Exclusive photoproduction of \(\pi^0\) up to large values of Mandelstam variables \(s, t\) and \(u\) with CLAS

• Published in: arXiv.org
• Main Authors: Kunkel, M C, Amaryan, M J, Ritman, J, Goldstein, G R, Adhikari, S, Avakian, H, Balossino, I, Barion, L, Battaglieri, M, Batourine, V, Bedlinskiy, I, Biselli, A S, Boiarinov, S, Brooks, W K, Bueltmann, S, Burkert, V D, Cao, F, Carman, D S, Celentano, A, Charles, G, Chetry, T, Clark, L, Cole, P L, Contalbrigo, M, Dashyan, N, De Vita, R, De Sanctis, E, Degtyarenko, P V, Defurne, M, Deur, A, Dugger, M, Dupre, R, Egiyan, H, L El Fassi, Elouadrhiri, L, Fedotov, G, Fersch, R, Filippi, A, Fradi, A, Gavalian, G, Ghosh, S, Giovanetti, K L, Girod, F X, Gohn, W, Gothe, R W, Griffioen, K A, Guo, L, Guidal, M, Hakobyan, H, Harrison, N, Hattawy, M, Hyde, C E, Ireland, D G, Ishkhanov, B S, Jenkins, D, Kabir, M L, Khachatryan, G, Kim, A, Kim, W, Klein, A, Kubarovsky, V, Kuhn, S E, Lanza, L, Lenisa, P, Mbianda, G, McKinnon, B, Mokeev, V, C Munoz Camacho, Nadel-Turonski, P, Niccolai, S, Niculescu, G, Osipenko, M, Ostrovidov, A I, Paolone, M, Park, K, Payette, D, Phelps, W, Procureur, S, Protopopescu, D, Ripani, M, Ritchie, B G, Rosner, G, Roy, A, Sabatie, F, Salgado, C, Schadmand, S, Sharabian, Y G, Skorodumina, Iu, Sokhan, D, Sober, D I, Strauch, S, Taiuti, M, Ungaro, M, Voskanyan, H, Voutier, E, Watts, D P, Weinstein, L, Wei, X, Zachariou, N, The CLAS Collaboration
• Format: Paper
• Language: English
• Published: Ithaca Cornell University Library, arXiv.org 29.12.2017
• Subjects: Angular distribution; Cross-sections; Photoproduction; Quantum chromodynamics
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1712.10314

Exclusive photoproduction cross sections have been measured for the process \(\gamma p \rightarrow p\pi^0(e^+e^-(\gamma))\) with the Dalitz decay final state using tagged photon energies in the range of \(E_{\gamma} = 1.275-5.425\) GeV. The complete angular distribution of the final state \(\pi^0\), for the entire photon energy range up to large values of \(t\) and \(u\), has been measured for the first time. The data obtained show that the cross section \(d\sigma/dt\), at mid to large angles, decreases with energy as \(s^{-6.89\pm 0.26} \). This is in agreement with the perturbative QCD quark counting rule prediction of \(s^{-7} \). Paradoxically, the size of angular distribution of measured cross sections is greatly underestimated by the QCD based Generalized Parton Distribution mechanism at highest available invariant energy \(s=11\) GeV\(^2\). At the same time, the Regge exchange based models for \(\pi^0\) photoproduction are more consistent with experimental data.