arXiv subjects

Iu. A. Karpenko

Publications and source records attributed to Iu. A. Karpenko.

28 records · Page 2Linked to original sources

arXiv2009

Is early thermalization really needed in A+A collisions?

In this note we review our ideas, first published in year 2006, and corresponding results, including the new ones, which show that whereas the assumption of (partial) thermalization in relativistic A+A collisions is really crucial to explain soft physics observables, the hypotheses of {\it early} thermalization at times less than 1 fm/c is not necessary. The reason for the later conclusion is that the initial transverse flow in thermal matter as well as its anisotropy, leading to asymmetry of the transverse momentum spectra, could be developed at pre-thermal, either partonic or classical field - Glasma, stage with even more efficiency than in the case of very early perfect hydrodynamics. Such radial and elliptic flows develop no matter whether a pressure already established. The general reason for them is an essential finiteness of the system in transverse direction.

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arXiv2009

Kinetics vs hydrodynamics: generalization of Landau/Cooper-Frye prescription for freeze-out

The problem of spectra formation in hydrodynamic approach to A+A collisions is considered within the Boltzmann equations. It is shown analytically and illustrated by numerical calculations that the particle momentum spectra can be presented in the Cooper-Frye form despite freeze-out is not sharp and has the finite temporal width. The latter is equal to the inverse of the particle collision rate at points $(t_σ({\bf r},p),{\bf r})$ of the maximal emission at a fixed momentum $p$. The set of these points forms the hypersurfaces $t_σ({\bf r},p)$ which strongly depend on the values of $p$ and typically do not enclose completely the initially dense matter. This is an important difference from the standard Cooper-Frye prescription (CFp), with a common freeze-out hypersurface for all $p$, that affects significantly the predicted spectra. Also, the well known problem of CFp as for negative contributions to the spectra from non-space-like parts of the freeze-out hypersurface is naturally eliminated in this improved prescription.

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arXiv2008

Hydro-kinetic approach to relativistic heavy ion collisions

We develop a combined hydro-kinetic approach which incorporates a hydrodynamical expansion of the systems formed in \textit{A}+\textit{A} collisions and their dynamical decoupling described by escape probabilities. The method corresponds to a generalized relaxation time ($τ_{\text{rel}}$) approximation for the Boltzmann equation applied to inhomogeneous expanding systems; at small $τ_{\text{rel}}$ it also allows one to catch the viscous effects in hadronic component - hadron-resonance gas. We demonstrate how the approximation of sudden freeze-out can be obtained within this dynamical picture of continuous emission and find that hypersurfaces, corresponding to a sharp freeze-out limit, are momentum dependent. The pion $m_{T}$ spectra are computed in the developed hydro-kinetic model, and compared with those obtained from ideal hydrodynamics with the Cooper-Frye isothermal prescription. Our results indicate that there does not exist a universal freeze-out temperature for pions with different momenta, and support an earlier decoupling of higher $p_{T}$ particles. By performing numerical simulations for various initial conditions and equations of state we identify several characteristic features of the bulk QCD matter evolution preferred in view of the current analysis of heavy ion collisions at RHIC energies.

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arXiv2007

Fast hadron freeze-out generator, part II: noncentral collisions

The fast Monte Carlo procedure of hadron generation developed in our previous work is extended to describe noncentral collisions of nuclei. We consider different possibilities to introduce appropriate asymmetry of the freeze-out hyper-surface and flow velocity profile. For comparison with other models and experimental data we demonstrate the results based on the standard parametrizations of the hadron freeze-out hyper-surface and flow velocity profile assuming either a common chemical and thermal freeze-out or the chemically frozen evolution from chemical to thermal freeze-out. The C++ generator code is written under the ROOT framework and is available for public use at http://uhkm.jinr.ru/

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arXiv2007

Thermal Dileptons at LHC

We predict dilepton invariant-mass spectra for central 5.5 ATeV Pb-Pb collisions at LHC. Hadronic emission in the low-mass region is calculated using in-medium spectral functions of light vector mesons within hadronic many-body theory. In the intermediate-mass region thermal radiation from the Quark-Gluon Plasma, evaluated perturbatively with hard-thermal loop corrections, takes over. An important source over the entire mass range are decays of correlated open-charm hadrons, rendering the nuclear modification of charm and bottom spectra a critical ingredient.

hep-ph↗

arXiv2007

Pion spectra and HBT radii at RHIC and LHC

We describe RHIC pion data in central A+A collisions and make predictions for LHC based on hydro-kinetic model, describing continuous 4D particle emission, and initial conditions taken from Color Glass Condensate (CGC) model.

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arXiv2006

A Fast Hadron Freeze-out Generator

We have developed a fast Monte Carlo procedure of hadron generation allowing one to study and analyze various observables for stable hadrons and hadron resonances produced in ultra-relativistic heavy ion collisions. Particle multiplicities are determined based on the concept of chemical freeze-out. Particles can be generated on the chemical or thermal freeze-out hypersurface represented by a parameterization or a numerical solution of relativistic hydrodynamics with given initial conditions and equation of state. Besides standard space-like sectors associated with the volume decay, the hypersurface may also include non-space-like sectors related to the emission from the surface of expanding system. For comparison with other models and experimental data we demonstrate the results based on the standard parameterizations of the hadron freeze-out hypersurface and flow velocity profile under the assumption of a common chemical and thermal freeze-out. The C++ generator code is written under the ROOT framework and is available for public use at http://uhkm.jinr.ru/.

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arXiv2006

Hydrodynamic source with continuous emission in Au+Au collisions at $\sqrt{s}=200$ GeV

We analyze single particle momentum spectra and interferometry radii in central Au+Au collisions at RHIC within a hydro-inspired parametrization accounting for continuous hadron emission through the whole lifetime of hydrodynamically expanding fireball. We found that a satisfactory description of the data is achieved for a physically reasonable set of parameters when the emission from non space-like sectors of the enclosed freeze-out hypersurface is fairly long: $ 9$ fm/c. This protracted surface emission is compensated in outward interferometry radii by positive $r_{out} - t$ correlations that are the result of an intensive transverse expansion. The main features of the experimental data are reproduced: in particular, the obtained ratio of the outward to sideward interferometry radii is less than unity and decreases with increasing transverse momenta of pion pairs. The extracted value of the temperature of emission from the surface of hydrodynamic tube approximately coincides with one found at chemical freeze-out in RHIC Au+Au collisions. A significant contribution of the surface emission to the spectra and to the correlation functions at relatively large transverse momenta should be taken into account in advanced hydrodynamic models of ultrarelativistic nucleus-nucleus collisions.

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arXiv2005

Ellipsoidal flows in relativistic hydrodynamics of finite systems

A new class of 3D anisotropic analytic solutions of relativistic hydrodynamics with constant pressure is found. We analyse, in particular, solutions corresponding to ellipsoidally symmetric expansion of finite systems into vacuum. They can be utilized for relativistic description of the system evolution in thermodynamic region near the softest point and at the final stage of the hydrodynamic expansion in A+A collisions. The solutions can be used also for testing of numerical hydrodynamic codes solving relativistic hydrodynamic equations for anisotropic expansion of finite systems

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arXiv2005

Quasi-inertial ellipsoidal flows in relativistic hydrodynamics

We search for non-trivial relativistic solutions of the hydrodynamic equations with quasi-inertial flows such as in the Bjorken-like models. The problem is analyzed in general and the known results are reproduced by a method proposed. A new class of 3D anisotropic analytic solutions with quasi-inertial property is found. An ellipsoidal generalization of the spherically symmetric Hubble flow with constant pressure is proposed as a particular case. The relativistic expansion of finite systems into vacuum is also described within this class. A region of applicability and possible utilization of the new solutions for processes of A+A collisions is discussed.

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