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  • Exclusive photoproduction of $\pi^0$ up to large values of Mandelstam variables $s, t$ and $u$ with CLAS
    Kunkel, M. C; 32; Amaryan, 18 M. J; Strakovsky, I. I; Ritman, 16 J; Goldstein, 18 G. R; Adhikari, 43 K. P; Ball, 39 J; Balossino, 7 I; Barion, 19 L; Battaglieri, 19 M; Batourine, 21 V; Bedlinskiy, 27 I; Biselli, 25 A. S; 11; Boiarinov, 5 S; Briscoe, 39 W. J; Brooks, 16 W. K; 40; Burkert, 32 V. D; Cao, 39 F; Carman, 9 D. S; Celentano, 39 A; Charles, 21 G; Chetry, 32 T; 19; Contalbrigo, 17 M; Crede, 17 V; 22; De Vita, 47 R; De Sanctis, 21 E; Degtyarenko, 20 P. V; Dupre, 2 R; Egiyan, 24 H; Fassi, 40 L. El; Elouadrhiri, 28 L; Fedotov, 14 G; Fersch, 31 R; 8; Fradi, 23 A; Ghandilyan, 29 Y; Gilfoyle, 10 G. P; Giovanetti, 34 K. L; Glazier, 39 D. I; Gohn, 42 W; Guo, 46 L; Guidal, 39 M; Hafidi, 24 K; Hakobyan, 1 H; Harrison, 47 N; Hattawy, 39 M; Holtrop, 31 M; Hyde, 29 C. E; Ireland, 32 D. G; Ishkhanov, 42 B. S; Isupov, 36 E. L; Jenkins, 36 D; Kabir, 9 M. L; Keller, 28 D; Khachatryan, 45 G; Khachatryan, 47 M; Khandaker, 32 M; Kim, A; Kim, 9 W; Klein, 27 A; Kubarovsky, 16 V; Kuhn, 39 S. E; Laget, 32 J. M; Lersch, 19 D; Livingston, 18 K; Mbianda, 9 G; Mokeev, 9 V; Movsisyan, 42 A; Camacho, 19 C. Munoz; Niculescu, 24 G; Ostrovidov, 21 A. I; Paolone, 14 M; Park, 38 K; Pogorelko, 16 O; Price, 32 J. W; Procureur, 4 S; Protopopescu, 45 D; Ripani, 42 M; Roy, 42 A; Sabatie, 10 F; Salgado, 7 C; Schadmand, 30 S; Sharabian, 5 Y. G; Skorodumina, 39 Iu; 37; Sokhan, 42 D; Strauch, 38 S; 21; Voskanyan, 33 H; Voutier, 47 E; Watts, 24 D. P; Zachariou, 8 N; Zhang, 41 J; 45; Zhao32, Z. W

    12/2017
    Journal Article

    Phys. Rev. C 98, 015207 (2018) 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.

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