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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

2017-04-26Artigo científico Acesso aberto
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dc.contributor.authorATLAS collaboration (2850 authors)
dc.contributor.authorAguilar-Saavedra, Juan Antonio
dc.contributor.authorAmor Dos Santos, Susana Patricia
dc.contributor.authorAnjos, Nuno
dc.contributor.authorAraque, Juan Pedro
dc.contributor.authorCarvalho, João
dc.contributor.authorCastro, Nuno Filipe
dc.contributor.authorConde Muiño, Patricia
dc.contributor.authorDa Cunha Sargedas De Sousa, Mario Jose
dc.contributor.authorFiolhais, Miguel
dc.contributor.authorGalhardo, Bruno
dc.contributor.authorGomes, Agostinho
dc.contributor.authorGonçalo, Ricardo
dc.contributor.authorJorge, Pedro
dc.contributor.authorMachado Miguens, Joana
dc.contributor.authorMaio, Amélia
dc.contributor.authorManeira, José
dc.contributor.authorOleiro Seabra, Luis Filipe
dc.contributor.authorOnofre, António
dc.contributor.authorPedro, Rute
dc.contributor.authorSantos, Helena
dc.contributor.authorSaraiva, João
dc.contributor.authorSilva, José
dc.contributor.authorTavares Delgado, Ademar
dc.contributor.authorVeloso, Filipe
dc.contributor.authorWolters, Helmut
dc.date.accessioned2019-02-04T11:54:42Z
dc.date.available2019-02-04T11:54:42Z
dc.date.issued2017-04-26
dc.date.updated2019-02-04T11:54:42Z
dc.description.abstractThis paper presents a measurement of the polarisation of W bosons from $t\bar{t}$ decays, reconstructed in events with one high- $p_{\text{ T }}$ 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.
dc.description.versionPeer Reviewed
dc.identifierEur.Phys.J. C79 (2019) 19 Eur. Phys. J. C 77 (2017) 264; DOI 10.1140/epjc/s10052-017-4819-4, 10.1140/epjc/s10052-018-6520-7
dc.identifier.urihttp://dx.doi.org/10.1140/epjc/s10052-017-4819-4, 10.1140/epjc/s10052-018-6520-7
dc.identifier.urihttp://hdl.handle.net/10400.26/27249
dc.language.isoeng
dc.titleMeasurement 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
dc.typejournal article
dspace.entity.typePublication
rcaap.rightsopenAccesspt
rcaap.typearticle

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