A 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 8TeV 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.

Measurement of top quark polarisation in t-channel single top quark production

ZOTTO, PIERLUIGI;BENATO, LISA;BISELLO, DARIO;BOLETTI, ALESSIO;CARLIN, ROBERTO;CHECCHIA, PAOLO;DALL'OSSO, MARTINO;GASPARINI, FABRIZIO;GASPARINI, UGO;GOZZELINO, ANDREA;LACAPRARA, STEFANO;MARGONI, MARTINO;PAZZINI, JACOPO;POZZOBON, NICOLA;RONCHESE, PAOLO;SIMONETTO, FRANCO;TOSI, MIA;ZANETTI, MARCO;ZUCCHETTA, ALBERTO;ZUMERLE, GIANNI;Triossi, A.;Gaz, A.;ROSSIN, ROBERTO;