Polarization Transfer in Wide-Angle Compton Scattering and Single-Pion Photoproduction from the Proton

• Published in: Physical review letters 2015-10, Vol.115 (15), p.152001-152001, Article 152001
• Main Authors: Fanelli, C, Cisbani, E, Hamilton, D J, Salmé, G, Wojtsekhowski, B, Ahmidouch, A, Annand, J R M, Baghdasaryan, H, Beaufait, J, Bosted, P, Brash, E J, Butuceanu, C, Carter, P, Christy, E, Chudakov, E, Danagoulian, S, Day, D, Degtyarenko, P, Ent, R, Fenker, H, Fowler, M, Frlez, E, Gaskell, D, Gilman, R, Horn, T, Huber, G M, de Jager, C W, Jensen, E, Jones, M K, Kelleher, A, Keppel, C, Khandaker, M, Kohl, M, Kumbartzki, G, Lassiter, S, Li, Y, Lindgren, R, Lovelace, H, Luo, W, Mack, D, Mamyan, V, Margaziotis, D J, Markowitz, P, Maxwell, J, Mbianda, G, Meekins, D, Meziane, M, Miller, J, Mkrtchyan, A, Mkrtchyan, H, Mulholland, J, Nelyubin, V, Pentchev, L, Perdrisat, C F, Piasetzky, E, Prok, Y, Puckett, A J R, Punjabi, V, Shabestari, M, Shahinyan, A, Slifer, K, Smith, G, Solvignon, P, Subedi, R, Wesselmann, F R, Wood, S, Ye, Z, Zheng, X
• Format: Article
• Language: English
• Subjects: Elastic scattering; Mathematical analysis; Photons; Photoproduction; PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; Polarization; Recoil protons; Scattering amplitude; Texts
• ISSN: 0031-9007; 1079-7114
• DOI: 10.1103/PhysRevLett.115.152001

Wide-angle exclusive Compton scattering and single-pion photoproduction from the proton have been investigated via measurement of the polarization transfer from a circularly polarized photon beam to the recoil proton. The wide-angle Compton scattering polarization transfer was analyzed at an incident photon energy of 3.7 GeV at a proton scattering angle of θ_{cm}^{p}=70°. The longitudinal transfer K_{LL}, measured to be 0.645±0.059±0.048, where the first error is statistical and the second is systematic, has the same sign as predicted for the reaction mechanism in which the photon interacts with a single quark carrying the spin of the proton. However, the observed value is ~3 times larger than predicted by the generalized-parton-distribution-based calculations, which indicates a significant unknown contribution to the scattering amplitude.