Chemical thermalization in relativistic heavy ion collisions

We compute by numerical integration of the Dirac equation the number of quark-antiquark pairs initially produced in the classical color fields of colliding ultrarelativistic nuclei. While the number of pairs is parametrically suppressed in the coupling constant, we find that in this classical field model their production rate is comparable to the thermal ratio of gluons/pairs=9Nf/32. After isotropization one thus would have a quark-gluon plasma in chemical equilibrium.     

Noncommutativity and Lorentz violation in relativistic heavy ion collisions

We show that relativistic heavy ion collisions at LHC energies could be used as an experimental probe to detect fundamental properties of spacetime long speculated about. Our results rely on the recent proposal that magnetic fields of intensity much larger than that of magnetars should be produced at the beginning of the collisions and this could have an important impact on the experimental manifestation of a noncommutative spacetime. Indeed, in the noncommutative generalization of electrodynamics the interplay between a nonzero noncommutative parameter and an external magnetic field leads us to predict the production of lepton pairs of low invariant mass by free photons (an event forbidden by Lorentz invariant electrodynamics) in relativistic heavy ion collisions at present and future available energies. This unique channel can be clearly considered as a signature of noncommutativity. On the other hand, the search for such decays is worth anyway because their absence would ameliorate of three orders of magnitude the current bound on the noncommutative parameter.     

A possible modified “bottom-up” thermalization in heavy ion collisions

We present a possible scaling solution to preequilibrium evolution which interpolates between the instability present in the dense gluon system produced immediately after a heavy ion collision and the final equilibration which occurs later. Our solution depends on a single parameter δ. Depending on the value of δ, our proposed solution matches onto the bottom-up picture either at an intermediate stage or toward the end of the evolution given by bottom-up. We discuss in detail the reasons why we believe our solution is self-consistent, and we also point out why it is difficult to actually prove consistency.     

Entropy in heavy ion collisions — A two-fluid scenario

Entropy balance is very important at ultra-high energy HIC’s, because there is not even approximate thermalisation there. Only a minor fragment of the incoming kinetic energy will be turned into “heat”, so internal energy, while the thermodynamic state variable is internal energy, not the total one. Here an approach is discussed calculating entropy directly, in a continuum physics scenario.     

Influence of thermalization on the initial condition for heavy ion collisions

In this paper, we discuss the important role of the thermalization process in the initial distribution of QGP. We find that the negligible heat conduction inside QGP can be expressed as an effective Fourier law and we further analyse qualitatively the results caused by a thermalized initial condition. Based on this arguments, we construct a simple phenomenological model and work with the hydro code, and then we compare our results with the experimental data and the results of the standard initial model. It is found that, as we have argued, a thermalized initial condition suppresses the value of the elliptic flow.     

CP violation in very high energyp \bar p collisions

We investigate the consequences of a CP violating gauge invariant pointlike four-fermion interaction at the TeV scale. It induces an enhancement of the production cross-sections \(\sigma \left( {p\bar p \to e^ - \bar v_e + X} \right)\) and \(\sigma \left( {p\bar p \to e^ + \bar v_e + X} \right)\) , together with a CP violating relative difference between these cross-sections at the % level, due to interference with radiative corrections. A complete calculation of the CP asymmetry is made for different values of the center of mass energy \(\sqrt s = 2, 10, 40 TeV\) , 40 TeV.     

Scaling properties of transverse flow in Bjorken’s scenario for heavy ion collisions

We report a simple analytical solution for the velocity u of the transverse flow of quark-gluon plasma at a hadronization front in Bjorken’s scenario. We establish scaling properties of the transverse flow as a function of the expansion time. We present simple scaling formula for the expansion velocity distribution. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 3, 183–188 (10 August 1998) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Equilibrium in heavy ion collisions

We discuss the question of equilibration in heavy ion collisions and how it can be addressed in experiment     

Femtoscopy in heavy ion collisions

Non-trivial space-time geometrical effects are at the core of bulk-sector heavy ion physics, and two-particle correlations at low relative velocity are the most direct probe of this geometry at the femtometer scale. I present a brief overview of the wealth of femtoscopic measurements from the past two decades of heavy ion experiments. Essentially every conceivable “knob” at our disposal has been turned; the response of two-particle correlations to these variations has revealed much about the space-momentum substructure of the hot source created in the collisions. I discuss the present status of the femtoscopic program and questions which remain, and point to new efforts which aim to resolve them. PACS 25.75.Ld; 25.75.Gz; 24.10.Nz     

P and CP violation mechanisms in nonassociative field theory

The octonion spinor field is studied. The nonassociativeness of the algebra makes it possible to introduce a new quantum number — the associator as a partner of spin — as a measure of nonassociativeness and as a generator of the Lorentz group. This makes it possible to classify a particle by spin and by the associator. In this formalism the eigenvalues of the C, P, and T operators can be determined and the superselection rules which reveal the mechanism of P and CP violation can be obtained. In particular, when the associator changes by one we have P violation and when it changes by two we have CP violation. This is confirmed by analysis of the diagrams describing the P- and CP-odd particle decays.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 92–97, October, 1990.     

Multifragmentation and dynamics in heavy ion collisions

A midrapidity zone formed in heavy-ion collisions has been investigated through special selections of light particles and intermediate mass fragments detected in the reaction ³⁵Cl on ¹²C at 43 MeV/nucleon and the reactions ⁵⁸Ni on ¹²C, ²⁴Mg, and ¹⁹⁷Au at 34.5 MeV/nucleon, and of neutron energy spectra measured in the reaction ³⁵Cl on ^natTa. Properties of the observables have been examined to characterize the neck-like structure formed between the two reaction partners. For the HERACLES collaboration.     

CP violation and the search for new physics

Beta-delayed proton decay of ⁵⁷Zn has been investigated at the GSI on-line isotope separator. The studied ⁵⁷Zn nuclei were produced in fusion evaporation reactions by using a 150 MeV ³²S beam on a ²⁸Si target. Beta-delayed protons were measured by a charged-particle telescope detector. The observed decay pattern was used to construct the level scheme of ⁵⁷Cu and to extract the beta feeding distribution. The experimental results are compared with shell-model calculations. An erratum to this article is available at .     

Collective phenomena in heavy ion collisions

Collective flow from ultra-relativistic heavy ion collisions is an important hadronic observable sensitive to the early stages of system evolution. We have calculated flow components from a tilted, ellipsoidally expanding source. We also reviewed the recent experimental techniques used for calculation of the v _nFourier coefficients and pointed out a few possible problems connected to these techniques, which may lead to serious inaccuracy in the flow analysis.     

Pion condensation in heavy ion collisions

We calculate the pion spectrum in dense nuclear matter for finite temperatures. The critical temperatureT _c(ρ) that marks the beginning of a second order phase transition due to pion condensation is given in a phase diagram. We show that in heavy ion collisions, pion condensation should occur, leading to an enhancement in the formation of nuclear shock waves.     

Resonances and Correlations in heavy ion collisions

Results of resonance production from RHIC at $\sqrt {s_{NN} } = 200$ GeV and SPS at $\sqrt {s_{NN} } = 17$ GeV are presented and discussed in context with a possible hadronic interaction phase after chemical freeze-out in a heavy ion collision. Momentum spectra and yield may change due to rescattering and regeneration of hadronic decaying resonances. We compare the decays of resonances into leptonic and hadronic channels in order to discuss the impact of a the possible medium modifications on the resonance and their decay products. Microscopic model calculations predicts that high momentum resonances are almost unaffected by the hadronic medium. This raises the idea of using high transverse momentum selection criteria in order to extract resonances created at an early stage of a heavy ion collision.     

Kaon flow in heavy ion collisions

Using transport models that include explicitly the kaon degree of freedom, we have studied kaon flow, i.e., the average kaon transverse momentum as a function of rapidity, and the associated flow parameter in heavy ion collisions at both SIS and AGS energies. It is found that the pattern of kaon flow in heavy ion collisions is sensitive to the kaon potential used in the model and thus provides a useful means for studying the kaon properties in nuclear medium.     

Event-by-event fluctuations in heavy ion collisions

We discuss the physics underlying event-by-event fluctuations in relativistic heavy ion collision. We will emphasize how the fluctuations of particle ratios can be utilzed to explore the properties of the matter created in these collisions. In particular we will argue that the fluctutions of the ratio of positively over negatively charged particles may serve as a unique signature for the Quark-Gluon Plasma.     

Nuclear flow in heavy ion collisions

Short overview of the flow phenomenon from the low upto relativistic heavy ion energies is given. Strict difference between spectator and participant flow is emphased. The latter is described by the modification of the nuclear blast model. Thermal source expanding in a plane perpendicular to the line connecting the centers of projectile and target is assumed. Observed dependences of squeeze-out, side-splash and of mean transverse-energy in relativistic heavy-ion collisions on the particle's mass are reproduced. Partioning of initial projectile energy into thermal and compressional parts in²⁰⁹Bi(1 GeV/u)+²⁰⁸Pb and¹⁹⁷Au(150–800 MeV/u)+¹⁹⁷Au collisions is discussed.Invited lecture given at the International School-Workshop Relativistic Heavy-Ion Physics, Prague (Czech Republic), 19–23 September 1994.Experimental data obtained at Bi+Pb collisions [6] are the result of the group effort. The contribution of V. Wagner, M. Pachr, Yu. G. Sobolev, R. Simon, S. Hlava, M. umbera as well as of my student R. Pleska, who carried out most of the fits, is gratefully acknowledged. This work was supported by the Granting Agency of the Czech Republic under contract No. 202/93/1144. A.K. gratefully acknowledges support from EC during his stay at KVI Groningen, where part of this work was done.