Differential cross section and photon-beam asymmetry for the gamma p -> pi- Delta++(1232) reaction at forward pi- angles for Egamma=1.5-2.95 GeV

H. Kohri,W. Gohn,M. Ungaro,W.C. Chang,S. Y. Wang,Y. Kato,T. Tsunemi,Yorihito Sugaya,Y. Maeda,S Y Ryu,J.K. Ahn,M. Niiyama,Y. Nakatsugawa,Y. Kon,Yuji Ohashi,Atsushi Hosaka,Sang-Ho Kim,Hiroyuki Noumi,T. Sawada,Y. D. Oh,H. Fujimura,Kyungseon Joo,H. Ejiri,T. Mibe,Mamoru Fujiwara,Takatsugu Ishikawa,Masaki Uchida,Makoto Oka,M. Yosoi,Manabu Miyabe,Hirohiko M. Shimizu,Y. Yanai,Sanghoon Hwang,J-Y Chen,K Hicks,C.Rangacharyulu,N. Muramatsu,T. Nakano,S.-H. Shiu,T. Hotta,M. Sumihama,Hyomin Lee,K. Imai,T. Ohta,Y. Morino,J. D. Parker,Shūji Fukui,D. S. Ahn

Differential cross section and photon-beam asymmetry for the gamma p -> pi- Delta++(1232) reaction at forward pi- angles for Egamma=1.5-2.95 GeV

2017

Differential cross sections and photon-beam asymmetries for the gamma p -> pi- Delta++(1232) reaction have been measured for 0.7SPring-8/LEPS. The first-ever high statistics cross section data are obtained in this kinematical region, and the asymmetry data for 1.5asymmetries are found to be negative in most of the present kinematical regions, suggesting the dominance of pi-exchange in the t-channel. The negative asymmetries at forward meson production angles are different from the asymmetries previously measured for the photoproduction reactions which produce a $d\bar{d}$ or an $s\bar{s}$ quark pair in the final state. Advanced theoretical models introducing nucleon resonances and additional unnatural parity exchanges are needed to reproduce the present data.

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