First measurement of the Sivers asymmetry for gluons from SIDIS data

C. Adolph , M. Aghasyan , R. Akhunzyanov , M.G. Alexeev , G.D. Alexeev , A. Amoroso , V. Andrieux , N.V. Anfimov

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V. Anosov A. Antoshkin K. Augsten W. Augustyniak A. Austregesilo C.D.R. Azevedo B. Badelek F. Balestra M. Ball J. Barth R. Beck Y. Bedfer J. Bernhard K. Bicker E. R. Bielert R. Birsa M. Bodlak P. Bordalo F. Bradamante C. Braun A. Bressan M. Buechele W.-C. Chang C. Chatterjee M. Chiosso I. Choi S.-U. Chung A. Cicuttin M.L. Crespo Q. Curiel S. Dalla Torre S.S. Dasgupta S. Dasgupta O.Yu. Denisov L. Dhara S.V. Donskov N. Doshita Ch. Dreisbach V. Duic W. Duennweber M. Dziewiecki A. Efremov P.D. Eversheim W. Eyrich M. Faessler A. Ferrero M. Finger M. Finger Jr. H. Fischer C. Franco N. du Fresne von Hohenesche J.M. Friedrich V. Frolov E. Fuchey F. Gautheron O.P. Gavrichtchouk S. Gerassimov J. Giarra F. Giordano I. Gnesi M. Gorzellik S. Grabmueller A. Grasso M. Grosse Perdekamp B. Grube T. Grussenmeyer A. Guskov F. Haas D. Hahne G. Hamar D. von Harrach F.H. Heinsius R. Heitz F. Herrmann N. Horikawa N. d'Hose C.-Y. Hsieh S. Huber S. Ishimoto A. Ivanov Yu. Ivanshin T. Iwata V. Jary R. Joosten P. Joerg E. Kabuss A. Kerbizi B. Ketzer G.V. Khaustov Yu.A. Khokhlov Yu. Kisselev F. Klein K. Klimaszewski J.H. Koivuniemi V.N. Kolosov K. Kondo K. Koenigsmann I. Konorov V.F. Konstantinov A.M. Kotzinian O.M. Kouznetsov M. Kraemer P. Kremser F. Krinner Z.V. Kroumchtein Y. Kulinich F. Kunne K. Kurek R.P. Kurjata A.A. Lednev A. Lehmann M. Levillain S. Levorato Y.-S. Lian J. Lichtenstadt R. Longo A. Maggiora A. Magnon N. Makins N. Makke G.K. Mallot B. Marianski A. Martin J. Marzec J. Matousek H. Matsuda T. Matsuda G.V. Meshcheryakov M. Meyer W. Meyer Yu.V. Mikhailov M. Mikhasenko E. Mitrofanov N. Mitrofanov Y. Miyachi A. Nagaytsev F. Nerling D. Neyret J. Novy W.-D. Nowak G. Nukazuka A.S. Nunes A.G. Olshevsky I. Orlov M. Ostrick D. Panzieri B. Parsamyan S. Paul J.-C. Peng F. Pereira M. Pesek D.V. Peshekhonov N. Pierre S. Platchkov J. Pochodzalla V.A. Polyakov J. Pretz M. Quaresma C. Quintans S. Ramos C. Regali G. Reicherz C. Riedl N.S. Rogacheva M. Roskot D.I. Ryabchikov A. Rybnikov A. Rychter R. Salac V.D. Samoylenko A. Sandacz C. Santos S. Sarkar I.A. Savin T. Sawada G. Sbrizzai P. Schiavon K. Schmidt H. Schmieden K. Schoenning E. Seder A. Selyunin L. Silva L. Sinha S. Sirtl M. Slunecka J. Smolik A. Srnka D. Steffen M. Stolarski O. Subrt M. Sulc H. Suzuki A. Szabelski T. Szameitat P. Sznajder S. Takekawa M. Tasevsky S. Tessaro F. Tessarotto F. Thibaud A. Thiel F. Tosello V. Tskhay S. Uhl J. Veloso M. Virius J. Vondra S. Wallner T. Weisrock M. Wilfert J. Ter Wolbeek K. Zaremba P. Zavada M. Zavertyaev E. Zemlyanichkina N. Zhuravlev M. Ziembicki A. Zink

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classification ✦ hep-ex hep-ph

keywords asymmetrysiversgluonstransverseanalysisdataextractedhadrons

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The Sivers function describes the correlation between the transverse spin of a nucleon and the transverse motion of its partons. It was extracted from measurements of the azimuthal asymmetry of hadrons produced in semi-inclusive deep inelastic scattering of leptons off transversely polarised nucleon targets, and it turned out to be non-zero for quarks. In this letter the evaluation of the Sivers asymmetry for gluons in the same process is presented. The analysis method is based on a Monte Carlo simulation that includes three hard processes: photon-gluon fusion, QCD Compton scattering and leading-order virtual-photon absorption process. The Sivers asymmetries of the three processes are simultaneously extracted using the LEPTO event generator and a neural network approach. The method is applied to samples of events containing at least two hadrons with large transverse momentum from the COMPASS data taken with a 160 GeV/$c$ muon beam scattered off transversely polarised deuterons and protons. With a significance of more than two standard deviations a negative value is obtained for the gluon Sivers asymmetry. The result of a similar analysis for a Collins-like asymmetry for gluons is consistent with zero.

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First measurement of the Sivers asymmetry for gluons from SIDIS data

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