# Measurement of $\mathrm{t\bar t}$ normalised multi-differential cross sections in pp collisions at $\sqrt{s} =13$ TeV, and simultaneous determination of the strong coupling strength, top quark pole mass, and parton distribution functions

## TL;DR

This paper measures detailed top quark pair production cross sections at 13 TeV, and uses these measurements to simultaneously determine the strong coupling constant, top quark pole mass, and parton distribution functions, improving our understanding of proton structure and QCD parameters.

## Contribution

It provides the first simultaneous extraction of the strong coupling, top quark mass, and PDFs using multi-differential top pair production data at 13 TeV.

## Key findings

- Measured normalized multi-differential cross sections in pp collisions at 13 TeV.
- Extracted values of α_S(m_Z) = 0.1135 and top quark pole mass = 170.5 GeV.
- Demonstrated significant impact on gluon PDFs and precise determination of QCD parameters.

## Abstract

Normalised multi-differential cross sections for top quark pair ($\mathrm{t\overline{t}}$) production are measured in proton-proton collisions at a centre-of-mass energy of 13 TeV using events containing two oppositely charged leptons. The analysed data were recorded with the CMS detector in 2016 and correspond to an integrated luminosity of 35.9 fb$^{-1}$. The double-differential $\mathrm{t\overline{t}}$ cross section is measured as a function of the kinematic properties of the top quark and of the $\mathrm{t\overline{t}}$ system at parton level in the full phase space. A triple-differential measurement is performed as a function of the invariant mass and rapidity of the $\mathrm{t\overline{t}}$ system and the multiplicity of additional jets at particle level. The data are compared to predictions of Monte Carlo event generators that complement next-to-leading-order (NLO) quantum chromodynamics (QCD) calculations with parton showers. Together with a fixed-order NLO QCD calculation, the triple-differential measurement is used to extract values of the strong coupling strength $\alpha_S$ and the top quark pole mass ($m_\mathrm{T}^\text{pole}$) using several sets of parton distribution functions (PDFs). Furthermore, a simultaneous fit of the PDFs, $\alpha_S$, and $m_\mathrm{T}^\text{pole}$ is performed at NLO, demonstrating that the new data have significant impact on the gluon PDF, and at the same time allow an accurate determination of $\alpha_S$ and $m_\mathrm{T}^\text{pole}$. The values $\alpha_S(m_\mathrm{Z})$ = 0.1135 $^{+0.0021}_{-0.0017}$ and $m_\mathrm{T}^\text{pole}$ = 170.5 $\pm$ 0.8 GeV are extracted, which account for experimental and theoretical uncertainties, the latter being estimated from NLO scale variations. Possible effects from Coulomb and soft-gluon resummation near the $\mathrm{t\overline{t}}$ production threshold are neglected in these parameter extractions.