, A. Starostin, S. Cherepnya, E. Heid, D. Hornidge, L. V. Fil'kov, A. Polonski, V. L. Kashevarov, H. Berghäuser, K. Livingston, T. C. Jude, P. Pedroni, Jason Brudvik, J. R. M. Annand, Sasa Micanovic, H. J. Arends, A. Fix, E. F. McNicoll, G. Rosner, S. Schumann, R. W. Novotny, P. B. Otte, B. Krusche, Michaela Thiel, D. M. Manley, M. Korolija, S. N. Prakhov, Andy Thomas, J. C. McGeorge, V. Lisin, O. Jahn, David Hamilton, P. Drexler, and I. Supek

Subjects
Physics, Nuclear reaction, Nuclear and High Energy Physics, Photon, Proton, 010308 nuclear & particles physics, media_common.quotation_subject, Resonance, Elementary particle, 01 natural sciences, Asymmetry, Delta baryon, Nuclear physics, 0103 physical sciences, Nuclear Experiment, 010306 general physics, Crystal Ball, media_common
Abstract

The circular photon asymmetry for π 0 η photoproduction on the proton was measured for the first time at the tagged photon facility of the MAMI C accelerator using the Crystal Ball/TAPS photon spectrometer. The experimental results are interpreted within a phenomenological isobar model that confirms the dominant role of the Δ ( 1700 ) D 33 resonance. The measured asymmetry allows us to identify small contributions from positive-parity resonances via interference terms with the dominant D 33 amplitude.

Published
2010

32. Photoproduction of $ \pi^{0}$ -pairs off protons and off neutrons

Author

A. Käser, D. Howdle, T. Rostomyan, J. Brudvik, S. N. Prakhov, P. Pedroni, J. Robinson, D. Branford, G. M. Huber, D. Mekterovic, Reinhard Beck, V. L. Kashevarov, B. Krusche, B. Oussena, P. A. Bartolome, Volker Metag, R. W. Novotny, E. Heid, D. P. Watts, P. B. Otte, M. Dieterle, M. Ostrick, K. Livingston, David Hamilton, T. C. Jude, B. Demissie, Lilian Witthauer, K. Bantawa, A. Starostin, V. S. Bekrenev, Steffen Schumann, A. Polonski, P. Drexler, J. C. McGeorge, Sasa Micanovic, W. J. Briscoe, M. Thiel, S. Garni, O. Jahn, N. K. Walford, Z. Marinides, A. Nikolaev, S. Costanza, Th. Strub, M. Korolija, J. Mancell, I. Supek, A. Braghieri, Yasser Maghrbi, Jrm Annand, M. Unverzagt, H. J. Arends, M. H. Sikora, D. G. Middleton, E. J. Downie, D. I. Sober, F. Pheron, E. F. McNicoll, M. Oberle, David Manley, A. Fix, D. Werthmüller, I. Keshelashvili, I. J. D. MacGregor, S. Cherepnya, Anthony W. Thomas, D. I. Glazier, A. Mushkarenkov, L. V. Fil'kov, H. Berghäuser, D. Hornidge, V. Lisin, R. Kondratiev, and J. Ahrens

Subjects
Nuclear reaction, Physics, Nuclear and High Energy Physics, Proton, Meson, Nuclear Theory, Bremsstrahlung, 7. Clean energy, Delta baryon, Nuclear physics, Physics::Accelerator Physics, Neutron, Atomic physics, Nuclear Experiment, Nucleon, Crystal Ball
Abstract

Total cross sections, angular distributions, and invariant-mass distributions have been measured for the photoproduction of $\pi^0\pi^0$ pairs off free protons and off nucleons bound in the deuteron. The experiments were performed at the MAMI accelerator facility in Mainz using the Glasgow photon tagging spectrometer and the Crystal Ball/TAPS detector. The accelerator delivered electron beams of 1508 and 1557~MeV, which produced bremsstrahlung in thin radiator foils. The tagged photon beam covered energies up to 1400~MeV. The data from the free proton target are in good agreement with previous measurements and were only used to test the analysis procedures. The results for differential cross sections (angular distributions and invariant-mass distributions) for free and quasi-free protons are almost identical in shape, but differ in absolute magnitude up to 15\%. Thus, moderate final-state interaction effects are present. The data for quasi-free neutrons are similar to the proton data in the second resonance region (final state invariant masses up to $\approx$1550~MeV), where both reactions are dominated by the $N(1520)3/2^-\rightarrow \Delta(1232)3/2^+\pi$ decay. At higher energies, angular and invariant-mass distributions are different. A simple analysis of the shapes of the invariant-mass distributions in the third resonance region is consistent with strong contributions of an $N^{\star}\rightarrow N\sigma$ decay for the proton, while the reaction is dominated by a sequential decay via a $\Delta\pi$ intermediate state for the neutron. The data are compared to predictions from the Two-Pion-MAID model and the Bonn-Gatchina coupled channel analysis., Comment: accepted for publication in Eur. Phys. J. A

Published
2015

34. First measurement of target and beam-target asymmetries in theγp→π0ηpreaction

Author

A. Nikolaev, S. N. Prakhov, Andy Thomas, P. P. Martel, V. L. Kashevarov, J. R. M. Annand, I. I. Strakovsky, C. Collicott, L. V. Fil'kov, D. P. Watts, T. Rostomyan, D. I. Glazier, Lilian Witthauer, D. M. Manley, M. Korolija, M. Ostrick, D. Howdle, D. G. Middleton, M. Oberle, B. Krusche, V. Lisin, V. V. Polyanski, D. Hornidge, M. Wolfes, A. B. Neganov, I. J. D. MacGregor, D. Werthmüller, A. J. Sarty, I. Supek, E. F. McNicoll, E. J. Downie, G. M. Huber, W. Gradl, G. Reicherz, J. Mancel, A. Polonski, R. Beck, H. Ortega, I. Keshelashvili, R. Kondratiev, S. Cherepnya, M. Unverzagt, S. Costanza, G. M. Gurevich, P. Pedroni, S. Schumann, David Hamilton, S. Garni, M. Dieterle, B. Oussena, K. Livingston, W. Meyer, P. B. Otte, N. S. Borisov, W. J. Briscoe, A. N. Mushkarenkov, H. J. Arends, A. Fix, L. Tiator, P. Hall Barrientos, A. B. Lazarev, A. Braghieri, Th. Strub, P. Ott, R. A. Miskimen, Yu. A. Usov, and O. Steffen

Subjects
Physics, Nuclear physics, Nuclear and High Energy Physics, Photon, Meson, Partial wave analysis, Bremsstrahlung, Physics::Accelerator Physics, Photon energy, Nuclear Experiment, Nucleon, Microtron, Crystal Ball
Abstract

The first data on target and beam-target asymmetries for the gamma p -> pi(0)eta p reaction at photon energies from 1050 up to 1450 MeV are presented. The measurements were performed using the Crystal Ball and TAPS detector setup at the Glasgow tagged photon facility of the Mainz Microtron MAMI. The general assumption that the reaction is dominated by the Delta 3/2-amplitude is confirmed. The data are in particular sensitive to small contributions from other partial waves.

Published
2015

35. Photoproduction of theωmeson on the proton near threshold

Author

V. L. Kashevarov, C. M. Tarbert, P. Drexler, B. Oussena, D. M. Manley, M. Korolija, T. Rostomyan, P. Aguar-Bartolomé, S. Schumann, R. W. Novotny, P. B. Otte, P. Pedroni, C. Collicott, A. Starostin, E. J. Downie, A. Polonski, M. Kotulla, D. I. Glazier, L. V. Fil'kov, V. Lisin, G. Rosner, J. Robinson, Z. Marinides, S. Costanza, F. Zehr, S. N. Prakhov, F. Pheron, M. H. Sikora, M. Unverzagt, Ya. I. Azimov, S. P. Kruglov, B. Krusche, R. Beck, Volker Metag, I. Keshelashvili, D. P. Watts, A. Braghieri, Andy Thomas, B. Demissie, A. Nikolaev, K. Bantawa, R. F. B. Codling, V. S. Bekrenev, I. Supek, D. Hornidge, M. Ostrick, E. F. McNicoll, W. J. Briscoe, A. N. Mushkarenkov, A. Koulbardis, I. I. Strakovsky, D. G. Middleton, I. J. D. MacGregor, B. M. K. Nefkens, E. Heid, Jason Brudvik, M. Thiel, J. R. M. Annand, H. Ortega, R. Gregor, Yasser Maghrbi, D. Werthmüller, J. C. McGeorge, I. Jaegle, R. Kondratiev, David Hamilton, H. Berghäuser, D. Mekterovic, M. F. Taragin, O. Jahn, K. Livingston, T. C. Jude, H. J. Arends, and S. Cherepnya

Subjects
Physics, Nuclear and High Energy Physics, Particle physics, Photon, Proton, Meson, Vector meson dominance, Scattering length, 7. Clean energy, Omega, Nuclear physics, Nuclear Experiment, Microtron, Crystal Ball
Abstract

An experimental study of omega photoproduction on the proton was conducted by using the Crystal Ball and TAPS multiphoton spectrometers together with the photon tagging facility at the Mainz Microtron MAMI. The gamma p -> omega p differential cross sections are measured from threshold to the incident-photon energy E-gamma = 1.40 GeV (W = 1.87 GeV for the center-of-mass energy) with 15-MeV binning in E-gamma and full production-angle coverage. The quality of the present data near threshold gives access to a variety of interesting physics aspects. As an example, an estimation of the omega N scattering length alpha(omega p) is provided.

Published
2015

36. A new measurement of the neutron detection efficiency for the NaI Crystal Ball detector

Author

D. Hornidge, Th. Strub, J. Linturi, Steffen Schumann, R. Miskimen, V. Sokhoyan, A. Lazarev, B. Krusche, T. Rostomyan, R. Kondratiev, I. Supek, H. J. Arends, I. J. D. MacGregor, D. Glowa, W. Gradl, M. I. Ferretti Bondy, S. Wagner, A. B. Neganov, D. Schott, C. S. Akondi, David Manley, P. Pedroni, Yu. A. Usov, O. Steffen, M. Ostrick, A. J. Sarty, S. Cherepnya, B. Demissie, G. M. Gurevich, P. P. Martel, J. Wettig, S. N. Prakhov, P. Ott, A. Braghieri, B. Oussena, M. Korolija, L. V. Fil'kov, V. L. Kashevarov, Reinhard Beck, C. Collicott, S. Costanza, K. Livingston, D. P. Watts, A. Kaeser, Lilian Witthauer, M. Thiel, N. S. Borisov, Guy Ron, A. Neiser, V. Lisin, A. Polonski, M. Oberle, W. J. Briscoe, M. Dieterle, P. B. Otte, M. A. Martemianov, M. Unverzagt, D. G. Middleton, S. Garni, Z. Marinides, Anthony W. Thomas, D. I. Glazier, A. Mushkarenkov, G. M. Huber, Igor Strakovsky, M. Wolfes, E. J. Downie, Jrm Annand, V. V. Kulikov, D. Werthmüller, and I. Keshelashvili

Subjects
Physics, Physics - Instrumentation and Detectors, Physics::Instrumentation and Detectors, Detector, Nuclear Theory, FOS: Physical sciences, Instrumentation and Detectors (physics.ins-det), Neutron temperature, High Energy Physics - Experiment, Nuclear physics, High Energy Physics - Experiment (hep-ex), Pion beam, Deuterium, Neutron detection, Physics::Accelerator Physics, High Energy Physics::Experiment, Photon beam, Nuclear Experiment (nucl-ex), Nuclear Experiment, Instrumentation, Microtron, Mathematical Physics, Crystal Ball
Abstract

We report on a measurement of the neutron detection efficiency in NaI crystals in the Crystal Ball detector obtained from a study of single π0 photoproduction on deuterium using the tagged photon beam at the Mainz Microtron. The results were obtained up to a neutron energy of 400 MeV . They are compared to previous measurements made more than 15 years ago at the pion beam at the BNL AGS.

Published
2015

37. New measurement of the rare decayη→π0γγwith the Crystal Ball/TAPS detectors at the Mainz Microtron

Author

R. Gregor, B. Oussena, A. Nikolaev, D. I. Glazier, C. Collicott, D. P. Watts, M. Ostrick, B. M. K. Nefkens, I. M. Suarez, M. Oberle, K. Bantawa, Susanna Costanza, Yasser Maghrbi, V. S. Bekrenev, S. Cherepnya, J. R. M. Annand, A. Starostin, R. Beck, W. J. Briscoe, A. N. Mushkarenkov, D. Werthmüller, S. N. Prakhov, B. Demissie, Jason Brudvik, I. Keshelashvili, V. L. Kashevarov, H. Ortega, E. J. Downie, I. Supek, Andy Thomas, J. Mancel, E. Heid, M. H. Sikora, Michaela Thiel, I. J. D. MacGregor, A. Koulbardis, P. Pedroni, C. M. Tarbert, A. Polonski, A. Käser, E. F. McNicoll, D. Howdle, P. Ott, M. Unverzagt, D. Hornidge, T. Rostomyan, S. Garni, P. Drexler, I. I. Strakovsky, D. M. Manley, M. Korolija, S. Schumann, R. W. Novotny, P. B. Otte, B. Krusche, Lilian Witthauer, V. Metag, S. P. Kruglov, M. Dieterle, R. F. B. Codling, A. Braghieri, Th. Strub, David Hamilton, G. Rosner, M. Kotulla, I. V. Danilkin, V. Lisin, P. Aguar-Bartolomé, O. Jahn, L. V. Fil'kov, R. Kondratiev, H. Berghäuser, K. Livingston, T. C. Jude, H. J. Arends, A. Fix, J. Robinson, A. G. Denig, and D. Mekterovic

Subjects
Physics, Nuclear and High Energy Physics, Photon, Spectrometer, Meson, Astrophysics::High Energy Astrophysical Phenomena, Detector, Gamma gamma, Nuclear physics, High Energy Physics::Experiment, Invariant mass, Atomic physics, Nuclear Experiment, Microtron, Crystal Ball
Abstract

A new measurement of the rare, doubly radiative decay eta->pi^0 gamma gamma was conducted with the Crystal Ball and TAPS multiphoton spectrometers together with the photon tagging facility at the Mainz Microtron MAMI. New data on the dependence of the partial decay width, Gamma(eta->pi^0 gamma gamma), on the two-photon invariant mass squared, m^2(gamma gamma), as well as a new, more precise value for the decay width, Gamma(eta->pi^0 gamma gamma) = (0.33+/-0.03_tot) eV, are based on analysis of 1.2 x 10^3 eta->pi^0 gamma gamma decays from a total of 6 x 10^7 eta mesons produced in the gamma p -> eta p reaction. The present results for dGamma(eta->pi^0 gamma gamma)/dm^2(gamma gamma) are in good agreement with previous measurements and recent theoretical calculations for this dependence.

Published
2014

38. Measurements of Double-Polarized Compton Scattering Asymmetries and Extraction of the Proton Spin Polarizabilities

Author

B. Oussena, D. P. Watts, I. Keshelashvili, I. I. Strakovsky, A. B. Lazarev, A. Nikolaev, I. Supek, D. Howdle, A. Braghieri, S. N. Prakhov, G. Reicherz, K. Livingston, T. C. Jude, M. H. Sikora, B. M. K. Nefkens, Th. Strub, M. Unverzagt, S. Schrauf, N. S. Borisov, Michaela Thiel, V. L. Kashevarov, David Hamilton, C. S. Akondi, D. M. Manley, M. Korolija, L. Tiator, W. J. Briscoe, P. Hall Barrientos, Anthony W. Thomas, D. Hornidge, M. Ostrick, D. I. Glazier, W. Meyer, P. P. Martel, P. Pedroni, I. J. D. MacGregor, A. Starostin, A. J. Sarty, A. Rajabi, S. Garni, R. Kondratiev, R. A. Miskimen, A. Kaeser, A. N. Mushkarenkov, S. Schumann, B. Krusche, J. Ahrens, G. M. Gurevich, G. M. Huber, J. R. M. Annand, A. G. Denig, Yu. A. Usov, E. J. Downie, Lilian Witthauer, P. Aguar-Bartolomé, P. B. Otte, A. B. Neganov, T. Rostomyan, L. V. Fil'kov, W. Barnes, C. Collicott, D. Werthmüller, S. Cherepnya, M. Wolfes, A. Polonski, W. Gradl, J. Mancell, Susanna Costanza, M. Oberle, R. Beck, M. Dieterle, Aron M. Bernstein, H. J. Arends, D. G. Middleton, O. Steffen, V. Polyansky, V. Lisin, H. Ortega Spina, and P. Ott

Subjects
Physics, Photon, Proton, Nuclear Theory, Compton scattering, General Physics and Astronomy, FOS: Physical sciences, 7. Clean energy, 3. Good health, Baryon, Nuclear physics, Proton spin crisis, spin polarizabilities, nucleon, photon, ∆(1232) region, MAMI, Nuclear Experiment (nucl-ex), Nucleon, Nuclear Experiment, Microtron, Spin-½
Abstract

The spin polarizabilities of the nucleon describe how the spin of the nucleon responds to an incident polarized photon. The most model-independent way to measure the nucleon spin polarizabilities is through polarized Compton scattering. Double-polarized Compton scattering asymmetries on the proton were measured in the $\Delta(1232)$ region using circularly polarized incident photons and a transversely polarized proton target at the Mainz Microtron. Fits to asymmetry data were performed using a dispersion model calculation and a baryon chiral perturbation theory calculation, and a separation of all four proton spin polarizabilities in the multipole basis was achieved. The analysis based on a dispersion model calculation yields $\gamma_{E1E1} = -3.5 \pm 1.2$, $\gamma_{M1M1}= 3.16 \pm 0.85$, $\gamma_{E1M2} = -0.7 \pm 1.2$, and $\gamma_{M1E2} = 1.99 \pm 0.29$, in units of $10^{-4}$ fm$^4$., Comment: 5 pages, 3 figures, 2 tables

Published
2014

39. Neutron Skin ofPb208from Coherent Pion Photoproduction

Author

M. Unverzagt, A. Knezevic, A. Polonski, R. F. B. Codling, A. Starostin, C. M. Tarbert, S. Schadmand, R.O. Owens, K. Livingston, L. Zana, G. Rosner, P. Grabmayr, D. Branford, T. Rostomyan, H. J. Arends, D. P. Watts, J. C. McGeorge, E. J. Downie, Volker Metag, I. J. D. MacGregor, V. S. Bekrenev, V. L. Kashevarov, M. Lang, E. Heid, F. Zehr, V. Lisin, W. J. Briscoe, D. Mekterovic, P. Aguar, A. Nikolaev, O. Jahn, P. Pedroni, D. Krambrich, D. M. Manley, M. Korolija, K Foehl, Jason Brudvik, R. Kondratiev, M. Rost, I. Supek, S. Cherepnya, S. Schumann, R. W. Novotny, R. Beck, J. Ahrens, M. Martinez, J. W. Price, A. Braghieri, R. Gregor, J. R. M. Annand, B. M. K. Nefkens, D. I. Glazier, D. Hornidge, M. Kotulla, B. Boillat, D. I. Sober, Th. Walcher, S. Lugert, S. N. Prakhov, Andy Thomas, and B. Krusche

Subjects
Physics, Equation of state, Meson, 010308 nuclear & particles physics, Scattering, General Physics and Astronomy, Radius, 01 natural sciences, Nuclear physics, Pion, 0103 physical sciences, High Energy Physics::Experiment, Neutron, Nuclear Experiment, 010306 general physics, Microtron, Crystal Ball
Abstract

Information on the size and shape of the neutron skin on (208)Pb is extracted from coherent pion photoproduction cross sections measured using the Crystal Ball detector together with the Glasgow tagger at the MAMI electron beam facility. On exploitation of an interpolated fit of a theoretical model to the measured cross sections, the half-height radius and diffuseness of the neutron distribution are found to be c(n)=6.70±0.03(stat.) fm and a(n)=0.55±0.01(stat.)(-0.03)(+0.02)(sys.) fm, respectively, corresponding to a neutron skin thickness Δr(np)=0.15±0.03(stat.)(-0.03)(+0.01)(sys.) fm. The results give the first successful extraction of a neutron skin thickness with an electromagnetic probe and indicate that the skin of (208)Pb has a halo character. The measurement provides valuable new constraints on both the structure of nuclei and the equation of state for neutron-rich matter.

Published
2014

40. New determination of theηtransition form factor in the Dalitz decayη→e+e−γwith the Crystal Ball/TAPS detectors at the Mainz Microtron

Author

David Hamilton, M. Unverzagt, C. Collicott, A. Starostin, J. C. McGeorge, D. I. Glazier, Michaela Thiel, V. L. Kashevarov, D. Hornidge, D. M. Manley, P. Drexler, M. Kotulla, M. Korolija, S. N. Prakhov, S. Costanza, B. Oussena, Yasser Maghrbi, Andy Thomas, Steffen Schumann, E. J. Downie, D. P. Watts, Lennart Isaksson, I. Jaegle, E. F. McNicoll, I. I. Strakovsky, I. M. Suarez, R. Kondratiev, K. Bantawa, B. M. K. Nefkens, P. Ott, V. Lisin, V. Metag, V. S. Bekrenev, O. Jahn, Pere Masjuan, P. B. Otte, A. Polonski, B. Krusche, E. Heid, M. Ostrick, J. R. M. Annand, A. G. Denig, A. N. Mushkarenkov, D. I. Sober, S. Cherepnya, D. Werthmüller, P. Aguar-Bartolomé, L. V. Fil'kov, I. Keshelashvili, F. Zehr, P. Pedroni, S. P. Kruglov, R. Gregor, A. Nikolaev, H. Berghäuser, J. Robinson, D. Mekterovic, C. M. Tarbert, K. Livingston, T. C. Jude, T. Rostomyan, H. J. Arends, I. Supek, A. Fix, M. H. Sikora, A. Koulbardis, Reinhard Beck, W. J. Briscoe, G. Rosner, F. Pheron, R. F. B. Codling, I. J. D. MacGregor, H. Ortega, J. Brudvik, R. Novotny, and A. Braghieri

Subjects
Physics, Nuclear and High Energy Physics, Particle physics, 010308 nuclear & particles physics, Detector, Form factor (quantum field theory), Gamma ray, Lambda, 01 natural sciences, Nuclear physics, 0103 physical sciences, High Energy Physics::Experiment, Nuclear Experiment, 010306 general physics, Microtron, Crystal Ball
Abstract

The Dalitz decay eta -> e(+) e(-) gamma has been measured in the gamma p -> eta p reaction with the Crystal Ball and TAPS multiphoton spectrometers, together with the photon-tagging facility at the Mainz Microtron MAMI. The experimental statistic used in this work is one order of magnitude greater than in any previous measurement of eta -> e(+) e(-) gamma. The value obtained for the slope parameter Lambda(-2) of the eta transition form factor, Lambda(-2) = (1.95 +/- 0.15(stat) +/- 0.10(syst)) GeV-2, is in good agreement with recent measurements conducted in eta -> e(+) e(-) gamma and eta -> mu(+) mu(-) gamma decays, as well as with recent form-factor calculations. The uncertainty obtained in the value of Lambda(-2) is lower compared to results from previous measurements of the eta -> e(+) e(-) gamma decay. (Less)

Published
2014

41. Photoproduction ofπ0Mesons off Neutrons in the Nucleon Resonance Region

Author

A. Nikolaev, B. M. K. Nefkens, A. Starostin, J. R. M. Annand, K. Livingston, T. C. Jude, B. Krusche, David Hamilton, I. Keshelashvili, D. P. Watts, V. L. Kashevarov, H. J. Arends, B. Oussena, M. Oberle, Jason Brudvik, A. Fix, D. M. Manley, M. Korolija, A. Kulbardis, P. Pedroni, V. Lisin, J. Robinson, F. Pheron, K. Bantawa, V. S. Bekrenev, P. A. Bartolome, Yasser Maghrbi, Sasa Micanovic, O. Jahn, Z. Marinides, E. F. McNicoll, E. J. Downie, R. Beck, D. I. Glazier, M. Dieterle, I. Supek, Lilian Witthauer, D. Werthmüller, I. Jaegle, S. N. Prakhov, D. Mekterovic, L. V. Fil'kov, M. H. Sikora, G. Rosner, A. Käser, M. Thiel, D. Branford, M. Ostrick, S. P. Kruglov, D. Howdle, G. M. Huber, D. I. Sober, M. Unverzagt, A. Polonski, J. Ahrens, D. Hornidge, Andy Thomas, T. Rostomyan, S. Cherepnya, I. J. D. MacGregor, P. Drexler, R. Kondratiev, S. Schumann, J. C. McGeorge, R. W. Novotny, W. J. Briscoe, A. N. Mushkarenkov, M. Martinez, J. Mancell, Volker Metag, E. Heid, B. Demissie, D. G. Middleton, and A. Braghieri

Subjects
Physics, Particle physics, Meson, Proton, Nuclear Theory, General Physics and Astronomy, Photon energy, 7. Clean energy, Nuclear physics, Isospin, Neutron, Nuclear Experiment, Nucleon, Microtron, Crystal Ball
Abstract

Precise angular distributions have been measured for the first time for the photoproduction of π0 mesons off neutrons bound in the deuteron. The effects from nuclear Fermi motion have been eliminated by a complete kinematic reconstruction of the final state. The influence of final-state-interaction effects has been estimated by a comparison of the reaction cross section for quasifree protons bound in the deuteron to the results for free protons and then applied as a correction to the quasifree neutron data. The experiment was performed at the tagged photon facility of the Mainz Microtron MAMI with the Crystal Ball and TAPS detector setup for incident photon energies between 0.45 and 1.4 GeV. The results are compared to the predictions from reaction models and partial-wave analyses based on data from other isospin channels. The model predictions show large discrepancies among each other and the present data will provide much tighter constraints. This is demonstrated by the results of a new analysis in the framework of the Bonn-Gatchina coupled-channel analysis which included the present data.

Published
2014

42. Determination of the $ \eta$ mass with the Crystal Ball at MAMI-B

Author

Reinhard Beck, C. M. Tarbert, A. Reiter, H. J. Arends, M. Unverzagt, W. J. Briscoe, Anthony W. Thomas, V. L. Kashevarov, Steffen Schumann, B. Boillat, D. P. Watts, David Manley, D. I. Glazier, D. Branford, S. N. Prakhov, A. Starostin, S. Lugert, V. S. Bekrenev, D. Mekterovic, M. Martinez-Fabregate, A. Polonski, A. Braghieri, J. C. McGeorge, U. Ludwig-Mertin, A. Jankowiak, D. Hornidge, T. Rostomyan, V. Lisin, M. Lang, M. Dehn, R. Kondratiev, P. Pedroni, S. Cherepnya, F. Zehr, G. Rosner, M. Korolija, R.O. Owens, K. Livingston, E. J. Downie, J. W. Price, D. I. Sober, I. Supek, O. Jahn, D. Krambrich, J. Ahrens, R. Gregor, K. H. Kaiser, A. Nikolaev, Jrm Annand, R. W. Novotny, B. Krusche, L. V. Fil'kov, B. M. K. Nefkens, R. F. B. Codling, I. J. D. MacGregor, M. Rost, Th. Walcher, Volker Metag, E. Heid, J. Brudvik, P. Aguar-Bartolomé, and M. Kotulla

Subjects
Physics, Nuclear and High Energy Physics, Particle physics, Meson, Spectrometer, Hadron, Eta meson, Nuclear physics, High Energy Physics::Experiment, Invariant mass, Nuclear Experiment, Nucleon, Energy (signal processing), Crystal Ball
Abstract

A new precise determination of the {\eta} meson mass is presented. It is based on a measurement of the threshold for the {\gamma}p -> p{\eta} reaction using the tagger focal-plane microscope detector at the MAMI-B facility in Mainz. The tagger microscope has a higher energy resolution than the standard tagging spectrometer and, hence, allowed an improvement in the accuracy compared to the previous {\eta} mass measurement at MAMI-B. The result m{\eta} = (547.851 +- 0.031 stat. +- 0.062 syst.) MeV agrees very well with the precise values of the NA48, KLOE and CLEO collaborations and deviates by about 5{\sigma} from the smaller, but also very precise value obtained by the GEM collaboration at COSY., Comment: Submitted for publication in EPJA

Published
2014

43. Neutron skin of (208)pb from coherent pion photoproduction

Author

C M, Tarbert, D P, Watts, D I, Glazier, P, Aguar, J, Ahrens, J R M, Annand, H J, Arends, R, Beck, V, Bekrenev, B, Boillat, A, Braghieri, D, Branford, W J, Briscoe, J, Brudvik, S, Cherepnya, R, Codling, E J, Downie, K, Foehl, P, Grabmayr, R, Gregor, E, Heid, D, Hornidge, O, Jahn, V L, Kashevarov, A, Knezevic, R, Kondratiev, M, Korolija, M, Kotulla, D, Krambrich, B, Krusche, M, Lang, V, Lisin, K, Livingston, S, Lugert, I J D, MacGregor, D M, Manley, M, Martinez, J C, McGeorge, D, Mekterovic, V, Metag, B M K, Nefkens, A, Nikolaev, R, Novotny, R O, Owens, P, Pedroni, A, Polonski, S N, Prakhov, J W, Price, G, Rosner, M, Rost, T, Rostomyan, S, Schadmand, S, Schumann, D, Sober, A, Starostin, I, Supek, A, Thomas, M, Unverzagt, Th, Walcher, L, Zana, and F, Zehr

Abstract

Information on the size and shape of the neutron skin on (208)Pb is extracted from coherent pion photoproduction cross sections measured using the Crystal Ball detector together with the Glasgow tagger at the MAMI electron beam facility. On exploitation of an interpolated fit of a theoretical model to the measured cross sections, the half-height radius and diffuseness of the neutron distribution are found to be c(n)=6.70±0.03(stat.) fm and a(n)=0.55±0.01(stat.)(-0.03)(+0.02)(sys.) fm, respectively, corresponding to a neutron skin thickness Δr(np)=0.15±0.03(stat.)(-0.03)(+0.01)(sys.) fm. The results give the first successful extraction of a neutron skin thickness with an electromagnetic probe and indicate that the skin of (208)Pb has a halo character. The measurement provides valuable new constraints on both the structure of nuclei and the equation of state for neutron-rich matter.

Published
2014

44. Measurement of theH1(γ⃗, p⃗)π0Reaction Using a Novel Nucleon Spin Polarimeter

Author

K. Livingston, T. C. Jude, B. Krusche, Yasser Maghrbi, D. G. Middleton, Volker Metag, B. McKinnon, R. F. B. Codling, E. F. McNicoll, D. Branford, V. Lisin, I. Jaegle, D. I. Sober, R. Kondratiev, H. J. Arends, B. Oussena, P. Pedroni, Jason Brudvik, J. Robinson, D. Werthmüller, O. Jahn, I. Supek, I. J. D. MacGregor, F. Pheron, Sasa Micanovic, S. Schumann, R. W. Novotny, Ron L. Workman, P. B. Otte, V. L. Kashevarov, A. Starostin, P. Aguar-Bartolomé, M. H. Sikora, A. Polonski, D. P. Watts, D. Mekterovic, M. Ostrick, Z. Marinides, D. I. Glazier, D. Howdle, A. Koulbardis, D. M. Manley, I. M. Suarez, M. Korolija, F. Zehr, K. Bantawa, M. Thiel, M. Kotulla, S. P. Kruglov, V. S. Bekrenev, A. Braghieri, J. C. McGeorge, G. Rosner, T. Rostomyan, L. V. Fil'kov, H. Berghäuser, S. N. Prakhov, David Hamilton, I. Keshelashvili, M. Martinez, Andy Thomas, B. Demissie, S. Cherepnya, P. Drexler, R. Gregor, J. R. M. Annand, A. Nikolaev, B. M. K. Nefkens, I. I. Strakovsky, E. Heid, M. Unverzagt, D. Hornidge, B. Freehart, I. Zamboni, R. Beck, L. K. Akasoy, W. J. Briscoe, A. N. Mushkarenkov, and E. J. Downie

Subjects
Physics, Particle physics, Meson production, Partial wave analysis, Nuclear Theory, General Physics and Astronomy, Polarimeter, Polarization (waves), 7. Clean energy, Nuclear physics, Hadron physics, Photon beam, Nuclear Experiment, Nucleon, Excitation
Abstract

We report the first large-acceptance measurement of polarization transfer from a polarized photon beam to a recoiling nucleon. The measurement pioneers a novel polarimetry technique, which can be applied to many other nuclear and hadron physics experiments. The commissioning reaction of $^{1}H(\mathrm{\ensuremath{\gamma}P\vec},\text{ }\mathrm{pP\vec}){\ensuremath{\pi}}^{0}$ in the range $0.4l{E}_{\ensuremath{\gamma}}l1.4\text{ }\text{ }\mathrm{GeV}$ validates the technique and provides essential new data to constrain the excitation spectrum of the nucleon.

Published
2014

45. Helicity dependence of the γ 3He → πX reactions in the Δ(1232) resonance region

Author

M. Unverzagt, I. J. D. MacGregor, R. Beck, F. Pheron, V. L. Kashevarov, F. Rigamonti, S. Cherepnya, B. M. K. Nefkens, W. J. Briscoe, A. N. Mushkarenkov, R. Kondratiev, J. R. M. Annand, G. Rosner, D. M. Manley, A. Starostin, M. Korolija, A. Nikolaev, P. Aguar Bartolomé, M. Oberle, B. Krusche, Giuseppe Mandaglio, A. Polonski, A. Kulbardis, M. Thiel, E. J. Downie, I. Jaegle, D. Hornidge, M. Ostrick, S. Costanza, A. J. Sarty, J. Ahrens, D. Howdle, B. Oussena, D. P. Watts, J. Mancell, D. Werthmüller, L. V. Fil'kov, D. G. Middleton, J. C. McGeorge, V. S. Bekrenev, H. Berghäuser, K. Livingston, T. C. Jude, J. Krimmer, T. Rostomyan, I. Supek, S. Schumann, H. J. Arends, P. B. Otte, A. Fix, P. Pedroni, I. Keshelashvili, A. Braghieri, M. Romaniuk, David Hamilton, S. P. Kruglov, V. Lisin, O. Jahn, Werner Heil, G. M. Huber, D. I. Glazier, S. N. Prakhov, Andy Thomas, C. Collicott, P. Drexler, H. Ortega, Volker Metag, and E. Heid

Subjects
Physics, Nuclear reaction, Nuclear and High Energy Physics, Meson, 010308 nuclear & particles physics, Nuclear Theory, Hadron, Elementary particle, 7. Clean energy, 01 natural sciences, Helicity, Nuclear physics, Pion, 0103 physical sciences, Neutron, Atomic physics, Nuclear Experiment, 010306 general physics, Crystal Ball
Abstract

The helicity dependences of the differential cross sections for the semi-inclusive γ 3He → π0 X and γ 3He → π± X reactions have been measured for the first time in the energy region 200 < E γ 450 MeV. The experiment was performed at the tagged photon beam facility of the MAMI accelerator in Mainz using a longitudinally polarised high-pressure 3He gas target. Hadronic products were measured with the large-acceptance Crystal Ball detector complemented with additional devices for charged-particle tracking and identification. Unpolarised differential cross sections and their helicity dependence are compared with theoretical calculations using the Fix-Arenhovel model. The effect of the intermediate excitation of the Δ(1232) resonance can be clearly seen from this comparison, especially for the polarised case, where nuclear effects are relatively small. The model provides a better theoretical description of the unpolarised charged pion photoproduction data than the neutral pion channel. It does significantly better in describing the helicity-dependent data in both channels. These comparisons provide new information on the mechanisms involved in pion photoproduction on 3He and suggest that a polarised 3He target can provide valuable information on the corresponding polarised quasi-free neutron reactions.

Published
2014

46. Measurement of the transverse target and beam-target asymmetries in η meson photoproduction at MAMI

Author

M. Oberle, P. P. Martel, M. Dieterle, B. Oussena, Aron M. Bernstein, C. Collicott, D. P. Watts, A. B. Neganov, E. F. McNicoll, S. Cherepnya, H. Ortega, David Hamilton, W. Gradl, A. N. Mushkarenkov, W. Meyer, W. J. Briscoe, J. Mancel, D. Hornidge, G. Reicherz, P. Hall Barrientos, B. Krusche, V. Lisin, E. J. Downie, I. J. D. MacGregor, V. L. Kashevarov, Lothar Tiator, K. Livingston, N. S. Borisov, P. Pedroni, D. Werthmüller, R. A. Miskimen, R. Kondratiev, G. M. Gurevich, A. Fix, D. M. Manley, M. Korolija, P. Ott, A. Polonski, S. Costanza, S. N. Prakhov, Yu. A. Usov, O. Steffen, V. V. Polyanski, R. Beck, M. Wolfes, A. B. Lazarev, A. Braghieri, Th. Strub, S. Garni, I. I. Strakovsky, H. J. Arends, D. G. Middleton, Lilian Witthauer, G. M. Huber, Anthony W. Thomas, D. I. Glazier, I. Keshelashvili, J. R. M. Annand, S. Schumann, P. B. Otte, A. Nikolaev, B. M. K. Nefkens, D. Howdle, L. V. Fil'kov, C. S. Akondi, M. Ostrick, A. J. Sarty, I. Supek, T. Rostomyan, and M. Unverzagt

Subjects
Physics, Particle physics, Photon, Proton, Meson, Nuclear Theory, media_common.quotation_subject, Partial wave analysis, General Physics and Astronomy, Asymmetry, High Energy Physics - Experiment, Nuclear physics, beam-target asymmetry F, γ⃗ p⃗ →ηp reaction, Mainz Microtron MAMI, High Energy Physics::Experiment, Nucleon, Nuclear Experiment, Microtron, Crystal Ball, media_common
Abstract

We present new data for the transverse target asymmetry T and the very first data for the beam-target asymmetry F in the $\vec \gamma \vec p\to\eta p$ reaction up to a center-of-mass energy of W=1.9 GeV. The data were obtained with the Crystal-Ball/TAPS detector setup at the Glasgow tagged photon facility of the Mainz Microtron MAMI. All existing model predictions fail to reproduce the new data indicating a significant impact on our understanding of the underlying dynamics of $\eta$ meson photoproduction. The peculiar nodal structure observed in existing T data close to threshold is not confirmed., Comment: 5 pages, 3 figures, accepted for publication in PRL

Published
2014

47. Energy related conservation law for fluids and multi-fluid plasmas with equilibrium flow

Author

M. Unverzagt

Subjects
Physics, Conservation law, Conservation of energy, Eulerian path, Condensed Matter Physics, symbols.namesake, Acoustic theory, Classical mechanics, Fluid dynamics, symbols, Statistical physics, Noether's theorem, Entropy (arrow of time), Free energy principle
Abstract

Within the framework of dissipationless multi-fluid theory for plasmas, all nonlinear perturbations of a stationary equilibrium that could be created from the equilibrium without breaking local entropy conservation are considered. Describing the fluid perturbations by Eulerian displacement vectors reveals a general symmetry and through Noether’s theorem leads to a conservation law. Its relation to the law of energy conservation is discussed since it will be important for the generalization of the energy principle known for static equilibria in magnetohyrodynamics to an energy principle of stationary equilibria in the framework of a multi-fluid theory.

Published
1998

48. Complete momentum balance for single ionization of helium by fast ion impact: Experiment

Author

C. J. Wood, Horst Schmidt-Böcking, R. E. Olson, M Unverzagt, R. Moshammer, W. Schmitt, J. Ullrich, and H. Kollmus

Subjects
Momentum, Physics, Scattering, Ionization, Electron, Atomic physics, Nuclear Experiment, Atomic and Molecular Physics, and Optics, Spectral line, Charged particle, Lepton, Ion
Abstract

The collision dynamics of He single ionization by 3.6MeV/uSe{sup 28+} impact was explored using the reaction microscope of the Gesellschaft f{umlt u}r Schwerionenforschung, a high-resolution integrated multielectron recoil-ion momentum spectrometer. The complete three-particle final-state momentum distribution (nine Cartesian components p{sub i}) was imaged with a resolution of {Delta}p{sub i}{approx}{plus_minus}0.1a.u. by measuring the three momentum components of the emitted electron and the recoiling target ion in coincidence. The projectile energy loss has been determined on a level of {Delta}E{sub p}/E{sub p}{approx}10{sup {minus}7} and projectile scattering angles as small as {Delta}{var_theta}{approx}10{sup {minus}7}rad became accessible. The experimental data which are compared with results of classical trajectory Monte Carlo calculations reveal an unprecedented insight into the details of the electron emission and the collision dynamics for ionization of helium by fast heavy-ion impact. {copyright} {ital 1997} {ital The American Physical Society}

Published
1997

49. Intra-atomic Electron-Electron Scattering inp-He Collisions (Thomas Process) Investigated by Cold Target Recoil Ion Momentum Spectroscopy

Author

Henrik Cederquist, J. Euler, M. Unverzagt, C. L. Cocke, S. Nüttgens, Lutz Spielberger, V. Mergel, S. Lencinas, M. Achler, C. J. Wood, A. Salin, Kh. Khayyat, Rami Ali, Reinhard Dörner, Joachim Ullrich, R E Olson, Ottmar Jagutzki, Horst Schmidt-Böcking, W. Wu, and Dž. Belkić

Subjects
Momentum, Physics, Recoil, Scattering, Ionization, General Physics and Astronomy, Electron, Atomic physics, Spectroscopy, Electron scattering, Ion
Abstract

We have performed a kinematically complete experiment for the transfer ionization reaction 0.15{endash}1.4 MeV p+He{r_arrow}H{sup 0}+He{sup 2+} +e{sup {minus}} by measuring the three-dimensional momentum vector of the He{sup 2+} ion in coincidence with the scattering angle and the plane of the H{sup 0} . In the measured fourfold differential cross section we can clearly distinguish between the independent two-step process of capture plus ionization and the correlated e -e Thomas scattering. We find a v{sup {minus}7.4{plus_minus}1}{sub P} scaling for the total cross section of the e -e Thomas process. {copyright} {ital 1997} {ital The American Physical Society}

Published
1997

50. Kinematically complete experiments using cold target recoil ion momentum spectroscopy

Author

Lutz Spielberger, Joachim Ullrich, Ottmar Jagutzki, V. Mergel, W. Schmitt, Kh. Khayyat, R. E. Olson, C. L. Cocke, James M. Feagin, M. Achler, Reinhard Dörner, H. Bräuning, M. H. Prior, Horst Schmidt-Böcking, T. Vogt, H. Khemliche, M. Unverzagt, R. Moshammer, and Th. Weber

Subjects
Physics, Nuclear and High Energy Physics, Photon, Momentum transfer, Position and momentum space, Electron, Ion, Nuclear physics, Momentum, Recoil, Atom, Physics::Atomic Physics, Atomic physics, Nuclear Experiment, Instrumentation
Abstract

Cold Target Recoil Ion Momentum Spectroscopy allows the detection of the three-dimensional momentum vector of the recoiling product ion from ion, electron or photon atom collisions with 4π solid angle and high resolution. It can be combined with large area position-sensitive detectors for electron detection or measurement of the projectile charge-state and scattering angle. Such ‘reaction microscopes’ cover the full correlated momentum space of all fragments of an atomic reaction yielding kinematically complete information for each reaction event. For the first time in atomic collision physics fully differential data became available in the sense that not only the momenta of all fragments, but also the complete momentum space is observed in one experiment. Recent results achieved with this new technique for slow p-He collisions and threshold photo ionization of He will be discussed.

Published
1997

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