NLO Monte Carlo predictions for heavy-quark production at the LHC: pp collisions in ALICE

M Klasen,J P Wessels,G Kramer,C Klein-Bösing,K Kovarik,M Topp

doi:10.1007/jhep08(2014)109

M Klasen, J P Wessels + Show 4 more

Open Access

https://doi.org/10.1007/jhep08(2014)109

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Journal: Journal of High Energy Physics	Publication Date: Aug 1, 2014
Citations: 51	License type: cc-by

Affiliation: University of Münster

Abstract

Next-to-leading order (NLO) QCD predictions for the production of heavy quarks in proton-proton collisions are presented within three different approaches to quark mass, resummation and fragmentation effects. In particular, new NLO and parton shower simulations with POWHEG are performed in the ALICE kinematic regime at three different centre-of-mass energies, including scale and parton density variations, in order to establish a reliable baseline for future detailed studies of heavy-quark suppression in heavy-ion collisions. Very good agreement of POWHEG is found with FONLL, in particular for centrally produced D^0, D^+ and D^*+ mesons and electrons from charm and bottom quark decays, but also with the generally somewhat higher GM-VFNS predictions within the theoretical uncertainties. The latter are dominated by scale rather than quark mass variations. Parton density uncertainties for charm and bottom quark production are computed here with POWHEG for the first time and shown to be dominant in the forward regime, e.g. for muons coming from heavy-flavour decays. The fragmentation into D_s^+ mesons seems to require further tuning within the NLO Monte Carlo approach.

Highlights

In this paper we compare the three different theoretical approaches mentioned above in the kinematic regime relevant for the ALICE experiment at the LHC
New Next-to-leading order (NLO) and parton shower simulations with POWHEG are performed in the ALICE kinematic regime at three different centre-of-mass energies, including scale and parton density variations, in order to establish a reliable baseline for future detailed studies of heavy-quark suppression in heavyion collisions
The goal is to establish the reliability of the proton-proton baseline for future studies of heavy-ion collisions, where the suppression of heavy quarks at large transverse momenta is an important signal for the deconfined state of matter, the so-called quark-gluon plasma (QGP)

Summary

Theoretical input

We describe the main features of the three different theoretical approaches to heavy-quark production (FONLL, GM-VFNS and POWHEG), that will later form the bases of our numerical predictions for pp collisions at various centre-of-mass energies of the LHC. As our central PDF set we employ the CTEQ6.6 parametrisation [7], again because it was already used in the FONLL calculations shown in the ALICE publications Note, that these PDFs have been obtained with mc = 1.3 GeV and mb = 4.5 GeV, which are slightly lower than our default quark mass values. The perturbative FFs are evolved to the factorisation scale μf and convoluted with the NLO cross sections for massless partons, subtracted in the MS scheme, so that socalled flavour excitation processes are included These involve the heavy quark as an active parton in the PDFs. The result is convoluted with non-perturbative functions to describe the hadronisation of heavy quarks into heavy hadrons. The produced heavy hadron is always collinear to the heavy quark, and there is no information on the kinematical distribution of its decay products

GM-VFNS

POWHEG

LHC predictions

Conclusions