Leading-order determination of the gluon polarisation from semi-inclusive deep inelastic scattering data

C. Adolph , M. Aghasyan , R. Akhunzyanov , M.G. Alexeev , G.D. Alexeev , A. Amoroso , V. Andrieux (1) , N.V. Anfimov , V. Anosov , W. Augustyniak , A. Austregesilo , C.D.R. Azevedo , B. Badelek , F. Balestra , J. Barth , R. Beck , Y. Bedfer (1) , J. Bernhard , K. Bicker , E.R. Bielert , R. Birsa , J. Bisplinghoff , M. Bodlak , M. Boer (1) , P. Bordalo , F. Bradamante , C. Braun , A. Bressan , M. Buchele , W.C. Chang , M. Chiosso , I. Choi , S.U. Chung , A. Cicuttin , M.L. Crespo , Q. Curiel (1) , S. Dalla Torre , S.S. Dasgupta , O.Yu. Denisov , L. Dhara , S.V. Donskov , N. Doshita , V. Duic , W. Dunnweber , M. Dziewiecki , A. Efremov , P.D. Eversheim , W. Eyrich , M. Faessler , A. Ferrero (1) , M. Finger , H. Fischer , C. Franco , N. Du Fresne von Hohenesche , J.M. Friedrich , V. Frolov , E. Fuchey (1) , F. Gautheron , O.P. Gavrichtchouk , S. Gerassimov , F. Giordano , I. Gnesi , M. Gorzellik , S. Grabmuller , A. Grasso , M. Grosse Perdekamp , B. Grube , T. Grussenmeyer , A. Guskov , F. Haas , D. Hahne , D. von Harrach , R. Hashimoto , F.H. Heinsius , R. Heitz , F. Herrmann , F. Hinterberger , N. Horikawa , N. d'Hose (1) , C.Y. Hsieh , S. Huber , S. Ishimoto , A. Ivanov , Yu. Ivanshin , T. Iwata , R. Jahn , V. Jary , R. Joosten , P. Jorg , E. Kabuss , B. Ketzer , G.V. Khaustov , Yu. A. Khokhlov , Yu. Kisselev , F. Klein , K. Klimaszewski , J.H. Koivuniemi , V.N. Kolosov , K. Kondo , K. Konigsmann , I. Konorov , V.F. Konstantinov , A.M. Kotzinian , O.M. Kouznetsov , M. Kramer , P. Kremser , F. Krinner , Z.V. Kroumchtein , Y. Kulinich , F. Kunne (1) , K. Kurek , R.P. Kurjata , A.A. Lednev , A. Lehmann , M. Levillain (1) , S. Levorato , J. Lichtenstadt , R. Longo , A. Maggiora , A. Magnon (1) , N. Makins , N. Makke , G.K. Mallot , C. Marchand (1) , B. Marianski , A. Martin , J. Marzec , S J.Matou , H. Matsuda , T. Matsuda , G.V. Meshcheryakov , W. Meyer , T. Michigami , Yu. V. Mikhailov , M. Mikhasenko , Y. Miyachi , P. Montuenga , A. Nagaytsev , F. Nerling , D. Neyret (1) , V.I. Nikolaenko , 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. Pe S , D.V. Peshekhonov , S. Platchkov (1) , J. Pochodzalla , V.A. Polyakov , J. Pretz , M. Quaresma , C. Quintans , S. Ramos , C. Regali , G. Reicherz , C. Riedl , M. Roskot , N.S. Rossiyskaya , 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. Schonning , S. Schopferer , E. Seder (1) , A. Selyunin , O.Yu. Shevchenko , L. Silva , L. Sinha , S. Sirtl , M. Slunecka , J. Smolik , F. Sozzi , A. Srnka , M. Stolarski , M. Sulc , H. Suzuki , A. Szabelski , T. Szameitat , P. Sznajder , S. Takekawa , M. Tasevsky , S. Tessaro , F. Tessarotto , F. Thibaud (1) , F. Tosello , V. Tskhay , S. Uhl , J. Veloso , M. Virius , J. Vondra , T. Weisrock , M. Wilfert , J. Ter Wolbeek , K. Zaremba , P. Zavada , M. Zavertyaev , E. Zemlyanichkina , M. Ziembicki , A. Zink

1 DPHN - Département de Physique Nucléaire (ex SPhN)

Using a novel analysis technique, the gluon polarisation in the nucleon is re-evaluated using the longitudinal double-spin asymmetry measured in the cross section of semi-inclusive single-hadron muoproduction with photon virtuality $Q^2>1~(\mathrm{GeV}/c)^2$ . The data were obtained by the COMPASS experiment at CERN using a 160 GeV/c polarised muon beam impinging on a polarised$^6$ LiD target. By analysing the full range in hadron transverse momentum $p_\mathrm{T}$ , the different $p_\mathrm{T}$ -dependences of the underlying processes are separated using a neural-network approach. In the absence of pQCD calculations at next-to-leading order in the selected kinematic domain, the gluon polarisation $\Delta g/g$ is evaluated at leading order in pQCD at a hard scale of $\mu ^2= \langle Q^2 \rangle = 3 (\mathrm{GeV}/c)^2$ . It is determined in three intervals of the nucleon momentum fraction carried by gluons, $x_\mathrm{g}$ , covering the range $0.04 \!<\! x_{ \mathrm g}\! <\! 0.28$   and does not exhibit a significant dependence on $x_\mathrm{g}$ . The average over the three intervals, $\langle \Delta g/g \rangle = 0.113 \pm 0.038_\mathrm{(stat.)}\pm 0.036_\mathrm{(syst.)}$ at $\langle x_\mathrm{g} \rangle \approx 0.10$ , suggests that the gluon polarisation is positive in the measured $x_\mathrm{g}$ range.

Mots clés: muon nucleus: inclusive reaction; gluon: polarization; hadron: transverse momentum; nucleon: momentum; beam: scattering; muon+: polarized beam; semi-inclusive reaction; neural network; polarization: longitudinal; spin: asymmetry; transverse momentum dependence; CERN Lab; COMPASS; CERN SPS; hadron: photoproduction; data analysis method; experimental results; 160 GeV/c

Domaines: Physique des Hautes Energies - Expérience [hep-ex]; Physique des Hautes Energies - Phénoménologie [hep-ph]

C. Adolph, M. Aghasyan, R. Akhunzyanov, M.G. Alexeev, G.D. Alexeev, et al.. Leading-order determination of the gluon polarisation from semi-inclusive deep inelastic scattering data. European Physical Journal C: Particles and Fields, 2017, 77 (4), pp.209. ⟨10.1140/epjc/s10052-017-4716-x⟩. ⟨hal-01582579⟩