No. 11 (00079)

Family name : Lo Re
Given name : Giuseppe
Affiliation : INFN-ALICE
Abbreviation : 
E-mail address : giuseppe.lore@cnaf.infn.it
Title : k*(892)0 reconstruction in ALICE
Authors : A. Badala', R. Barbera, G. Lo Re, A. Palmeri, G. S.
Pappalardo, A. 
Pulvirenti, F. Riggi
Abstract : 
For the ALICE Collaboration.

The study of resonances which have lifetimes comparable to that  of the
dense matter created in heavy-ion collisions at ultrarelativistic
energies is an important tool to have information on the collision
dynamics. Modifications of the properties of such resonances and of
their production rate may be expected when they are produced in a dense
medium, as one of the proposed signals of a possible phase transition of
nuclear matter to a deconfined plasma of quarks and gluons.  The study
of such resonances, compared to that of other particles produced in the
collision, may also probe the role of the rescattering phase between
chemical and kinetic freeze-out. Since these resonances may decay still
in the hot hadronic matter, rescattering of the daughter particles may
take place, depending on the source size and lifetime, as well as on the
parent transverse momentum. Finally, the combined investigation of
resonances with strange quark content, as the K*(892) and Phi mesons, is
also important due to the expected overall strangeness enhancement in
heavy-ion collisions.

Recently, a simulation study concerning the K*(892)0 resonance and its
antiparticle was carried out within the ALICE Collaboration, in order to
evaluate to what  extent the detector will be able to reconstruct such
signal in a high multiplicity environment, as expected in PbPb
collisions at the LHC energy.

The observation of this resonance is actually critical in heavy-ion
experiments, due to the large combinatorial background and to detector
limitations. Recent results on K*(892)0 come from the NA49 experiment at
the CERN SPS (PbPb at 158 AGeV/nucleon) and from the STAR experiment at
RHIC, which analyzed AuAu collisions at 130 AGeV and 200 AGeV in the cm
system.  In this study, we analyzed both pp and PbPb collisions, in the
framework of AliRoot, the C++ package for simulation, reconstruction and
analysis developed within the ALICE Collaboration. PITHYA and  HIJING
event generators were used for pp and PbPb collision respectively. Full
response of the detector was included in the simulation. The mixed event
technique was used to evaluate the combinatorial background. The large
amount of events (of the order of 10**5 for pp) and cpu needed brought
us to consider the use of the GRID middleware AliEn, the ALICE package
for distributed computing.

Typical results from such investigation will be presented, including the
reconstruction procedure for the K*(892)0 resonance, the improvement of
the signal-to-background ratio by means of kinematical cuts, the
efficiency and the statistical significance. A brief description of
AliEn as distributed analysis tool, together with some recent
evelopments concerning job handling and results retrieving, will also be
given.