1. General Seminars

Jet measurement in p+p and Pb+Pb collisions with the ALICE experiment at LHC.

by Magali Estienne (SUBATECH CNRS/IN2P3)

Aula Edificio 22 (Laboratori Nazionali di Frascati)

Aula Edificio 22

Laboratori Nazionali di Frascati

Via E. Fermi, 40 Frascati
The observation of the strong suppression of high pT hadrons in ultra-relativistic heavy ion collisions has motivated a large experimental program using hard probes to characterize the deconfined medium created. A few selected results from RHIC which indicate a non negligeable interaction of high energy partons with a dense color medium before hadronization will be first discussed. Despite many observables such as the nuclear modification factor, two and three particle azimuthal correlations have shown that partons lose energy in the dense medium by gluon radiations, the physical properties of the produced medium such as the value of the transport coefficient, qhat, or the initial gluon rapidity density, are not yet fully characterized by the available models. Moreover the center of mass energy available at RHIC has allowed a deep ``leading particle physics'' study which clearly presents some limitations. For instance, trigger bias induced by the steeply falling particle spectra and surface emission bias, which provides only a lower bound to the initial color charge density, limit strongly the conclusions that can be drawn and motivate the study of more penetrating probes. The gain in the center of mass energy expected at the LHC will definitively help our understanding on how the energy is lost in the system but will also open a new major window of study in high pT physics: the physics of jets on an event-by-event basis. I will concentrate on this topic and illustrate the new possibilities that the ALICE experiment will offer to first test pQCD and characterize the fragmentation function of the produced charged particles but also to better understand the medium created with the measurement of such observables. Jet reconstruction in p+p and Pb+Pb collisions, improvements brought by the EMCal calorimeter as well as some expected physics performances will be presented.