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5 results on '"Capitani, Gp"'

1. Ratios of helicity amplitudes for exclusive ρ⁰ electroproduction on transversely polarized protons

Author

Airapetian, A, Akopov, N, Akopov, Z, Aschenauer, EC, Augustyniak, W, Belostotski, S, Blok, HP, Borissov, A, Bryzgalov, V, Capitani, GP, Ciullo, G, Contalbrigo, M, Deconinck, W, De Leo, R, De Sanctis, E, Duren, M, Elbakian, G, Ellinghaus, F, Felawka, L, Frullani, S, Garibaldi, F, Gavrilov, G, Gharibyan, V, Goloskokov, SV, Holler, Y, Ivanilov, A, Jackson, HE, Joosten, Sylvester, Kaiser, R, Karyan, G, Kisselev, A, Korotkov, V, Kozlov, V, Kravchenko, P, Kroll, P, Lagamba, L, Lapikas, L, Lehmann, I, Lenisa, P, Lorenzon, W, Manaenkov, SI, Marianski, B, Marukyan, H, Miyachi, Y, Movsisyan, A, Muccifora, V, Nass, A, Nowak, W-D, Pappalardo, LL, Petrosyan, A, Reimer, PE, Reolon, R, Riedl, C, Rith, K, Rosner, G, Rostomyan, A, Ryckbosch, Dirk, Salomatin, Y, Schaefer, A, Schnell, Gunar, Seitz, B, Shibata, T-A, Shutov, V, Statera, M, Terkulov, A, Truty, R, Trzcinski, A, Tytgat, Michael, Van Haarlem, Yves, Van Hulse, Charlotte, Veretennikov, D, Vikhrov, V, Vilardi, I, Yaschenko, S, Zihlmann, B, and Zupranski, P

Subjects
ELASTIC ELECTROPRODUCTION, Physics and Astronomy, J/PSI MESONS, SPIN, LEPTOPRODUCTION, GENERALIZED PARTON DISTRIBUTIONS, HERA, SCATTERING, High Energy Physics::Experiment, HYDROGEN, Nuclear Experiment, CROSS-SECTION, VECTOR-MESON PRODUCTION
Abstract

Exclusive rho(0)-meson electroproduction is studied by the HERMES experiment, using the 27.6 GeV longitudinally polarized electron/positron beam of HERA and a transversely polarized hydrogen target, in the kinematic region 1.0 GeV2 < Q(2) < 7.0GeV(2), 3.0GeV< W < 6.3 GeV, and -t' < 0.4 GeV2. Using an unbinned maximum-likelihood method, 25 parameters are extracted. These determine the real and imaginary parts of the ratios of several helicity amplitudes describing rho(0)-meson production by a virtual photon. The denominator of those ratios is the dominant amplitude, the nucleon-helicity-non-flip amplitude F-0 (1/2 0 1/2), which describes the production of a longitudinal rho(0)-meson by a longitudinal virtual photon. The ratios of nucleon-helicity-nonflip amplitudes are found to be in good agreement with those from the previous HERMES analysis. The transverse target polarization allows for the first time the extraction of ratios of a number of nucleon-helicity-flip amplitudes to F-0 (1/2 0 1/2). Results obtained in a handbag approach based on generalized parton distributions taking into account the contribution from pion exchange are found to be in good agreement with these ratios. Within the model, the data favor a positive sign for the pi - rho transition form factor. By also exploiting the longitudinal beam polarization, a total of 71.0 spin-density matrix elements is determined from the extracted 25 parameters, in contrast to only 53 elements as directly determined in earlier analyses.

Published
2017

2. Spin density matrix elements in exclusive ω electroproduction on ¹H and ²H targets at 27.5 GeV beam energy

Author

Airapetian, A, Akopov, N, Akopov, Z, Augustyniak, W, Avetissian, A, Blok, HP, Borissov, A, Bryzgalov, V, Capiluppi, M, Capitani, GP, Cisbani, E, Ciullo, G, Contalbrigo, M, Dalpiaz, PF, Deconinck, W, De Leo, R, De Sanctis, E, Diefenthaler, M, Di Nezza, P, Düren, M, Ehrenfried, M, Elbakian, G, Ellinghaus, F, Etzelmüller, E, Fabbri, R, Felawka, L, Frullani, S, Gabbert, D, Gapienko, G, Gapienko, V, Garibaldi, F, Gavrilov, G, Gharibyan, V, Hartig, M, Hasch, D, Holler, Y, Hristova, I, Ivanilov, A, Jackson, HE, Joosten, S, Kaiser, R, Karyan, G, Keri, T, Kinney, E, Kisselev, A, Korotkov, V, Kozlov, V, Kravchenko, P, Krivokhijine, VG, Lagamba, L, Lapikás, L, Lehmann, I, Lenisa, P, Lorenzon, W, Ma, BQ, Mahon, D, Manaenkov, SI, Mao, Y, Marianski, B, Marukyan, H, Movsisyan, A, Murray, M, Naryshkin, Y, Nass, A, Nowak, WD, Pappalardo, LL, Perez-Benito, R, Petrosyan, A, Reimer, PE, Reolon, AR, Riedl, C, Rith, K, Rostomyan, A, Ryckbosch, Dirk, Schäfer, A, Schnell, G, Schüller, KP, Seitz, B, Shibata, TA, Stahl, M, Stancari, M, Statera, M, Steffens, E, Steijger, JJM, Taroian, S, Terkulov, A, Truty, R, Trzcinski, A, Tytgat, Michael, Van Haarlem, Y, VanHulse, C, Vikhrov, V, Vilardi, I, Wang, S, Yaschenko, S, Yen, S, Zeiler, D, Zihlmann, B, and Zupranski, P

Subjects
Physics and Astronomy, PARTON DISTRIBUTIONS, VECTOR-MESON LEPTOPRODUCTION, High Energy Physics::Experiment, Nuclear Experiment, QCD, VIRTUAL COMPTON-SCATTERING
Abstract

Exclusive electroproduction of. mesons on unpolarized hydrogen and deuterium targets is studied in the kinematic region of Q(2) > 1.0 GeV2, 3.0 GeV < W < 6.3 GeV, and -t ' < 0.2 GeV2. Results on the angular distribution of the omega meson, including its decay products, are presented. The data were accumulated with the HER-MES forward spectrometer during the 1996-2007 running period using the 27.6 GeV longitudinally polarized electron or positron beam of HERA. The determination of the virtual-photon longitudinal-to-transverse cross-section ratio reveals that a considerable part of the cross section arises from transversely polarized photons. Spin density matrix elements are presented in projections of Q(2) or -t '. Violation of s-channel helicity conservation is observed for some of these elements. Asizable contribution from unnatural-parity-exchange amplitudes is found and the phase shift between those amplitudes that describe transverse omega production by longitudinal and transverse virtual photons,gamma(L)* -> omega(T) and gamma(T)* -> omega(T), is determined for the first time. A hierarchy of helicity amplitudes is established, which mainly means that the unnatural-parity-exchange amplitude describing the gamma(T)* -> omega(T) transition dominates over the two natural-parity-exchange amplitudes describing the gamma(L)* -> omega(L) and gamma(T)* -> omega(T) transitions, with the latter two being of similar magnitude. Good agreement is found between the HERMES proton data and results of a pQCD-inspired phenomenological model that includes pion-pole contributions, which are of unnatural parity.

Published
2014

3. Measurement of the virtual-photon asymmetry A₂ and the spin-structure function g₂ of the proton

Author

Airapetian, A, Akopov, N, Akopov, Z, Aschenauer, EC, Augustyniak, W, Avakian, R, Avetissian, A, Avetisyan, E, Belostotski, S, Bianchi, N, Blok, HP, Borissov, A, Bowles, J, Bryzgalov, V, Burns, J, Capiluppi, M, Capitani, GP, Cisbani, E, Ciullo, G, Contalbrigo, M, Dalpiaz, PF, Deconinck, W, De Leo, R, De Nardo, Lara, De Sanctis, E, Diefenthaler, M, Di Nezza, P, Duren, M, Ehrenfried, M, Elbakian, G, Ellinghaus, F, Fantoni, A, Felawka, L, Frullani, S, Gabbert, Dominik, Gapienko, G, Gapienko, V, Garibaldi, F, Gavrilov, G, Gharibyan, V, Giordano, F, Gliske, S, Golembiovskaya, M, Hadjidakis, C, Hartig, M, Hasch, D, Hillenbrand, A, Hoek, M, Holler, Y, Hristova, I, Imazu, Y, Ivanilov, A, Jackson, HE, Jo, HS, Joosten, S, Kaiser, R, Karyan, G, Keri, T, Kinney, E, Kisselev, A, Korotkov, V, Kozlov, V, Kravchenko, P, Krivokhijine, VG, Lagamba, L, Lapikas, L, Lehmann, I, Lenisa, P, Lopez Ruiz, Alejandro, Lorenzon, W, Ma, BQ, Mahon, D, Makins, NCR, Manaenkov, SI, Manfre, L, Mao, Y, Marianski, B, de la Ossa, AM, Marukyan, H, Miller, CA, Miyachi, Y, Movsisyan, A, Muccifora, V, Murray, M, Mussgiller, A, Nappi, E, Naryshkin, Y, Nass, A, Negodaev, M, Nowak, WD, Pappalardo, LL, Perez-Benito, R, Petrosyan, A, Reimer, PE, Reolon, AR, Riedl, C, Rith, K, Rosner, G, Rostomyan, A, Rubin, J, Ryckbosch, Dirk, Salomatin, Y, Sanftl, F, Schafer, A, Schnell, G, Schuler, KP, Seitz, B, Shibata, TA, Shutov, V, Stancari, M, Statera, M, Steffens, E, Steijger, JJM, Stewart, J, Stinzing, F, Taroian, S, Terkulov, A, Truty, R, Trzcinski, A, Tytgat, Michael, Vandenbroucke, A, Van Haarlem, Y, Van Hulse, Charlotte, Veretennikov, D, Vikhrov, V, Vilardi, I, Wang, S, Yaschenko, S, Ye, Z, Yen, S, Zagrebelnyy, V, Zeiler, D, Zihlmann, B, and Zupranski, P

Subjects
DEEP-INELASTIC-SCATTERING, SUM-RULES, POLARIZATION, TARGET, Physics and Astronomy, ELECTRON STORAGE-RING, HERA, POLARIMETER, High Energy Physics::Experiment, Nuclear Experiment
Abstract

A measurement of the virtual-photon asymmetry A(2)(x, Q(2)) and of the spin-structure function g(2)(x, Q(2)) of the proton are presented for the kinematic range 0.004 < x < 0.9 and 0.18 GeV2 < Q(2) < 20 GeV2. The data were collected by the HERMES experiment at the HERA storage ring at DESY while studying inclusive deep-inelastic scattering of 27.6 GeV longitudinally polarized leptons off a transversely polarized hydrogen gas target. The results are consistent with previous experimental data from CERN and SLAC. For the x-range covered, the measured integral of g(2)(x) converges to the null result of the Burkhardt-Cottingham sum rule. The x(2) moment of the twist-3 contribution to g(2)(x) is found to be compatible with zero.

Published
2012

4. Single-spin azimuthal asymmetry in exclusive electroproduction of pi+ mesons on transversely polarized protons

Author

Airapetian, A, Akopov, N, Akopov, Z, Aschenauer, EC, Augustyniak, W, Avetissian, A, Avetisyan, E, Ball, B, Belostotski, S, Bianchi, N, Blok, HP, Bottcher, H, Bonomo, C, Borissov, A, Bryzgalov, V, Burns, J, Capiluppi, M, Capitani, GP, Cisbani, E, Ciullo, G, Contalbrigo, M, Dalpiaz, PF, Deconinck, W, De Leo, R, De Nardo, Lara, De Sanctis, E, Diefenthaler, M, Di Nezza, P, Dreschler, J, Duren, M, Ehrenfried, M, Elbakian, G, Ellinghaus, F, Fabbri, R, Fantoni, A, Felawka, L, Frullani, S, Gabbert, Dominik, Gapienko, V, Garibaldi, F, Gharibyan, V, Giordano, F, Gliske, S, Hadjidakis, C, Hartig, M, Hasch, D, Hill, G, Hillenbrand, A, Hoek, M, Holler, Y, Hristova, I, Imazu, Y, Ivanilov, A, Jackson, HE, Jo, HS, Joosten, S, Kaiser, R, Keri, T, Kinney, E, Kisselev, A, Kobayashi, N, Korotkov, V, Kravchenko, P, Lagamba, L, Lamb, R, Lapikas, L, Lehmann, I, Lenisa, P, Linden-Levy, LA, Lopez Ruiz, Alejandro, Lorenzon, W, Lu, XG, Lu, XR, Ma, BQ, Mahon, D, Makins, NCR, Manaenkov, SI, Manfre, L, Mao, Y, Marianski, B, de la Ossa, BM, Marukyan, H, Miller, CA, Miyachi, Y, Movsisyan, A, Muccifora, V, Murray, M, Mussgiller, A, Nappi, E, Naryshkin, Y, Nass, A, Nowak, WD, Pappalardo, LL, Perez-Benito, R, Reimer, PE, Reolon, AR, Riedl, C, Rith, K, Rosner, G, Rostomyan, A, Rubin, J, Ryckbosch, Dirk, Salomatin, Y, Sanftl, F, Schafer, A, Schnell, Gunar, Schuler, KP, Seitz, B, Shibata, TA, Shutov, V, Stancari, M, Statera, M, Steijger, JJM, Stenzel, H, Stewart, J, Taroian, S, Terkulov, A, Trzcinski, A, Tytgat, Michael, Vandenbroucke, A, van der Nat, PB, Van Haarlem, Y, Van Hulse, Charlotte, Varanda, M, Veretennikov, D, Vikhrov, V, Vilardi, I, Vogel, C, Wang, S, Yaschenko, S, Ye, H, Ye, Z, Yen, S, Yu, W, Zeiler, D, Zihlmann, B, and Zupranski, P

Subjects
14.40.Aq, RING, IMPACT PARAMETER SPACE, FOS: Physical sciences, HYDROGEN, 13.60.-rm, 13.60.Le, 13.85.Lg, 14.20.Dh, PHYSICS EVENT GENERATION, LIMIT, High Energy Physics - Experiment, High Energy Physics - Experiment (hep-ex), TARGET, Physics and Astronomy, GENERALIZED PARTON DISTRIBUTIONS, SCATTERING, ddc:530, High Energy Physics::Experiment, NUCLEON, Nuclear Experiment, TO-LEADING ORDER
Abstract

Exclusive electroproduction of pi+ mesons was studied by scattering 27.6 GeV positrons or electrons off a transversely polarized hydrogen target. The single-spin azimuthal asymmetry with respect to target polarization was measured as a function of the Mandelstam variable t, the Bjorken scaling variable x_B, and the virtuality Q^2 of the exchanged photon. The extracted Fourier components of the asymmetry were found to be consistent with zero, except one that was found to be large and that involves interference of contributions from longitudinal and transverse virtual photons., 7 pages, 2 figures

Published
2009
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5. Spin density matrix elements in exclusive ρ0 electroproduction on ¹H and ²H targets at 27.5 GeV beam energy

Author

Airapetian, A, Akopov, N, Akopov, Z, Andrus, A, Aschenauer, EC, Augustyniak, W, Avakian, R, Avetissian, A, Avetissian, E, Belostotski, S, Bianchi, N, Blok, HP, Bottcher, H, Bonomo, C, Borissov, A, Brull, A, Bryzgalov, V, Capiluppi, M, Capitani, GP, Cisbani, E, Ciullo, G, Contalbrigo, M, Dalpiaz, PF, Deconinck, W, De Leo, R, Demey, M, De Nardo, L, De Sanctis, E, Diefenthaler, M, Di Nezza, P, Dreschler, J, Duren, M, Ehrenfried, M, Elalaoui-Moulay, A, Elbakian, G, Ellinghaus, F, Elschenbroich, U, Fabbri, R, Fantoni, A, Felawka, L, Frullani, S, Funel, A, Gabbert, Dominik, Gapienko, G, Gapienko, V, Garibaldi, F, Gavrilov, G, Gharibyan, V, Giordano, F, Gliske, S, Grebeniouk, O, Gregor, IM, Guler, H, Hadjidakis, C, Hartig, M, Hasch, D, Hasegawa, T, Hesselink, WHA, Hill, G, Hillenbrand, A, Hoek, M, Holler, Y, Hommez, B, Hristova, I, Iarygin, G, Imazu, Y, Ivanilov, A, Izotov, A, Jackson, HE, Jgoun, A, Kaiser, R, Keri, T, Kinney, E, Kisselev, A, Kobayashi, T, Kopytin, M, Korotkov, V, Kozlov, V, Kravchenko, P, Krivokhijine, VG, Lagamba, L, Lamb, R, Lapikas, L, Lehmann, I, Lenisa, P, Liebing, P, Linden-Levy, LA, Lorenzon, W, Lu, S, Lu, XR, Ma, BQ, Maiheu, B, Makins, NCR, Manaenkov, SI, Mao, Y, Marianski, B, Marukyan, H, Mexner, V, Miller, CA, Miyachi, Y, Muccifora, V, Murray, M, Mussgiller, A, Nagaitsev, A, Nappi, E, Naryshkin, Y, Nass, A, Negodaev, M, Nowak, WD, Osborne, A, Pappalardo, LL, Perez-Benito, R, Pickert, N, Raithel, M, Reggiani, D, Reimer, PE, Reischl, A, Reolon, AR, Riedl, C, Rith, K, Rock, SE, Rosner, G, Rostomyan, A, Rubacek, L, Rubin, J, Ryckbosch, Dirk, Salomatin, Y, Sanjiev, I, Schafer, A, Schnell, Gunar, Schuler, KP, Seitz, B, Shearer, C, Shibata, TA, Shutov, V, Stancari, M, Statera, M, Steffens, JE, Steijger, JJM, Stenzel, H, Stewart, J, Stinzing, F, Streit, J, Tait, P, Taroian, S, Tchuiko, B, Terkulov, A, Trzcinski, A, Tytgat, Michael, Vandenbroucke, A, van der Nat, PB, van der Steenhoven, G, Van Haarlem, Y, Van Hulse, Charlotte, Varanda, M, Veretennikov, D, Vikhrov, V, Vilardi, I, Vogel, C, Wang, S, Yaschenko, S, Ye, H, Ye, Y, Ye, Z, Yen, S, Yu, W, Zeiler, D, Zihlmann, B, and Zupranski, P

Subjects
Physics and Astronomy, P(0) MESONS, LEPTOPRODUCTION, HERA, POLARIMETER, DISTRIBUTIONS, High Energy Physics::Experiment, HYDROGEN, Nuclear Experiment, CROSS-SECTION, INELASTIC-SCATTERING, QCD, VECTOR-MESON PRODUCTION
Abstract

Spin Density Matrix Elements (SDMEs) describing the angular distribution of exclusive rho (0) electroproduction and decay are determined in the HERMES experiment with 27.6 GeV beam energy and unpolarized hydrogen and deuterium targets. Eight (fifteen) SDMEs that are related (unrelated) to the longitudinal polarization of the beam are extracted in the kinematic region 1 < Q (2)< 7 GeV2, 3.0 < W < 6.3 GeV, and -t < 0.4 GeV2. Within the given experimental uncertainties, a hierarchy of relative sizes of helicity amplitudes is observed. Kinematic dependences of all SDMEs on Q (2) and t are presented, as well as the longitudinal-to-transverse rho (0) electroproduction cross-section ratio as a function of Q (2). A small but statistically significant deviation from the hypothesis of s-channel helicity conservation is observed. An indication is seen of a contribution of unnatural-parity-exchange amplitudes; these amplitudes are naturally generated with a quark-exchange mechanism.

Published
2009

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