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Krajczar K.,KFKI Research Institute
Journal of Physics G: Nuclear and Particle Physics | Year: 2011

Measurements of the charged hadron multiplicity and transverse energy are presented for minimum bias PbPb collisions at a centre-of-mass energy of 2.76 TeV per nucleon pair. The number of charged hadrons was obtained by two different methods based on the silicon pixel system of the CMS detector at the LHC. The two methods are in excellent agreement, resulting a charged hadron density of 1612 ± 55 for the 5% most central collisions. For the transverse energy measurement, CMS has almost Hermetic calorimetry coverage with fine granularity and excellent resolution. In addition, for particles near central rapidity, momenta from the tracker can be combined with the calorimeter data to give a significant improvement of the system resolution. A transverse energy density of 2.1 TeV is observed for the most central 2.5% collisions. The measurements are compared with heavy-ion results from earlier experiments, where a smooth dependence on the collision energy and impact parameter is observed. © 2011 IOP Publishing Ltd. Source


Levai P.,KFKI Research Institute
Nuclear Physics A | Year: 2011

The suppression of hadron production originated from the induced jet energy loss is one of the most accepted and well understood phenomena in heavy ion collisions, which indicates the formation of color deconfined matter consists of quarks, antiquarks and gluons. This phenomena has been seen at RHIC energies and now the first LHC results display a very similar effect. In fact, the suppression is so close to each other at 200 AGeV and 2.76 ATeV, that it is interesting to investigate if such a suppression pattern can exist at all. We use the Gyulassy-Levai-Vitev description of induced jet energy loss combined with different nuclear shadowing functions and describe the experimental data. We claim that a consistent picture can be obtained for the produced hot matter with a weak nuclear shadowing. The interplay between nuclear shadowing and jet energy loss playes a crucial role in the understanding of the experimental data. © 2011. Source


Levai P.,KFKI Research Institute | Skokov V.,Gesellschaft fur Schwerionenforschung MbH
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2010

Nonperturbative charm and bottom quark-pair production is investigated in the early stage of heavy-ion collisions. The time-dependent study is based on a kinetic description of fermion-pair production in strong non-Abelian fields. We introduce a time-dependent chromo-electric external field with a pulselike time evolution to simulate the overlap of two colliding heavy ions. The calculations is performed in a SU(2) color model with finite current quark masses. Yields of heavy quark pairs are compared to the ones of light and strange quark pairs. We show that the small inverse duration time of the field pulse determines the efficiency of the quark-pair production. The expected suppression for heavy quark production, as follows from the Schwinger formula for a constant field, is not seen, but rather an enhanced heavy quark production appears at ultrarelativistic energies. © 2010 The American Physical Society. Source


Balogh A.,Imperial College London | Erdos G.,KFKI Research Institute
Space Science Reviews | Year: 2013

The Heliospheric Magnetic Field (HMF) is the physical framework in which energetic particles and cosmic rays propagate. Changes in the large scale structure of the magnetic field lead to short- and long term changes in cosmic ray intensities, in particular in anti-phase with solar activity. The origin of the HMF in the corona is well understood and inner heliospheric observations can generally be linked to their coronal sources. The structure of heliospheric magnetic polarities and the heliospheric current sheet separating the dominant solar polarities are reviewed here over longer than a solar cycle, using the three dimensional heliospheric observations by Ulysses. The dynamics of the HMF around solar minimum activity is reviewed and the development of stream interaction regions following the stable flow patterns of fast and slow solar wind in the inner heliosphere is described. The complex dynamics that affects the evolution of the stream interaction regions leads to a more chaotic structure of the HMF in the outer heliosphere is described and discussed on the basis of the Voyager observations. Around solar maximum, solar activity is dominated by frequent transients, resulting in the interplanetary counterparts of Coronal Mass Ejections (ICMEs). These produce a complex aperiodic pattern of structures in the inner heliosphere, at all heliolatitudes. These structures continue to interact and evolve as they travel to the outer heliosphere. However, linking the observations in the inner and outer heliospheres is possible in the case of the largest solar transients that, despite their evolutions, remain recognizably large structures and lead to the formation of Merged Interaction Regions (MIRs) that may well form a quasi-spherical, "global" shell of enhanced magnetic fields around the Sun at large distances. For the transport of energetic particles and cosmic rays, the fluctuations in the magnetic field and their description in alternative turbulent models remains a very important research topic. These are also briefly reviewed in this paper. © 2011 Springer Science+Business Media B.V. Source


Nagy M.I.,KFKI Research Institute
Physical Review C - Nuclear Physics | Year: 2011

New exact solutions of relativistic perfect-fluid hydrodynamics are presented, including the first family of exact rotating solutions. The method used to search for them is a simultaneous investigation of the relativistic hydrodynamical equations and the collisionless Boltzmann equation. Possible connections to the evolution of hot and dense partonic matter in heavy-ion collisions is discussed. © 2011 American Physical Society. Source

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