Measurement of the $W$ boson polarisation in $t\bar{t}$ events from $pp$ collisions at $\sqrt{s}$ = 8 TeV in the lepton+jets channel with ATLAS

M Aaboud N. Berger 1 A.M. Burger 1 M. Delmastro 1 L. Di Ciaccio 1 S. Elles 1 K. Grevtsov 1 T. Guillemin 1 T. Hryn’ova 1 S. Jézéquel 1 I. Koletsou 1 R. Lafaye 1 J. Levêque 1 P. Mastrandea 1 E. Sauvan 1 B.H. Smart 1 T. Todorov 1 I. Wingerter-Seez 1 E. Yatsenko 1 D. Boumediene 2 E. Busato 2 D. Calvet 2 S. Calvet 2 A.R. Chomont 2 J. Donini 2 S. Ganguly 2 Ph. Gris 2 R. Madar 2 D. Pallin 2 S.M. Romano Saez 2 C. Santoni 2 D. Simon 2 F. Vazeille 2 G. Aad 3 M. Alstaty 3 M. Barbero 3 A. Calandri 3 T.P. Calvet 3 Y. Coadou 3 C. Diaconu 3 F. Djama 3 V. Ellajosyula 3 L. Feligioni 3 A. Hadef 3 G.D. Hallewell 3 F. Hubaut 3 S.J. Kahn 3 E. B. F. G. Knoops 3 E. Le Guirriec 3 K. Liu 3 D. Madaffari 3 E. Monnier 3 S. Muanza 3 E. Nagy 3 P. Pralavorio 3 Y. Rodina 3 A. Rozanov 3 M. Talby 3 T. Theveneaux-Pelzer 3 R.E. Ticse Torres 3 S. Tisserant 3 J. Toth 4, 3 F. Touchard 3 L. Vacavant 3 Chen Wang 5, 3 R. Wolff 3 S. Albrand 6 S. Berlendis 6 A. Bethani 6 C. Camincher 6 J. Collot 6 S. Crépé-Renaudin 6 P.A. Delsart 6 C. Gabaldon 6 M.H. Genest 6 P.O.J. Gradin 6 J.Y. Hostachy 6 F. Ledroit-Guillon 6 A. Lleres 6 A. Lucotte 6 F. Malek 6 E. Petit 6 J. Stark 6 B. Trocmé 6 M. Wu 6 G. Rahal 7
Abstract : This paper presents a measurement of the polarisation of $W$ bosons from $t\bar{t}$ decays, reconstructed in events with one high-$p_{\mbox{T}}$ lepton and at least four jets. Data from $pp$ collisions at the LHC were collected at $\sqrt{s}$ = 8 TeV and correspond to an integrated luminosity of 20.2 fb$^{-1}$. The angle $\theta^{*}$ between the $b$-quark from the top quark decay and a direct $W$ boson decay product in the $W$ boson rest frame is sensitive to the $W$ boson polarisation. Two different $W$ decay products are used as polarisation analysers: the charged lepton and the down-type quark for the leptonically and hadronically decaying $W$ boson, respectively. The most precise measurement of the $W$ boson polarisation via the distribution of $\cos{\theta^{*}}$ is obtained using the leptonic analyser and events in which at least two of the jets are tagged as $b$-quark jets. The fitted fractions of longitudinal, left- and right-handed polarisation states are $F_{\mathrm{0}}= 0.709 \pm {0.019}$, $F_{\mathrm{L}}= 0.299 \pm {0.015}$ and $F_{\mathrm{R}}= -0.008 \pm {0.014}$, and are the most precisely measured $W$ boson polarisation fractions to date. Limits on anomalous couplings of the $Wtb$ vertex are set.
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European Physical Journal C: Particles and Fields, Springer Verlag (Germany), 2017, 77, pp.264. 〈https://link.springer.com/article/10.1140%2Fepjc%2Fs10052-017-4819-4〉. 〈10.1140/epjc/s10052-017-4819-4〉
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Soumis le : vendredi 9 décembre 2016 - 09:28:04
Dernière modification le : lundi 9 avril 2018 - 12:22:08

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M Aaboud, N. Berger, A.M. Burger, M. Delmastro, L. Di Ciaccio, et al.. Measurement of the $W$ boson polarisation in $t\bar{t}$ events from $pp$ collisions at $\sqrt{s}$ = 8 TeV in the lepton+jets channel with ATLAS. European Physical Journal C: Particles and Fields, Springer Verlag (Germany), 2017, 77, pp.264. 〈https://link.springer.com/article/10.1140%2Fepjc%2Fs10052-017-4819-4〉. 〈10.1140/epjc/s10052-017-4819-4〉. 〈in2p3-01412923〉

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