arXiv subjects

S. V. Akkelin

Publications and source records attributed to S. V. Akkelin.

33 records · Page 2Linked to original sources

arXiv2007

Characteristic length of dynamical reduction models and decay of cosmological vacuum

Characteristic length of mass density resolution in dynamical reduction models is calculated utilizing energy conservation law and viable cosmological model with decreasing energy density of vacuum (dark energy density). The value found, $ \sim 10^{-5}$ cm, numerically coincides with phenomenological spatial short-length cutoff parameter introduced in the Ghirardi-Rimini-Weber model. It seems that our results support the gravity induced mechanism of dynamical reduction.

quant-ph↗

arXiv2006

HBT search for new states of matter in A+A collisions

A method allowing studies of the hadronic matter at the early evolution stage in A+A collisions is developed. It is based on an interferometry analysis of approximately conserved values such as the averaged phase-space density (APSD) and the specific entropy of thermal pions. The plateau found in the APSD behavior vs collision energy at SPS is associated, apparently, with the deconfinement phase transition at low SPS energies; a saturation of this quantity at the RHIC energies indicates the limiting Hagedorn temperature for hadronic matter. It is shown that if the cubic power of effective temperature of pion transverse spectra grows with energy similarly to the rapidity density (that is roughly consistent with experimental data), then the interferometry volume is inverse proportional to the pion APSD that is about a constant because of limiting Hagedorn temperature. This sheds light on the HBT puzzle.

nucl-th↗

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.

nucl-th↗

arXiv2005

Interferometry search for new forms of matter in A+A collisions

nucl-th↗

arXiv2004

Phase-space densities and effects of resonance decays in hydrodynamic approach to heavy ion collisions

A method allowing analysis of the overpopulation of phase-space in heavy ion collisions in a model independent way is proposed within the hydrodynamic approach. It makes it possible to extract a chemical potential of thermal pions at freeze out irrespective of the form of freeze-out (isothermal) hypersurface in Minkowski space and transverse flows on it. The contributions of resonance (with masses up to 2 GeV) decays to spectra, interferometry volumes and phase-space densities are calculated and discussed in detail. The estimates of average phase-space densities and chemical potentials of thermal pions are obtained for SPS and RHIC energies. They demonstrate that multibosonic phenomena at those energies might be considered as a correction factor rather than as a significant physical effect. The analysis of the evolution of the pion average phase-space density in chemically frozen hadron systems shows that it is almost constant or slightly increases with time while the particle density and phase-space density at each space point drops down rapidly during the system's expansion. We found that, unlike the particle density, the average phase-space density has no direct link to the freeze-out criterion and final thermodynamic parameters, being connected rather to the initial phase-space density of hadronic matter formed in relativistic nucleus-nucleus collisions.

nucl-th↗

arXiv2004

Observables and initial conditions for self-similar ellipsoidal flows

Single-particle spectra and two-particle Bose-Einstein correlation functions are determined analytically utilizing a self-similar solution of non-relativistic hydrodynamics for ellipsoidally-symmetric, expanding fireballs, by assuming that the symmetry axes of the ellipsoids are tilted in the frame of the observation. The directed, elliptic and third flows are calculated analytically. The mass dependences of the slope parameters in the principal directions of the expansion, together with the mass and angular dependences of the HBT radius parameters, reflect directly the ellipsoidal properties of the flow.

hep-ph↗

arXiv2004

Sudden freeze-out vs continuous emission: duality in hydro-kinetic approach to A+A collisions

The problem of spectra formation in hydrodynamic approach to A+A collisions is discussed. It is analyzed in terms of the two different objects: distribution and emission functions. We show that though the process of particle liberation, described by the emission function, is, usually, continuous in time, the observable spectra can be also expressed by means of the Landau/Cooper-Frye prescription. We argue that such an approximate duality results from some symmetry properties that systems in A+A collisions reach to the end of hydrodynamic evolution and reduction of the collision rate at post hydrodynamic stage

nucl-th↗

arXiv2004

Pion entropy and phase-space densities in A+A collisions

We propose a method to estimate the entropy of thermal pions in A+A collisions irrespective of unknown form of freeze-out (isothermal) hypersurface and transverse flows developed. We analyse the average phase-space densities and entropies of the thermal pions vs their multiplicities and collision energies. The behaviour of these values apparently indicates the deconfinement and chiral phase transitions in relativistic nuclear-nucleus collisions

nucl-th↗

arXiv2003

Correlation search for coherent pion emission in heavy ion collisions

The methods allowing to extract the coherent component of pion emission conditioned by the formation of a quasi-classical pion source in heavy ion collisions are suggested. They exploit a nontrivial modification of the quantum statistical and final state interaction effects on the correlation functions of like and unlike pions in the presence of the coherent radiation. The extraction of the coherent pion spectrum from pi+pi-, pi+pi+ and pi-pi- correlation functions and single--pion spectra is discussed in detail for large expanding systems produced in ultra-relativistic heavy ion collisions.

nucl-th↗

arXiv2002

Reconstruction of Hadronization Stage in Pb+Pb Collisions at 158A GeV/c

Recent data on hadron multiplicities in central Pb+Pb collisions at 158A GeV/c at mid-rapidity are analyzed within the concept of chemical freeze-out. A non-uniformity of the baryon chemical potential along the beam axis is taken into account. An approximate analytical solution of the hydrodynamic equations for a chemically frozen Boltzmann-like gas is found. The Cauchy conditions for hydrodynamic evolution of the hadron resonance gas are fixed at the thermal freeze-out hypersurface from analysis of one-particle momentum spectra and HBT correlations. The proper time of chemical freeze-out and physical conditions at the hadronization stage, such as energy density and averaged transverse velocity, are found.

nucl-th↗

arXiv2002

On freeze-out problem in hydro-kinetic approach to A+A collisions

A new method for evaluating spectra and correlations in the hydrodynamic approach is proposed. It is based on an analysis of Boltzmann equations (BE) in terms of probabilities for constituent particles to escape from the interacting system. The conditions of applicability of Cooper-Frye freeze-out prescription are considered within the method. The results are illustrated with a non-relativistic exact solution of BE for expanding spherical fireball as well as with approximate solutions for ellipsoidally expanding ones.

nucl-th↗

arXiv2001

Simple solutions of fireball hydrodynamics for self-similar elliptic flows

Simple, self-similar, elliptic solutions of non-relativistic fireball hydrodynamics are presented, generalizing earlier results for spherically symmetric fireballs with Hubble flows and homogeneous temperature profiles. The transition from one dimensional to three dimensional expansions is investigated in an efficient manner.

hep-ph↗

arXiv1999

Thermodynamics of multi-boson phenomena

Using the method of locally equilibrium statistical operator we consider the thermalized relativistic quantum fields in an oscillatory trap. We compare this thermal picture of the confined boson gas with non-relativistic model of independent factorized sources. We find that they are equivalent in the limit of very large effective sizes $R$, more exactly, when the Compton wave length $1/m$ and thermal wave length $1/\sqrt{% mT}$ are much smaller than {\}$R$ . Under this conditions we study the influence of Bose condensation in finite volumes on the structure of the Wigner function, momentum spectra and correlation function.

nucl-th↗

arXiv1999

"Pion laser" phenomenon and other possible signatures of the DCC at RHIC and LHC energies

The decay of fireballs containing the disoriented chiral condensate (DCC) in A+A collisions has been analyzed. We found that the high phase-space density and probably the large final fireball volume are the favorable factors to extract a DCC signal from the thermal background. Both of these factors are expected to take place at RHIC and LHC energies. A coherent pion component then can be observed in pion spectra, in Bose-Einstein correlations and in distribution of the ratio of neutral to total pions.

nucl-th↗

arXiv1998

On final conditions in high energy heavy ion collisions

Motivated by the recent experimental observations, we discuss the freeze-out properties of the fireball created in central heavy ion collisions. We find that the freeze-out conditions, like temperature, velocity gradient near center of the fireball, are similar for different colliding systems and beam energies. This means that the transverse flow is stronger in the collisions of heavy nuclei than that of the light ones.

nucl-th↗