38 research outputs found
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 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, 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 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 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.