118 research outputs found
Identified baryon and meson distributions at large transverse momenta from Au+Au collisions at GeV
Transverse momentum spectra of , and up to 12 GeV/c
at mid-rapidity in centrality selected Au+Au collisions at GeV are presented. In central Au+Au collisions, both and
show significant suppression with respect to binary scaling at
4 GeV/c. Protons and anti-protons are less suppressed than
, in the range 1.5 6 GeV/c. The and
ratios show at most a weak dependence and no significant
centrality dependence. The ratios in central Au+Au collisions approach
the values in p+p and d+Au collisions at 5 GeV/c. The results at high
indicate that the partonic sources of , and have
similar energy loss when traversing the nuclear medium.Comment: 6 pages, 4 figure
Longitudinal double-spin asymmetry for inclusive jet production in p+p collisions at sqrt(s)=200 GeV
We report a new STAR measurement of the longitudinal double-spin asymmetry
A_LL for inclusive jet production at mid-rapidity in polarized p+p collisions
at a center-of-mass energy of sqrt(s) = 200 GeV. The data, which cover jet
transverse momenta 5 < p_T < 30 GeV/c, are substantially more precise than
previous measurements. They provide significant new constraints on the gluon
spin contribution to the nucleon spin through the comparison to predictions
derived from one global fit of polarized deep-inelastic scattering
measurements.Comment: 7 pages, 4 figures + 1 tabl
Longitudinal double-spin asymmetry and cross section for inclusive jet production in polarized proton collisions at sqrt(s) = 200 GeV
We report a measurement of the longitudinal double-spin asymmetry A_LL and
the differential cross section for inclusive midrapidity jet production in
polarized proton collisions at sqrt(s)=200 GeV. The cross section data cover
transverse momenta 5 < pT < 50 GeV/c and agree with next-to-leading order
perturbative QCD evaluations. The A_LL data cover 5 < pT < 17 GeV/c and
disfavor at 98% C.L. maximal positive gluon polarization in the polarized
nucleon.Comment: 6 pages, 3 figures. Minor changes from review process in Phys. Rev.
Lett. Plain text tables of data in STAR publications may be found at
http://www.star.bnl.gov/central/publications
Multiplicity and Pseudorapidity Distributions of Charged Particles and Photons at Forward Pseudorapidity in Au + Au Collisions at sqrt{s_NN} = 62.4 GeV
We present the centrality dependent measurement of multiplicity and
pseudorapidity distributions of charged particles and photons in Au + Au
collisions at sqrt{s_NN} = 62.4 GeV. The charged particles and photons are
measured in the pseudorapidity region 2.9 < eta < 3.9 and 2.3 < eta < 3.7,
respectively. We have studied the scaling of particle production with the
number of participating nucleons and the number of binary collisions. The
photon and charged particle production in the measured pseudorapidity range has
been shown to be consistent with energy independent limiting fragmentation
behavior. The photons are observed to follow a centrality independent limiting
fragmentation behavior while for the charged particles it is centrality
dependent. We have carried out a comparative study of the pseudorapidity
distributions of positively charged hadrons, negatively charged hadrons,
photons, pions, net protons in nucleus--nucleus collisions and pseudorapidity
distributions from p+p collisions. From these comparisons we conclude that
baryons in the inclusive charged particle distribution are responsible for the
observed centrality dependence of limiting fragmentation. The mesons are found
to follow an energy independent behavior of limiting fragmentation while the
behavior of baryons seems to be energy dependent.Comment: 17 pages and 20 figure
System-Size Independence of Directed Flow Measured at the BNL Relativistic Heavy-Ion Collider
We measure directed flow (ν_1) for charged particles in Au+Au and Cu+Cu collisions at √S_(NN)=200 and 62.4 GeV, as a function of pseudorapidity (η), transverse momentum (p_t), and collision centrality, based on data from the STAR experiment. We find that the directed flow depends on the incident energy but, contrary to all available model implementations, not on the size of the colliding system at a given centrality. We extend the validity of the limiting fragmentation concept to ν_1 in different collision systems, and investigate possible explanations for the observed sign change in ν_1(p_t)
Enhanced strange baryon production in Au+Au collisions compared to p+p at sqrts = 200 GeV
We report on the observed differences in production rates of strange and
multi-strange baryons in Au+Au collisions at sqrts = 200 GeV compared to pp
interactions at the same energy. The strange baryon yields in Au+Au collisions,
then scaled down by the number of participating nucleons, are enhanced relative
to those measured in pp reactions. The enhancement observed increases with the
strangeness content of the baryon, and increases for all strange baryons with
collision centrality. The enhancement is qualitatively similar to that observed
at lower collision energy sqrts =17.3 GeV. The previous observations are for
the bulk production, while at intermediate pT, 1 < pT< 4 GeV/c, the strange
baryons even exceed binary scaling from pp yields.Comment: 7 pages, 4 figures. Printed in PR
Spin alignment measurements of the and vector mesons at RHIC
We present the first spin alignment measurements for the and
vector mesons produced at mid-rapidity with transverse momenta up
to 5 GeV/c at = 200 GeV at RHIC. The diagonal spin density
matrix elements with respect to the reaction plane in Au+Au collisions are
= 0.32 0.04 (stat) 0.09 (syst) for the
( GeV/c) and = 0.34 0.02 (stat) 0.03
(syst) for the ( GeV/c), and are constant with transverse
momentum and collision centrality. The data are consistent with the unpolarized
expectation of 1/3 and thus no evidence is found for the transfer of the
orbital angular momentum of the colliding system to the vector meson spins.
Spin alignments for and in Au+Au collisions were also measured
with respect to the particle's production plane. The result,
= 0.41 0.02 (stat) 0.04 (syst), is consistent with that in p+p
collisions, = 0.39 0.03 (stat) 0.06 (syst), also
measured in this work. The measurements thus constrain the possible size of
polarization phenomena in the production dynamics of vector mesons.Comment: 7 pages, 4 figures. fig.1 updated; one more reference added, one typo
corrected, published in PRC.77.06190
Strangelet Search in AuAu Collisions at 200 GeV
We have searched for strangelets in a triggered sample of 61 million central
(top 4%) Au+Au collisions at \sNN = 200 GeV near beam rapidities at the STAR
detector. We have sensitivity to metastable strangelets with lifetimes of order
, in contrast to limits over ten times longer in AGS studies and
longer still at the SPS. Upper limits of a few 10^{-6} to 10^{-7} per central
Au+Au collision are set for strangelets with mass GeV/c^{2}.Comment: As publishe
Performance of the first prototype of the CALICE scintillator strip electromagnetic calorimeter
A first prototype of a scintillator strip-based electromagnetic calorimeter
was built, consisting of 26 layers of tungsten absorber plates interleaved with
planes of 45x10x3 mm3 plastic scintillator strips. Data were collected using a
positron test beam at DESY with momenta between 1 and 6 GeV/c. The prototype's
performance is presented in terms of the linearity and resolution of the energy
measurement. These results represent an important milestone in the development
of highly granular calorimeters using scintillator strip technology. This
technology is being developed for a future linear collider experiment, aiming
at the precise measurement of jet energies using particle flow techniques
Minijet deformation and charge-independent angular correlations on momentum subspace in Au-Au collisions at = 130 GeV
First measurements of charge-independent correlations on angular difference
variables (pseudorapidity) and (azimuth)
are presented for primary charged hadrons with transverse momentum GeV/ and from Au-Au collisions at
GeV. Strong charge-independent angular correlations are
observed associated with jet-like structures and elliptic flow. The width of
the jet-like peak on increases by a factor 2.3 from
peripheral to central collisions, suggesting strong coupling of semi-hard
scattered partons to a longitudinally-expanding medium. New methods of jet
analysis introduced here provide evidence for nonperturbative QCD medium
effects in heavy ion collisions.Comment: 8 pages, 4 figure
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