Abstract:
Normalised multidifferential cross sections for top quark pair (${\mathrm{t}}\bar{\mathrm{t}}$) production are measured in pp collisions at a centreofmass energy of 13 TeV using events containing two oppositesign leptons. The analysed dataset was recorded by the CMS detector in 2016 and corresponds to an integrated luminosity of 35.9 fb$^{1}$. The ${\mathrm{t}}\bar{\mathrm{t}}$ cross section is measured doubledifferentially as a function of the kinematic properties of the top quark and the ${\mathrm{t}}\bar{\mathrm{t}}$ system at parton level in the full phase space. A tripledifferential measurement is performed as a function of the invariant mass and rapidity of the ${\mathrm{t}}\bar{\mathrm{t}}$ system and the multiplicity of additional jets at particle level in the event. The data are compared to predictions of Monte Carlo event generators that complement nexttoleadingorder (NLO) QCD calculations with parton showers. Together with a fixed order NLO QCD calculation the tripledifferential measurement is used to extract values of the strong coupling strength ($\alpha_{\mathrm{s}}$) and the top quark pole mass ($m_{\mathrm{t}}^{\mathrm{pole}}$) using several parton distribution function (PDF) sets. Furthermore, a simultaneous fit of PDFs, $\alpha_{\mathrm{s}}$ and $m_{\mathrm{t}}^{\mathrm{pole}}$ is performed at NLO, demonstrating that the new data have significant impact on the gluon PDF and at the same time allow to accurately determine $\alpha_{\mathrm{s}}$ and $m_{\mathrm{t}}^{\mathrm{pole}}$.
