401 research outputs found
Methods to study event-by-event fluctuations in the NA61/SHINE experiment at the CERN SPS
Theoretical calculations locate the critical point of strongly interacting
matter (CP) at energies accessible at the CERN SPS. Event-by-event transverse
momentum and multiplicity fluctuations are considered as one of the most
important tools to search for the CP. Pilot studies of the energy dependence
and the system size dependence of both and multiplicity fluctuations were
performed by the NA49 experiment. The NA61/SHINE ion program is a continuation
of these efforts. After briefly recalling the essential NA49 results on
fluctuations we will discuss the technical methods (removing Non-Target
interactions) which we plan to apply for future transverse momentum and
multiplicity fluctuation analyses.Comment: Proceedings of CPOD 2010, 23-29 August, JINR, Dubn
Size fluctuations of the initial source and the event-by-event transverse momentum fluctuations in relativistic heavy-ion collisions
We show that the event-by-event fluctuations of the transverse size of the
initial source, which follow directly from the Glauber treatment of the
earliest stage of relativistic heavy-ion collisions, cause, after hydrodynamic
evolution, fluctuations of the transverse flow velocity at hadronic freeze-out.
This in turn leads to event-by-event fluctuations of the average transverse
momentum, p_T. Simulations with GLISSANDO for the Glauber phase, followed by a
realistic hydrodynamic evolution and statistical hadronization carried out with
THERMINATOR, lead to agreement with the RHIC data. In particular, the magnitude
of the effect, its centrality dependence, and the weak dependence on the
incident energy are properly reproduced. Our results show that bulk of the
observed event-by-event p_T fluctuations may be explained by the fluctuations
of the size of the initial source.Comment: 5 pages, 4 figures, version accepted in PR
Strongly Intensive Measures for Multiplicity Fluctuations
The recently proposed two families of strongly intensive measures of
fluctuations and correlations are studied within Hadron-String-Dynamics (HSD)
transport approach to nucleus-nucleus collisions. We consider the measures
and for kaon and pion multiplicities in Au+Au
collisions in a wide range of collision energies and centralities. These
strongly intensive measures appear to cancel the participant number
fluctuations. This allows to enlarge the centrality window in the analysis of
event-by-event fluctuations up to at least of 10% most central collisions. We
also present a comparison of the HSD results with the data of NA49 and STAR
collaborations. The HSD describes reasonably well. However, the
HSD results depend monotonously on collision energy and do not reproduce the
bump-deep structure of observed from the NA49 data in the
region of the center of mass energy of nucleon pair
GeV. This fact deserves further studies. The origin of this `structure' is not
connected with simple geometrical or limited acceptance effects, as these
effects are taken into account in the HSD simulations
New results from fluctuation analysis in NA49 at the CERN SPS
The exploration of the phase diagram of strongly interacting matter,
particularly the study of the phase transition from hadronic to partonic matter
and the search for a hypothetical critical endpoint of the first order
transition line, is one of the most challenging tasks in present heavy ion
physics.
In this talk new results on chemical (particle ratio), transverse momentum,
multiplicity and azimuthal angle fluctuations will be presented. We also
discuss their connection to the onset of deconfinement and to the critical
endpoint.Comment: The Proceedings of the International Conference "Critical Point and
Onset of Deconfinement - CPOD 2011", Wuhan, November 7-11, 201
Status and plans of the ion program of NA61 at the CERN SPS
The NA61/SHINE at the CERN SPS is a new experiment to study hadron production
in p+p p+A, h+A and A+A interactions. The main goal of the NA61 ion program is
to explore the phase diagram (T - mu_B) of strongly interacting matter. In
particular, we plan to study the properties of the onset of deconfinement and
to search for the signatures of the critical point. A two-dimensional scan of
the phase diagram will be performed by varying the energy (13A-158A GeV) and
system size (p+p, Be+Be, Ar+Ca, Xe+La) of collisions. This paper summarizes the
status and plans of the NA61/SHINE ion program. In particular the detector
upgrades, data taking schedule and the first results on spectra and
correlations are discussed.Comment: Proceedings of "Critical Point and Onset of Deconfinement - CPOD
2011", Wuhan, November 7-11, 2011, version accepted by Central European
Journal of Physic
System-size dependence of the pion freeze-out volume as a potential signature for the phase transition to a Quark Gluon Plasma
Hanburry-Brown-Twiss (HBT) correlation functions and radii of negatively
charged pions from C+C, Si+Si, Cu+Cu, and In+In at lower RHIC/SPS energies are
calculated with the UrQMD transport model and the CRAB analyzing program. We
find a minimum in the excitation function of the pion freeze-out volume at low
transverse momenta and around GeV which can be related to
the transition from hadronic to string matter (which might be interpreted as a
pre-cursor of the QGP). The existence of the minimum is explained by the
competition of two mechanisms of the particle production, resonance decays and
string formation/fragmentation.Comment: 12 pages, 4 fig
Wounded nucleon model with realistic nucleon-nucleon collision profile and observables in relativistic heavy-ion collisions
We investigate the influence of the nucleon-nucleon collision profile
(probability of interaction as a function of the nucleon-nucleon impact
parameter) in the wounded nucleon model and its extensions on several
observables measured in relativistic heavy-ion collisions. We find that the
participant eccentricity coefficient, , as well as the higher
harmonic coefficients, , are reduced by 10-20% for
mid-peripheral collisions when the realistic (Gaussian) profile is used, as
compared to the case with the commonly-used hard-sphere profile. Similarly, the
multiplicity fluctuations, treated as the function of the number of wounded
nucleons in one of the colliding nuclei, are reduced by 10-20%. This
demonstrates that the Glauber Monte Carlo codes should necessarily use the
realistic nucleon-nucleon collision profile in precision studies of these
observables. The Gaussian collision profile is built-in in {\tt GLISSANDO}.Comment: 8 pages, 7 figure
Phase-space dependence of particle-ratio fluctuations in Pb+Pb collisions from 20A to 158A GeV beam energy
A novel approach, the identity method, was used for particle identification
and the study of fluctuations of particle yield ratios in Pb+Pb collisions at
the CERN Super Proton Synchrotron (SPS). This procedure allows to unfold the
moments of the unknown multiplicity distributions of protons (p), kaons (K),
pions () and electrons (e). Using these moments the excitation function of
the fluctuation measure [A,B] was measured, with A and
B denoting different particle types. The obtained energy dependence of
agrees with previously published NA49 results on the related
measure . Moreover, was found to depend
on the phase space coverage for [K,p] and [K,] pairs. This feature most
likely explains the reported differences between measurements of NA49 and those
of STAR in central Au+Au collisions
Production of deuterium, tritium, and He in central Pb+Pb collisions at 20A, 30A, 40A, 80A, and 158A GeV at the CERN SPS
Production of , , and He nuclei in central Pb+Pb interactions was
studied at five collision energies ( 6.3, 7.6, 8.8, 12.3, and
17.3 GeV) with the NA49 detector at the CERN SPS. Transverse momentum spectra,
rapidity distributions, and particle ratios were measured. Yields are compared
to predictions of statistical models. Phase-space distributions of light nuclei
are discussed and compared to those of protons in the context of a coalescence
approach. The coalescence parameters and , as well as coalescence
radii for and He were determined as a function of transverse mass at
all energies.Comment: 22 pages, 29 figures, 8 tables, for submission to Phys. Rev.
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