First measurement of the polarization observable E in the [formula omitted] reaction up to 2.25 GeV

S Strauch,R De Vita,H Voskanyan,Y Ghandilyan,H Egiyan,H Moutarde,M Battaglieri,S Pozdniakov,S Anefalos Pereira,L El Fassi,A Celentano,O Cortes,S Stepanyan,S Pisano,L Colaneri,H Hakobyan,B Mckinnon,P Peng,I Niculescu,E Golovatch,G Khachatryan,M Khandaker,A Filippi,E De Sanctis,D Rönchen,K Hafidi,W Phelps,M Contalbrigo,N Gevorgyan,I Zonta,F Sabatié,M Hattawy,M Guidal,D Adikaram,Ye Tian,E Voutier,D Sokhan,S Procureur,M Ripani,I Senderovich,S Niccolai,Y Prok,A Simonyan,P Lenisa,P Eugenio,D Protopopescu,G Rosner,G Charles,V Sytnik,M Ungaro,C Hanretty,E Seder,E Pasyuk,A Deur,M Holtrop,V Batourine,P Roy,S Joosten,C Djalali,K Livingston,Y Ilieva,A Movsisyan,W Kim,A El Alaoui,S Chandavar,A Fradi,N Markov,Iu Skorodumina,M Osipenko,G Niculescu,N Dashyan,P Stoler,K Hicks,W Gohn,M Taiuti,I Bedlinskiy,N Benmouna,O Pogorelko,N Sparveris,D I Glazier ,R Badui ,E Munévar ,R A Schumacher ,V Mokeev,Michael Döring ,E Klempt,A S Biselli ,Ross Tucker ,J Brock,L Zana,A Sarantsev ,R Dupré ,A J R Puckett ,M Dugger,T A Forest ,D P Watts ,E L Isupov ,A Rizzo,A D’angelo ,K P Adhikari ,S E Kuhn ,R W Gothe ,Y G Sharabian ,Jian Zhang ,Hao Jiang ,S M Hughes ,N Harrison,H S Jo ,I J D Macgregor ,L Guo,R A Montgomery ,S Fegan,N K Walford ,L A Net ,P L Cole ,F X Girod ,M H Wood ,G V O’rielly ,J A Fleming ,A Klein,C Muñoz Camacho ,R L Workman ,C I Moody ,J W Price ,D Jenkins,A I Ostrovidov ,A V Anisovich ,T Cao,D Keller,K A Griffioen ,F J Klein ,D G Ireland ,G D Smith ,D Schott,A Kim,K L Giovanetti ,G Fedotov,A Trivedi,W K Brooks ,C A Meyer ,D I Sober ,C Carlin,C Salgado,D Ho,K Park,K S Joo ,J J Phillips ,N Compton,D S Carman ,B G Ritchie ,P Nadel-Turoński ,X Wei,L Elouadrhiri,V Kubarovsky,H Y Lu ,B S Ishkhanov ,W J Briscoe ,B A Raue ,D Meekins ,N Zachariou,V Credé ,Volker Burkert ,Z W Zhao ,C Keith ,V A Nikonov ,J Ball,I I Strakovsky ,M L Seely

doi:10.1016/j.physletb.2015.08.053

Abstract

First results from the longitudinally polarized frozen-spin target (FROST) program are reported. The double-polarization observable E, for the reaction γ→p→→π+n, has been measured using a circularly polarized tagged-photon beam, with energies from 0.35 to 2.37 GeV. The final-state pions were detected with the CEBAF Large Acceptance Spectrometer in Hall B at the Thomas Jefferson National Accelerator Facility. These polarization data agree fairly well with previous partial-wave analyses at low photon energies. Over much of the covered energy range, however, significant deviations are observed, particularly in the high-energy region where high-L multipoles contribute. The data have been included in new multipole analyses resulting in updated nucleon resonance parameters. We report updated fits from the Bonn–Gatchina, Jülich–Bonn, and SAID groups.

Highlights

First measurement of the polarization observable E in the p(γ, π +)n reaction up to 2.25 GeV
Four complex amplitudes govern the photoproduction of single pions, and a complete experiment requires the measurement of at least eight well-chosen observables at each energy and production angle for both isospin-related reactions γ p → π 0 p and γ p → π +n [7]
In this Letter we present a measurement of the doublepolarization observable E in the γ p → π +n reaction of circularly polarized photons with longitudinally polarized protons

Summary

Introduction

First measurement of the polarization observable E in the p(γ , π +)n reaction up to 2.25 GeV. The double-polarization observable E, for the reaction γ p → π +n, has been measured using a circularly polarized tagged-photon beam, with energies from 0.35 to 2.37 GeV. The data have been included in new multipole analyses resulting in updated nucleon resonance parameters.

Results

Conclusion