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

(A2 Collaboration at MAMI)

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We report a first measurement of the double-polarisation observable, Cx, in π+ photoproduction off the proton. The Cx 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 Cx 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.

Original languageEnglish
Article number138283
Number of pages7
JournalPhysics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics
Publication statusPublished - 10 Dec 2023

Bibliographical note

© 2023 The Authors. Published by Elsevier B.V.

Funding Information:
In accordance with UK data management policy, all data are available for downloading from PURE [34] . This work has been supported by the U.K. STFC ( ST/V002570/1 , ST/L00478X/2 , ST/V001035/1 , ST/P004385/2 , ST/T002077/1 , ST/L005824/1 , 57071/1 , 50727/1 ) grants, the Deutsche Forschungsgemeinschaft ( SFB443 , SFB/TR16 , and SFB1044 ), DFG-RFBR (Grant No. 09-02-91330 ), Schweizerischer Nationalfonds (Contracts No. 200020-175807 , No. 200020-156983 , No. 132799 , No. 121781 , No. 117601 ), the U.S. Department of Energy (Offices of Science and Nuclear Physics, Awards No. DE-SC0016583 , DE-SC0016582 , DE-SC0014323 , DEFG02-99-ER41110 , No. DE-FG02-88ER40415 , No. DEFG02-01-ER41194 ) and National Science Foundation (Grants NSF OISE-1358175 ; PHY-1039130 , PHY-1714833 , No. IIA-1358175 , PHY-2012940 ), INFN (Italy), and NSERC of Canada (Grant No. FRN-SAPPJ2015-00023 ). This infrastructure is part of a project that has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 824093 .


  • Photoproduction

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