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Evidence for Top Quark Production in Nucleus-Nucleus Collisions.

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  • 1Yerevan Physics Institute, Yerevan, Armenia.

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|December 14, 2020
PubMed
Summary
This summary is machine-generated.

Scientists observed top quark production in heavy ion collisions for the first time. This opens new avenues for studying the quark-gluon plasma (QGP) and the early universe using the heaviest known elementary particle.

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Area of Science:

  • High-energy particle physics
  • Nuclear physics
  • Cosmology

Background:

  • Ultrarelativistic heavy ion collisions simulate early universe conditions, enabling the study of quark-gluon plasma (QGP).
  • The QGP is a state of quantum chromodynamics (QCD) matter where partons are deconfined.
  • Top quarks, the heaviest known elementary particles, are now accessible in nucleus-nucleus collisions at the CERN LHC.

Purpose of the Study:

  • To report the first evidence of top quark production in nucleus-nucleus collisions.
  • To utilize top quarks as a novel probe for studying the QGP.
  • To measure the cross section for top quark pair production in these collisions.

Main Methods:

  • Analysis of lead-lead collision data at a nucleon-nucleon center-of-mass energy of 5.02 TeV from the CMS experiment.
  • Two distinct methods employed for measuring the top quark pair production cross section (σ_ttbar).
  • Selection of charged leptons (electrons or muons) and bottom quarks to identify top quark events.

Main Results:

  • First evidence for the production of top quarks in nucleus-nucleus collisions is presented.
  • Measured cross sections for top quark pair production are σ_ttbar = 2.54^{+0.84}_{-0.74} μb and σ_ttbar = 2.03^{+0.71}_{-0.64} μb.
  • The experimental results are consistent with predictions from scaled proton-proton data and QCD.

Conclusions:

  • The production of top quarks in nucleus-nucleus collisions has been observed for the first time.
  • Top quarks serve as a valuable new probe for investigating the properties of the quark-gluon plasma.
  • These findings validate theoretical predictions and enhance our understanding of matter under extreme conditions.