多粒子玻色关联对夸克胶子等离子体颗粒源的检测

对由空间离散分布的夸克－胶子等离子体热滴发射的玻色子，本文进行了多粒子玻色关联的蒙特卡罗模拟研究．与两粒子玻色关联相比，多粒子玻色关联能够更敏感地检测玻色子发射源的颗粒性．通过对多粒子可观测量的分析，能够获得夸克－胶子等离子体和强子气体混合相存在的检测信号．     

Quantum clan model description of Bose-Einstein correlations

We propose a novel numerical method of <i≯modeling</i≯ Bose–Einstein correlations (BEC) observed among identical (bosonic) particles produced in multiparticle production reactions. We argue that the most natural approach is to work directly in the momentum space in which the Bose statistics of secondaries reveals itself in their tendency to bunch in a specific way in the available phase space. Because such procedure is essentially identical to the clan model of multiparticle distributions proposed some time ago, therefore we call it the <i≯Quantum Clan Model</i≯.     

Verification of the model of a collision of a 800-GeV proton with an emulsion-nucleus tube

The production of quark-gluon plasma is discussed within the hydrodynamic theory of multiparticle hadron production in head-on collisions of nucleons with nucleons and nuclei. In searches for collisions of a proton with a tube of a track-emulsion nucleus, the use of parametrically invariant quantities is proposed. An experimental verification of statistical models involving qualitatively different pseudorapidity distributions of weakly ionizing secondary particles is performed. The results of this verification are discussed.     

Fluctuations and correlations in STAR

The study of correlations and fluctuations can provide evidence for the production of the quark-gluon plasma (QGP) in relativistic heavy-ion collisions. Various theories predict that the production of a QGP phase in relativistic heavy-ion collisions could produce significant event-by-event correlations and fluctuations in transverse momentum, multiplicity, etc. Some of the recent results using STAR at RHIC will be presented along with results from other experiments at RHIC. The focus is on forward-backward multiplicity correlations, balance function, charge and transverse-momentum fluctuations, and correlations.     

Two-photon correlations as the signal of a sharp transition in quark-gluon plasma

The photon production arising due to time variation of a medium has been considered. The Hamilton formalism for photons in a time-variable medium (plasma) has been developed with application to inclusive photon production. The results have been used for calculation of the photon production in the course of the transition from a quark-gluon phase to a hadronic phase in relativistic heavy-ion collisions. The relative strength of the effect and the specific two-photon correlations have been evaluated. It is demonstrated that the opposite-side two-photon correlations are indicative of a sharp transition from the quark-gluon phase to hadrons.     

柱形夸克胶子等离子体的2π干涉学检测

在2п干涉学中,对不同的п源2п,关联函数可以是不同的. 如果在相对论重离子碰撞中出现柱形夸克胶子等离子体,п介子将从柱形夸克胶子等离子体表面发射,此时2п关联函数将出现一种特殊的振荡行为.这种振荡行为可以用来探明夸克胶子等离子体的存在性,同时也是相对论重离子碰撞中出现夸克胶子等离子体的一个信号.     

Test of Quark-Gluon Plasma of Cylinder Shape by Two-Pion Interferometry

The two-pion correlation functions are different for some pion source distributions in two-pion interferometry.If quark-gluon plasma of cylindrical shape is produced in relativistic heavy ion collisions, the pion mesons will emit from the surface of quark-gluon plasma of cylindrical shape and the corresponding correlation function will have a special oscillation behavior. The oscillation behavior can be used to verify the existence of quark-gluon plasma and is also a signature of the appearance of quark-gluon plasma.     

高能重离子碰撞中有QGP形成时的多π关联信号

对高能重离子碰撞中有夸克–胶子等离子体(QGP)形成时的多粒子玻色–爱因斯坦关联进行了分析.通过考查多π关联平均强度随事件π多重数的变化表明,当有QGP产生时,多π关联平均强度在某一高多重数区域会有明显的上升;这种信号能够敏感地检测在高能重离子碰撞中少数有QGP形成的高π多重数事件.     

An Explanation of a Phenomenon in Relativistic Heavy-Ion Collisions

The multi-source pion interferometry in relativistic heavy-ion collisions is presented and two-source models for hadron gas and hadron gas plus quark-gluon plasma are proposed. The models can resolve the HBT puzzle. For the same $q$ and different direction of \bar{q}, the two-pion correlation functions show characteristic oscillation behaviors, which may be used to distinguish the two-source models. Our research also showes that the multi-source pion correlations can resolve the HBT puzzle.     

QCD at finite temperature

Quantum chromodynamics is studied at finite temperatures and densities using the temperature Green functions method. For the Green functions the renormalized Schwinger-Dyson equations are obtained and their qualitative properties are discussed. The equality of the renormalization constants for the equations obtained at T, μ ≠ 0 with those for quantum field theory is pointed out. General properties of the gluon polarization tensor are investigated at T, μ ≠ 0. The temperature Green functions are calculated within the one-loop approximation using both relativistic and axial gauges. The fulfilment of the Slavnov-Taylor identities is verified. The asymptotic behaviour of the polarization tensor at T, μ ≠ 0 is established and the excitation spectrum of quark-gluon plasma is found. Both Fermi and Bose excitations are considered and the gauge invariance of the spectra is demonstrated. The renormalization group extension of the dispersion laws into the regions of high temperatures and densities is presented. The exact representation of the thermodynamical potential in QCD is found in terms of the temperature Green functions. For the quark-gluon plasma the thermodynamical potential is calculated with the g³-term taken into account. The equation of state of the hot quark-gluon plasma is found and its properties are discussed. The complete evolutional diagram of the hadronic matter is outlined. The phase curve asymptotics, which put bounds on the quark-gluon plasma domain, are found for the two limiting cases (μ = 0, T → T₀; T = 0, μ → μ₀). The phase transition of the hot quark-gluon plasma placed in external Abelian field is studied. The instability of such plasma has been found and the program of its stabilization is indicated. The infrared behaviour of the non-Abelian gauge theory is studied for finite temperatures when power divergencies are essential. The propagator of transverse gluons is shown to be singular for momenta |p| ˜ g²T and this cannot be avoided by summing the simplest bubble chains. The infrared asymptotic behaviour of the tree-gluon vertex is found and the results obtained are checked using the Slavnov-Taylor identities. The Green functions asymptotics found indicate either an instability of the quark-gluon plasma in the infrared momentum domain or the inconsistency of the perturbational methods. A non-perturbative approach to the infrared problem in QCD is developed within the axial gauge. The closed equations for the structure functions that determine the gluon polarization tensor are obtained by using the Slavnov-Taylor identities to found approximately the three-gluon vertex. It is shown that the solution of the equations obtained by iterations does not remove the infrared singularity from the temperature Green functions. The nonperturbative solution of such equations is discussed.     

The role of multiparticle correlations and Cooper pairing in the formation of molecules in an ultracold gas of Fermi atoms with a negative scattering length

The influence of multiparticle correlation effects and Cooper pairing in an ultracold Fermi gas with a negative scattering length on the formation rate of molecules is investigated. Cooper pairing is shown to cause the formation rate of molecules to increase, as distinct from the influence of Bose-Einstein condensation in a Bose gas on this rate. This trend is retained in the entire range of temperatures below the critical one.     

Photons,Dileptons and Hadrons Produced by Quark-Gluon Plasma

Altarelli-Parisi equations in perturbative QCD are applied to getting evolution equations of quark-gluon plasma. The equations describe the cooling process of quark-gluon plasma by emitting photons. The numbers of observable photons and dileptons are calculated directly from these equations. The cooled quark-gluon plasma hadronizes and the production rates of hadrons are calculated with separable scalar confinement potentials.     

Photon production from baryon rich quark-gluon plasma

We study high energy photon production from a quark-gluon plasma at finite baryon density. We find that the photon production spectrum from the quark-gluon plasma maintained at constant temperature is only mildly dependent on the quark chemical potential.     

Measuring quark-gluon-plasma thermalization time with dileptons

We calculate the medium dilepton yield from a quark-gluon plasma which has a time-dependent local momentum-space anisotropy. A phenomenological model for the hard momentum scale, p(hard)(tau), and plasma anisotropy parameter, xi(tau), is constructed which interpolates between longitudinal free streaming at early times (tautau(iso)). We show that high-energy dilepton production is sensitive to the plasma isotropization time, tau(iso), and can therefore be used to experimentally determine the time of onset for hydrodynamic expansion of a quark-gluon plasma and the magnitude of expected early-time momentum-space anisotropies.     

Structural properties of the condensate in two-dimensional mesoscopic systems of strongly correlated excitons

A two-dimensional mesoscopic Bose system of dipoles in a 2D trap is considered using computer simulation by the quantum path-integral Monte Carlo method. The model describes a rarefied system of spatially indirect excitons in a confining potential. Bose condensation in the system and its superfluid and structural properties are studied over a wide range of interparticle spatial correlations, from an almost ideal Bose gas to the regime of a strongly correlated system. It is found that, at strong interparticle spatial correlations, particles in the condensate form a crystal-like structure. In this case, the spatial correlations of particles in the condensate are less pronounced than the correlations of noncondensed particles. The effect of recurrent crystallization is observed in the regime of strong interparticle correlations.     

Physics of collisions between ultrarelativistic nuclei: Manifestation of collective effects

Experimental results concerning heavy-ion collisions studied by means of the Relativistic Heavy-Ion Collider (RHIC) at an energy of 100 GeV per nucleon and showing manifestations of collective effects are surveyed. These effects are interpreted as a consequence of the formation of a dense thermalized medium referred to as quark-gluon plasma (strongly interacting quark-gluon plasma, quark-gluon matter, parton medium). An azimuthal anisotropy of particles, the suppression of the particle yield at high transverse momenta in relation to proton-proton collisions, and a change in the shape of the peak from a hadron jet in nucleus-nucleus collisions are spectacular manifestations of collective effects.     

Entropy and multi-particle correlations in two-dimensional lattice gases

We analyse the statistical entropy of two-dimensional lattice-gas models in terms of the contributions which arise from space correlations of increasing order. The “residual multiparticle entropy”, defined as the contribution to the excess entropy that is associated with correlations involving more than two particles, is calculated for the Ising and Coulomb lattice gases. The thermodynamic behaviour of the residual multiparticle entropy is then discussed in relation to the phase diagram of the model and the existence of underlying signatures of order-disorder phase transitions is also investigated. Received 31 December 1998 and Received in final form 8 March 1999     

Effect of partonic "wind" on charm quark correlations in high-energy nuclear collisions

In high-energy collisions, massive heavy quarks are produced back to back initially and they are sensitive to early dynamical conditions. The strong collective partonic wind from the fast expanding quark-gluon plasma created in high-energy nuclear collisions modifies the correlation pattern significantly. While the hot and dense medium in collisions at the BNL Relativistic Heavy Ion Collider (sqrt[_s{NN}]=200 GeV) can only smear the initial back-to-back D_D correlation, a clear and strong near side D_D correlation is expected at the CERN Large Hadron Collider (sqrt[_s{NN}]=5500 GeV). This is considered as a signature for the strongly coupled quark-gluon plasma.