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arXiv · 1712.10314

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

M. C. Kunkel·32·18 M. J. Amaryan·I. I. Strakovsky·16 J. Ritman·3·18 G. R. Goldstein·43 K. P. Adhikari·28 S Adhikari·13 H. Avakian·39 J. Ball·7 I. Balossino·19 L. Barion·19 M. Battaglieri·21 V. Batourine·39·27 I. Bedlinskiy·25 A. S. Biselli·11·5 S. Boiarinov·39 W. J. Briscoe·16 W. K. Brooks·40·39 S. Bueltmann·32 V. D. Burkert·39 F. Cao·9 D. S. Carman·39 A. Celentano·21 G. Charles·32 T. Chetry·31 G. Ciullo·19·12 L. Clark·42 P. L. Cole·17 M. Contalbrigo·19 O. Cortes·17 V. Crede·14 A. DAngelo·22·35 N. Dashyan·47 R. De Vita·21 E. De Sanctis·20 P. V. Degtyarenko·39 M. Defurne·7 A. Deur·39 C. Djalali·37 M. Dugger·2 R. Dupre·24 H. Egiyan·39 A. El Alaoui·40 L. El Fassi·28 L. Elouadrhiri·39 P. Eugenio·14 G. Fedotov·31 R. Fersch·8·46 A. Filippi·23 A. Fradi·24 G. Gavalian·29 Y. Ghandilyan·47 S. Ghosh·10 G. P. Gilfoyle·34 K. L. Giovanetti·26 F. X. Girod·39 D. I. Glazier·42 W. Gohn·9·E. Golovatch·36 R. W. Gothe·37 K. A. Griffioen·46 L. Guo·13·39 M. Guidal·24 K. Hafidi·1 H. Hakobyan·47 N. Harrison·39 M. Hattawy·1 K. Hicks·31 M. Holtrop·29 C. E. Hyde·32 D. G. Ireland·42 B. S. Ishkhanov·36 E. L. Isupov·36 D. Jenkins·44 K. Joo·9 M. L. Kabir·28 D. Keller·45 G. Khachatryan·47 M. Khachatryan·32 M. Khandaker·30·A. Kim·9 W. Kim·27 A. Klein·32 F. Klein·6·16 V. Kubarovsky·39 S. E. Kuhn·32 J. M. Laget·7 L. Lanza
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Abstract

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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M. C. Kunkel, 32, 18 M. J. Amaryan, I. I. Strakovsky, 16 J. Ritman, 3, 18 G. R. Goldstein, 43 K. P. Adhikari, 28 S Adhikari, 13 H. Avakian, 39 J. Ball, 7 I. Balossino, 19 L. Barion, 19 M. Battaglieri, 21 V. Batourine, 39, 27 I. Bedlinskiy, 25 A. S. Biselli, 11, 5 S. Boiarinov, 39 W. J. Briscoe, 16 W. K. Brooks, 40, 39 S. Bueltmann, 32 V. D. Burkert, 39 F. Cao, 9 D. S. Carman, 39 A. Celentano, 21 G. Charles, 32 T. Chetry, 31 G. Ciullo, 19, 12 L. Clark, 42 P. L. Cole, 17 M. Contalbrigo, 19 O. Cortes, 17 V. Crede, 14 A. DAngelo, 22, 35 N. Dashyan, 47 R. De Vita, 21 E. De Sanctis, 20 P. V. Degtyarenko, 39 M. Defurne, 7 A. Deur, 39 C. Djalali, 37 M. Dugger, 2 R. Dupre, 24 H. Egiyan, 39 A. El Alaoui, 40 L. El Fassi, 28 L. Elouadrhiri, 39 P. Eugenio, 14 G. Fedotov, 31 R. Fersch, 8, 46 A. Filippi, 23 A. Fradi, 24 G. Gavalian, 29 Y. Ghandilyan, 47 S. Ghosh, 10 G. P. Gilfoyle, 34 K. L. Giovanetti, 26 F. X. Girod, 39 D. I. Glazier, 42 W. Gohn, 9, E. Golovatch, 36 R. W. Gothe, 37 K. A. Griffioen, 46 L. Guo, 13, 39 M. Guidal, 24 K. Hafidi, 1 H. Hakobyan, 47 N. Harrison, 39 M. Hattawy, 1 K. Hicks, 31 M. Holtrop, 29 C. E. Hyde, 32 D. G. Ireland, 42 B. S. Ishkhanov, 36 E. L. Isupov, 36 D. Jenkins, 44 K. Joo, 9 M. L. Kabir, 28 D. Keller, 45 G. Khachatryan, 47 M. Khachatryan, 32 M. Khandaker, 30, A. Kim, 9 W. Kim, 27 A. Klein, 32 F. Klein, 6, 16 V. Kubarovsky, 39 S. E. Kuhn, 32 J. M. Laget, 7 L. Lanza. 2017-12-29. Exclusive photoproduction of $\pi^0$ up to large values of Mandelstam variables $s, t$ and $u$ with CLAS. https://doi.org/10.1103/physrevc.98.015207

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