Abstract
We propose a simple and model-independent procedure to account for the impact of the nuclear modification of the gluon density as encoded in nuclear collinear PDF sets on two-to-two partonic hard processes in proton–nucleus collisions. This applies to a good approximation to quarkonium, D and B meson production, generically referred to mathcal {H}. Our procedure consists in parametrising the square of the parton scattering amplitude, {mathcal {A}}_{gg rightarrow {mathcal {H}} X} and constraining it from the proton–proton data. Doing so, we have been able to compute the corresponding nuclear modification factors for J/psi , Upsilon and D^0 as a function of y and P_T at sqrt{s_mathrm{NN}}=5 and 8 TeV in the kinematics of the various LHC experiments in a model independent way. It is of course justified since the most important ingredient in such evaluations is the probability of each kinematical configuration. Our computations for D mesons can also be extended to B meson production. To further illustrate the potentiality of the tool, we provide – for the first time – predictions for the nuclear modification factor for eta _c production in pPb collisions at the LHC.
Highlights
For many years, open and closed heavy-flavour production in hadron-hadron, hadron-nucleus and nucleus-nucleus collisions has been a major subject of investigations, on both experimental and theoretical sides
Many effects can be at play: break up within the nucleus [7,8] or with comovers for the quarkonia [9,10,11,12], coherent or incoherent energy loss [13,14,15,16,17], colour filtering [18], saturation/small-x/coherence effects [19,20,21,22,23], and the modification of the parton fluxes, as encoded in nuclear Parton Distribution Functions [24,25,26,27,28]
As will be explained below, the tool which we propose is based on HELAC-Onia [43,44] can use any nuclear Parton Distribution Functions (nPDFs) set included in the library LHAPDF5 [45,46] and LHAPDF6 [47] and does not rely on any model for the hard-probe production, but on pp measurements which are used to tune the partonic-scattering elements, keeping in mind the limitation that it should be tuned for each process and in principle for possible different kinematical region with the chosen proton PDF and factorisation scale
Summary
Open and closed heavy-flavour production in hadron-hadron, hadron-nucleus and nucleus-nucleus collisions has been a major subject of investigations, on both experimental and theoretical sides (see [1] for a review in the context of the first LHC results and [2,3,4,5,6] for earlier reviews). Heavy-flavour production can be affected by other nuclear effects which are not related to a phase transition; they should in principle be subtracted in a way or another to study the QGP. These are typically believed to be the only ones acting in proton/deuteron-nucleus ( p A) collisions at fixed-target, RHIC and LHC energies. Experimental results from RHIC and the LHC in p A collisions [1] have shown that the yields and the spectra of J/ψ, Υ, D and B are modified in a magnitude which cannot be ignored in QGP studies. Many effects can be at play: break up within the nucleus [7,8] or with comovers for the quarkonia [9,10,11,12], coherent or incoherent energy loss [13,14,15,16,17], colour filtering [18], saturation/small-x/coherence effects [19,20,21,22,23], and the modification of the parton fluxes, as encoded in nuclear Parton Distribution Functions (nPDFs) [24,25,26,27,28]
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