Abstract:
Observation of ttbar production in lepton+jets and dilepton channels
in p+Pb collisions at
√s = 8.16 TeV with the ATLAS detector.
Top-quarks and Higgs boson are the only elementary particles that have
not been observed in heavy-ion collisions in the ATLAS detector yet.
In particular top quarks, the heaviest elementary particles carrying
color charges, have been argued to be attractive candidates for
probing the quark-gluon plasma produced in heavy-ion collisions. In
proton-lead collisions, top-quark production is expected to be
sensitive to nuclear modifications of parton distribution functions
(PDF) at high Bjoerken-x values which are hard to access
experimentally using other probes available so far. I participate in
the analysis of measurement of the top quark pairs production in
proton-lead collisions at √s=8.16 TeV in the ATLAS experiment. The
dataset was recorded in 2016 and corresponds to an integrated
luminosity of 165 nb-1. The top quarks are reconstructed in lepton+jet
and di-lepton decay channels with electrons and muons in the final
state. The dilepton channel is studied in heavy-ion collisions for the
first time. The main task from my side was to estimate the background
contribution to the signal sample. These results were important inputs
to the analysis. Namely, the inclusive ross section measurement for
the top-quark pairs production in dilepton and lepton+jets decay modes
with electrons and muons recorded by the ATLAS experiment. The
measurement is compared to the NNLO predictions for top-quark
production using various PDF sets.