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Johann Rafelski

Publications and source records attributed to Johann Rafelski.

At least 109 records · Page 6Linked to original sources
arXiv2009

Resonance Production in Heavy Ion Collisions: Suppression of $Λ(1520)$ and Enhancement of $Σ(1385)$

We investigate the yield of $Λ(1520)$ resonance in heavy ion collisions within the framework of a kinetic master equation without the assumption of chemical equilibrium. We show that reactions such as $Λ(1520)+π\leftrightarrow Σ^*$ can favor $Σ^*$ production, thereby decreasing the $Λ(1520)$ yield. Within the same approach we thus find a yield enhancement for $Σ(1385)$ and a yield suppression for $Λ(1520)$.

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arXiv2008

Vacuum Decay Time in Strong External Fields

We consider dynamics of vacuum decay and particle production in the context of short pulse laser experiments. We identify and evaluate the invariant "materialization time," $τ$, the timescale for the conversion of an electromagnetic field energy into particles, and we compare to the laser related time scales.

hep-ph↗
arXiv2008

Pion and muon production in electron-positron photon plasma

We study production and equilibration of pions and muons in relativistic electron-positron-photon plasma at a temperature $T\ll m_μ, m_π$. We argue that the observation of pions and muons can be a diagnostic tool in the study of the initial properties of such a plasma formed by means of strong laser fields. Conversely, properties of muons and pions in thermal environment become accessible to precise experimental study.

hep-ph↗
arXiv2008

Enhanced Production of Delta(1230) and Sigma(1385) Resonances

Yields of Delta(1230), Sigma(1385) resonances produced in heavy ion collisions are studied within the framework of a kinetic master equation. The time evolution is driven by the process Delta(1230) \leftrightarrow N π, Sigma(1385) \leftrightarrow Λπ. We obtain resonance yield both below and above chemical equilibrium, depending on initial hadronization condition and separation of kinetic and chemical freeze-out.

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arXiv2008

Strangeness Enhancement: Challenges and Successes

Highly effective conversion of kinetic energy into abundant particle multiplicity is the remarkable feature discovered in high energy heavy ion collisions. This short and pedagogic review addresses topical issues related to the understanding of this phenomenon, originating in the creation of the deconfined quark--gluon plasma phase. I consider in depth the apparently simple, yet sometimes misunderstood, intricate issues: a) statistical hadro-chemistry, chemical parameters, b) strange flavor chemical equilibration in quark--gluon plasma, and c) particle yields and sudden hadronization, in the historic perspective of work and competition with my friend Jozsef Zimanyi.

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arXiv2008

Hadron Production and Phase Changes in Relativistic Heavy Ion Collisions

We study soft hadron production in relativistic heavy ion collisions in a wide range of reaction energy, 4.8 GeV sqrt{s_NN} \ge 200 GeV, we use continuity of particle yields and statistical parameters to predict the hadron production at sqrt{s_NN}=62.4 GeV, and obtain total yields of hadrons at sqrt{s_NN}=130 GeV. We consider, in depth, the pattern we uncover within the hadronization condition, and discuss possible mechanisms associated with the identified rapid change in system properties at sqrt{s_NN ^cr}. We propose that the chemically over-saturated 2+1 flavor hadron matter system undergoes a 1st order phase transition.

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arXiv2008

Strangeness and threshold of phase changes

We explore entropy and strangeness as signature of QGP for top AGS energy and the energy scan at SPS. We find that the hadronization dynamics changes between 20 and 30 $A$ GeV projectile energy. The high energy results are consistent with QGP.

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arXiv2008

Strangeness enhancement at LHC

We study production of strangeness in the hot QGP fireball in conditions achieved at LHC, and use these results to obtain soft (strange) hadron multiplicities. We compare the chemical equilibrium and non-equilibrium conditions and identify characteristic experimental observables.

hep-ph↗
arXiv2007

Quarks in the universe

Matter in its present form was formed when our Universe emerged from the quark-gluon phase (QGP) at about 30mus into its evolution. To explore this early period in the laboratory, we study highly excited matter formed in relativistic heavy ion collision experiments: heavy nuclei crash into each other, and form compressed and energetically excited nuclear matter, resembling in its key features the stuff which filled the early Universe. In these experiments we further explore the physics of the vacuum structure of strongly interacting gauge theory, Quantum Chromodynamics (QCD). The common beginning for both, heavy ion collisions, and vacuum structure investigations, is the physics of the quantum electrodynamic (QED) vacuum in the presence of the supercritical external field that is formed when two highly charged heavy ions are brought together near to the Coulomb barrier in a considerably lower reaction energy collision.

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arXiv2007

Delta-33 medium mass modification and pion spectra

We study the pi+- spectra obtained in 2,4,6,8 A GeV Au-Au collisions within the thermal model. We find that the main features of the data can be well described after we include the pions from the decay of the Delta-resonance with medium mass modification.

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arXiv2007

Heavy Flavor Hadrons in Statistical Hadronization of Strangeness-rich QGP

We study b, c quark hadronization from QGP. We obtain the yields of charm and bottom flavored hadrons within the statistical hadronization model. The important novel feature of this study is that we take into account the high strangeness and entropy content of QGP, conserving strangeness and entropy yields at hadronization.

hep-ph↗
arXiv2007

Hadron Resonances and Phase Threshold in Heavy Ion Collisions

We show that a measurement of the reaction energy dependence of relative hadron resonance yields in heavy ion collisions can be used to study the phase structure of the dense QCD matter created in these collisions, and investigate the origin of the trends observed in the excitation functions of certain soft hadronic observables. We show that presence of chemical nonequilibrium in light quark abundance imparts a characteristic signature on the energy dependence of resonance yields, that differs considerably from what is expected in the equilibrium picture.

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arXiv2007

Strangeness Chemical Equilibration in QGP at RHIC and LHC

We study, in the dynamically evolving QGP fireball formed in relativistic heavy ion collisions at RHIC and LHC, the growth of strangeness yield toward and beyond the chemical equilibrium. We account for the contribution of the direct strangeness production and evaluate the thermal-QCD strangeness production mechanisms. The specific yield of strangeness per entropy, s/S, is the primary target variable. We explore the effect of collision impact parameter, i.e., fireball size, on kinetic strangeness chemical equilibration in QGP. Insights gained in study the RHIC data with regard to the dynamics of the fireball are applied to the study strangeness production at the LHC. We use these results and consider the strange hadron relative particle yields at RHIC and LHC in a systematic fashion. We consider both the dependence on s/S and directly participant number dependence.

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arXiv2006

Quantum Collective QCD String Dynamics

The string breaking model of particle production is extended in order to help explain the transverse momentum distribution in elementary collisions. Inspired by an idea of Bialas', we treat the string using a collective coordinate approach. This leads to a chromo-electric field strength which fluctuates, and in turn implies that quarks are produced according to a thermal distribution.

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arXiv2006

Charmed Hadrons from Strangeness-rich QGP

The yields of charmed hadrons emitted by strangeness rich QGP are evaluated within chemical non-equilibrium statistical hadronization model, conserving strangeness, charm, and entropy yields at hadronization.

hep-ph↗
arXiv2006

Particle yield fluctuations and chemical non-equilibrium at RHIC

We study charge fluctuations within the statistical hadronization model. Considering both the particle yield ratios and the charge fluctuations we show that it is possible to differentiate between chemical equilibrium and non-equilibrium freeze-out conditions. As an example of the procedure we show quantitatively how the relative yield ratio $Λ/K^-$ together with the normalized net charge fluctuation $v(Q)=\ave{ΔQ^2}/\ave{\Nch}$ constrain the chemical conditions at freeze-out. We also discuss the influence of the limited detector acceptance on fluctuation measurements, and show how this can be accounted for within a quantitative analysis.

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arXiv2005

Strangeness and thresholds of phase changes in relativistic heavy ion collisions

We discuss how the dynamics of the evolving hot fireball of quark--gluon matter impacts phase transition between the deconfined and confined state of matter. The rapid expansion of the fireball of deconfined matter created in heavy ion collisions facilitates formation of an over-saturated strange quark phase space. The related excess abundance of strangeness is compensating the suppression of this semi-heavy quark yield by its quark mass. In addition, the dynamical expansion of colored quanta pushes against the vacuum structure, with a resulting supercooling of the transition temperature. We address the status of the search for the phase boundary as function of reaction energy and collision centrality and show evidence for a change in reaction mechanism at sufficiently low energies. The phase diagram derived from the study of hadron production conditions shows two boundaries, one corresponding to the expected transition between confined and deconfined matter, with a downward temperature shift, and the other a high quark density hadronization which appears to involve heavy effective quarks, at relatively large temperatures.

hep-ph↗