CMS collaboration (2299 authors)Hollar, JonathanCalpas, BettyNayak, ArunaBargassa, PedrameBeirão Da Cruz E Silva, CristóvãoDi Francesco, AgostinoFaccioli, PietroFerreira Parracho, Pedro GuilhermeGallinaro, MicheleLeonardo, NunoLloret Iglesias, LaraNguyen, FedericoRodrigues Antunes, JoaoSeixas, JoaoToldaiev, OleksiiVadruccio, DanieleVarela, JoaoVischia, PietroDavid Tinoco Mendes, AndreSilva, PedroMusella, PasqualePela, Joao2019-02-042019-02-042016-04-13http://dx.doi.org/10.1007/JHEP04(2016)073http://hdl.handle.net/10400.26/26967A first measurement of the top quark spin asymmetry, sensitive to the top quark polarisation, in t-channel single top quark production is presented. It is based on a sample of pp collisions at a centre-of-mass energy of 8 TeV corresponding to an integrated luminosity of 19.7 fb$^{−1}$. A high-purity sample of t-channel single top quark events with an isolated muon is selected. Signal and background components are estimated using a fit to data. A differential cross section measurement, corrected for detector effects, of an angular observable sensitive to the top quark polarisation is performed. The differential distribution is used to extract a top quark spin asymmetry of 0.26 ± 0.03(stat) ± 0.10(syst), which is compatible with a p-value of 4.6% with the standard model prediction of 0.44.engjournal article2019-02-04