Measurement of spin correlations in top pair events in the lepton + jets channel with the matrix element method at $8 \text{TeV}$

The consistency of the top quark pair events produced with standard model (SM) correlated spins is tested in the muon+jets final state. The events are obtained from $pp$ collisions at a center of mass energy of $\sqrt{s} = 8 \text{ TeV}$, corresponding to an integrated luminosity of $\int Ldt\, =\, 19.7\, \text{fb}^{-1}$, collected with the Compact Muon Solenoid (CMS) detector at the Large Hadron Collider (LHC). The data agree with the SM hypothesis within 2.2 $\sigma$ (standard deviation) and agree with the uncorrelated hypothesis within 2.9 $\sigma$ based on a hypothesis testing procedure. In addition, using a template fit method, the fraction of events which show SM spin correlations $f$, is extracted. This fraction is measured to be $f\,=\,0.72\,\pm\,0.09\,\mathrm{(stat)}\, ^{+\,0.15}_{-\,0.13}\,\mathrm{(syst)}$, representing the most precise measurement of this quantity in the lepton+jets channel at present.