Beam Spin Asymmetry in Semi-Inclusive Electroproduction of Hadron Pairs.

M Mirazita,K Hafidi,P Eugenio,C Dilks,V Kubarovsky,M Guidal,H Egiyan,N Markov,Y Ilieva,T O’Connell,C Mullen,D Marchand,Y Ghandilyan,H Avakian,M Defurne,H Hakobyan,M Ehrhart,N Zachariou,S Boiarinov,L Lanza,L Barion,C Salgado,P Lenisa,O Pogorelko,J Poudel,Y Prok,B Yale,T Chetry,P Rossi,A Vossen,I Bedlinskiy,A Deur,M Khandaker,A Filippi,A Rizzo,K Wei,D Jenkins,D Keller,A Bianconi,M Hattawy,H Atac,N Dashyan,M Ripani,A El Alaoui,A Khanal,V Mascagna,E Golovatch,N Sparveris,A D’Angelo,M Holtrop,K Neupane,G Niculescu,R De Vita,A Celentano,S Fegan,M Paolone,M Leali,K Hicks,A Hobart,R Fersch,M Ungaro,J Ritman,M Contalbrigo,H Voskanyan,F Sabatié,R Paremuzyan,S Adhikari,L El Fassi,W Phelps,G Gavalian,M Battaglieri,D Heddle,G Ciullo,B Mckinnon,C Djalali,M Osipenko,L Venturelli,L Marsicano,L Guo,S Stepanyan,E Pasyuk,D Bulumulla,E Voutier,V Mokeev,P Chatagnon,K Livingston,X Wei,T Mineeva,S Strauch,S Pisano,M J Amaryan ,G P Gilfoyle ,I I Strakovsky ,O Soto ,W J Briscoe ,E L Isupov ,T B Hayward ,Aurore Courtoy ,K S Joo ,C W Kim ,R A Schumacher ,S E Kuhn ,D I Glazier ,D Počanić ,Y G Sharabian ,H S Jo ,K A Griffioen ,N J C Tyler ,Б С Ишханов ,J Carvajal ,T A Forest ,I J D Macgregor ,J Zhang ,F X Girod ,G Angelini ,B A Clary ,F J Klein ,A S Biselli ,Uttam Shrestha ,Axel Schmidt ,R Milner ,M H Wood ,D G Ireland ,R Dupré ,K L Giovanetti ,N A Baltzell ,R W Gothe ,V Credé ,W K Brooks ,D S Carman ,W Kim ,Qi Huang ,L L Pappalardo ,F Bossú ,B A Raue ,Stefan Diehl ,Volker Burkert ,K Park ,F Benmokhtar ,P L Cole ,D P Watts ,C Muñoz Camacho ,Z W Zhao

doi:10.1103/physrevlett.126.062002

Abstract

A first measurement of the longitudinal beam spin asymmetry A_{LU} in the semi-inclusive electroproduction of pairs of charged pions is reported. A_{LU} is a higher-twist observable and offers the cleanest access to the nucleon twist-3 parton distribution function e(x). Data have been collected in the Hall-B at Jefferson Lab by impinging a 5.498-GeV electron beam on a liquid-hydrogen target, and reconstructing the scattered electron and the pion pair with the CLAS detector. One-dimensional projections of the A_{LU}^{sinϕ_{R}} moments are extracted for the kinematic variables of interest in the valence quark region. The understanding of dihadron production is essential for the interpretation of observables in single-hadron production in semi-inclusive DIS, and pioneering measurements of single-spin asymmetries in dihadron production open a new avenue in studies of QCD dynamics.

Highlights

21INFN, Sezione di Roma Tor Vergata, 00133 Rome, Italy 22INFN, Sezione di Torino, 10125 Torino, Italy 23INFN, Sezione di Pavia, 27100 Pavia, Italy
The understanding of dihadron production is essential for the interpretation of observables in single-hadron production in semi-inclusive DIS, and pioneering measurements of single-spin asymmetries in dihadron production open a new avenue in studies of QCD dynamics
Asymmetries from semi-inclusive deep inelastic scattering (SIDIS), where a highly virtual photon interacts with a hadronic target and at least one hadron is detected in the final state, have appeared to be effective tools to access quark distributions and fragmentation information

Summary

Published by the American Physical Society

At the energy of fixed-target facilities, contributions of order OðM=QÞ, with M the target mass and Q2 the photon virtuality, become sizable and, relevant Such contributions are labeled twist-3 effects, and can encode quark-gluon correlations. An essential role is played by the chiral-odd PDF eðxÞ, that is related to the nucleon scalar charge—poorly determined through phenomenology—and a fortiori to the pion-nucleon sigma term [1] It encodes information on the quark mass, as well as genuine quark-gluon correlations [2]. Measurements of twist-3 observables are available from HERMES [7], CLAS [8,9,10], and COMPASS [11] for single-pion SIDIS, for which the PDF eðxÞ is accessible only when the transverse momentum of the final hadron is not integrated out. ; ð1Þ with ε the ratio of longitudinal to transverse photon flux, and the structure functions (SFs) [13]

FsLiUn φR

RT RT j

ALU R sinφ