Generalizing Phi-measure of event-by-event fluctuations in high-energy heavy-ion collisions

The Phi-measure of event-by-event fluctuations in high-energy heavy-ion collisions corresponds to the second moment of the fluctuating quantity distribution of interest. It is shown that the measure based on the third moment preserves the properties of Phi but those related to the higher moments do not. In particular, only the second and third moment measures are intensive as thermodynamic quantities. The Phi_2- and Phi_3-measure of p_T-fluctuations are computed for the hadron gas in equilibrium and the results are analyzed in context of the experimental data.Comment: 6 pages, 2 figures, minor corrections, to appear in Phys. Lett.

Color filamentation in ultrarelativistic heavy-ion collisions

We study color fluctuations in the quark-gluon plasma produced at the early stage of nucleus-nucleus collision at RHIC or LHC. The fluctuating color current, which flows along the beam, can be very {\it large} due to the strong anisotropy of the parton momentum distribution. A specific fluctuation, which splits the parton system into the current filaments parallel to the beam direction, is argued to grow exponentially. The physical mechanism responsible for the phenomenon, which is known as a filamentation instability, is discussed.Comment: 4 pages, no macro

Hadronic matter compressibility from event-by-event analysis of heavy-ion collisions

We propose a method to measure the hadronic matter compressibility by means of the event-by-event analysis of heavy-ion collisions at high energies. The method, which utilizes the thermodynamical relation between the compressibility and the particle number fluctuations, requires a simultaneous measurement of the particle source size, temperature and particle multiplicity.Comment: 5 pages, no macro

Correlation of transverse momentum and multiplicity in a superposition model of nucleus-nucleus collisions

In p-p collisions the average transverse momentum is known to be correlated with the multiplicity of produced particles. The correlation is shown to survive in a superposition model of nucleus-nucleus collisions. When properly parameterized, the correlation strength appears to be independent of the collision centrality - it is the same in p-p and central A-A collisions. However, the correlation is strongly suppressed by the centrality fluctuations.Comment: 7 pages, 2 figures, minor corrections, to appear in Phys. Rev.

Momentum Broadening of a Fast Parton in a Perturbative Quark-Gluon Plasma

The average transverse momentum transfer per unit path length to a fast parton scattering elastically in a perturbative quark-gluon plasma is related to the radiative energy loss of the parton. We first calculate the momentum transfer coefficient $\hat q$ in terms of a classical Langevin problem and then define it quantum-mechanically through scattering matrix element. After treating the well known case of a quark-gluon plasma in equilibrium we consider an off-equilibrium unstable plasma. As a specific example, we treat the two-stream plasma with unstable modes of longitudinal chromoelectric field. In the presence of the instabilities, $\hat q$ is shown to exponentially grow in time.Comment: Updated version containing an analysis of insufficiencies in previous calculations of momentum broadening in unstable plasma

Deciphering Azimuthal Correlations in Relativistic Heavy-Ion Collisions

We discuss various sources of azimuthal correlations in relativistic heavy-ion collisions. The integral measure Phi is applied to quantify the correlations. We first consider separately the correlations caused by the elliptic flow, resonance decays, jets and transverse momentum conservation. An effect of randomly lost particles is also discussed. Using the PYTHIA and HIJING event generators we produce a sample of events which mimic experimental data. By means of kinematic cuts and particle's selection criteria, the data are analyzed to identify a dominant source of correlations.Comment: 8 pages, minor corrections, to appear in Phys. Rev.

Towards reliable calculations of the correlation function

The correlation function of two identical pions interacting via Coulomb potential is computed for a general case of anisotropic particle's source of finite life time. The effect of halo is taken into account as an additional particle's source of large spatial extension. Due to the Coulomb interaction, the effect of halo is not limited to very small relative momenta but it influences the correlation function in a relatively large domain. The relativistic effects are discussed in detail and it is argued that the calculations have to be performed in the center-of-mass frame of particle's pair where the (nonrelativistic) wave function of particle's relative motion is meaningful. The Bowler-Sinyukov procedure to remove the Coulomb interaction is tested and it is shown to significantly underestimate the source's life time.Comment: 18 pages, presented at XIth International Workshop on Correlation and Fluctuation in Multiparticle Production, Hangzhou, China, November 21-24, 200

Strongly and Weakly Unstable Anisotropic Quark-Gluon Plasma

Using explicit solutions of the QCD transport equations, we construct an effective potential for an anisotropic quark-gluon plasma which under plausible assumptions holds beyond the Hard Loop approximation. The configurations, which are unstable in the linear response approach, are characterized by a negative quadratic term of the effective potential. The signs of higher order terms can be either negative or positive, depending on the parton momentum distribution. In the case of a Gaussian momentum distribution, the potential is negative and unbound from below. Therefore, the modes, which are unstable for gauge fields of small amplitude, remain unstable for arbitrary large amplitudes. We also present an example of a momentum distribution which gives a negative quadratic term of the effective potential but the whole potential has a minimum and it grows for sufficiently large gauge fields. Then, the system is weakly unstable. The character of the instability is important for the dynamical evolution of the plasma system.Comment: 13 pages, 1 figure, revised, to appear in Phys. Rev.

Density Fluctuations in the Quark-Gluon Plasma

Using the kinetic theory we discuss how the particle and energy densities of the quark-gluon plasma fluctuate in a space-time cell. The fluctuations in the equilibrium plasma and in that one from the early stage of ultrarelativistic heavy-ion collisions are estimated. Within the physically interesting values of the parameters involved the fluctuations appear sizeable in both cases.Comment: 8 pages, no macro

Chemical fluctuations in high-energy nuclear collisions

Fluctuations of the chemical composition of the hadronic system produced in nuclear collisions are discussed using the $\Phi-$measure which has been earlier applied to study the transverse momentum fluctuations. The measure is expressed through the moments of the multiplicity distribution and then the properties of $\Phi$ are discussed within a few models of multiparticle production. A special attention is paid to the fluctuations in the equilibrium ideal quantum gas. The system of kaons and pions, which is particularly interesting from the experimental point of view, is discussed in detail.Comment: 8 pages, 4 figures, revised version to appear in Phys. Lett.