Observation of Beam Spin Asymmetries in the Process ep→e^{'}π^{+}π^{-}X with CLAS12

DOI

10.1103/PhysRevLett.126.152501

T B. Hayward, College of William and Mary, Williamsburg, Virginia 23187-8795, USA.
C Dilks, Duke University, Durham, North Carolina 27708-0305, USA.
A Vossen, Duke University, Durham, North Carolina 27708-0305, USA.
H Avakian, Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606, USA.
S Adhikari, Florida International University, Miami, Florida 33199, USA.
G Angelini, The George Washington University, Washington, D.C. 20052, USA.
M Arratia, Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606, USA.
H Atac, Temple University, Philadelphia, Pennsylvania 19122, USA.
C Ayerbe Gayoso, College of William and Mary, Williamsburg, Virginia 23187-8795, USA.
N A. Baltzell, Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606, USA.
L Barion, INFN, Sezione di Ferrara, 44100 Ferrara, Italy.
M Battaglieri, Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606, USA.
I Bedlinskiy, National Research Centre Kurchatov Institute-ITEP, Moscow 117259, Russia.
F Benmokhtar, Duquesne University, 600 Forbes Avenue, Pittsburgh, Pennsylvania 15282, USA.
A Bianconi, Università degli Studi di Brescia, 25123 Brescia, Italy.
A S. Biselli, Fairfield University, Fairfield, Connecticut 06824, USA.
M Bondì, INFN, Sezione di Genova, 16146 Genova, Italy.
F Bossù, IRFU, CEA, Université Paris-Saclay, F-91191 Gif-sur-Yvette, France.
S Boiarinov, Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606, USA.
W J. Briscoe, The George Washington University, Washington, D.C. 20052, USA.
W K. Brooks, Universidad Técnica Federico Santa María, Casilla 110-V Valparaíso, Chile.
D Bulumulla, Old Dominion University, Norfolk, Virginia 23529, USA.
V D. Burkert, Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606, USA.
D S. Carman, Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606, USA.
J C. Carvajal, Florida International University, Miami, Florida 33199, USA.
A Celentano, INFN, Sezione di Genova, 16146 Genova, Italy.
P Chatagnon, Université Paris-Saclay, CNRS/IN2P3, IJCLab, 91405 Orsay, France.
T Chetry, Mississippi State University, Mississippi State, Mississippi 39762-5167, USA.
G Ciullo, INFN, Sezione di Ferrara, 44100 Ferrara, Italy.
B A. Clary, University of Connecticut, Storrs, Connecticut 06269, USA.
P L. Cole, Lamar University, 4400 MLK Boulevard, P.O. Box 10046, Beaumont, Texas 77710, USA.
M Contalbrigo, INFN, Sezione di Ferrara, 44100 Ferrara, Italy.

Document Type

Journal Article

Publication Date

4-16-2021

Publication Title

Physical review letters

Volume

126

Issue

15

First Page

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 10.6 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 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.

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Preprint

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