Electromagnetic radiation from hot and dense hadronic matter

The modifications of hadronic masses and decay widths at finite temperature and baryon density are investigated using a phenomenological model of hadronic interactions in the Relativistic Hartree Approximation. We consider an exhaustive set of hadronic reactions and vector meson decays to estimate the photon emission from hot and dense hadronic matter. The reduction in the vector meson masses and decay widths is seen to cause an enhancement in the photon production. It is observed that the effect of p-decay width on photon spectra is negligible. The effects on dilepton production from pion annihilation are also indicated.     

Relativistic hadronic cascade analysis of two-pion Bose-Einstein correlation for Si + Au collisions at AGS energy

Using a simple kinetic model we study whether a pion condensate can be formed during the hadronization of the quark-gluon plasma in ultra-relativistic heavy-ion collisions. Unless the effective mass of the hadronizing pions is close to zero, no onset of the Bose-Einstein condensation is observed. The constraints on the condensation process coming from the requirement of the entropy increase are discussed in detail.     

Estimation of transport coefficients of dense hadronic and quark matter

In this study, we calculated transport coefficients including the shear viscosity and electrical conductivity relative to the density of dense hadronic and quark matter. By considering the simple massless limit for the quark matter and two different effective models for the hadronic matter, we estimated the transport coefficients of the two phases separately. Accordingly, density profiles of the transport coefficients were depicted in two parts: the phase-space part and the relaxation time part. From calculating the shear viscosity to density ratio, we also explored the nearly perfect fluid domain of the quark and hadronic matter.     

On the production of hidden-flavored hadronic states at high energy

I discuss the production mechanism of hidden-flavored hadrons at high energy. Using e+e-collisions and light-meson pair production in high energy exclusive processes, I demonstrate that hidden quark pairs do not necessarily participate in short-distance hard scattering. Implications are then explored in a few examples. Finally, I discuss the production mechanism of X(3872) in hadron collisions, where some misunderstandings have arisen in the literature.     

Probing dense and hot matter with low-mass di-leptons and photons

Results on low-mass di-leptons, covering the very broad energy range from the BEVALAC up to the SPS, are reviewed. The emphasis is on the open questions raised by the intriguing results obtained so far and the prospects for addressing them in the near future with the second generation of experiments, in particular HADES, NA60 and PHENIX. Arrival of the final proofs: 26 June 2005 Work supported by the Israeli Science Foundation     

The spectrum of hot hadronic matter and finite-temperature QCD sum rules

The sum rules method, which is widely used for the investigation of the resonance physics within the QCD framework, is generalized to the case of finite temperatures and densities. Conditions are formulated under which this method is quite efficient for the determination of the spectrum of hadronic matter at T ≠ 0. The finite-temperature QCD sum rules are analysed in the vector channel J^PC = 1⁻⁻. Sharp and qualitative changes in the spectrum are found in the temperature interval T = 130–150 MeV. It is naturally explained as a consequence of the disappearance of confinement at the temperature T_c = 140±10 MeV. The finite-temperature QCD sum rules also show that the restoration of chiral symmetry at some temperature T_F cannot precede deconfinement. In the case T_F⪢T_c the sum rules indicate that the intermediate phase at T_c<T<T_F is dominated by quasi-free quarks with nonzero dynamical mass m_q^T ≈ 300 MeV.     

(3+1)-dimensional relativistic hydrodynamical expansion of hot and dense matter in ultra-relativistic nuclear collision

A full (3+1)-dimensional calculation using Lagrangian hydrodynamics is proposed for relativistic nuclear collisions. This calculation enables us to evaluate the anisotropic flow of the hadronic matter which appears in non-central and/or asymmetrical relativistic nuclear collisions. Applying hydrodynamical calculations to the deformed uranium collisions in the AGS energy region, we discuss the nature of the space-time structure and particle distributions in detail. Received: 18 July 2000 / Published online: 23 October 2000     

Generation of beams of charged particles with transverse energy

The paper describes the operation and construction of an electron gun designed to form beams with variable transverse energy and a variable spread of magnetic moments. Transverse energy is acquired by the electrons as the beam passes through a weakly non-adiabatic magnetic step, and in an adiabatic motion through a growing magnetic field. The small spread of magnetic moments of the beam electrons is achieved by fulfilling the so-called focusing conditions which ensure that the spread of moments resulting from different initial radii of the particles is compensated by their initial radial velocities.     

Charmonium production in hadronic experiments at an energy of 70 GeV

The production of charmonium states in hadronic experiments is considered in the third order in the strong-coupling constant. It is shown that some significant difficulties that arise if such reactions are treated in the leading order can be overcome within this approach. In particular, the method applied here makes it possible to obtain transverse-momentum distributions of final-state charmonia. Also, the experimental observation of a χ _c1 meson, which cannot be produced in the lowest order in α _s , is then explained in a natural way.     

Bound states of light and heavy quarks in hot hadronic matter

The correlators of currents \(\bar q\) Q,γ _v γ ₅ Q,q andQ being correspondingly light and heavy quark fields, in hot hadronic matter are investigated by means of finite temperature QCD sum rules. AtT? 100 MeV the modification of the effective spectrum parameters takes place, similar to that found earlier in the correlators of light quark currents. AtT?150 MeV the form of the spectrum is obtained, which indicates an appearance in hadronic matter of quasifree quarks with nonzero mass being fixed by the value of the quark condensate 〈 \(\bar q\) q〉 (T).     

Two problems concerning hot hadronic matter and high energy collisions (Equilibrium formation,plasma deflagration)

This paper addresses two questions concerning the hydrodynamical approach to high energy collisions producing large multiplicities of hadrons. The first one concerns the difficulty of understanding in terms of successive parton interactions the formation of local thermal equilibrium for the small and short-lived blobs of excited hadronic matter created in such collisions. We argue that the number of successive parton interactions is not the only relevant factor for equilibrium formation, another factor being the early randomization present in all experiments which observe a subsystem of the complete final state and average over many unobserved degrees of freedom. This conjecture helps to understand the high degree of universality of hadronic jets and the fact that quite different dynamical models manage to describe the same data. The second problem concerns the hadronization of a blob of quark-gluon plasma as could be produced in a very high energy collision. Assuming the transition of plasma to hadron gas to have high latent heat, we show for small chemical potential that the plasma can deflagrate and convert a fraction of its latent heat into collective flow of the hadron gas. In such deflagrations very little entropy is produced, but the flow velocity of the hadron gas with respect to the plasma can be more than half of the velocity of light.     

Composition and equation of state of hot dense matter

The composition and equation of state of an equilibrium mixture of non-interacting baryons, pions and leptons is computed in the density range 10¹⁴–10^15.5 g/cm³ for two values of the entropy per baryon, S=1 and 2. These parameters are chosen because of their possible importance in the supernova explosion problem. The threshold densities for the appearance of hyperons are found to be lowered compared to the zero temperature case.     

Simulation of energy scan of pion interferometry in central Au+Au collisions at relativistic energies

We present a systematic analysis of two-pion interferometry for the central Au+Au collisions at √s_NN=3, 5, 7, 11, 17, 27, 39, 62, 130 and 200 GeV/c with the help of a multiphase transport (AMPT) model. Emission source-size radius parameters R_long, R_out, R_side and the chaotic parameter λ are extracted and compared with the experimental data. Transverse momentum and azimuthal angle dependencies of the HBT radii are also discussed for central Au+Au collisions at 200 GeV/c. The results show that the HBT radii in central collisions do not change much above 7 GeV/c. For central collisions at 200 GeV/c, the radii decrease with the increasing of transverse momentum p_T but are not sensitive to the azimuthal angle. These results provide a theoretical reference for the energy scan program of the RHIC-STAR experiment.     

Measurement of energy of medium-mass and heavy cosmic-ray nuclei by a specific energy deposition at the maximum of hadron showers in dense matter

The possibility of measuring the energy of cosmic-ray nuclei (for energies higher than 1 TeV) by means of recording the greatest specific energy deposition in hadron showers generated in dense matter is investigated. This method makes it possible to improve the accuracy of energy measurements by thin calorimeters in studying high-energy cosmic rays at high altitudes. Attainable accuracies in measuring energy are considered for the cases of light and heavy nuclei. The results of a relevant simulation are compared with data from the Kosmos-1713 satellite-borne experiment.