ALICE at Quark Matter

Mateusz Ploskon

The 22nd Quark Matter conference is well under way in picturesque Annecy, France. With 41 oral presentations and more than 70 posters ALICE is exposing the large variety of results from the first year of data taking including the first heavy-ion run of the LHC.

The very first Pb-Pb collision at the LHC was collected barely six months ago. However, ALICE already makes a strong contribution to the field of heavy-ion physics by providing versatile and resourceful insights to the properties of the hot and dense QCD matter at LHC.

By exploiting its tracking and particle identification capabilities ALICE has extracted crucial observables for the characterization of the heavy-ion collisions and collective features of the created system such as the particle production, the elliptic flow and extensive studies of correlations of produced particles.The quick ALICE publication (December 2010) of the elliptic flow (v2) measurement has shown that the quark-gluon medium at LHC behaves as a close-to-ideal liquid. At Quark Matter 2011 ALICE for the first time presented the results on elliptic flow for variety of identified particles (protons, pions and kaons). A characteristic dependence of v2 as a function of transverse momentum exhibits hydrodynamic features of the hot medium.

In addition the higher moments of the azimuthal anisotropy of the particle production have been presented. They allow disentangling the true features of the medium from the effects trivially related to the number and relative orientation of the struck nucleons within the colliding lead nuclei. These observations are made on the unprecedented level of precision - this is truly the qualitative strength of the measurements at LHC.

Apart from the detailed studies of the particle production in heavy-ion collisions one of the most important themes at the conference is the parton energy loss in the hot QCD medium. In this context, one of the highlights is the ALICE result on the production of charged hadrons as a function of transverse momentum in Pb-Pb collisions.

ALICE presented results confirming a strong suppression of the number of produced particles in head-on Pb-Pb as compared to p-p collisions. It is remarkable that the kinematic reach of the measurement was extended up to the unprecedented 100 GeV/c in the particles transverse momentum.

Additional interesting measurement addressing the parton energy loss is the azimuthal correlation of charged hadrons. The studies by ALICE, exhibit the suppression of the back-to-back jets. They are an important input for our understanding of the jet quenching and provide additional constrains to the theoretical calculations.

ALICE has also presented the very first results on the flavor and mass dependence of the parton energy loss. ALICE measurements quantify the production of charm and beauty quarks in proton-proton and Pb-Pb collisions via fully reconstructed D meson decays, and via the measurement of electrons - the products of the charm and bottom decays.

The presentations at Quark Matter by ALICE cover a wealth of topics. From the characterization of the so called initial conditions of heavy-ion collisions, through various correlations sensitive to the equation-of-state of the hot QCD medium at LHC, to interesting findings on charm and bottom quark production ALICE's measurements stimulate the community opening a new era in the heavy-ion research. We certainly have very exciting times ahead.

Alice Matters