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1. OBSERVATION OF THE ABC EFFECT IN THE FIRST EXCLUSIVE MEASUREMENTS OF pn → dπ0π0

Author

Magnus Wolke, J. Stepaniak, Akira Yamamoto, R. Meier, Pawel Marciniewski, V. Tikhomirov, G. Ivanov, A. Povtoreyko, T. Skorodko, B. Morosov, Hans Calén, J. Zabierowski, P.-E. Tegnér, C. Bargholtz, S. Keleta, A. A. Kuznetsov, C. Ekström, F. Cappellaro, S. Kullander, B. Shwartz, Murat M. Kaskulov, M. Bashkanov, A. Kupść, K. Lindberg, I. Zartova, K. Fransson, A. Schwick, Marek Jacewicz, R. J. M. Y. Ruber, E. Jiganov, H. Clement, Bo Höistad, D. Bogoslowsky, I. Koch, Wolfgang Scobel, O. Khakimova, P. Thörngren-Engblom, Jozef Zlomanczuk, Leif Gustafsson, V. Sopov, V. Tchernyshev, F. Kren, A. Turowiecki, Y. Petukhov, W. Oelert, L. Geren, T. Johansson, C. Pauly, R. Shafigullin, and G. J. Wagner

Subjects
Physics, Nuclear and High Energy Physics, Complete data, Quantum mechanics, Spectrum (functional analysis), Bound state, Theoretical models, Prove it, Astronomy and Astrophysics, Invariant mass, Atomic physics, Atomic and Molecular Physics, and Optics, Excitation
Abstract

The reaction pn → dπ0π0 constitutes the most fundamental system for the study of the ABC effect - a puzzling threshold enhancement in the ππ invariant mass spectrum of the ππ system in double-pionic fusion to nuclear bound states. The first exclusive measurements of this reaction have now been carried out at CELSIUS-WASA. They exhibit a striking low-mass enhancement in the ππ invariant mass spectrum, prove it to be a σ-channel phenomenon and falsify conventional theoretical models, which predict an associated high-mass enhancement not present in the new exclusive data. In the kinematically complete data sample we observe a ΔΔ excitation, where the interaction between the two Δ obviously plays a crucial role for the generation of the ππ low-mass enhancement.

Published
2007

2. ππ PRODUCTION IN PROTON-PROTON COLLISIONS

Author

M. Bashkanov, F. Cappellaro, L. Demiroers, D. Bogoslowsky, Jozef Zlomanczuk, V. Tchernyshev, W. Oelert, Akira Yamamoto, B. Morosov, A. Kupść, Pawel Marciniewski, T. Johansson, C. Ekström, A. A. Kuznetsov, A. Turowiecki, K. Fransson, C. Pauly, V. Tikhomirov, B. Shwartz, R. Shafigullin, G. J. Wagner, A. Schwick, Marek Jacewicz, A. Povtorejko, E. Jiganov, H. Clement, P. Thörngren-Engblom, J. Greiff, Hans Calén, Y. Petukhov, M. Kaskulov, O. Khakimova, V. Sopov, F. Kren, R. Meier, S. Kullander, I. Koch, G. Ivanov, Magnus Wolke, Leif Gustafsson, R. J. M. Y. Ruber, J. Stepaniak, Bo Höistad, J. Zabierowski, S. Keleta, W. Scobel, and T. Skorodko

Subjects
Physics, Nuclear and High Energy Physics, Fusion, Complete data, Range (particle radiation), Proton, Excited state, Astronomy and Astrophysics, Invariant mass, Production (computer science), Atomic physics, Atomic and Molecular Physics, and Optics, Excitation
Abstract

At CELSIUS-WASA the two-pion production in proton-proton collisisons has been measured exclusively from threshold up to the energy regime, where both of the collision partners are expected to be excited to the Δ state. The measurements constitute the first kinematically complete data samples of solid statistics in this energy range. Most of the data have been obtained for the π+π- and π0π0channels. Whereas at near-threshold energies the differential distributions can be succesfully explained by chiral dynamics and Roper excitation, respectively, the data for the π+π- channel in the ΔΔ region can be described only, if the special configuration (ΔΔ)0+ is assumed. The data for the π0π0 channel moreover exhibit a low-mass enhancement in the π0π0 invariant mass spectrum, which is reminiscent of the ABC-effect found in double-pionic fusion to light nuclei.

Published
2007

3. LOW-MASS ππ ENHANCEMENT IN BARYONIC ππ PRODUCTION: ABC EFFECT REVISED BY EXCLUSIVE MEASUREMENTS

Author

C. Ekström, R. J. M. Y. Ruber, Magnus Wolke, J. Stepaniak, G. Ivanov, B. Morosov, I. Zartova, P. Thörngren-Engblom, W. Scobel, B. Shwartz, R. Shafigullin, G. J. Wagner, Y. Petukhov, Jozef Zlomanczuk, L. Geren, D. Bogoslowsky, S. Kullander, A. A. Kuznetsov, V. Tchernyshev, W. Oelert, M. Bashkanov, F. Cappellaro, C. Bargholtz, Pawel Marciniewski, A. Povtoreyko, O. Khakimova, E. Jiganov, H. Clement, A. Turowiecki, Leif Gustafsson, Hans Calén, V. Tikhomirov, T. Johansson, Akira Yamamoto, A. Kupść, K. Fransson, T. Skorodko, C. Pauly, A. Schwick, Marek Jacewicz, K. Lindberg, P.-E. Tegnér, R. Meier, I. Koch, Bo Höistad, M. Kaskulov, J. Zabierowski, S. Keleta, V. Sopov, and F. Kren

Subjects
Baryon, Physics, Nuclear physics, Nuclear and High Energy Physics, Complete data, Bound state, Prove it, Astronomy and Astrophysics, Production (computer science), Invariant mass, Low Mass, Atomic and Molecular Physics, and Optics, Spectral line
Abstract

The ABC effect - a puzzling threshold enhancement in the ππ invariant mass spectrum of double-pionic fusion to nuclear bound states - has been investigated since 40 years by inclusive measurements without providing a conclusive interpretation. First exclusive measurements to this topic have now been carried out at CELSIUS-WASA. They confirm a huge ππ threshold enhancement, prove it to be of scalar-isoscalar nature, i.e., a σ-channel phenomenon and reveal the theoretically predicted high-mass enhancement in inclusive spectra to be of πππ rather than of ππ nature - falsifying thus corresponding model predictions for the ABC effect. From the kinematically complete data samples we infer that the interaction between the two Δ particles created in this process is of crucial importance.

Published
2007

4. Measurement of the η→π+π−e+e− decay branching ratio

Author

J. Zabierowski, E. Jiganov, V. Tchernyshev, L. Demiroers, Bo Höistad, P. Thörngren-Engblom, H. Clement, Marek Jacewicz, Wolfgang Scobel, M. Bashkanov, R. Shafigullin, G. J. Wagner, P.-E. Tegnér, H. Pettersson, Karin Schönning, A. A. Kuznetsov, K. Lindberg, W. Oelert, D. Bogoslawsky, A. Turowiecki, Y. Petukhov, Jozef Zlomanczuk, Tord Johansson, V. Sopov, Pawel Marciniewski, V. Tikhomirov, Leif Gustafsson, C. Pauly, R. Meier, Roger Ruber, I. Zartova, Sven Kullander, Akira Yamamoto, L. Geren, I. Koch, T. Skorodko, A. Povtorejko, Chr. Bargholtz, I. V. Laukhin, Hans Calén, Magnus Wolke, Kjell Fransson, Andrzej Kupsc, G. Ivanov, Curt Ekstrom, B. Morosov, B. Shwartz, J. Stepaniak, F. Cappellaro, and S. Negasi Keleta

Subjects
Physics, Nuclear physics, Nuclear and High Energy Physics, Particle physics, Meson, Branching fraction, Detector, High Energy Physics::Experiment, Nuclear Experiment
Abstract

The reaction pd -> He-3 eta at threshold was used to provide a clean source of eta mesons for decay studies with the WASA detector at CELSIUS. The branching ratio of the decay eta -> pi(+)pi( ...

Published
2007

5. Exclusive measurements of pd→He3ππ: The ABC effect revisited

Author

Akira Yamamoto, K. Fransson, S. Kullander, F. Cappellaro, A. Turowiecki, Pawel Marciniewski, V. Tikhomirov, O. Khakimova, E. Jiganov, Leif Gustafsson, H. Clement, D. Bogoslawsky, A. Povtorejko, Jozef Zlomanczuk, P. Thörngren-Engblom, C. Ekström, Hans Calén, W. Scobel, C. Pauly, G. Ivanov, I. Koch, R. J. M. Y. Ruber, Magnus Wolke, B. Morosov, A. Kupść, T. Johansson, M. Bashkanov, B. Shwartz, J. Stepaniak, Y. Petukho, M. Kaskulov, V. Sopov, F. Kren, G. J. Wagner, J. Zabierowski, Marek Jacewicz, V. Tchernyshev, J. Greiff, L. Demiroers, R. Meier, A. A. Kuznetsov, W. Oelert, Bo Höistad, T. Skorodko, and S. Keleta

Subjects
Mass enhancement, Nuclear physics, Physics, Nuclear and High Energy Physics, Angular distribution, Isoscalar, Dalitz plot, Atomic physics, Storage ring
Abstract

Exclusive measurements of the reactions p d → He 3 π + π − and p d → He 3 π 0 π 0 have been carried out at T p = 0.893 GeV at the CELSIUS storage ring using the WASA detector. The π + π − channel evidences a pronounced enhancement at low invariant ππ masses—as anticipated from previous inclusive measurements of the ABC effect. This enhancement is seen to be even much larger in the isoscalar π 0 π 0 channel. The differential distributions prove this enhancement to be of scalar–isoscalar nature. ΔΔ calculations give a good description of the data, if a boundstate condition is imposed for the intermediate ΔΔ system.

Published
2006

6. First results from the CELSIUS/WASA facility

Author

Z. Wilhelmi, V. Tchernyshev, V. Tikhomirov, P.-E. Tegnér, L. Gustafsson, N. Kimura, R. Shafigulin, D. Reistad, M. Bashkanov, K. Lindberg, J. Zabierowski, D. Bogoslawsky, J. Greiff, A. Nawrot, C. Bargholz, Arne Johansson, P. Marciniewski, T. Skorodko, S. Keletea, H. Yamaoka, Hans Calén, H. Clement, L. Demiroers, Y. Petukhov, Bo Höistad, A. Kipsc, F. Cappellaro, S. Kullander, B.A. Shwartz, Kjell Fransson, W. Oelert, Tord Johansson, S. Sandukovsky, B. M. K. Nefkens, V. Sopov, J. Zlomanczuk, A. Povtorejko, E. Jiganov, Ulrich Wiedner, W. Scobel, Marek Jacewicz, E. Dorochkevitch, Curt Ekstrom, I. Koch, Roger Ruber, B. Morosov, P. Thörngren Engblom, J. Stepaniak, G.J. Wagner, M. Gornov, Akira Yamamoto, A. Turowiecki, G. Ivanov, C. Pauly, A. A. Kuznetsov, and C.-J. Fridén

Subjects
Physics, Nuclear and High Energy Physics, Degree Celsius, Nuclear engineering
Published
2003

7. Excitation of the Roper resonance in single- and double-pion production in nucleon-nucleon collisions⋆

Author

B. Morosov, Henrik Petterson, K. Franssen, E. Jiganov, M. Wolke, Hans Calén, O. Khakimova, F. Cappellaro, T. Skorodko, Karin Schönning, L. Gustafsson, H. Clement, P. Thörngren-Engblom, I. Koch, L. Demiroers, B.A. Shwartz, J. Stepeniak, R. Meier, D. Duniec, Sven Kullander, G. Ivanov, P. Marciniewski, G.J. Wagner, Akira Yamamoto, A. Povtorejko, Marek Jacewicz, M. Bashkanov, A. A. Kuznetsov, Curt Ekstrom, Y. Petukhov, M. Kaskulov, V. Sopov, J. Zlomanczuk, F. Kren, Bo Höistad, Wolfgang Scobel, C. Pauly, V. Tikhomirov, E. Doroshkevich, J. Zabierowski, S. Keleta, A. Kupść, D. Bogoslawsky, and Tord Johansson

Subjects
Nuclear physics, Physics, Nuclear and High Energy Physics, Particle decay, Roper resonance, Pair production, Pion, Meson, Branching fraction, Nuclear Theory, Nuclear Experiment, Nucleon, Excitation
Abstract

In most investigations the Roper resonance is sensed only very indirectly via complex partial-wave analyses. We find indications for its excitation in the invariant nπ+ mass spectrum of the pp → npπ+ reaction at M ≈ 1360 MeV with a width of ≈ 150 MeV . The values fit very favorably to the most recent phase shift results as well as to the observations at BES. In the near-threshold two-pion production pp → ppπ0π0 , where the Roper excitation and its subsequent decays via the routes N * → Δπ → Nππ and N * → Nσ are the only dominant processes, we find its direct decay into the Nσ channel to be the by far dominating decay process --in favor of a monopole excitation of the Roper resonance.

Published
2008

8. Excitation of the Roper resonance in single- and double-pion production in nucleon-nucleon collisions

Author

M. Bashkanov, L. Gustafsson, Wolfgang Scobel, O. Khakimova, Y. Petukhov, I. Koch, Henrik Petterson, Karin Schönning, E. Jiganov, C. Pauly, G. Ivanov, L. Demiroers, D. Duniec, S. Keleta, B.A. Shwartz, Curt Ekstrom, Sven Kullander, A. A. Kuznetsov, Marek Jacewicz, A. Povtorejko, V. Tikhomirov, Akira Yamamoto, H. Clement, E. Doroshkevich, F. Cappellaro, B. Morosov, Bo Höistad, J. Zabierowski, M. Kaskulov, V. Sopov, J. Zlomanczuk, F. Kren, J. Stepeniak, P. Thörngren-Engblom, R. Meier, G.J. Wagner, K. Franssen, A. Kupść, D. Bogoslawsky, M. Wolke, Hans Calén, Tord Johansson, P. Marciniewski, and T. Skorodko

Subjects
Physics, Nuclear physics, Roper resonance, Pion, Nuclear Theory, Mass spectrum, Magnetic monopole, Production (computer science), Nuclear Experiment, Nucleon, Excitation
Abstract

In most investigations the Roper resonance is sensed only very indirectly via complex partial-wave analyses. We find indications for its excitation in the invariant nπ+ mass spectrum of the pp → npπ+ reaction at M ≈ 1360 MeV with a width of ≈ 150 MeV . The values fit very favorably to the most recent phase shift results as well as to the observations at BES. In the near-threshold two-pion production pp → ppπ0π0 , where the Roper excitation and its subsequent decays via the routes N * → Δπ → Nππ and N * → Nσ are the only dominant processes, we find its direct decay into the Nσ channel to be the by far dominating decay process --in favor of a monopole excitation of the Roper resonance.

Published
2008

9. Anisotropy in the pion angular distribution of the reactionpp→ppπ0at 400 MeV

Author

M. Bashkanov, O. Khakimova, B. Höistad, S. Negasi Keleta, C. Pauly, F. Cappellaro, S. Kullander, F. Kren, H. Pettersson, Karin Schönning, I. Koch, Magnus Wolke, Hans Calén, Marek Jacewicz, L. Demirörs, H. Clement, J. Stepaniak, A. Kupść, T. Johansson, Wolfgang Scobel, T. Skorodko, J. Zabierowski, Jozef Zlomanczuk, P. Thörngren Engblom, K. Fransson, and Pawel Marciniewski

Subjects
Nuclear physics, Physics, Nuclear and High Energy Physics, Angular distribution, Pion, Gamma ray, Pi, High Energy Physics::Experiment, Center of mass, Few-body systems, Nuclear Experiment, Anisotropy, Storage ring
Abstract

The reaction pp -> pp pi(0) was studied with the WASA detector at the CELSIUS storage ring. The center of mass angular distribution of the pi(0) was obtained by detection of the gamma decay prod ...

Published
2007

10. Single- and Double-Pion Production in Nucleon Collisions on the Nucleon and on Nuclei -- the ABC Effect and its Possible Origin in a Dibaryonic Resonance

Author

H. Clement, M. Bashkanov, C. Bargholtz, D. Bogoslawsky, H. Calen, F. Cappellaro, L. Demiroers, E. Doroshkevich, D. Duniec, C. Ekström, K. Franssen, L. Geren, L. Gustafsson, B. Höistad, G. Ivanov, M. Jacewicz, E. Jiganov, T. Johansson, M. Kaskulov, O. Khakimova, S. Keleta, I. Koch, F. Kren, S. Kullander, A. Kupść, A. Kuznetsov, K. Lindberg, P. Marciniewski, R. Meier, B. Morosov, C. Pauly, H. Petterson, Y. Petukhov, A. Povtorejko, A. Pricking, K. Schönning, W. Scobel, B. Shwartz, T. Skorodko, V. Sopov, J. Stepeniak, P.-E. Tegner, P. Thörngren-Engblom, V. Tikhomirov, G.J. Wagner, M. Wolke, A. Yamamoto, J. Zabierowski, I. Zartova, and J. Złomanczuk

Subjects
Physics, Nuclear and High Energy Physics, Isoscalar, Nuclear Theory, Resonance, FOS: Physical sciences, Context (language use), Nuclear physics, Pion, Nuclear fusion, Invariant mass, Production (computer science), Nuclear Experiment (nucl-ex), Nucleon, Nuclear Experiment
Abstract

The ABC effect -- an intriguing low-mass enhancement in the $\pi\pi$ invariant mass spectrum -- is known from inclusive measurements of two-pion production in nuclear fusion reactions. First exclusive measurements carried out at CELSIUS-WASA for the fusion reactions leading to d or $^3$He reveal this effect to be a $\sigma$ channel phenomenon associated with the formation of a $\Delta\Delta$ system in the intermediate state and combined with a resonance-like behavior in the total cross section. Together with the observation that the differential distributions do not change in shape over the resonance region the features fulfill the criteria of an isoscalar s-channel resonance in $pn$ and $NN\pi\pi$ systems, if the two emitted nucleons are bound. It obviously is robust enough to survive in nuclei as a dibaryonic resonance configuration. In this context also the phenomenon of $N\Delta$ resonances is reexamined., Comment: 8 pages,3 figures, Proc. Int. School Nucl. Phys., 29th course on Quarks in Hadrons and Nuclei, Erice 2007 (to be published in Progress in Particle and Nuclear Physics)

Published
2007
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11. Two-Pion Production in Proton-Proton Collisions

Author

T. Sefzick, Ulrich Wiedner, E. Doroshkevich, M. Bashkanov, Marc Wagner, Curt Ekstrom, K. Kilian, L. Demiroers, H. P. Morsch, T. Skorodko, H. Freiesleben, P. Marciniewski, Hans Calén, A. Gillitzer, B. Morosov, Bo Höistad, Y. Petukhov, Kjell Fransson, M. Fritsch, M. Schulte-Wissermann, C. Pauly, P. Wintz, E. Kuhlmann, Marek Jacewicz, H. Clement, P. Zupranski, S. Keleta, J. Stepaniak, W. Schröder, Andrzej Kupsc, F. Cappellaro, S. Kullander, R. Meier, S. Dshemuchadse, Wolfgang Scobel, L. Gustafsson, A. Erhardt, Tord Johansson, E. Roderburg, G.J. Wagner, S. Abdel-Samad, W. Eyrich, K. Möller, P. Schönmeier, Leonhard Karsch, P. Wüstner, J. Kress, I. Koch, J. Zlomanczuk, S. Marcello, J. Zabierowski, and K.-Th. Brinkmann

Subjects
Nuclear physics, Physics, Particle physics, Pion, Proton, Nuclear Theory, Nuclear Experiment, Measure (mathematics), Beam (structure), Excitation
Abstract

A program to measure the two‐pion production in nucleon‐nucleon collisions exclusively and in all channels from threshold up to Tp = 1360 MeV has been started at CELSIUS‐WASA. First preliminary results for ppπ+π− and ppπ0π0 channels are presented. In the near‐threshold region they are consistent with a dominance of the Roper excitation and its successive decay into Nσ and Δπ channels. At energies Tp > 1 GeV we observe a very different behavior, which is at variance with theoretical predictions. At COSY‐TOF exclusive measurements of the pp → ppπ+π− reaction have been carried out with polarized beam. Preliminary results show non‐zero analyzing powers which point to a sizeable admixture of l ≠ 0 partial waves indicating possibly an influence of the ρ‐channel.

Published
2004

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