D-meson enhancement in pp collisions at the LHC due to nonlinear gluon evolution Page: 3 of 16
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transverse momentum' PT ~ 0, charm production at the LHC is sensitive to the gluon
enhancement. The resulting charm enhancement was quantified in Ref.  by the LO
ratios of the differential cross sections computed with the nonlinearly-evolved EHKQS
PDFs , obtained from DGLAP+GLRMQ evolution, relative to the DGLAP-evolved
The enhancement of the nonlinearly-evolved gluons increases as x and Q2 decrease.
Consequently, the charm enhancement increases with center of mass energy, Vs. Thus
the maximum enhancement at the LHC will be at as = 14 TeV and small charm
quark transverse momentum. The sensitivity of the charm enhancement to the value
of the charm quark mass, mc, as well as to the choice of the factorization, QF, and
renormalization, QR, scales was studied in Ref.  assuming Q2 = QF = Q2 a mr,
the charm transverse mass squared, rmi = p2 + M.2. For the most significant charm
enhancement, rc and Q2/rn should both be small. A comparison of the NLO to-
tal cross sections with low energy data shows that the data prefer such small rmc and
Q2 combinations [11, 12]. The smallest scales and thus the largest enhancement are
obtained with m, = 1.3 GeV and Q2 = H12. In this case, the ratio of the inclusive differ-
ential cross section, d3a/dpTdydy2, computed with EHKQS set 1 relative to CTEQ61L
is greater than 5 for rapidities ly, Y21 2 where y and Y2 are the c and c rapidities,
In Ref. , the enhancement was described only for charm production. Neither its
subsequent hadronization to D mesons nor its decay and detection were considered.
In this paper, we address these issues to determine whether the charm enhancement
survives hadronization and decay to be measured in the ALICE detector .
We first consider how much of the LO charm enhancement survives in the final
state D meson distributions. Charm quarks are hadronized using the PYTHIA string
fragmentation model . We show that, for the most optimistic case with a factor of
five charm enhancement for PT -- 0, the D enhancement is a factor of three for pT -- 0.
Since the ALICE detector allows direct measurement of the D meson PT distribu-
tion through D0 reconstruction in the K-r+ decay channel, we then determine whether
or not the surviving D enhancement can be detected above the expected experimental
statistical and systematic uncertainties. To determine realistic statistical uncertainties,
we calculate the NLO cross section in the way most compatible with our LO enhance-
ment, as described below. Then, using the error analysis developed by one of us (A.D.)
in Ref. , we demonstrate that detection of the enhancement is possible.
Finally, we consider whether NLO charm cross sections, calculated with linearly-
evolved PDFs and different combinations of ne, QF and Q2, can mimic the charm
enhancement. Our results show that this is unlikely.
This paper is organized as follows. In Section 2, we describe our charm calculations
and define how the NLO cross section most compatible with the LO enhancement is
computed. Hadronization and reconstruction of D0 mesons are considered in Sections
3 and 4, respectively, along with a discussion of the experimental uncertainties. We
'Here we use PT for the transverse momentum of the charm quark and pT for the transverse
momentum of the D meson.
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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. (digital.library.unt.edu/ark:/67531/metadc782648/m1/3/: accessed May 21, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.