학술논문
Neutron polarisation transfer, $C_{x'}^n$, in $\pi^+$ photoproduction off the proton
Document Type
Working Paper
Author
Bashkanov, M.; Watts, D. P.; Kay, S. J. D.; Abt, S.; Achenbach, P.; Adlarson, P.; Afzal, F.; Ahmed, Z.; Akondi, C. S.; Annand, J. R. M.; Beck, R.; Biroth, M.; Borisov, N.; Braghieri, A.; Briscoe, W. J.; Cividini, F.; Collicott, C.; Costanza, S.; Denig, A.; Downie, E. J.; Drexler, P.; Fegan, S.; Fix, A.; Gardner, S.; Ghosal, D.; Glazier, D. I.; Gorodnov, I.; Gradl, W.; Gurevich, D.; Heijkenskjöld, L.; Hornidge, D.; Huber, G. M.; Kashevarov, V. L.; Korolija, M.; Krusche, B.; Lazarev, A.; Livingston, K.; Lutterer, S.; MacGregor, I. J. D.; Manley, D. M.; Martel, P. P.; Miskimen, R.; Mornacchi, E.; Mullen, C.; Neganov, A.; Neiser, A.; Ostrick, M.; Otte, P. B.; Paudyal, D.; Pedroni, P.; Rostomyan, T.; Sokhoyan, V.; Spieker, K.; Steffen, O.; Strakovsky, I. I.; Strub, T.; Supek, I.; Thiel, A.; Thiel, M.; Thomas, A.; Usov, Yu. A.; Wagner, S.; Walford, N. K.; Wettig, J.; Wolfes, M.; Zachariou, N.
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Subject
Language
Abstract
We report a first measurement of the double-polarisation observable, $C_{x'}$, in $\pi^+$ photoproduction off the proton. The $C_{x'}$ double-polarisation observable represents the transfer of polarisation from a circularly polarised photon beam to the recoiling neutron. The MAMI circularly polarised photon beam impinged on a liquid deuterium target cell, with reaction products detected in the Crystal Ball calorimeter. Ancillary apparatus surrounding the target provided tracking, particle identification and determination of recoil nucleon polarisation. The $C_{x'}$ observable is determined for photon energies 800-1400 MeV, providing new constraints on models aiming to elucidate the spectrum and properties of nucleon resonances. This is the first determination of any polarisation observable from the beam-recoil group of observables for this reaction, providing a valuable constraint and systematic check of the current solutions of partial wave analysis based theoretical models.