11 research outputs found
Relativistic Nucleus-Nucleus Collisions: from the BEVALAC to RHIC
I briefly describe the initial goals of relativistic nuclear collisions
research, focusing on the LBL Bevatron/Bevalac facility in the 1970's. An early
concept of high hadronic density fireball formation, and subsequent isentropic
decay (preserving information as to the high density stage) led to an outline
of physics observables that could determine the nuclear matter equation of
state at several times nuclear ground state matter density. With the advent of
QCD the goal of locating, and characterizing the hadron-parton deconfinement
phase transformation suggested the need for higher , the research
thus moving to the BNL AGS and CERN SPS, finally to RHIC at BNL. A set of
physics observables is discussed where present data span the entire
domain, from Bevalac and SIS at GSI, to top RHIC energy. Referring,
selectively, to data concerning bulk hadron production, the overall
evolution of directed and radial flow observables, and of pion pair
Bose-Einstein correlation are discussed. The hadronization process is studied
in the grand canonical statistical model. The resulting hadronization points in
the plane T vs. converge onto the parton-hadron phase boundary
predicted by finite lattice QCD, from top SPS to RHIC energy. At lower
SPS and top AGS energy a steep strangeness maximum occurs at which the
Wroblewski parameter 0.6; a possible connection to the QCD
critical point is discussed. Finally the unique new RHIC physics is addressed:
high hadron suppression and jet "tomography".Comment: 19 pages, 11 figure
Transport model analysis of the transverse momentum and rapidity dependence of pion interferometry at SPS energies
Based on the UrQMD transport model, the transverse momentum and the rapidity
dependence of the Hanbury-Brown-Twiss (HBT) radii , , as well
as the cross term at SPS energies are investigated and compared with
the experimental NA49 and CERES data. The rapidity dependence of the ,
, is weak while the is significantly increased at large
rapidities and small transverse momenta. The HBT "life-time" issue (the
phenomenon that the calculated value is larger than
the correspondingly extracted experimental data) is also present at SPS
energies.Comment: 17 pages, 11 figure
Review of HBT or Bose-Einstein correlations in high energy heavy ion collisions
A brief review is given on the discovery and the first five decades of the
Hanbury Brown - Twiss effect and its generalized applications in high energy
nuclear and particle physics, that includes a meta-review. Interesting and
inspiring new directions are also highlighted, including for example source
imaging, lepton and photon interferometry, non-Gaussian shape analysis as well
as many other new directions. Existing models are compared to two-particle
correlation measurements and the so-called RHIC HBT puzzle is resolved.
Evidence for a (directional) Hubble flow is presented and the conclusion is
confirmed by a successful description of the pseudorapidity dependence of the
elliptic flow as measured in Au+Au collisions by the PHOBOS Collaboration.Comment: 14 pages, 1 figure, 8 sub-figures, invited plenary talk at the
ICPA-QGP 2005 conference in Kolkata, Indi
Strangeness from 20 AGeV to 158 AGeV
New results from the energy scan programme of NA49, in particular kaon
production at 30 AGeV and phi production at 40 and 80 AGeV are presented. The
K+/pi+ ratio shows a pronounced maximum at 30 AGeV; the kaon slope parameters
are constant at SPS energies. Both findings support the scenario of a phase
transition at about 30 AGeV beam energy. The phi/pi ratio increases smoothly
with beam energy, showing an energy dependence similar to K-/pi-. The measured
particle yields can be reproduced by a hadron gas model, with chemical
freeze-out parameters on a smooth curve in the T-muB plane. The transverse
spectra can be understood as resulting from a rapidly expanding, locally
equilibrated source. No evidence for an earlier kinetic decoupling of heavy
hyperons is found.Comment: Contribution to the proceedings of "Strangeness in Quark Matter 2003"
(March 2003, Atlantic Beach NC, USA), to be published in Journal of Physics
G. 11 pages, 14 figure
Omega(-) and (Omega)over-bar(+) production in central Pb+Pb collisions at 40 and 158A GeV
Results are presented on Omega production in central Pb+Pb collisions at
40 and 158A GeV beam energy. For the first time in heavy ion reactions,
rapidity distributions and total yields were measured for the sum
Omega(-)+(Omega) over bar (+) at 40A GeV and for Omega(-) and (Omega)
over bar (+) separately at 158A GeV. The yields are strongly
underpredicted by the string-hadronic UrQMD model but agree better with
predictions from hadron gas models
System size and centrality dependence of the balance function in A+A collisions at root S-NN=17.2 GeV
Electric charge correlations were studied for p+p, C+C, Si+Si, and
centrality selected Pb+Pb collisions at root s(NN) = 17.2 GeV with the
NA49 large acceptance detector at the CERN SPS. In particular,
long-range pseudorapidity correlations of oppositely charged particles
were measured using the balance function method. The width of the
balance function decreases with increasing system size and centrality of
the reactions. This decrease could be related to an increasing delay of
hadronization in central Pb+Pb collisions
Pion and kaon production in central Pb plus Pb collisions at 20A and 30A GeV: Evidence for the onset of deconfinement
Results on charged pion and kaon production in central Pb+Pb collisions
at 20A and 30A GeV are presented and compared to data at lower and
higher energies. Around 30A GeV a rapid change of the energy dependence
for the yields of pions and kaons as well as for the shape of the
transverse mass spectra is observed. The change is compatible with the
prediction that the threshold for production of a state of deconfined
matter at the early stage of the collisions is located at low CERN Super
Proton Synchroton energies
High transverse momentum hadron spectra at root s(NN)=17.3 GeV in Pb+Pb and p+p collisions
Transverse momentum spectra up to 4.5 GeV/c around midrapidity of
pi(+/-), p, (p) over bar, and K-+/- in Pb+Pb reactions were measured at
root s(NN) = 17.3 GeV by the CERN-NA49 experiment. The nuclear
modification factors R-AA for pi(+/-) and R-CP for pi(+/-), p, (p) over
bar, K-+/- were extracted and compared with results obtained at the BNL
Relativistic Heavy Ion Collider (RHIC) at root s(NN) = 200 GeV. The
modification factor R-AA shows a rapid increase with transverse momentum
in the covered region. This indicates that the Cronin effect is the
dominating effect in our energy range. The modification factor R-CP, in
which the contribution of the Cronin effect is reduced, shows a
saturation well below unity in the pi(+/-) channel. The extracted R-CP
values follow the 200 GeV RHIC results closely in the available
transverse momentum range, except for pi(+/-) above 2.5 GeV/c transverse
momentum. There the measured suppression is smaller than that observed
at RHIC
Elliptic flow of Lambda hyperons in Pb+Pb collisions at 158A GeV
The elliptic flow of Lambda hyperons has been measured by the NA49
Collaboration at the CERN-SPS in semicentral Pb+Pb collisions at 158A
GeV. The standard method of correlating particles with the event plane
was used. Measurements of v(2) near midrapidity are reported as a
function of rapidity, centrality and transverse momentum. Elliptic flow
of Lambda particles increases both with the impact parameter and with
the transverse momentum. It is compared with v(2) for pions and protons
as well as with model calculations. The observation of significant
elliptic flow and its mass dependence suggest strong collective behavior
of the matter produced in collisions of heavy nuclei already at the SPS.
Scaling properties of elliptic flow of different particle species have
been tested at 158A GeV. The limited p(T) range of the data does not
allow for a decisive test of the coalescence model
Centrality and system size dependence of multiplicity fluctuations in nuclear collisions at 158A GeV
The centrality and system size dependence of multiplicity fluctuations
of charged particles produced in nuclear collisions at 158A GeV was
studied by the NA49 Collaboration. Centrality selected Pb+Pb collisions,
semicentral C+C and Si+Si collisions as well as inelastic p+p
interactions were analyzed. The number of projectile participants
determined on an event-by-event basis was used to characterize the
collision centrality. The scaled variance of the multiplicity
distribution obtained in the forward rapidity region (1.1 < y(c.m.)<
2.6) shows a significant increase toward peripheral collisions. The
results are similar for negatively and positively charged particles and
about 50% larger for all charged particles. String-hadronic models of
nuclear reactions without the fusion process do not reproduce the rise
of fluctuations from central toward peripheral collisions. The measured
centrality dependence can be reproduced in superposition models with the
assumption of contributions from target participants to particle
production in the forward hemisphere or in string models with fusion