Heavy Flavours in Heavy-ion Collisions at the Lhc: Alice Performance

The ALICE experiment1 will study nucleus–nucleus (AA) collisions at the LHC, with a centreof-mass energy √ sNN = 5.5 TeV per nucleon–nucleon (NN) pair for the Pb–Pb system, in order to investigate the properties of QCD matter at energy densities of up to several hundred times the density of atomic nuclei. In these conditions a deconfined state of quarks and gluons is expected to be formed. As we shall detail in the following paragraphs, heavy quarks are sensitive probes of such a medium. Heavy-quark pairs (QQ) are produced in the early stage of the collision in primary partonic scatterings with large virtuality Q and, thus, on temporal and spatial scales, ∆t ∼ ∆r ∼ 1/Q, which are sufficiently small for the production to be unaffected by the properties of the medium. In fact, the minimum virtuality Qmin = 2mQ in the production of a QQ pair implies a spacetime scale of ∼ 1/(2mQ) ≃ 1/2.4 GeV ≃ 0.1 fm (for charm), to be compared to the expected life-time of the deconfined state at the LHC, > ∼ 10 fm. Thus, the initially-produced heavy quarks experience the full collision history. Hard partons are regarded as probes of the medium as they are expected to lose energy by gluon radiation while propagating through high-density QCD matter.2,3,4 The attenuation (quenching) of leading hadrons observed in Au–Au collisions at RHIC5 is thought to be due to such a mechanism. Due to the large values of their masses, the charm and beauty quarks are