Contribution of exclusive diffractive processes to the measured azimuthal asymmetries in SIDIS

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

doi:10.1016/j.nuclphysb.2020.115039

Abstract

Hadron leptoproduction in Semi-Inclusive measurements of Deep-Inelastic Scattering (SIDIS) on unpolarised nucleons allows one to get information on the intrinsic transverse momentum of quarks in a nucleon and on the Boer-Mulders function through the measurement of azimuthal modulations in the cross section. These modulations were recently measured by the HERMES experiment at DESY on proton and deuteron targets, and by the COMPASS experiment using the CERN SPS muon beam and a 6LiD target. In both cases, the amplitudes of the cos⁡ϕh and cos⁡2ϕh modulations show strong kinematic dependences for both positive and negative hadrons. It has been known since some time that the measured final-state hadrons in those SIDIS experiments receive a contribution from exclusive diffractive production of vector mesons, particularly important at large values of z, the fraction of the virtual photon energy carried by the hadron. In previous measurements of azimuthal asymmetries this contribution was not taken into account, because it was not known that it could distort the azimuthal modulations. Presently, a method to evaluate the contribution of the exclusive reactions to the azimuthal asymmetries measured by COMPASS has been developed. The subtraction of this contribution results in a better understanding of the kinematic effects, and the remaining non-zero cos⁡2ϕh modulation gives indication for a non-zero Boer-Mulders effect.

Highlights

The exclusive-vector mesons (VM) hadron contributions to the unsubtracted azimuthal asymmetries r acUoUs φ,ehxcl and r acUoUs 2,φexhcl are calculated in each x, z and pTh bin of Ref. [3]
The last column of the figure shows the comparison between the asymmetries as published in Ref. [3] and after subtracting the contribution of exclusive VMs for h+
The results for AUcoUs 2φh for positive and negative hadrons are compared to the unsubtracted asymmetries in Fig. 7 and 8

Summary

Introduction

The possible explanation of the origin of unpolarised azimuthal asymmetries in SIDIS was given by Cahn using the simple parton model based on unpolarised TMD PDFs and FFs [4] In this model the AUcoUs φh and AUcoUs 2φh asymmetries arise at O(1/Q) and O(1/Q2), respectively, as kinematic corrections to the leading order cross-section. We have measured azimuthal asymmetries for h+ and h− originating from the decay of exclusively produced VMs (referred to as exclusive-VM hadrons in the following), and found them to be large Since they do not have an interpretation in the framework of the parton model TMD formalism, we have subtracted this contribution from the COMPASS asymmetries published in.

Azimuthal modulations of exclusive-VM hadrons

Fraction of exclusive-VM hadrons in the SIDIS sample

Results for the unpolarised SIDIS azimuthal asymmetries

Conclusions