jeudi 7 mars 2013 à 11:20
Amphi G. Besse
ALICE is the LHC experiment dedicated to the study of the nuclear matter at the high temperatures and densities reached in heavy-ion collisions, where a transition to a quark-gluon plasma (QGP) state is expected. Due to their large mass and their production at the early collision stage, heavy quarks (charm and bottom) are well-suited probes to study the properties of the QGP. The measurement of Λc yield relative to D mesons in Pb-Pb collisions would answer the question whether the baryon over meson enhancement at intermediate momentum, observed in the light-flavour sector at RHIC and LHC, also holds in the heavy-quark sector. In pp collisions, the measurement of the Λc production cross-section provides the necessary baseline to understand the heavy ions results. Moreover, it has an interest per se, since it is needed to measure the total charm cross section and has never been measured in hadronic collisions. This charm baryon is observed in ALICE in pp collisions in the decay channels Λc+ → π+ + K- + p and Λc+ → KS0 + p exploiting kinematical and geometrical selections, together with particle identification. So far, the Λc+ has never been observed in Pb-Pb collisions: in this high multiplicity environment, the combinatorial background explodes and tighter cuts on the topology of the decay are needed to extract the signal. The replacement of the current Inner Tracking System with a new detector with better resolution, smaller material thickness and with high-rate readout capabilities is fundamental to perform the measurement of the charmed baryon. The ALICE upgrade program has been approved and will start in 2018. The decay channel of Λc is presently being used as benchmark. We present the analysis strategy to observe the Λc signal in different pT bins, in the pseudorapidity range |η| < 0.9, in both decay channels, in pp collisions at √s = 7 TeV and the results forseen with the ITS upgrade program.