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Now showing items 17 - 32 of 41

  • Exclusive rho(0) electroproduction on the proton at CLAS RID E-8618-2010

    Morrow, S. A.   Guidal, M.   Garcon, M.   Laget, J. M.   Smith, E. S.   Adams, G.   Adhikari, K. P.   Aghasyan, M.   Amaryan, M. J.   Anghinolfi, M.   Asryan, G.   Audit, G.   Avakian, H.   Bagdasaryan, H.   Baillie, N.   Ball, J. P.   Baltzell, N. A.   Barrow, S.   Battaglieri, M.   Bedlinskiy, I.   Bektasoglu, M.   Bellis, M.   Benmouna, N.   Berman, B. L.   Biselli, A. S.   Blaszczyk, L.   Bonner, B. E.   Bookwalter, C.   Bouchigny, S.   Boiarinov, S.   Bradford, R.   Branford, D.   Briscoe, W. J.   Brooks, W. K.   Bueltmann, S.   Burkert, V. D.   Butuceanu, C.   Calarco, J. R.   Careccia, S. L.   Carman, D. S.   Carnahan, B.   Casey, L.   Cazes, A.   Chen, S.   Cheng, L.   Cole, P. L.   Collins, P.   Coltharp, P.   Cords, D.   Corvisiero, P.   Crabb, D.   Crannell, H.   Crede, V.   Cummings, J. P.   Dale, D.   Dashyan, N.   De Masi, R.   De Vita, R.   De Sanctis, E.   Degtyarenko, P. V.   Denizli, H.   Dennis, L.   Deur, A.   Dhamija, S.   Dharmawardane, K. V.   Dhuga, K. S.   Dickson, R.   Didelez, J. -P.   Djalali, C.   Dodge, G. E.   Doughty, D.   Dugger, M.   Dytman, S.   Dzyubak, O. P.   Egiyan, H.   Egiyan, K. S.   El Fassi, L.   Elouadrhiri, L.   Eugenio, P.   Fatemi, R.   Fedotov, G.   Fersch, R.   Feuerbach, R. J.   Forest, T. A.   Fradi, A.   Gavalian, G.   Gevorgyan, N.   Gilfoyle, G. P.   Giovanetti, K. L.   Girod, F. X.   Goetz, J. T.   Gohn, W.   Gordon, C. I. O.   Gothe, R. W.   Graham, L.   Griffioen, K. A.   Guillo, M.   Guler, N.   Guo, L.   Gyurjyan, V.   Hadjidakis, C.   Hafidi, K.   Hakobyan, H.   Hanretty, C.   Hardie, J.   Hassall, N.   Heddle, D.   Hersman, F. W.   Hicks, K.   Hleiqawi, I.   Holtrop, M.   Hourany, E.   Hyde-Wright, C. E.   Ilieva, Y.   Ireland, D. G.   Ishkhanov, B. S.   Isupov, E. L.   Ito, M. M.   Jenkins, D.   Jo, H. S.   Johnstone, J. R.   Joo, K.   Juengst, H. G.   Kalantarians, N.   Keller, D.   Kellie, J. D.   Khandaker, M.   Khetarpal, P.   Kim, W.   Klein, A.   Klein, F. J.   Klimenko, A. V.   Kossov, M.   Kramer, L. H.   Kubarovsky, V.   Kuhn, J.   Kuhn, S. E.   Kuleshov, S. V.   Kuznetsov, V.   Lachniet, J.   Langheinrich, J.   Lawrence, D.   Li, Ji   Livingston, K.   Lu, H. Y.   MacCormick, M.   Marchand, C.   Markov, N.   Mattione, P.   McAleer, S.   McCracken, M.   McKinnon, B.   McNabb, J. W. C.   Mecking, B. A.   Mehrabyan, S.   Melone, J. J.   Mestayer, M. D.   Meyer, C. A.   Mibe, T.   Mikhailov, K.   Minehart, R.   Mirazita, M.   Miskimen, R.   Mokeev, V.   Morand, L.   Moreno, B.   Moriya, K.   Moteabbed, M.   Mueller, J.   Munevar, E.   Mutchler, G. S.   Nadel-Turonski, P.   Nasseripour, R.   Niccolai, S.   Niculescu, G.   Niculescu, I.   Niczyporuk, B. B.   Niroula, M. R.   Niyazov, R. A.   Nozar, M.   O'Rielly, G. V.   Osipenko, M.   Ostrovidov, A. I.   Park, K.   Park, S.   Pasyuk, E.   Paterson, C.   Pereira, S. Anefalos   Philips, S. A.   Pierce, J.   Pivnyuk, N.   Pocanic, D.   Pogorelko, O.   Polli, E.   Popa, I.   Pozdniakov, S.   Preedom, B. M.   Price, J. W.   Procureur, S.   Prok, Y.   Protopopescu, D.   Qin, L. M.   Raue, B. A.   Riccardi, G.   Ricco, G.   Ripani, M.   Ritchie, B. G.   Rosner, G.   Rossi, P.   Rubin, P. D.   Sabatie, F.   Saini, M. S.   Salamanca, J.   Salgado, C.   Santoro, J. P.   Sapunenko, V.   Schott, D.   Schumacher, R. A.   Serov, V. S.   Sharabian, Y. G.   Sharov, D.   Shvedunov, N. V.   Skabelin, A. V.   Smith, L. C.   Sober, D. I.   Sokhan, D.   Stavinsky, A.   Stepanyan, S. S.   Stepanyan, S.   Stokes, B. E.   Stoler, P.   Strakovsky, I. I.   Strauch, S.   Taiuti, M.   Tedeschi, D. J.   Tkabladze, A.   Tkachenko, S.   Todor, L.   Tur, C.   Ungaro, M.   Vineyard, M. F.   Vlassov, A. V.   Watts, D. P.   Weinstein, L. B.   Weygand, D. P.   Williams, M.   Wolin, E.   Wood, M. H.   Yegneswaran, A.   Yurov, M.   Zana, L.   Zhang, J.   Zhao, B.   Zhao, Z. W.  

    The ep -> e'pp(0) reaction has been measured using the 5.754 GeV electron beam of Jefferson Lab and the CLAS detector. This represents the largest ever set of data for this reaction in the valence region. Integrated and differential cross-sections are presented. The W, Q(2) and t dependences of the cross-section are compared to theoretical calculations based on the t-channel meson-exchange Regge theory, on the one hand, and on quark handbag diagrams related to Generalized Parton Distributions (GPDs) on the other hand. The Regge approach can describe at the approximate to 30% level most of the features of the present data while the two GPD calculations that are presented in this article which succesfully reproduce the high-energy data strongly underestimate the present data. The question is then raised whether this discrepancy originates from an incomplete or inexact way of modelling the GPDs or the associated hard scattering amplitude or whether the GPD formalism is simply inapplicable in this region due to higher-twists contributions, incalculable at present.
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  • Polarization: A Must for Fusion

    Didelez, J. P.   Deutsch, C.   Guidal, M.  

    Recent realistic simulations confirm that the polarization of the fuel would improve significantly the DT fusion efficiency. We have proposed an experiment to test the persistence of the polarization in a fusion process, using a terawatt laser hitting a polarized HD target. The polarized deuterons heated in the plasma induced by the laser can fuse producing a He-3 and a neutron in the final state. The angular distribution of the neutrons and the change in the corresponding total cross section are related to the polarization persistence. The experimental polarization of DT fuel is a technological challenge. Possible paths for Magnetic Confinement Fusion (MCF) and for Inertial Confinement Fusion (ICF) are reviewed. For MCF, polarized gas can be used. For ICF, cryogenic targets are required. We consider both, the polarization of gas and the polarization of solid DT, emphasizing the Dynamic Nuclear polarization (DNP) of HD and DT molecules.
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  • Measurement of eta photoproduction on the proton from threshold to 1500 MeV RID B-1239-2012 RID A-2439-2012

    Bartalini, O.   Bellini, V.   Bocquet, J. P.   Calvat, P.   Capogni, M.   Casano, L.   Castoldi, M.   D'Angelo, A.   Didelez, J.-P.   Di Salvo, R.   Fantini, A.   Franco, D.   Gaulard, C.   Gervino, G.   Ghio, F.   Giardina, G.   Girolami, B.   Giusa, A.   Guidal, M.   Hourany, E.   Kunne, R.   Lapik, A.   Sandri, P. Levi   Lleres, A.   Mammoliti, F.   Mandaglio, G.   Moricciani, D.   Mushkarenkov, A. N.   Nedorezov, V.   Nicoletti, L.   Perrin, C.   Randieri, C.   Rebreyend, D.   Renard, F.   Rudnev, N.   Russew, T.   Russo, G.   Schaerf, C.   Sperduto, M.-L.   Sutera, M.-C.   Turinge, A.   Vegna, V.  

    Beam asymmetry and differential cross-section for the reaction gamma p -> eta p were measured from production threshold to 1500MeV photon laboratory energy. The two dominant neutral decay modes of the eta-meson, eta -> 2 gamma and eta -> 3 pi(0) , were analyzed. The full set of measurements is in good agreement with previously published results. Our data were compared with three models. They all fit satisfactorily the results but their respective resonance contributions are quite different. The possible photoexcitation of a narrow state N(1670) was investigated and no evidence was found.
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  • Constraints on the (H)over-tilde generalized parton distribution from deep virtual Compton scattering measured at HERMES

    Guidal, M.  

    We have analyzed the longitudinally polarized proton target asymmetry data of the Deep Virtual Compton process recently published by the HERMES Collaboration in terms of Generalized Parton Distributions. We have fitted these new data in a largely model-independent fashion and the procedure results in numerical constraints on the Him Compton Form Factor. We present its t- and xi-dependencies. We also find improvement on the determination of two other Compton Form Factors. H(Re) and H(Im). (C) 2010 Elsevier B.V. All rights reserved.
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  • Generalized Parton Distributions from Deeply Virtual Compton Scattering at HERMES

    Guidal, M.   Moutarde, H.  

    The HERMES Collaboration has recently published a set of (correlated) beam charge, beam spin and target spin asymmetries for the Deeply Virtual Compton Scattering (DVCS) process. This reaction allows in principle to access the Generalized Parton Distributions (GPDs) of the nucleon. We have fitted, in the QCD leading-order and leading-twist handbag approximation, but in a model-independent way, this set of data and we report our results for the extracted Compton form factors. In particular, we are able to extract constrains on the H GPD.
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  • Evidence for a backward peak in the gamma d -> pi(0)d cross section near the eta threshold RID E-8618-2010 RID B-4083-2012

    Ilieva, Y.   Berman, B. L.   Kudryavtsev, A. E.   Strakovsky, I. I.   Tarasov, V. E.   Amarian, M.   Ambrozewicz, P.   Anghinolfi, M.   Asryan, G.   Avakian, H.   Bagdasaryan, H.   Baillie, N.   Ball, J. P.   Baltzell, N. A.   Batourine, V.   Battaglieri, M.   Bedlinskiy, I.   Bellis, M.   Benmouna, N.   Biselli, A. S.   Bouchigny, S.   Boiarinov, S.   Bradford, R.   Branford, D.   Briscoe, W. J.   Brooks, W. K.   Bueltmann, S.   Burkert, V. D.   Butuceanu, C.   Calarco, J. R.   Careccia, S. L.   Carman, D. S.   Chen, S.   Cole, P. L.   Collins, P.   Coltharp, P.   Crabb, D.   Crede, V.   De Masi, R.   De Sanctis, E.   De Vita, R.   Degtyarenko, P. V.   Deur, A.   Dickson, R.   Djalali, C.   Dodge, G. E.   Donnelly, J.   Doughty, D.   Dugger, M.   Dzyubak, O. P.   Egiyan, H.   Egiyan, K. S.   Elouadrhiri, L.   Eugenio, P.   Fedotov, G.   Feldman, G.   Funsten, H.   Garcon, M.   Gavalian, G.   Gilfoyle, G. P.   Giovanetti, K. L.   Girod, F. X.   Goetz, J. T.   Gonenc, A.   Gothe, R. W.   Griffioen, K. A.   Guidal, M.   Guler, N.   Guo, L.   Gyurjyan, V.   Hafidi, K.   Hakobyan, R. S.   Hersman, F. W.   Hicks, K.   Hleiqawi, I.   Holtrop, M.   Hyde-Wright, C. E.   Ireland, D. G.   Ishkhanov, B. S.   Isupov, E. L.   Ito, M. M.   Jenkins, D.   Jo, H. S.   Joo, K.   Juengst, H. G.   Kalantarians, N.   Kellie, J. D.   Khandaker, M.   Kim, W.   Klein, A.   Klein, F. J.   Kossov, M.   Krahn, Z.   Kramer, L. H.   Kubarovsky, V.   Kuhn, J.   Kuhn, S. E.   Kuleshov, S. V.   Lachniet, J.   Laget, J. M.   Langheinrich, J.   Lawrence, D.   Livingston, K.   Lu, H.   MacCormick, M.   Markov, N.   McKinnon, B.   Mecking, B. A.   Mestayer, M. D.   Meyer, C. A.   Mibe, T.   Mikhailov, K.   Mirazita, M.   Miskimen, R.   Mokeev, V.   Moriya, K.   Morrow, S. A.   Moteabbed, M.   Munevar, E.   Mutchler, G. S.   Nadel-Turonski, P.   Nasseripour, R.   Niccolai, S.   Niculescu, G.   Niculescu, I.   Niczyporuk, B. B.   Niroula, M. R.   Niyazov, R. A.   Nozar, M.   Osipenko, M.   Ostrovidov, A. I.   Park, K.   Pasyuk, E.   Paterson, C.   Pierce, J.   Pivnyuk, N.   Pogorelko, O.   Pozdniakov, S.   Price, J. W.   Prok, Y.   Protopopescu, D.   Raue, B. A.   Ricco, G.   Ripani, M.   Ritchie, B. G.   Ronchetti, F.   Rosner, G.   Rossi, P.   Sabatie, F.   Salgado, C.   Santoro, J. P.   Sapunenko, V.   Schumacher, R. A.   Serov, V. S.   Sharabian, Y. G.   Shvedunov, N. V.   Smith, E. S.   Smith, L. C.   Sober, D. I.   Stavinsky, A.   Stepanyan, S. S.   Stepanyan, S.   Stokes, B. E.   Stoler, P.   Strauch, S.   Taiuti, M.   Tedeschi, D. J.   Thoma, U.   Tkabladze, A.   Tkachenko, S.   Tur, C.   Ungaro, M.   Vineyard, M. F.   Vlassov, A. V.   Watts, D. P.   Weinstein, L. B.   Weygand, D. P.   Williams, M.   Wolin, E.   Wood, M. H.   Yegneswaran, A.   Zana, L.   Zhang, J.   Zhao, B.   Zhao, Z.  

    High-quality cross sections for the reaction gamma d -> pi(0)d have been measured using the CLAS at Jefferson Lab over a wide energy range near and above the eta-meson photoproduction threshold. At backward c.m. angles for the outgoing pions, we observe a resonance-like structure near E(gamma) = 700 MeV. Our model analysis shows that it can be explained by eta excitation in the intermediate state. The effect is the result of the contribution of the N(1535) S(11)-resonance to the amplitudes of the subprocesses occurring between the two nucleons and of a two-step process in which the excitation of an intermediate eta-meson dominates.
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  • Pion and kaon photoproduction at high energies: forward and intermediate angles

    Guidal, M.   Laget, J.-M.   Vanderhaeghen, M.  

    A model for high energy pion and kaon photoproduction (E gammagsim4 GeV) is presented which interpolates between the low and higher momentum transfer regions. At low momentum transfer (which is described in terms of Regge trajectory exchanges), the model is able to give an economical description of unpolarized and polarized data for both the charged and neutral pion photoproduction reactions as well as for K +Lambda and K +Sigma photoproduction data, available at high energy. At higher momentum transfer, an extrapolation based on saturating Regge trajectories, and which satisfies scaling laws at asymptotically large transfers, is found able to describe the few existing gammaprarrnpi + data. The model can be used as a guidance to interpret forthcoming data at larger momentum transfers
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  • Polarization observable measurements for gamma p -> K+ Lambda and gamma p -> K+ Sigma(0) for energies up to 1.5 GeV RID B-1239-2012

    Lleres, A.   Bartalini, O.   Bellini, V.   Bocquet, J. P.   Calvat, P.   Capogni, M.   Casano, L.   Castoldi, M.   D'Angelo, A.   Didelez, J. -P.   Di Salvo, R.   Fantini, A.   Gaulard, C.   Gervino, G.   Ghio, F.   Girolami, B.   Giusa, A.   Guidal, M.   Hourany, E.   Kouznetsov, V.   Kunne, R.   Lapik, A.   Sandri, P. Levi   Moricciani, D.   Mushkarenkov, A. N.   Nedorezov, V.   Nicoletti, L.   Perrin, C.   Randieri, C.   Rebreyend, D.   Renard, F.   Rudnev, N.   Russew, T.   Russo, G.   Schaerf, C.   Sperduto, M. -L.   Sutera, M. -C.   Turinge, A.  

    Beam asymmetries and hyperon recoil polarizations for the reactions gamma p --> K+ Lambda and gamma p --> K+ Sigma(0) have been measured from the threshold production to 1500 MeV with the GRAAL facility located at the ESRF in Grenoble. These results complement the database for the beam asymmetry, covering for the first time the production threshold region. Recent theoretical analyses are presented for which the beam asymmetry data bring interesting new information and allow to better determine some resonance parameters. Most importantly, these results strengthen the need of a new D-13 state around 1900 MeV.
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  • Recent experimental results on Deep Virtual Compton Scattering and Generalized Parton Distributions

    Guidal, M.  

    We review and discuss briefly the recent experimental results on Deep Virtual Compton Scattering on the proton. With the variety of independent observables beginning to be available and, in some instances, some very high precision data, some first global analysis for this process can be started, based on dedicated fitter codes, aiming at revealing the Generalized Parton Distributions content of the nucleon.
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  • Measurement of the x- and Q(2)-dependence of the asymmetry A(1) on the nucleon RID A-2074-2012 RID E-8618-2010 RID B-4083-2012

    Dharmawardane, K. V.   Kuhn, S. E.   Bosted, P.   Prok, Y.   Adams, G.   Ambrozewicz, P.   Anghinolfi, M.   Asryan, G.   Avakian, H.   Bagdasaryan, H.   Baillie, N.   Ball, J. P.   Baltzell, N. A.   Barrow, S.   Batourine, V.   Battaglieri, M.   Beard, K.   Bedlinskiy, I.   Bektasoglu, M.   Bellis, M.   Benmouna, N.   Biselli, A. S.   Bonner, B. E.   Bouchigny, S.   Boiarinov, S.   Bradford, R.   Branford, D.   Brooks, W. K.   Bultmann, S.   Burkert, V. D.   Butuceanu, C.   Calarco, J. R.   Careccia, S. L.   Carman, D. S.   Carnahan, B.   Cazes, A.   Chen, S.   Cole, P. L.   Collins, P.   Coltharp, P.   Cords, D.   Corvisiero, P.   Crabb, D.   Crannell, H.   Crede, V.   Cummings, J. P.   De Masi, R.   DeVita, R.   De Sanctis, E.   Degtyarenko, P. V.   Denizli, H.   Dennis, L.   Deur, A.   Djalali, C.   Dodge, G. E.   Donnelly, J.   Doughty, D.   Draigovitsch, P.   Dugger, M.   Dytman, S.   Dzyubak, O. P.   Egiyan, H.   Egiyan, K. S.   Elouadrhiri, L.   Eugenio, P.   Fatemi, R.   Fedotov, G.   Feuerbach, R. J.   Forest, T. A.   Funsten, H.   Garcon, M.   Gavalian, G.   Gilfoyle, G. P.   Giovanetti, K. L.   Girod, F. X.   Goetz, J. T.   Golovatch, E.   Gonenc, A.   Gothe, R. W.   Griffioen, K. A.   Guidal, M.   Guillo, M.   Guler, N.   Guo, L.   Gyurjyan, V.   Hadjidakis, C.   Hafidi, K.   Hakobyan, R. S.   Hardie, J.   Heddle, D.   Hersman, F. W.   Hicks, K.   Hleiqawi, I.   Holtrop, M.   Huertas, M.   Hyde-Wriyht, C. E.   Ilieva, Y.   Ireland, D. G.   Ishkhanov, B. S.   Isupov, E. L.   Ito, M. M.   Jenkins, D.   Jo, H. S.   Joo, K.   Juengst, H. G.   Keith, C.   Kellie, J. D.   Khandaker, M.   Kim, K. Y.   Kim, K.   Kim, W.   Klein, A.   Klein, F. J.   Klusman, M.   Kossov, M.   Kramer, L. H.   Kubarovsky, V.   Kuhn, J.   Kuleshov, S. V.   Lachniet, J.   Laget, J. M.   Langheinrich, J.   Lawrence, D.   Li, Ji   Lima, A. C. S.   Livingston, K.   Lu, H.   Lukashin, K.   MacCormick, M.   Manak, J. J.   Markov, N.   McAleer, S.   McKinnon, B.   McNabb, J. W. C.   Mecking, B. A.   Mestayer, M. D.   Meyer, C. A.   Mibe, T.   Mikhailov, K.   Minehart, R.   Mirazita, M.   Miskimen, R.   Mokeev, V.   Morand, L.   Morrow, S. A.   Moteabbed, M.   Mueller, J.   Mutchler, G. S.   Nadel-Turonski, P.   Napolitano, J.   Nasseripour, R.   Niccolai, S.   Niculescu, G.   Niculescu, I.   Niczyporuk, B. B.   Niroula, M. R.   Nyazov, R. A.   Nozar, M.   O'Rielly, G. V.   Osipenko, M.   Ostrovidov, A. I.   Park, K.   Pasyuk, E.   Paterson, C.   Philips, S. A.   Pierce, J.   Pivnyuk, N.   Pocanic, D.   Pogorelko, O.   Polli, E.   Pozdniakov, S.   Preedom, B. M.   Price, J. W.   Protopopescu, D.   Qin, L. M.   Raue, B. A.   Riccardi, G.   Ricco, G.   Ripani, M.   Ritchie, B. G.   Ronchetti, F.   Rosner, G.   Rossi, P.   Rowntree, D.   Rubin, P. D.   Sabatie, E.   Salgado, C.   Santoro, J. P.   Sapunenko, V.   Schumacher, R. A.   Serov, V. S.   Sharabian, Y. G.   Shaw, J.   Shvedunov, N. V.   Skabelin, A. V.   Smith, E. S.   Smith, L. C.   Sober, D. I.   Stavinsky, A.   Stepanyan, S. S.   Stepanyan, S.   Stokes, B. E.   Stoler, P.   Strakovsky, I. I.   Strauch, S.   Suleiman, R.   Taiuti, M.   Taylor, S.   Tedeschi, D. J.   Thoma, U.   Thompson, R.   Tkabladze, A.   Tkachenko, S.   Todor, L.   Tur, C.   Ungaro, M.   Vineyard, M. F.   Vlassov, A. V.   Weinstein, L. B.   Weygand, D. P.   Williams, M.   Wolin, E.   Wood, M. H.   Yegneswaran, A.   Yun, J.   Zana, L.   Zhang, J.   Zhao, B.   Zhao, Z.  

    We report results for the virtual photon asymmetry A I on the nucleon from new Jefferson Lab measurements. The experiment, which used the CEBAF Large Acceptance Spectrometer and longitudinally polarized proton ((NH3)-N-15) and deuteron ((ND3)-N-15) targets, collected data with a longitudinally polarized electron beam at energies between 1.6 GeV and 5.7 GeV. In the present. Letter, we concentrate on our results for A(1) (x, Q(2)) and the related ratio g(1)/F-1 (x, Q(2))) in the resonance and the deep inelastic regions for our J west and highest beam energies, covering a range in momentum transfer Q(2) from 0.05 to 5.0 (GeV/c)(2) and in final-state invariant mass W up to about 3 GeV. Our data show detailed structure in the resonance re-ion, which leads to a strong Q(2) dependence of A(1) (x, Q(2)) to. W below 2 GeV. At higher W, a smooth approach to the scaling limit, established by earlier experiments, can be seen, but A I (x, Q(2)) is not strictly Q(2)-independent. We add significantly to the world data set at high x, up to x = 0.6. Our data exceed the SU(6)-symmetric quark model expectation for both the proton and the deuteron while being consistent with a negative d-quark polarization up to our highest x. This data set should improve next-to-leading order (NLO) pQCD fits of the parton polarization distributions. (c) 2006 Elsevier B.V.All rights reserved.
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  • PARTONS: PARtonic Tomography Of Nucleon Software

    Berthou, B.   Binosi, D.   Chouika, N.   Colaneri, L.   Guidal, M.   Mezrag, C.   Moutarde, H.   Rodriguez-Quintero, J.   Sabatie, F.   Sznajder, P.   Wagner, J.  

    We describe the architecture and functionalities of a C++ software framework, coined PARTONS, dedicated to the phenomenology of Generalized Parton Distributions. These distributions describe the three-dimensional structure of hadrons in terms of quarks and gluons, and can be accessed in deeply exclusive lepto- or photo-production of mesons or photons. PARTONS provides a necessary bridge between models of Generalized Parton Distributions and experimental data collected in various exclusive production channels. We outline the specification of the PARTONS framework in terms of practical needs, physical content and numerical capacity. This framework will be useful for physicists - the-orists or experimentalists - not only to develop new models, but also to interpret existing measurements and even design new experiments.
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  • Timelike Compton Scattering at JLab 12 GeV

    Nadel-Turonski, P.   Guidal, M.   Horn, T.   Paremuzyan, R.   Stepanyan, S.  

    A major goal of Jefferson Lab at 12 GeV is to map out the 3-D structure of the proton through Generalized Parton Distributions (GPDs). An important tool in this endeavor is Deeply Virtual Compton Scattering, traditionally performed in kinematics where the incoming photon has a spacelike virtuality and the outgoing photon is real. However, measuring the corresponding timelike process, known as Timlike Compton Scattering (TCS), where the incoming photon is real and the outgoing one timelike, offers a unique opportunity to test the universality of GPDs. It also allows to take advantage of the straightforward access in TCS to the real part of the Compton Form Factors, providing constraints on global GPD fits. In addition, the experiment will provide a high-statistics measurement of the J/psi photoproduction cross section near threshold, as this process shares the same final state.
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  • Results from the Graal experiment

    Bartalini, O.   Capogni, M.   D'Angelo, A.   Moricciani, D.   Schaerf, C.   Gaulard, C.   Sandri, P.L.   Anghinolfi, M.   Battaglieri, M.   Castoldi, M.   Corvisiero, P.   Ripani, M.   Sanzone, M.   Taiuti, M.   Zucchiatti, A.   Bellini, V.   Sutera, C.   Bocquet, J.P.   Lleres, A.   Nicoletti, L.   Rebreyend, D.   Renard, F.   Didelez, J.P.   Guidal, M.   Jeicic, A.   Hourany, E.   Ghio, F.   Girolami, B.   Kilvington, I.   Lapik, A.   Kouznetsov, V.   Nedorezov, V.   Turinge, A.   Rudnev, N.  

    The features of the Graal experiment at ESRF are presented. The obtained results are discussed and future developments outlined. The Graal experiment started data taking in 1997. It was run for one year with the green laser line giving rise to a photon beam of maximum energy of 1100 MeV and for one year with UV multi-line and the corresponding gamma-ray beam of 1470 MeV maximum energy. Asymmetry data and cross sections have been produced for eta, pi 0 and pi + photoproduction channels providing, for these reactions, the most extended and coherent data base available until now. Future developments of the experiment will include the study of the same channels with deuteron target and the study of the photoreaction mechanism on the quasi-free neutron. The use of a polarised target of new concept will allow to access double polarisation observables for meson photoproduction on polarised proton and polarised neutron. Finally the increase in the maximum photon energy, up to 1.8 GeV will allow to study in details eta' photoproduction and to reach the threshold for scalar mesons production
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  • Timelike Compton scattering off the proton and generalized parton distributions

    Boer, M.   Guidal, M.   Vanderhaeghen, M.  

    We study the exclusive photoproduction of a lepton pair off the proton with the aim of studying the proton quark structure via the Generalized Parton Distributions (GPD) formalism. After deriving the amplitudes of the processes contributing to the gamma P --> P'e(+)e(-), the timelike Compton scattering and the Bethe-Heitler process, we calculate all unpolarized, single- and double- spin beam-target observables in the valence region in terms of GPDs.
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  • Near-threshold photoproduction of phi mesons from deuterium RID G-2589-2011 RID E-8618-2010

    Qian, X.   Chen, W.   Gao, H.   Hicks, K.   Kramer, K.   Laget, J. M.   Mibe, T.   Qiang, Y.   Stepanyan, S.   Tedeschi, D. J.   Xu, W.   Adhikari, K. P.   Amaryan, M.   Anghinolfi, M.   Ball, J.   Battaglieri, M.   Batourine, V.   Bedlinskiy, I.   Bellis, M.   Biselli, A. S.   Bookwalter, C.   Branford, D.   Briscoe, W. J.   Brooks, W. K.   Burkert, V. D.   Careccia, S. L.   Carman, D. S.   Cole, P. L.   Collins, P.   Crede, V.   D'Angelo, A.   Daniel, A.   Dashyan, N.   De Vita, R.   De Sanctis, E.   Deur, A.   Dey, B.   Dhamija, S.   Djalali, C.   Doughty, D.   Dupre, R.   Egiyan, H.   El Alaoui, A.   Eugenio, P.   Fegan, S.   Gabrielyan, M. Y.   Gevorgyan, N.   Gilfoyle, G. P.   Giovanetti, K. L.   Girod, F. X.   Goetz, J. T.   Gohn, W.   Gothe, R. W.   Graham, L.   Griffioen, K. A.   Guidal, M.   Guo, L.   Hafidi, K.   Hakobyan, H.   Hanretty, C.   Hassall, N.   Holtrop, M.   Ilieva, Y.   Ireland, D. G.   Jawalkar, S. S.   Jo, H. S.   Joo, K.   Keller, D.   Khandaker, M.   Khetarpal, P.   Kim, A.   Kim, W.   Klein, A.   Klein, F. J.   Konczykowski, P.   Kubarovsky, V.   Kuleshov, S. V.   Kuznetsov, V.   Livingston, K.   Martinez, D.   Mayer, M.   McAndrew, J.   McCracken, M. E.   McKinnon, B.   Meyer, C. A.   Mikhailov, K.   Mineeva, T.   Mirazita, M.   Mokeev, V.   Moreno, B.   Moriya, K.   Morrison, B.   Moutarde, H.   Munevar, E.   Nadel-Turonski, P.   Ni, A.   Niccolai, S.   Niculescu, I.   Niroula, M. R.   Osipenko, M.   Ostrovidov, A. I.   Paremuzyan, R.   Park, K.   Park, S.   Pereira, S. Anefalos   Pisano, S.   Pogorelko, O.   Pozdniakov, S.   Price, J. W.   Procureu, S.   Protopopescu, D.   Ricco, G.   Ripani, M.   Ritchie, B. G.   Rosner, G.   Rossi, P.   Sabatie, F.   Saini, M. S.   Salgado, C.   Schott, D.   Schumacher, R. A.   Seder, E.   Seraydaryan, H.   Sharabian, Y. G.   Smith, E. S.   Smith, G. D.   Sober, D. I.   Sokhan, D.   Stepanyan, S. S.   Stoler, P.   Strakovsky, I. I.   Strauch, S.   Taiuti, M.   Taylor, C. E.   Tkachenko, S.   Ungaro, M.   Vernarsky, B.   Vineyard, M. F.   Voutier, E.   Weinstein, L. B.   Weygand, D. P.   Wood, M. H.   Zachariou, N.   Zana, L.   Zhang, J.   Zhao, B.   Zhao, Z. W.  

    We report the first, kinematically-complete measurement of the differential cross section of phi-meson photoproduction from deuterium near the production threshold for a proton using the CLAS detector and a tagged-photon beam in Hall B at Jefferson Lab. The measurement was carried out by a triple coincidence detection of a proton, K+ and K- near the theoretical production threshold of 1.57 GeV. The extracted differential cross sections d sigma/dt for the initial photon energy range of 1.65-1.75 GeV are consistent with predictions based on a quasifree mechanism. Our finding is different from recent LEPS results on phi-meson photoproduction from deuterium in a similar incident photon energy range, but in a different momentum transfer region. (C) 2011 Elsevier B.V. All rights reserved.
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  • The central neutron detector for CLAS12

    Niccolai, S.   Hull, G.   Bettane, J.   Chatagnon, P.   Garillon, B.   Genolini, B.   Guegan, B.   Guidal, M.   Imre, M.   Josselin, M.   Marchand, D.   Maroni, A.   Mathon, B.   Murdoch, G.   Trung, T. Nguyen   Peyre, J.   Pouthas, J.   Rosier, P.   Sokhan, D.   Theneau, C.   Wang, R.  

    The Central Neutron Detector, a recently constructed scintillator barrel which is used in CLAS12 at Jefferson Lab to detect 0.2-1 GeV neutrons at backwards angles, is here described. The motivations and R&D tests leading to its final design, based on three radial layers of coupled paddles with one-side light readout by photomultipliers plus "U-turn" lightguides on the other side, are outlined. The performance of the detector, evaluated from cosmic-ray tests and simulations, which satisfies the physics requirements, is reported.
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