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Title page for ETD etd-03212014-140016

Type of Document Dissertation
Author Appelt, Eric Andrew
URN etd-03212014-140016
Title Measurements of Charged-Particle Transverse Momentum Spectra in PbPb Collisions at a Center-of-Mass Energy of 2.76 TeV per Nucleon Pair and in pPb Collisions at a Center-of-Mass Energy of 5.02 TeV per Nucleon Pair with the CMS Detector
Degree PhD
Department Physics
Advisory Committee
Advisor Name Title
Julia Velkovksa Committee Chair
Charles Maguire Committee Member
Paul Sheldon Committee Member
Robert Weller Committee Member
  • Heavy Ion
  • CMS
  • LHC
  • Quark Gluon Plasma
  • QGP
  • Transverse Momentum Spectrum
Date of Defense 2014-03-18
Availability unrestricted
The transverse momentum spectra of charged particles at both midrapidity and forward

rapidity in PbPb collisions at a center-of-mass energy of 2.76 TeV per

nucleon pair and pPb collisions

at a center-of-mass energy of 5.02 TeV per nucleon pair have been measured by the CMS detector at the LHC.

At low transverse momentum the charged-particle spectra

reflect the

dynamics of the

hot and dense medium produced in PbPb collisions, while

at high transverse momentum they

are sensitive to

partonic energy loss and the initial state of the

collision system.

The PbPb spectra are presented for a transverse momentum range of 0.3 to 5.0 GeV/c in

12 classes of centrality ranging from 0 to 80%. These PbPb spectra



extrapolated to zero transverse momentum to determine the mean transverse momentum.

The values of the mean transverse momentum increase from the most peripheral

collisions to

reach an approximately constant value for collisions in the

centrality range of 0 to 35%,

indicating similar dynamical evolution in the more central collisions.

When compared to lower collision energy measurements, the values of

the mean transverse momentum

are found to be 20% higher,

indicating an increase in the initial energy density and in the expansion

velocity of the produced system.

The pPb spectra are presented for a transverse momentum range of

0.4 to 100 GeV/c.

The nuclear modification factor is determined by normalizing the measured

pPb spectrum to an interpolated pp reference spectrum constructed from previous

measurements, and is significantly enhanced for particles with a value of

transverse momentum above 30 GeV/c.

This enhancement is stronger than predicted by next-to-leading order

theoretical calculations.

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