Neutron polarisation transfer, Cx′, in π+ photoproduction off the proton, d(γ⊙,n→π+)nspec

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.; ...., ...; Supek, Ivan; ...., ...; Wolfes, M.; Workman, R. L.; Zachariou, N. (2023) Neutron polarisation transfer, Cx′, in π+ photoproduction off the proton, d(γ⊙,n→π+)nspec. Physics Letters B, 847 . ISSN 03702693

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Abstract

We report a first measurement of the double-polarisation observable, , in photoproduction off the proton. The 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 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. Inclusion of the new data in the database of the SAID partial wave analysis shifted the solution to a new global minima which, not only gives better agreement with the current data, but also improves the description of a range of other single and double polarisation observables for charged pion photoproduction.

Item Type:	Article
Uncontrolled Keywords:	photoproduction off the proton; double-polarisation observable; polarised photon beam; MAMI
Subjects:	NATURAL SCIENCES NATURAL SCIENCES > Physics NATURAL SCIENCES > Physics > Physics of Elementary Particles and Fields
Divisions:	Division of Experimental Physics
Depositing User:	Virna Brumnić
Date Deposited:	05 May 2025 08:46
URI:	http://fulir.irb.hr/id/eprint/9804
DOI:	10.1016/j.physletb.2023.138283

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