First Measurement of Hard Exclusive π- Δ++ Electroproduction Beam-Spin Asymmetries off the Proton

Diehl, S.; Trotta, N.; Joo, K.; Achenbach, P.; Akbar, Z.; Armstrong, W. R.; Atac, H.; Avakian, H.; Baashen, L.; Baltzell, N. A.; Barion, L.; Bashkanov, M.; Battaglieri, M.; Bedlinskiy, I.; Benmokhtar, F.; Bianconi, A.; Biselli, A. S.; Bossu, F.; Brinkmann, K. -T.; Briscoe, W. J.; Bulumulla, D.; Burkert, V.; Capobianco, R.; Carman, D. S.; Carvajal, J. C.; Celentano, A.; Charles, G.; Chatagnon, P.; Chesnokov, V.; Ciullo, G.; Cole, P. L.; Contalbrigo, M.; Costantini, G.; Crede, V.; D'Angelo, A.; Dashyan, N.; De Vita, R.; Deur, A.; Djalali, C.; Dupre, R.; Ehrhart, M.; El Alaoui, A.; El Fassi, L.; Elouadrhiri, L.; Fegan, S.; Filippi, A.; Gavalian, G.; Glazier, D. I.; Golubenko, A. A.; Gosta, G.; Gothe, R. W.; Gotra, Y.; Griffioen, K.; Hafidi, K.; Hakobyan, H.; Hattawy, M.; Hayward, T. B.; Heddle, D.; Hobart, A.; Holtrop, M.; Illari, I.; Ireland, D. G.; Isupov, E. L.; H. S., Jo; Johnston, R.; Keller, D.; Khachatryan, M.; Khanal, A.; Kim, A.; Kim, W.; Klimenko, V.; Kripko, A.; Kubarovsky, V.; Kuhn, S. E.; Lagerquist, V.; Lanza, L.; Leali, M.; Lee, S.; Lenisa, P.; Li, X.; Macgregor, I. J. D.; Marchand, D.; Mascagna, V.; Matousek, G.; Mckinnon, B.; Mclauchlin, C.; Meziani, Z. E.; Migliorati, S.; Milner, R. G.; Mineeva, T.; Mirazita, M.; Mokeev, V.; Moran, P.; Munoz Camacho, C.; Naidoo, P.; Neupane, K.; Niccolai, S.; Niculescu, G.; Osipenko, M.; Pandey, P.; Paolone, M.; Pappalardo, L. L.; Paremuzyan, R.; Paul, S. J.; Phelps, W.; Pilleux, N.; Pokhrel, M.; Poudel, J.; Price, J. W.; Prok, Y.; Radic, A.; Raue, B. A.; Reed, T.; Richards, J.; Ripani, M.; Ritman, J.; Rossi, P.; Sabatie, F.; Salgado, C.; Schadmand, S.; Schmidt, A.; Sharabian, Y. G.; Shrestha, U.; Sokhan, D.; Sparveris, N.; Spreafico, M.; Stepanyan, S.; Strakovsky, I.; Strauch, S.; Turisini, M.; Tyson, R.; Ungaro, M.; Vallarino, S.; Venturelli, L.; Voskanyan, H.; Voutier, E.; Watts, D. P.; Wei, X.; Williams, R.; Wishart, R.; Wood, M. H.; Yurov, M.; Zachariou, N.; Zhao, Z. W.; Zurek, M.

doi:10.1103/PhysRevLett.131.021901

The polarized cross-section ratio σLT′/σ0 from hard exclusive π-Δ++ electroproduction off an unpolarized hydrogen target has been extracted based on beam-spin asymmetry measurements using a 10.2 GeV/10.6 GeV incident electron beam and the CLAS12 spectrometer at Jefferson Lab. The study, which provides the first observation of this channel in the deep-inelastic regime, focuses on very forward-pion kinematics in the valence regime, and photon virtualities ranging from 1.5 GeV2 up to 7 GeV2. The reaction provides a novel access to the d-quark content of the nucleon and to p→Δ++ transition generalized parton distributions. A comparison to existing results for hard exclusive π+n and π0p electroproduction is provided, which shows a clear impact of the excitation mechanism, encoded in transition generalized parton distributions, on the asymmetry.