The first observation of top quark production in proton-nucleus collisions is reported using proton-lead
data collected by the CMS experiment at the CERN LHC at a nucleon-nucleon center-of-mass energy of ffiffiffiffiffiffiffiffi
sNN p ¼ 8.16 TeV. The measurement is performed using events with exactly one isolated electron or muon
candidate and at least four jets. The data sample corresponds to an integrated luminosity of 174 nb−1.
The significance of the t¯t signal against the background-only hypothesis is above 5 standard deviations.
The measured cross section is σt¯t ¼ 45 8 nb, consistent with predictions from perturbative quantum
chromodynamics.