D-meson production in pp and p-Pb collisions measured with ALICE at the LHC

Abstract

Abstract. The open heavy-flavour production studied with ALICE at the LHC in pp collisions at √ s = 7 TeV and p-Pb collisions at √ sNN = 5.02 TeV is presented. Focus is given to the dependence of the production on the multiplicity of charged particles produced in the collision. IntroductionHeavy quarks (charm and beauty) can be used to study several aspects of QCD in high-energy hadronic collisions. They are produced in hard partonic scattering processes occurring in the initial stage of the collisions with large momentum transfer. Therefore, the study of their production in pp collisions provides a precision test of perturbative QCD (pQCD) calculations. In proton-nucleus collisions, heavy-flavour production could be modified by the presence of a nucleus in the colliding system. The cross section and p T distributions of heavy-flavour hadrons could be influenced by the modification of the parton distributions functions in the nucleus (nPDF), especially at small Bjorken x (see e.g.[1]), by the k T -broadening caused by soft scatterings of the partons in the incoming nucleus [2], and by possible energy loss of the produced heavy quarks in the nucleus [3]. These effects are commonly called Cold Nuclear Matter (CNM) effects. They are explored through the measurement of the nuclear modification factor R pPb , i.e. the comparison of p-Pb measurements with pp results, to test whether the yield and the transverse momentum distributions follow or not a scaling with the number of binary nucleon-nucleon collisions in p-Pb collisions. The study of the nuclear modification factor in different event multiplicity classes is also interesting to assess the possible modification of the p T spectrum in high multiplicity events. Moreover, the measurement of heavy-flavour production, both in pp and p-Pb collisions, as a function of the multiplicity of charged particles produced in hadronic collisions can improve our understanding of their production mechanisms and could give insight into the role of MultiParton Interactions (MPI), i.e. several partonic interactions occurring in a single collision between two nucleons. If the production of heavy quarks is affected by the presence of additional hard scatterings between incoming partons, their yield should increase with multiplicity. The shape of the increasing trend depends on how the MPI contribute to the production of particles: if they equally contribute to soft and hard production, from small to large multiplicities, the increase would be linear. Indications of the relevance of MPI in heavy-quark production have been observed by NA27 [4] and recently by ALICE in the J/ψ and D-meson production measurement as a function of charged-particle multiplicity [5,6].