Observation of top quark production in proton-nucleus collisions

TL;DR

This paper reports the first observation of top quark production in proton-lead collisions at the LHC, confirming the ability to study heavy elementary particles in nuclear environments.

Contribution

It presents the first measurement of top quark production in proton-nucleus collisions, expanding the scope of particle physics research in nuclear matter.

Findings

Measured top quark pair production cross section as 45±8 nb.

Achieved statistical significance above five standard deviations.

Results agree with advanced quantum chromodynamics predictions.

Abstract

The multi-TeV energies available at LHC have opened up the possibility to measure, for the first time, various large-mass elementary particles in nuclear collisions. The current study presents the first observation of top quark--the heaviest elementary particle in the standard model--using proton-lead collisions. The measurement is based on a data set whose integrated luminosity amounts to 174 nb$^{-1}$, as recorded by CMS at a center-of-mass energy per nucleon pair of 8.16 TeV. The pair production process is measured using events with exactly one isolated lepton, electron or muon, and at least four jets, leading to a cross section of $45\pm8\ \rm{nb}$. This is well compatible with theoretical predictions from perturbative quantum chromodynamics at next-to-next-to-leading order with soft gluon resummation at next-to-next-to-leading logarithmic accuracy. The statistical significance of the signal against the background-only hypothesis is above five standard deviations.