533 research outputs found
Nuclear Transparency in Heavy Ion Collisions at 14.6 GeV/nucleon
The probability of a projectile nucleon to traverse a target nucleus without
interaction is calculated for central Si-Pb collisions and compared to the data
of E814. The calculations are performed in two independent ways, via Glauber
theory and using the transport code UrQMD. For central collisions Glauber
predictions are about 30 to 50% higher than experiment, while the output of
UrQMD does not show the experimental peak of beam rapidity particles.Comment: 9 pages, 4 figures. submitted to Nucl. Phys.
Thermal Equilibration and Expansion in Nucleus-Nucleus Collision at the AGS
The rather complete data set of hadron yields from central Si + A collisions
at the Brookhaven AGS is used to test whether the system at freeze-out is in
thermal and hadro-chemical equilibrium. Rapidity and transverse momentum
distributions are discussed with regards to the information they provide on
hydrodynamic flow.Comment: 11 pages + 2 uuencoded figure
Anisotropic flow in 4.2A GeV/c C+Ta collisions
Anisotropic flow of protons and negative pions in 4.2A GeV/c C+Ta collisions
is studied using the Fourier analysis of azimuthal distributions. The protons
exhibit pronounced directed flow. Directed flow of pions is positive in the
entire rapidity interval and indicates that the pions are preferentially
emitted in the reaction plane from the target to the projectile. The elliptic
flow of protons and negative pions is close to zero. Comparison with the
quark-gluon-string model (QGSM) and relativistic transport model (ART 1.0) show
that they both yield a flow signature similar to the experimental data.Comment: 4 pages, 3 figures, Accepted for publication in Phys. Rev.
New method for measuring azimuthal distributions in nucleus-nucleus collisions
The methods currently used to measure azimuthal distributions of particles in
heavy ion collisions assume that all azimuthal correlations between particles
result from their correlation with the reaction plane. However, other
correlations exist, and it is safe to neglect them only if azimuthal
anisotropies are much larger than 1/sqrt(N), with N the total number of
particles emitted in the collision. This condition is not satisfied at
ultrarelativistic energies. We propose a new method, based on a cumulant
expansion of multiparticle azimuthal correlations, which allows to measure much
smaller values of azimuthal anisotropies, down to 1/N. It is simple to
implement and can be used to measure both integrated and differential flow.
Furthermore, this method automatically eliminates the major systematic errors,
which are due to azimuthal asymmetries in the detector acceptance.Comment: final version (misprints corrected), to be published in Phys.Rev.
Effects of momentum conservation on the analysis of anisotropic flow
We present a general method for taking into account correlations due to
momentum conservation in the analysis of anisotropic flow, either by using the
two-particle correlation method or the standard flow vector method. In the
latter, the correlation between the particle and the flow vector is either
corrected through a redefinition (shift) of the flow vector, or subtracted
explicitly from the observed flow coefficient. In addition, momentum
conservation contributes to the reaction plane resolution. Momentum
conservation mostly affects the first harmonic in azimuthal distributions,
i.e., directed flow. It also modifies higher harmonics, for instance elliptic
flow, when they are measured with respect to a first harmonic event plane such
as one determined with the standard transverse momentum method. Our method is
illustrated by application to NA49 data on pion directed flow.Comment: RevTeX 4, 10 pages, 1 eps figure. Version accepted for publication in
Phys Rev
Predictions for p+Pb at 4.4A TeV to Test Initial State Nuclear Shadowing at energies available at the CERN Large Hadron Collider
Collinear factorized perturbative QCD model predictions are compared for p+Pb
at 4.4A TeV to test nuclear shadowing of parton distribution at the Large
Hadron Collider (LHC). The nuclear modification factor (NMF),
R_{pPb}(y=0,p_T<20 GeV/c) = dn_{p Pb} /(N_{coll}(b)dn_{pp}), is computed with
electron-nucleus (e+A) global fit with different nuclear shadow distributions
and compared to fixed Q^2 shadow ansatz used in Monte Carlo Heavy Ion Jet
Interacting Generator (HIJING) type models. Due to rapid DGLAP reduction of
shadowing with increasing Q^2 used in e+A global fit, our results confirm that
no significant initial state suppression is expected (R_{pPb} (p_T) = 1 \pm
0.1) in the p_T range 5 to 20 GeV/ c. In contrast, the fixed Q^2 shadowing
models assumed in HIJING type models predict in the above p_T range a sizable
suppression, R_{pPb} (p_T) = 0.6-0.7 at mid-pseudorapidity that is similar to
the color glass condensate (CGC) model predictions. For central (N_{coll} = 12)
p+ Pb collisions and at forward pseudorapidity (\eta = 6) the HIJING type
models predict smaller values of nuclear modification factors (R_{pPb}(p_T))
than in minimum bias events at mid-pseudorapidity (\eta = 0). Observation of
R_{pPb}(p_T= 5-20 GeV/c) less than 0.6 for minimum bias p+A collisions would
pose a serious difficulty for separating initial from final state interactions
in Pb+Pb collisions at LHC energies.Comment: Revised version accepted for publication; Phys. Rev. C, in press, 16
pages, 4 figures, text modifications, added references, new figure 4, revtex
Charged Particle Pseudorapidity Distributions in Au+Al, Cu, Au, and U Collisions at 10.8 AGeV/c
We present the results of an analysis of charged particle pseudorapidity
distributions in the central region in collisions of a Au projectile with Al,
Cu, Au, and U targets at an incident energy of 10.8~GeV/c per nucleon. The
pseudorapidity distributions are presented as a function of transverse energy
produced in the target or central pseudorapidity regions. The correlation
between charged multiplicity and transverse energy measured in the central
region, as well as the target and projectile regions is also presented. We give
results for transverse energy per charged particle as a function of
pseudorapidity and centrality.Comment: 31 pages + 12 figures (compressed and uuencoded by uufiles), LATEX,
Submitted to PR
Hadron yields and spectra in Au+Au collisions at the AGS
Inclusive double differential multiplicities and rapidity density
distributions of hadrons are presented for 10.8 A GeV/c Au+Au collisions as
measured at the AGS by the E877 collaboration. The results indicate that large
amounts of stopping and collective transverse flow effects are present. The
data are also compared to the results from the lighter Si+Al system.Comment: 12 pages, latex, 10 figures, submitted to Nuclear Physics A (Quark
Matter 1996 Proceedings
Strong Color Field Baryonic Remnants in Nucleus-Nucleus Collisions at 200A GeV
The effects of strong color electric fields (SCF) on the baryon production at
RHIC are studied in the framework of HIJING/B\=B (v2.0) model. The particle
species dependence of nuclear modification factors (NMF) are analyzed for Au+Au
collisions at 200A GeV. A doubling of the string tension leading to a
modification of the strangeness suppression according to Schwinger mechanism is
shown to provide an alternate explanation to coalescence models for the
interpretation of the observed baryon and meson production at moderate
and results in a predicted enhancement in the (multi)strange (anti)hyperon
production.Comment: 6 pages, Latex(Revtex), 4 figures;Added new references, one figure,
text slightly modified. final version accepted for publication in Pnys. Rev.
C (october,05
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