arXiv subjects

Georg Wolschin

Publications and source records attributed to Georg Wolschin.

At least 37 records · Page 2Linked to original sources

arXiv2015

Ultraviolet energy dependence of particle production sources in relativistic heavy-ion collisions

The energy dependence of particle production sources in relativistic heavy-ion collisions is investigated from RHIC to LHC energies. Whereas charged-hadron production in the fragmentation sources follows a ln(s_NN/s_0) law, particle production in the mid-rapidity gluon-gluon source exhibits a much stronger dependence proportional to ln^3(s_NN/s_0), and becomes dominant between RHIC and LHC energies. The production of particles with pseudorapidities beyond the beam rapidity is also discussed.

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arXiv2014

Bottomium suppression in PbPb collisions at LHC energies

We substantially refine our previously developed model for the suppression of Upsilon mesons in the quark-gluon plasma (QGP) formed in 2.76 TeV PbPb collisions at the LHC. It accounts for gluodissociation of the six bottomium states Y(nS), chi_b(nP) with n = 1,2,3, collisional damping of these states as described in a complex potential, screening of the real part of the potential, and the subsequent decay cascade. In the hydrodynamical calculation of the expanding fireball, we take into account the effect of transverse expansion on the suppression factors, and finite transverse momenta of the heavy mesons in the medium. The running of the coupling is considered, resulting in larger gluodissociation decay widths. The initial central temperature is found to be 550 MeV at 0.1 fm/c. Our results are in good agreement with recent centrality-dependent CMS and ALICE data. The calculated suppression of the excited states relative to the ground state Y(1S) is not strong enough in peripheral collisions. Additional mechanisms are discussed. Predictions for 5.52 TeV are made.

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arXiv2013

Particle production sources at LHC energies

Particle production sources at RHIC and LHC energies are investigated in pseudorapidity space. A nonequilibrium-statistical relativistic diffusion model (RDM) with three sources is applied to the analysis of charged-hadron distributions in AuAu collisions at RHIC energies, in PbPb collisions at the current LHC energy of 2.76 TeV, in pPb at 5.02 TeV, and in pp. The size of the midrapidity source relative to the fragmentation sources in heavy-ion collisions is investigated as function of the incident energy. At LHC energies, the midrapidity value is mostly determined by particle production from gluon-gluon collisions.

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arXiv2013

Upsilon suppression in PbPb collisions at the LHC

We suggest that the combined effect of screening, gluon-induced dissociation, collisional damping, and reduced feed-down explains most of the sequential suppression of Upsilon(nS) states that has been observed in PbPb relative to pp collisions at sqrt(s_NN) = 2.76 TeV. The suppression is thus a clear, albeit indirect, indication for the presence of a QGP. The Upsilon(1S) ground state suppression is essentially due to reduced feed-down, collisional damping and gluodissociation, whereas screening prevails for the suppression of the excited states.

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arXiv2012

Centrality dependence of charged-hadron pseudorapidity distributions in PbPb collisions at LHC energies in the RDM

The centrality dependence of charged-hadron production in relativistic heavy-ion collisions at LHC energies is investigated in a nonequilibrium-statistical relativistic diffusion model (RDM) with three sources. Theoretical pseudorapidity distributions are compared with preliminary PbPb ALICE data at LHC energy of sqrt(s_NN) = 2.76 TeV for seven centralities, and a previous RDM prediction for this energy is confronted with the data. Refined predictions for 5.52 TeV PbPb based on RDM parameter extrapolations are presented.

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arXiv2012

Upsilon Suppression in PbPb Collisions at sqrt(s_NN) = 2.76 TeV

We suggest that the combined effect of screening, gluon-induced dissociation, collisional damping, and reduced feed-down explains most of the sequential suppression of Y(nS) states that has been observed in PbPb relative to pp collisions at sqrt(s_NN) = 2.76 TeV. The suppression is thus a clear, albeit indirect, indication for the presence of a qgp.

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arXiv2012

Gluodissociation and Screening of Upsilon States in PbPb Collisions at sqrt (s_NN) = 2.76 TeV

We suggest that gluon-induced dissociation and screening of the Y(nS) states explain the suppression of the Y(2S+3S) states relative to the Y(1S) ground state that has been observed by CMS in PbPb collisions at sqrt(s_NN)= 2.76 TeV at the CERN LHC. The minimum-bias gluodissociation cross sections of the 1S-3S states are calculated using a screened Cornell potential and a thermal gluon distribution. The 3S state dissolves due to screening before sizeable gluodissociation occurs, but for the 2S and 1S states there is an interplay between screening, gluodissociation, and feed-down from the chi_b(2P) and chi_b(1P) states. Based on a schematic approach, we find that the calculated suppression of the Y(2S) and Y(3S) states relative to Y(1S) is consistent with the CMS result, but allows for additional suppression mechanisms. The Y(1S) suppression through gluodissociation is, however, in good agreement with the CMS data.

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arXiv2011

Pseudorapidity distributions of produced charged hadrons in pp collisions at RHIC and LHC energies

The energy dependence of charged-hadron production in proton-proton collisions at RHIC and LHC energies is investigated in a nonequilibrium-statistical relativistic diffusion model (RDM) with three sources for particle production. Calculated charged-hadron pseudorapidity distributions for pp at RHIC energies of sqrt(s) = 0.2 and 0.41 TeV, and at LHC energies of 0.9, 2.36 and 7 TeV are optimized with respect to the available data. Predictions for 14 TeV are made. The central source arising from gluon-gluon collisions becomes the major origin of particle production at LHC energies. The midrapidity dip is essentially determined by the interplay of the three sources.

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arXiv2011

Stopping in central Pb + Pb collisions at SPS energies and beyond

We investigate stopping and baryon transport in central relativistic Pb + Pb and Au + Au collisions. At energies reached at the CERN Super Proton Synchrotron [sqrt(s_NN) = 6.3-17.3 GeV] and at RHIC (62.4 GeV), we determine the fragmentation-peak positions from the data. The resulting linear growth of the peak positions with beam rapidity is in agreement with our results from a QCD-based approach that accounts for gluon saturation. No discontinuities in the net-proton fragmentation peak positions occur in the expected transition region from partons to hadrons at 6-10 GeV.

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arXiv2011

Produced charged hadrons in central Pb + Pb collisions at LHC energies in the RDM

The energy dependence of charged-hadron production in relativistic heavy-ion collisions is investigated in a nonequilibrium-statistical relativistic diffusion model (RDM) with three sources. Theoretical pseudorapidity distributions are compared with Au + Au data at RHIC energies of sqrt(s_NN) = 0.13 and 0.2 TeV, and computed for Pb + Pb central collisions at LHC energies of 2.76 and 5.52 TeV. The central, nearly equilibrated source arising from gluon-gluon collisions becomes the major origin of particle production at LHC energies. The midrapidity dip is determined by the interplay of the three sources.

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arXiv2010

Predictions for net-proton and net-kaon distributions at LHC energies

We investigate baryon and charge transport in relativistic heavy-ion collisions, compare with Au + Au RHIC data at sqrt(s_NN)=0.2 TeV, and make predictions for net-proton rapidity distributions in central Pb + Pb collisions at CERN LHC energies of sqrt(s_NN)=2.8, 3.9, and 5.5 TeV. We use the gluon saturation model and put special emphasis on the midrapidity valley |y|< 2. Net-kaon distributions are calculated and compared to BRAHMS Au + Au data at RHIC energies of sqrt(s_NN)= 0.2 TeV, and predicted for Pb + Pb at 5.5 TeV.

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arXiv2009

Baryon stopping and saturation physics in relativistic collisions

We investigate baryon transport in relativistic heavy-ion collisions at energies reached at the CERN Super Proton Synchrotron, BNL Relativistic Heavy-Ion Collider (RHIC), and CERN LHC in the model of saturation. An analytical scaling law is derived within the color glass condensate framework based on small-coupling QCD. Transverse momentum spectra, net-baryon rapidity distributions and their energy, mass and centrality dependences are well described. In a comparison with RHIC data in Au + Au collisions at sqrt (s_NN) = 62.4 GeV and 200 GeV, the gradual approach to the gluon saturation regime is investigated, and limits for the saturation-scale exponent are determined. Predictions for net-baryon rapidity spectra and the mean rapidity loss in central Pb + Pb collisions at LHC energies of sqrt (s_NN) = 5.52 TeV are made.

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arXiv2009

Baryon Stopping as a new Probe of Geometric Scaling

We suggest to use net-baryon rapidity distributions in central relativistic heavy-ion collisions at SPS, RHIC and LHC energies in order to probe saturation physics. Within the color glass condensate framework based on small-coupling QCD, net-baryon rapidity distributions are shown to exhibit geometric scaling. In a comparison with RHIC data in Au + Au collisions at sqrt(s_NN) = 62.4 GeV and 200 GeV the gradual approach to the gluon saturation regime is investigated. Predictions for net-baryon rapidity spectra and the mean rapidity loss in central Pb + Pb collisions at LHC energies of sqrt (s_NN) = 5.5 TeV are made.

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arXiv2008

Particle production and nonlinear diffusion in relativistic systems

The short parton production phase in high-energy heavy-ion collisions is treated analytically as a nonlinear diffusion process. The initial buildup of the rapidity density distributions of produced charged hadrons within tau_p = 0.25 fm/c occurs in three sources during the colored partonic phase. In a two-step approach, the subsequent diffusion in pseudorapidity space during the interaction time of tau_int = 7-10 fm/c (mean duration of the collision) is essentially linear as expressed in the Relativistic Diffusion Model (RDM) which yields excellent agreement with the data at RHIC energies, and allows for predictions at LHC energies. Results for d+Au are discussed in detail.

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arXiv2008

Diffusion or bounce back in relativistic heavy-ion collisions?

The time evolution of pseudorapidity distributions of produced charged hadrons in d+Au collisions at sqrt(s_NN) = 200 GeV is investigated. Results of a nonequilibrium-statistical Relativistic Diffusion Model with three sources are compared with a macroscopic "bounce back" model that does not allow for statistical equilibration at large times, but instead leads to motion reversal. When compared to the data, the results of the diffusion approach are more precise, thus emphasizing that the system is observed to be on its way to thermal equilibrium.

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arXiv2007

Hadron production in heavy relativistic systems

We investigate particle production in heavy-ion collisions at RHIC energies as function of incident energy, and centrality in a three-sources Relativistic Diffusion Model. Pseudorapidity distributions of produced charged hadrons in Au + Au and Cu + Cu collisions at sqrt(s_NN) = 19.6 GeV, 62.4 GeV, 130 GeV and 200 GeV show an almost equilibrated midrapidity source that tends to increase in size towards higher incident energy, and more central collisions. It may indicate quark-gluon plasma formation prior to hadronization.

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arXiv2006

From RHIC to LHC: A relativistic diffusion approach

We investigate the energy dependence of stopping and hadron production in high-energy heavy-ion collisions based on a three-sources Relativistic Diffusion Model. The transport coefficients are extrapolated from Au + Au and Cu + Cu at RHIC energies (sqrt{s_NN)=19.6 - 200 GeV) to Pb + Pb at LHC energies sqrt{s_NN)= 5.52 TeV. Rapidity distributions for net protons, and pseudorapidity spectra for produced charged particles in central collisions are compared to data at RHIC energies, and discussed for several extrapolations to LHC energies.

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arXiv2006

Rapidity equilibration in d + Au and Au + Au systems

In a Relativistic Diffusion Model (RDM), the evolution of net-proton rapidity spectra with sqrt(s_NN) in heavy systems is proposed as an indicator for local equilibration and longitudinal expansion. The broad midrapidity valley recently discovered at RHIC in central Au + Au collisions at sqrt(s_NN)= 200 GeV suggests rapid local equilibration which is most likely due to deconfinement, and fast longitudinal expansion. Rapidity spectra of produced charged hadrons in d + Au and Au + Au systems at RHIC energies and their centrality dependence are well described in a three-sources RDM. In central collisions, about 19 % of the produced particles are in the equilibrated midrapidity region for d + Au.

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