Longitudinal double spin asymmetries in single hadron quasi-real photoproduction at high pT

C Adolph,S Ramos,M Gorzellik,M Virius,A Rychter,D Neyret,J Lichtenstadt,C.D.R Azevedo,C Quintans,C Riedl,G Nukazuka,F Kunne,A Austregesilo,D.I Ryabchikov,N Du Fresne Von Hohenesche,R Jahn,E Zemlyanichkina,M Ostrick,J Ter Wolbeek,Yu Kisselev,A.A Lednev,A Magnon,M Finger,D Panzieri,A Srnka,Yu.V Mikhailov,F Krinner,A Maggiora,L Dhara,R Akhunzyanov,V.N Kolosov,V.D Samoylenko,A Sandacz,F Tessarotto,D.V Peshekhonov,A Guskov,M Ziembicki,R Beck,I Konorov,A Grasso,Yu Ivanshin,P Schiavon,E Burtin,D Von Harrach,V Tskhay,J Bisplinghoff,K Kondo,Y Bedfer,Q Curiel,S Platchkov,F Thibaud,S Levorato,W Augustyniak,V Andrieux,A Amoroso,F Balestra,M Büchele,S Tessaro,T Michigami,V.A Polyakov,P Kremser,T Matsuda,S Grabmüller,O.P Gavrichtchouk,S Ishimoto,M Wilfert,J Pretz,A Zink,D Hahne,R Joosten,A Nagaytsev,W Eyrich,G Sbrizzai,S Huber,P Sznajder,G.V Khaustov,M Levillain,O.Yu Shevchenko,T Weisrock,N Kuchinski,C Regali,R Birsa,A Lehmann,M Quaresma,F Tosello,N Horikawa,L Sinha,K Königsmann,J Nový,W Dünnweber,M Chiosso,P Jörg,F Nerling,V Duic,B Grube,S Uhl,S Schopferer,K Kurek,E.R Bielert,S Sirtl,H Schmieden,K Bicker,G Reicherz,F Hinterberger,J Barth,P Montuenga,P Bordalo,P.D Eversheim,J.H Koivuniemi,J Pochodzalla,T Grussenmeyer,E Fuchey,N.S Rossiyskaya,T Szameitat,M Grosse Perdekamp,B Ketzer,Z.V Kroumchtein,Yu.A Khokhlov,C Santos,M.L Crespo,S Gerassimov,N Makke,F Klein,A Martin,N Makins,C Braun,F Herrmann,M Faessler,G Meshcheryakov,F Gautheron,B Parsamyan,M Stolarski,C.-Y Hsieh,H Fischer,F H Heinsius ,И Орлов ,I Savin ,V Jarý ,B Mariański ,К Заремба ,А В Ефремов ,R Kurjata ,J.f.c.a Veloso ,Hiromasa Suzuki ,Hiroki Matsuda ,M Šulc ,M Alexeev ,В.ф Константинов ,А.g Оlshevsky ,M Boër ,А Иванов ,Claude Marchand ,Riccardo Longo ,G D Alexeev ,Florian Haas ,I J Choi ,Friedrich Jm ,Ryo Hashimoto ,В Аносов ,Ralf Kühn ,J C Peng ,A S Nunes ,V Nikolaenko ,О Денисов ,W C Chang ,S U Chung ,Jan Matoušek ,N D’hose ,M Slunečka ,V V Frolov ,J Bernhard,A Selyunin,J Marzec,B Badełek,O Kouznetsov,M Bodlak,F Bradamante,G.K Mallot,S Dalla Torre,A.M Kotzinian,E Kabuß,C Franco,K Schmidt,S Dasgupta,F Sozzi,A Szabelski,N Doshita,M Zavertyaev,T Iwata,A Bressan,S Takekawa,Y Miyachi,M Pešek,A Cicuttin,S.V Donskov,F Pereira,M Dziewiecki,W Meyer,F Giordano,M Krämer,I Gnesi,K Klimaszewski,S Paul,L Silva,K Schönning,A Ferrero,S Sarkar,W.-D Nowak

doi:10.1016/j.physletb.2015.12.035

Abstract

We measured the longitudinal double spin asymmetries ALL for single hadron muoproduction off protons and deuterons at photon virtuality Q2<1(GeV/c)2 for transverse hadron momenta pT in the range 1 GeV/c to 4 GeV/c. They were determined using COMPASS data taken with a polarised muon beam of 160 GeV/c or 200 GeV/c impinging on polarised 6LiD or NH3 targets. The experimental asymmetries are compared to next-to-leading order pQCD calculations, and are sensitive to the gluon polarisation ΔG inside the nucleon in the range of the nucleon momentum fraction carried by gluons 0.05<xg<0.2.

Highlights

The spin structure of the nucleon is one of the major unresolved issues in hadronic physics
In this Letter, we present a new analysis of COMPASS data for single-inclusive hadron quasi-real photoproduction at high pT 1, which differs from our previous analysis in that all measured hadrons within a given pT bin are included in the analysis, and the hadron(s) with highest pT
We compare our asymmetries with theoretical calculations at next-to-leading order (NLO) without threshold resummation based on the framework described in Ref. [14] and summarised in the following

Summary

Introduction

The spin structure of the nucleon is one of the major unresolved issues in hadronic physics. The spin-averaged gluon density g(xg), where xg denotes the nucleon momentum fraction carried by gluons, is well constrained by DIS experiments with unpolarised beam and target because of their high statistics and large kinematic coverage. The fewer data from DIS experiments with polarised beam and target, can not sufficiently constrain the gluon helicity distribution ∆g(xg). This affects directly our knowledge of the contribution of the gluon spin to the spin of the nucleon, known as ∆G = ∆g(xg)dxg, and to a lesser extent that of the quarks [2]. In order to better constrain ∆g(xg), one has to resort to processes where contributions from gluons appear at leading order, such as hadron production at high transverse momenta or production of open charm in polarised lepton–nucleon [3, 4, 5, 6, 7] or hadron– hadron interactions [8, 9, 10, 11]

Methods

Results

Conclusion