| Summary: | 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
measurements
are
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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