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arXiv · 1512.05053

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·N. V. Anfimov·V. Anosov·W. Augustyniak·A. Austregesilo·C. D. R. Azevedo·B. Badelek·F. Balestra·J. Barth·R. Beck·Y. Bedfer·J. Bernhard·K. Bicker·E. R. Bielert·R. Birsa·J. Bisplinghoff·M. Bodlak·M. Boer·P. Bordalo·F. Bradamante·C. Braun·A. Bressan·M. Buechele·W. -C. Chang·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·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·F. Giordano·I. Gnesi·M. Gorzellik·S. Grabmueller·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·C. -Y. Hsieh·S. Huber·S. Ishimoto·A. Ivanov·Yu. Ivanshin·T. Iwata·R. Jahn·V. Jary·R. Joosten·P. Joerg·E. Kabuss·B. Ketzer·G. V. Khaustov·Yu. A. Khokhlov·Yu. Kisselev·F. Klein·K. Klimaszewski·J. H. Koivuniemi·V. N. Kolosov
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Abstract

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 $Q^2>1~({\rm GeV}/c)^2$. 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 $p_{\rm T}$, the different $p_{\rm T}$-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 $\mu^2= \langle Q^2 \rangle = 3 ({\rm GeV}/c)^2$. It is determined in three intervals of the nucleon momentum fraction carried by gluons, $x_{\rm g}$, covering the range $0.04 \!<\! x_{ \rm g}\! <\! 0.28$~ and does not exhibit a significant dependence on $x_{\rm g}$. The average over the three intervals, $\langle \Delta g/g \rangle = 0.113 \pm 0.038_{\rm (stat.)}\pm 0.036_{\rm (syst.)}$ at $\langle x_{\rm g} \rangle \approx 0.10$, suggests that the gluon polarisation is positive in the measured $x_{\rm g}$ range.

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C. Adolph, M. Aghasyan, R. Akhunzyanov, M. G. Alexeev, G. D. Alexeev, A. Amoroso, V. Andrieux, N. V. Anfimov, V. Anosov, W. Augustyniak, A. Austregesilo, C. D. R. Azevedo, B. Badelek, F. Balestra, J. Barth, R. Beck, Y. Bedfer, J. Bernhard, K. Bicker, E. R. Bielert, R. Birsa, J. Bisplinghoff, M. Bodlak, M. Boer, P. Bordalo, F. Bradamante, C. Braun, A. Bressan, M. Buechele, W. -C. Chang, 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, 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, F. Giordano, I. Gnesi, M. Gorzellik, S. Grabmueller, 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, C. -Y. Hsieh, S. Huber, S. Ishimoto, A. Ivanov, Yu. Ivanshin, T. Iwata, R. Jahn, V. Jary, R. Joosten, P. Joerg, E. Kabuss, B. Ketzer, G. V. Khaustov, Yu. A. Khokhlov, Yu. Kisselev, F. Klein, K. Klimaszewski, J. H. Koivuniemi, V. N. Kolosov. 2015-12-16. Leading-order determination of the gluon polarisation from semi-inclusive deep inelastic scattering data. https://arxiv.org/abs/1512.05053

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