Observation of Beam Spin Asymmetries in the Process $ep\rightarrow{e}^{'}{\pi}^{+}{\pi}^{-}X$ with CLAS12

T.B. Hayward , C. Dilks , A. Vossen , H. Avakian , S. Adhikari , G. Angelini , M. Arratia , H. Atac , C. Ayerbe Gayoso , N.A. Baltzell , L. Barion , M. Battaglieri , I. Bedlinskiy , F. Benmokhtar , A. Bianconi , A.S. Biselli , M. Bondì , F. Bossù (1) , S. Boiarinov , W.J. Briscoe , W.K. Brooks , D. Bulumulla , V.D. Burkert , D.S. Carman , J.C. Carvajal , A. Celentano , P. Chatagnon (2) , T. Chetry , G. Ciullo , B.A. Clary , P.L. Cole , M. Contalbrigo , G. Costantini , V. Crede , A. d'Angelo , N. Dashyan , R. de Vita , M. Defurne (1) , A. Deur , S. Diehl , C. Djalali , R. Dupre (2) , M. Dugger , H. Egiyan , M. Ehrhart (2) , A. El Alaoui , L. El Fassi , L. Elouadrhiri , S. Fegan , A. Filippi , T.A. Forest , G. Gavalian , G.P. Gilfoyle , F.X. Girod , D.I. Glazier , A.A. Golubenko , R.W. Gothe , Y. Gotra , K.A. Griffioen , M. Guidal (2) , K. Hafidi , H. Hakobyan , M. Hattawy , F. Hauenstein , K. Hicks , A. Hobart (2) , M. Holtrop , D.G. Ireland , E.L. Isupov , H.S. Jo , K. Joo , S. Joosten , D. Keller , M. Khachatryan , A. Khanal , A. Kim , W. Kim , A. Kripko , V. Kubarovsky , S.E. Kuhn , L. Lanza , M. Leali , S. Lee , P. Lenisa , K. Livingston , I.J.D. Macgregor , D. Marchand (2) , N. Markov , L. Marsicano , V. Mascagna , B. Mckinnon , Z.E. Meziani , M. Mirazita , V. Mokeev , A. Movsisyan , C. Munoz Camacho (2) , P. Nadel-Turonski , P. Naidoo , S. Nanda , K. Neupane , S. Niccolai (2) , G. Niculescu , T.R. O'Connell , M. Osipenko , M. Paolone , L.L. Pappalardo , R. Paremuzyan , E. Pasyuk , W. Phelps , O. Pogorelko , Y. Prok , B.A. Raue , M. Ripani , J. Ritman , A. Rizzo , P. Rossi , J. Rowley , F. Sabatié (1) , C. Salgado , A. Schmidt , E.P. Segarra , Y.G. Sharabian , U. Shrestha , D. Sokhan , O. Soto , N. Sparveris , S. Stepanyan , I.I. Strakovsky , S. Strauch , A. Thornton , N. Tyler , R. Tyson , M. Ungaro , L. Venturelli , H. Voskanyan , E. Voutier (2) , D.P. Watts , K. Wei , X. Wei , M.H. Wood , B. Yale , N. Zachariou , J. Zhang

1 IRFU - Institut de Recherches sur les lois Fondamentales de l'Univers
2 IJCLab - Laboratoire de Physique des 2 Infinis Irène Joliot-Curie

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 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 G1⊥. 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.

Mots clés: Nuclear Physics; spin: asymmetry; parton: distribution function; helicity: asymmetry: measured; electron: beam; deep inelastic scattering: semi-inclusive reaction; p: target; two-pion; quark; CLAS; Newport News CEBAF Linac; fragmentation function; Jefferson Lab; spectrometer; collinear; gluon; GeV

Domaines: Physique Nucléaire Expérimentale [nucl-ex]

T.B. Hayward, C. Dilks, A. Vossen, H. Avakian, S. Adhikari, et al.. Observation of Beam Spin Asymmetries in the Process $ep\rightarrow{e}^{'}{\pi}^{+}{\pi}^{-}X$ with CLAS12. Physical Review Letters, 2021, 126 (15), pp.152501. ⟨10.1103/PhysRevLett.126.152501⟩. ⟨hal-03203660⟩