Observation of Beam Spin Asymmetries in the Process ep→e′π+π−X with CLAS12

T B Hayward ,S Joosten,M Ungaro,W Phelps,L Marsicano,M Arratia,A D’Angelo,S Boiarinov,A Rizzo,S Adhikari,K Neupane,L Elouadrhiri,R Paremuzyan,E Voutier,M Leali,P Rossi,D Keller,N Sparveris,A Deur,H Egiyan,V Mascagna,M Paolone,E Pasyuk,P Lenisa,F Benmokhtar,K Hicks,S Lee,Y Prok,M Khachatryan,M Battaglieri,M Holtrop,M Dugger,L Venturelli,M Hattawy,R Tyson,H Avakian,T Chetry,S Stepanyan,A El Alaoui,A Vossen,D Bulumulla,C Salgado,K Wei,Y Gotra,N Markov,L El Fassi,H Atac,C Dilks,J Rowley,H Hakobyan,A Celentano,P Chatagnon,V Mokeev,A Bianconi,I Bedlinskiy,K Hafidi,A Hobart,K Joo,F Sabatié,W Kim,L Lanza,S Strauch,M Osipenko,L Barion,A Khanal,M Guidal,A Filippi,J Ritman,S Nanda,G Costantini,C Ayerbe Gayoso,P Naidoo,S Niccolai,M Mirazita,N Dashyan,B Mckinnon,J Zhang,M Contalbrigo,A Kim,M Ripani,A Movsisyan,H Voskanyan,M Ehrhart,X Wei,V Kubarovsky,D Marchand,G Niculescu,R De Vita,G Ciullo,D Sokhan,S Fegan,K Livingston,G Gavalian,N Zachariou,F Hauenstein,M Defurne,B Yale,O Pogorelko,C Djalali,G Angelini,Axel Schmidt ,Stefan Diehl ,B A Raue ,N J C Tyler ,L L Pappalardo ,P Nadel-Turoński ,A A Golubenko ,S E Kuhn ,Uttam Shrestha ,H S Jo ,A Biselli ,E L Isupov ,N A Baltzell ,Y G Sharabian ,P L Cole ,T A Forest ,V D Burkert ,J Carvajal ,M H Wood ,F X Girod ,C Muñoz Camacho ,I I Strakovsky ,V Credé ,Z E Meziani ,D P Watts ,O Soto ,R Dupré ,W K Brooks ,E P Segarra ,Adam Thornton ,Á Kripkó ,D S Carman ,D G Ireland ,K A Griffioen ,F Bossú ,B A Clary ,W J Briscoe ,T O’connell ,M Bondì ,D I Glazier ,G P Gilfoyle ,R W Gothe ,I J D Macgregor

doi:10.1103/physrevlett.126.152501

Abstract

The observation of beam spin asymmetries in two-pion production in semi-inclusive deep inelastic scattering off an unpolarized proton target is reported. The data presented here were taken in the fall of 2018 with the CLAS12 spectrometer using a 10.6GeV longitudinally spin-polarized electron beam delivered by CEBAF at JLab. The measured asymmetries provide the first opportunity to extract the parton distribution function e(x), which provides information about the interaction between gluons and quarks, in a collinear framework that offers cleaner access than previous measurements. The asymmetries also constitute the first ever signal sensitive to the helicity-dependent two-pion fragmentation function G_{1}^{⊥}. A clear sign change is observed around the ρ mass that appears in model calculations and is indicative of the dependence of the produced pions on the helicity of the fragmenting quark.

Highlights

The observation of beam spin asymmetries in two-pion production in semi-inclusive deep inelastic scattering off an unpolarized proton target is reported
The data presented here were taken in the fall of 2018 with the CLAS12 spectrometer using a 10.6 GeV longitudinally spin-polarized electron beam delivered by Continuous Electron Beam Accelerator Facility (CEBAF) at JLab
The nonperturbative dynamics of hadronization, the process of the formation of hadrons out of quarks and gluons, are described by fragmentation functions (FFs), which at leading twist can be interpreted in the parton model as the probability that a quark forms a certain hadron

Summary

Introduction

The observation of beam spin asymmetries in two-pion production in semi-inclusive deep inelastic scattering off an unpolarized proton target is reported. The data presented here were taken in the fall of 2018 with the CLAS12 spectrometer using a 10.6 GeV longitudinally spin-polarized electron beam delivered by CEBAF at JLab. The measured asymmetries provide the first opportunity to extract the parton distribution function eðxÞ, which provides information about the interaction between gluons and quarks, in a collinear framework that offers cleaner access than previous measurements. The asymmetries constitute the first ever signal sensitive to the helicity-dependent two-pion fragmentation function G⊥1 .

Results

Conclusion