Measurement of the top quark polarization and $\mathrm{t\bar{t}}$ spin correlations using dilepton final states in proton-proton collisions at $\sqrt{s}=$ 13 TeV
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Abstract (data abstract)
Unfolded normalized differential cross sections for angular observables sensitive to the top quark polarization and $t\bar{t}$ spin correlations measured in dileptonic $t\bar{t}$ events at CMS, and the corresponding extracted coefficients and values of $f_\text{SM}$. Statistical and systematic covariance matrices are given for all measured bins (or coefficients) together, in the same order as the distributions are given on this page. Care must be taken in the choice of distributions for simultaneous fitting. When using a simple $\chi^2$ minimization procedure, the statistical uncertainty in the fitted parameter can be reduced by adding to the fit an observable which has little or no sensitivity to the fitted parameter, but which is not independent of the other observables in the fit. This problem can be avoided by requiring the set of fitted observables to be mutually independent. For example, $\cos\theta_{1}^{k}$ and $\cos\theta_{1}^{k*}$ should not be used together, because $|\cos\theta_{1}^{k}|=|\cos\theta_{1}^{k*}|$.