Nuclear physics is on the verge of entering a new regime of physical investigation.  Recent experimental studies of the high energy central heavy ion collisions at CERN indicated closing to the regime of deconfinement and chiral symmetry restoration in nuclear matter.  Creation and characterization in the laboratory conditions such a new phase of matter, the Quark-Gluon Plasma (QGP), which according to the modern scenario of the Universe evolution existed in the first few microseconds following the Big Bang are obviously ambitious goals listed in the Long-Range Plan for Nuclear Physics as the highest priority of recently completed RHIC accelerator capable to produce collisions of Au nuclei at the center-of -mass energy 200 A GeV. 

During the last decade the Relativistic Nuclear Physics Laboratory of the PNPI High Energy Physics Division participated in the PHENIX experiment at RHIC.

The principle goal of the PHENIX experiment is to measure a maximal set of QGP signatures based upon present theoretical knowledge. Hence, it should be no surprise that the experiment is extraordinarily complex, featuring 11 different detector subsystems (technologies) and hundreds of thousands of electronic channels.  PHENIX is the largest and most complex detector at RHIC.  Although the most salient feature of the plasma is quark deconfinement, measurements of quark-containing particles seem be the least favorable signatures of the plasma.  The reason for this is simple.  Despite being deconfined interior to the plasma volume, quarks must hadronize while leaving the collision zone.  This process and subsequent reinteractions of the resulting hadronic species threaten to erase plasma signatures from all hadronic spectra.  Only non-strongly interacting species (leptons and photons) are emitted directly from the Plasma State without suffering debilitating final state interactions.  Among all RHIC experiments, only PHENIX measures these so-called "penetrating probes", muons, electrons, and photons.  The detectors conceived and constructed by the RNPL team comprise the most vital ones for electron measurements – the Drift Chambers (DC) placed in the central arms.

All parts for the PHENIX drift chambers were designed, manufactured, and tested in PNPI. Because the drift chamber is too large and fragile to ship half way around the world, it was shipped in pieces to Stony Brook for assembly.

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Early Physics from PHENIX

   During the first three years of RHIC operation the PHENIX collected a huge amount of data. According to the preliminary estimates increase of the collision energy allowed to create much higher  energy density in the central region of collision as compared to the previous experiments at SPS and, hence, to observe new phenomena. One of them already discovered at RHIC is the so called effect of Jet Quenching.  Jets are formed as a result of hard collisions among quarks and gluons.  In free space they are well understood within perturbative QCD.  In the presence of plasma, jets are predicted to undergo a severe energy loss and essentially thermalize with the surrounding medium.  One simple way to identify the presence of jets in a high-energy collision involves simple measuring the distribution in transverse momentum of all charged ejectiles.  At low transverse momentum, this spectrum exhibits an exponential (thermal) behavior indicative of those particles that have reached equilibrium.  At high transverse momentum, the character changes to a power law behavior indicative of jets.  An analysis of the transverse momentum spectrum at RHIC, particularly as a function of event centrality, yields direct and fast insight into the fate of jets in the medium.  Jets produced near the surface of the plasma state directed outwards will not be quenched even under the most optimistic of scenarios. Since in the transverse plane jets are produced back-to-back, if one jet leaves the surface of the plasma, the second one will be directed into the plasma and surely lost.  Just the disappearance of back-to-back jet angular correlations which is a sensitive probe of jet quenching in a plasma state has been revealed comparing the effects measured in the central Au-Au collisions to that observed in deuteron-gold interaction where there is no chance to produce the hot dense deconfined medium.

 

                FUTURE   WITH ALICE AT CERN

 

     Although it is generally believed that the deconfined state of nuclear matter has been created already at the RHIC energies it is clear now – the detailed investigations of this exciting phenomenon will be realized at higher energies at Large Hadron Collider at CERN where operation of ALICE detector is scheduled on 2007.

The RNPL is participating in the ALICE collaboration from the very beginning with responsibility for the Muon Stations in Muon Arm of the detector. The mass production of the muon chambers in the RNPL starts in 2004 and should be finished in the middle of 2005.

After the ALICE starts to take data the efforts of the RNPL team in ALICE collaboration will be aimed to measure yield of heavy quarkonia with ALICE at LHC. Basing on the results of theoretical calculations the estimates of the corresponding counting rates for the yield of charmonium in ultraperipheral ion collisions obtained in result of simulations in kinematical conditions of the ALICE are looking quite promising.  The physics of the ultraperipheral heavy ion collisions is considered as one of  the priorities in the RNPL experimental researches at LHC.