92 research outputs found
Sum rule of the correlation function
We discuss a sum rule satisfied by the correlation function of two particles
with small relative momenta. The sum rule, which results from the completeness
condition of the quantum states of the two particles, is first derived and then
we check how it works in practice. The sum rule is shown to be trivially
satisfied by free particle pair, and then there are considered three different
systems of interacting particles. We discuss a pair of neutron and proton in
the s-wave approximation and the case of the so-called hard spheres with the
phase shifts taken into account up to l=4. Finally, the Coulomb system of two
charged particles is analyzed.Comment: 18 pages, 18 figures, revised, to appear in Phys. Rev.
Femtoscopy of Pb-Pb and pp collisions at the LHC with the ALICE experiment
We report on the results of femtoscopic analysis of Pb-Pb collisions at
sqrt(s_NN)=2.76 TeV and pp collisions at sqrt(s)=0.9, 2.76 and 7 TeV with
identical pions and kaons. Detailed femtoscopy studies in heavy-ion collisions
at SPS and RHIC have shown that emission region sizes ("HBT radii") decrease
with increasing pair transverse momentum k_T, which is understood as a
manifestation of the collective behavior of matter. The trend was predicted to
persist at the LHC. The data from Pb-Pb collisions confirm the existence of a
flowing medium and provide strict constraints on the dynamical models. Similar
analysis is carried out for pp collisions for pions and kaons and qualitative
similarities to heavy-ion data are seen, especially in collisions producing
large number of particles. The observed trends give insight into the soft
particle production mechanism in pp collisions. 3D radii were also found to
universally scale with event multiplicity in heavy-ion collisions. We extend
the range of multiplicities both upwards with the Pb-Pb data and downwards with
the pp data to test the scaling in new areas. In particular the high
multiplicity pp collisions reach particle densities comparable to the ones
measured in peripheral Cu-Cu and Au-Au collisions at RHIC. This allows for the
first time to directly compare freeze-out sizes for systems with very different
initial states.Comment: 8 pages, 5 figures, Proceedings of the Quark Matter 2011 plenary tal
Study of correlations at LHC and RHIC energies in collisions within the quark-gluon string model
The Quark Gluon String Model (QGSM) reproduces well the global
characteristics of the collisions at RHIC and LHC, e.g., the
pseudorapidity and transverse momenta distributions at different centralities.
The main goal of this work is to employ the Monte Carlo QGSM for description of
femtoscopic characteristics in collisions at RHIC and LHC. The study is
concentrated on the low multiplicity and multiplicity averaged events, where no
collective effects are expected. The different procedures for fitting the
one-dimensional correlation functions of pions are studied and compared with
the space-time distributions extracted directly from the model. Particularly,
it is shown that the double Gaussian fit reveals the contributions coming
separately from resonances and from directly produced particles. The comparison
of model results with the experimental data favors decrease of particle
formation time with rising collision energy.Comment: 9 pages, 14 figures, 2 table
Sum rule of the correlation function
We derive a sum rule satisfied by the correlation function of two particles
with small relative momenta, which results from the completeness condition of
the quantum states.Comment: 6 pages, no macro
Deciphering nonfemtoscopic two-pion correlations in collisions with simple analytical models
A simple model of nonfemtoscopic particle correlations in proton-proton
collisions is proposed. The model takes into account correlations induced by
the conservation laws as well as correlations induced by minijets. It
reproduces well the two-pion nonfemtoscopic correlations of like-sign and
unlike-sign pions in proton-proton collision events at GeV
analyzed by the ALICE Collaboration. We also argue that similar nonfemtoscopic
correlations can appear in the hydrodynamic picture with event-by-event
fluctuating nonsymmetric initial conditions that are typically associated with
nonzero higher-order flow harmonics.Comment: 21 pages, 10 figures, misprints correcte
(Strange) Meson Interferometry at RHIC
We make predictions for the kaon interferometry measurements in Au+Au
collisions at the Relativistic Heavy Ion Collider (RHIC). A first order phase
transition from a thermalized Quark-Gluon-Plasma (QGP) to a gas of hadrons is
assumed for the transport calculations. The fraction of kaons that are directly
emitted from the phase boundary is considerably enhanced at large transverse
momenta K_T ~ 1 GeV/c. In this kinematic region, the sensitivity of the
R_out/R_side ratio to the QGP-properties is enlarged. Here, the results of the
1-dimensional correlation analysis are presented. The extracted interferometry
radii, depending on , are not unusually large and are strongly affected by
momentum resolution effects.Comment: 8 pages, 6 figure
Relative space-time asymmetries in pion and nucleon production in non-central nucleus-nucleus collisions at high energies
We propose to use the ratio of the pion-proton correlation functions
evaluated under different conditions to study the relative space-time
asymmetries in pion and proton emission (pion and nucleon source relative
shifts) in high energy heavy ion collision. We address the question of the
non-central collisions, where the sources can be shifted spatially both in the
longitudinal and in the transverse directions in the reaction plane. We use the
RQMD event generator to illustrate the effect and the technique.Comment: RevTex, 4 pages, 3 figures included as eps file
A Fast Hadron Freeze-out Generator
We have developed a fast Monte Carlo procedure of hadron generation allowing
one to study and analyze various observables for stable hadrons and hadron
resonances produced in ultra-relativistic heavy ion collisions. Particle
multiplicities are determined based on the concept of chemical freeze-out.
Particles can be generated on the chemical or thermal freeze-out hypersurface
represented by a parameterization or a numerical solution of relativistic
hydrodynamics with given initial conditions and equation of state. Besides
standard space-like sectors associated with the volume decay, the hypersurface
may also include non-space-like sectors related to the emission from the
surface of expanding system. For comparison with other models and experimental
data we demonstrate the results based on the standard parameterizations of the
hadron freeze-out hypersurface and flow velocity profile under the assumption
of a common chemical and thermal freeze-out. The C++ generator code is written
under the ROOT framework and is available for public use at
http://uhkm.jinr.ru/.Comment: 28 pages,7 figure
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.Comment: 23 pages, 8 figures, minor correction
Analysis of nucleus-nucleus collisions at high energies and Random Matrix Theory
We propose a novel statistical approach to the analysis of experimental data
obtained in nucleus-nucleus collisions at high energies which borrows from
methods developed within the context of Random Matrix Theory. It is applied to
the detection of correlations in momentum distributions of emitted particles.
We find good agreement between the results obtained in this way and a standard
analysis based on the method of effective mass spectra and two-pair correlation
function often used in high energy physics. The method introduced here is free
from unwanted background contributions.Comment: 11 pages, 10 figure
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