Elsevier

Physics Letters B

Volume 772, 10 September 2017, Pages 854-864
Physics Letters B

First measurement of the Sivers asymmetry for gluons using SIDIS data

https://doi.org/10.1016/j.physletb.2017.07.018Get rights and content
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Abstract

The Sivers function describes the correlation between the transverse spin of a nucleon and the transverse motion of its partons. For quarks, it was studied in previous measurements of the azimuthal asymmetry of hadrons produced in semi-inclusive deep inelastic scattering of leptons off transversely polarised nucleon targets, and it was found to be non-zero. In this letter the evaluation of the Sivers asymmetry for gluons is presented. The contribution of the photon–gluon fusion subprocess is enhanced by requiring two high transverse-momentum hadrons. The analysis method is based on a Monte Carlo simulation that includes three hard processes: photon–gluon fusion, QCD Compton scattering and the 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 about 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.

Keywords

Deep inelastic scattering
Gluon
Sivers
TMD
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Cited by (0)

16

Supported by BMBF – Bundesministerium für Bildung und Forschung (Germany).

18

Supported by MEYS, Grant LG13031 (Czech Republic).

19

Supported by SAIL (CSR) and B. Sen fund (India).

20

Supported by CERNRFBR Grant 12-02-91500.

21

Supported by FCT – Fundo Regional para a Ciência e Tecnologia, COMPETE and QREN, Grants CERN/FP 116376/2010, 123600/2011 and CERN/FIS-NUC/0017/2015 (Portugal).

22

Supported by MEXT and JSPS, Grants 18002006, 20540299 and 18540281, the Daiko and Yamada Foundations (Japan).

17

Supported by FP7, HadronPhysics3, Grant 283286 (European Union).

23

Supported by the Ministry of Science and Technology, Taiwan (Taiwan).

24

Supported by the Israel Academy of Sciences and Humanities (Israel).

25

Supported by NSF – National Science Foundation (USA).

26

Supported by NCN, Grant 2015/18/M/ST2/00550 (Poland).

1

Also at Instituto Superior Técnico, Universidade de Lisboa, Lisbon, Portugal.

2

Also at Dept. of Physics, Pusan National University, Busan 609-735, Republic of Korea and at Physics Dept., Brookhaven National Laboratory, Upton, NY 11973, USA.

3

Supported by the DFG cluster of excellence ‘Origin and Structure of the Universe’ (http://www.universe-cluster.de) (Germany).

4

Supported by the Laboratoire d'excellence P2IO (France).

5

Supported by the DFG Research Training Group Programmes 1102 and 2044 (Germany).

6

Also at Chubu University, Kasugai, Aichi 487-8501, Japan.

7

Also at Dept. of Physics, National Central University, 300 Jhongda Road, Jhongli 32001, Taiwan.

8

Also at KEK, 1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan.

9

Also at Moscow Institute of Physics and Technology, Moscow Region, 141700, Russia.

10

Supported by Presidential Grant NSh-999.2014.2 (Russia).

11

Also at Yerevan Physics Institute, Alikhanian Br. Street, Yerevan, Armenia, 0036.

12

Also at Dept. of Physics, National Kaohsiung Normal University, Kaohsiung County 824, Taiwan.

13

Also at University of Eastern Piedmont, 15100 Alessandria, Italy.

14

Present address: RWTH Aachen University, III. Physikalisches Institut, 52056 Aachen, Germany.

15

Present address: Uppsala University, Box 516, 75120 Uppsala, Sweden.

27

Deceased.