Measurement of PT-weighted Sivers asymmetries in leptoproduction of hadrons

M Alexeev ,E Mitrofanov,P Jörg,S Ishimoto,M Jandek,M Grosse Perdekamp,M Zavertyaev,A Moretti,F Balestra,F Bradamante,A.M Kotzinian,M Pešková,M Stolarski,Ch Dreisbach,A Selyunin,M Büchele,J Marzec,R Salac,F Tosello,B Ketzer,A Nagaytsev,N Pierre,S Platchkov,M Virius,K Kondo,M Chiosso,W Meyer,Yu.V Mikhailov,A Gridin,S Gerassimov,S Sirtl,L Dhara,F Gautheron,P Bordalo,S Paul,M Gorzellik,H Fischer,W Dünnweber,K Bicker,P.D Eversheim,Y Bedfer,K Augsten,M Faessler,A Bressan,A Martin,D Neyret,N Du Fresne Von Hohenesche,C Riedl,Z.V Kroumchtein,N Horikawa,A Kveton,W Augustyniak,N Mitrofanov,T Sawada,B Parsamyan,A.G Chumakov,S Dalla Torre,V Andrieux,F Pereira,J Tomsa,E Seder,N Doshita,E Kabuß,F Sozzi,J Bernhard,O.P Gavrichtchouk,F Tessarotto,M Mikhasenko,V.D Samoylenko,J Nový,J.H Koivuniemi,A Ferrero,V.A Polyakov,A Kerbizi,E Zemlyanichkina,L Sinha,D Von Harrach,A Thiel,F Kunne,J Giarra,Yu Kisselev,S.A Mamon,M Bodlak,M Ball,S Uhl,F Krinner,P Sznajder,C Chatterjee,F Herrmann,N Makins,T Szameitat,M Pešek,V.E Burtsev,S Sarkar,R Joosten,J Barth,A Maggiora,P Schiavon,A Magnon,A Grasso,S.V Donskov,A Sandacz,D Panzieri,W.-D Nowak,V.N Kolosov,S Tessaro,A Szabelski,O Subrt,J Lichtenstadt,G.K Mallot,G Nukazuka,C Quintans,Y Miyachi,I Konorov,C.D.R Azevedo,S Huber,E.R Bielert,Yu.A Khokhlov,A Vauth,A.A Lednev,M Wilfert,R Beck,T Matsuda,J Pretz,L Silva,M Dziewiecki,S Ramos,A Vidon,C Regali,M.L Crespo,M Meyer,K Juraskova,G.V Khaustov,M Ziembicki,C Elia,R Heitz,A Rychter,D Steffen,A Amoroso,S Wallner,A Cicuttin,G Reicherz,G Sbrizzai,B.M Veit,M Ostrick,I Gnesi,A Antoshkin,B Grube,H Schmieden,D.I Ryabchikov,J Pochodzalla,N Makke,D.V Peshekhonov,S Levorato,A Srnka,C Franco,M Krämer,C.-Y Hsieh,M Quaresma,T Iwata,K Kurek,V Tskhay,S Dasgupta,M Finger,Y.-S Lian,D Hahne,B Badełek,G Hamar,A Guskov,A S Nunes ,Y P Kulinich ,R Kurjata ,G D Alexeev ,V Jarý ,В.ф Константинов ,M Šulc ,G Meshcheryakov ,S U Chung ,I Savin ,F Kašpar ,J Smolík ,Ф Клейн ,Riccardo Longo ,И Орлов ,В Аносов ,О Денисов ,M Taševský ,А Рыбников ,К Заремба ,Vincenzo Barone ,O Kouznetsov ,Hiromasa Suzuki ,А.g Оlshevsky ,B Mariański ,W C Chang ,А.в Ефремов ,J.f.c.a Veloso ,R R Dusaev ,J C Peng ,Friedrich Jm ,А Иванов ,Н Анфимов ,V V Frolov ,Valery E Lyubovitskij ,B I Vasilishin ,Y X Zhao ,N D’hose ,P Závada ,Mathias Wagner ,M Slunečka ,Zdeněk Král ,Jan Matoušek

doi:10.1016/j.nuclphysb.2018.12.024

Abstract

The transverse spin asymmetries measured in semi-inclusive leptoproduction of hadrons, when weighted with the hadron transverse momentum PT, allow for the extraction of important transverse-momentum-dependent distribution functions. In particular, the weighted Sivers asymmetries provide direct information on the Sivers function, which is a leading-twist distribution that arises from a correlation between the transverse momentum of an unpolarised quark in a transversely polarised nucleon and the spin of the nucleon. Using the high-statistics data collected by the COMPASS Collaboration in 2010 with a transversely polarised proton target, we have evaluated two types of PT-weighted Sivers asymmetries, which are both proportional to the product of the first transverse moment of the Sivers function and of the fragmentation function. The results are compared to the standard unweighted Sivers asymmetries and used to extract the first transverse moments of the Sivers distributions for u and d quarks.

Highlights

The COMPASS Collaboration / Nuclear Physics B 940 (2019) 34–53 direction of the quark transverse momentum vector kT, and their contribution to the hadronic tensor vanishes when integrating over kT .Among the TMDs, an important rôle is played by the Sivers distribution function f1⊥Tq [4,5,6,7], which for an unpolarised quark of flavour q describes the correlation between its transverse momentum and the transverse polarisation of the nucleon
COMPASS has measured the weighted Sivers asymmetries in semi-inclusive measurements of deep-inelastic scattering (SIDIS) of 160 GeV muons on transversely polarised protons, extending the standard analysis of unweighted asymmetries. These new observables provide the direct access to the first moment of the Sivers function avoiding the transverse-momentum convolution of the TMD Sivers and fragmentation functions, which enter in the standard Sivers asymmetry
The weighted asymmetries were determined for positive and negative hadrons using as weight either PT /zM or PT /M

Summary

Introduction

The COMPASS Collaboration / Nuclear Physics B 940 (2019) 34–53 direction of the quark transverse momentum vector kT , and their contribution to the hadronic tensor vanishes when integrating over kT. Data on pion production off a transversely polarised 3He target were made available by the Hall A Collaboration at JLab [14] Combined analyses of these measurements [15,16,17,18,19,20,21,22,23,24,25] allowed for extractions of the Sivers functions and of their first transverse moments f1⊥T(1) q : f1⊥T (1) q (x) =. [26] a different approach was adopted: the COMPASS measurements on proton and deuteron targets in the same kinematics were used to extract point-by-point the first transverse moments of the Sivers distributions f1⊥T(1) directly from the data by combining the various asymmetries. The results are compared to the standard unweighted Sivers asymmetries and used to extract the first transverse moments of the Sivers functions for u and d quarks

The Sivers asymmetries

Experimental set-up and data analysis

Point-by-point extraction of the first moments of the Sivers functions

Conclusions and outlook