D-meson enhancement in pp collisions at the LHC due to nonlinear gluon evolution Page: 11 of 16
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m, Q2/m2 PDF set mc Q2/m2 PDF set
------ 1.1 GeV 4 CTEQ6 ------ 1.2 GeV 4 CTEQ6
2.51 1.2 GeV 4 2.5 -.-.-. 1.3 GeV 4 "
.1
............ 1.3 GeV 4 1.3 GeV 1 "
.. - .. 1.5 GeV 4 " ...........1.5 GeV 1 "
2 - - -.1.3 GeV 1 2 1.3 GeV 1 MRST
1.2 GeV 4 MRST
1 1
a) 0)
-1.5 t i 1.5
0.5 Simulated data: 0.5 Simulated data:
r=1.2Ge, cG=4 rj=1.3GeV, Q'=rn
0 2 4 6 8 1012141618 202224 0 2 4 6 8 1012141618202224
pT [GeV] pT [GeV]
Figure 4: Ratio of the generated ALICE data relative to calculations of the alternative NLO
cross sections with several sets of parameters and PYTHIA string fragmentation. The left-
hand side shows the result for m, = 1.2 GeV and Q2 = 4m2 while the right-hand side is the
result for m, = 1.3 GeV and Q2 = mT.
a2 < a L. This decrease will in turn reduce the O(a') contribution to the alterna-
tive NLO result relative to the LO component of Eq. (2). In addition, the standard
NLO cross section would be reduced overall relative to a calculation with the same
AQD at LO and NLO. However, these factors alone cannot explain the rather large
difference between the standard and alternative NLO cross sections at low p. The
most important contribution is the large differences between the LO and NLO gluon
distributions, especially at low scales. The slope of the CTEQ61L gluon distribution
at Q2 = 1.69 GeV2 with x is very small until x > 0.01. On the other hand, the
CTEQ6M gluon x slope is large and has the opposite sign relative to CTEQ61L for
x < 0.04. The ratio of the two sets at x t 10-s is very large, CTEQ61L/CTEQ6M
~ 100. At Q2 = 5.76 GeV2, the scale corresponding to 4H12 with m, = 1.2 GeV, this
ratio decreases to a factor of two. We note that at fixed-target energies, as < 40 GeV,
the standard and alternative NLO results are indistinguishable from each other since
the LO and NLO gluon distributions are rather similar in this relatively high x region,
0.05 < x < 0.1.
In order to address the question of the experimental sensitivity to the effect of
nonlinear gluon evolution on low-pT charm production, we consider, as a function of10
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Dainese, A.; Vogt, R.; Bondila, M.; Eskola, K.J. & Kolhinen, V.J. D-meson enhancement in pp collisions at the LHC due to nonlinear gluon evolution, article, August 22, 2004; Berkeley, California. (https://digital.library.unt.edu/ark:/67531/metadc782648/m1/11/: accessed April 23, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.