286 research outputs found
J/psi suppression at forward rapidity in Au+Au collisions at sqrt(s_NN)=39 and 62.4 GeV
We present measurements of the J/psi invariant yields in sqrt(s_NN)=39 and
62.4 GeV Au+Au collisions at forward rapidity (1.2<|y|<2.2). Invariant yields
are presented as a function of both collision centrality and transverse
momentum. Nuclear modifications are obtained for central relative to peripheral
Au+Au collisions (R_CP) and for various centrality selections in Au+Au relative
to scaled p+p cross sections obtained from other measurements (R_AA). The
observed suppression patterns at 39 and 62.4 GeV are quite similar to those
previously measured at 200 GeV. This similar suppression presents a challenge
to theoretical models that contain various competing mechanisms with different
energy dependencies, some of which cause suppression and others enhancement.Comment: 365 authors, 10 pages, 11 figures, 4 tables. Submitted to Phys. Rev.
C. Plain text data tables for the points plotted in figures for this and
previous PHENIX publications are (or will be) publicly available at
http://www.phenix.bnl.gov/papers.htm
Nuclear dependence of the transverse-single-spin asymmetry for forward neutron production in polarized collisions at GeV
During 2015 the Relativistic Heavy Ion Collider (RHIC) provided collisions of
transversely polarized protons with Au and Al nuclei for the first time,
enabling the exploration of transverse-single-spin asymmetries with heavy
nuclei. Large single-spin asymmetries in very forward neutron production have
been previously observed in transversely polarized collisions at
RHIC, and the existing theoretical framework that was successful in describing
the single-spin asymmetry in collisions predicts only a moderate
atomic-mass-number () dependence. In contrast, the asymmetries observed at
RHIC in collisions showed a surprisingly strong dependence in
inclusive forward neutron production. The observed asymmetry in Al
collisions is much smaller, while the asymmetry in Au collisions is a
factor of three larger in absolute value and of opposite sign. The interplay of
different neutron production mechanisms is discussed as a possible explanation
of the observed dependence.Comment: 315 authors, 8 pages, 4 figures, 1 table. v2 is version accepted for
publication in Phys. Rev. Lett. Plain text data tables for the points plotted
in figures for this and previous PHENIX publications are (or will be)
publicly available at http://www.phenix.bnl.gov/papers.htm
Quantitative Constraints on the Transport Properties of Hot Partonic Matter from Semi-Inclusive Single High Transverse Momentum Pion Suppression in Au+Au collisions at sqrt(s_NN) = 200 GeV
The PHENIX experiment has measured the suppression of semi-inclusive single
high transverse momentum pi^0's in Au+Au collisions at sqrt(s_NN) = 200 GeV.
The present understanding of this suppression is in terms of energy-loss of the
parent (fragmenting) parton in a dense color-charge medium. We have performed a
quantitative comparison between various parton energy-loss models and our
experimental data. The statistical point-to-point uncorrelated as well as
correlated systematic uncertainties are taken into account in the comparison.
We detail this methodology and the resulting constraint on the model
parameters, such as the initial color-charge density dN^g/dy, the medium
transport coefficient , or the initial energy-loss parameter epsilon_0.
We find that high transverse momentum pi^0 suppression in Au+Au collisions has
sufficient precision to constrain these model dependent parameters at the +/1
20%-25% (one standard deviation) level. These constraints include only the
experimental uncertainties, and further studies are needed to compute the
corresponding theoretical uncertainties.Comment: 422 authors, 13 pages text, RevTeX-4, 9 figures, 2 tables. This
version is updated with changes made during the review process and is now the
same as what was published in Physical Review C. Plain text data tables for
the points plotted in figures for this and previous PHENIX publications are
publicly available at http://www.phenix.bnl.gov/papers.htm
Cross sections and double-helicity asymmetries of midrapidity inclusive charged hadrons in p+p collisions at sqrt(s)=62.4 GeV
Unpolarized cross sections and double-helicity asymmetries of
single-inclusive positive and negative charged hadrons at midrapidity from p+p
collisions at sqrt(s)=62.4 GeV are presented. The PHENIX measurements for 1.0 <
p_T < 4.5 GeV/c are consistent with perturbative QCD calculations at
next-to-leading order in the strong coupling constant, alpha_s. Resummed pQCD
calculations including terms with next-to-leading-log accuracy, yielding
reduced theoretical uncertainties, also agree with the data. The
double-helicity asymmetry, sensitive at leading order to the gluon polarization
in a momentum-fraction range of 0.05 ~< x_gluon ~< 0.2, is consistent with
recent global parameterizations disfavoring large gluon polarization.Comment: PHENIX Collaboration. 447 authors, 12 pages, 5 figures, 5 tables.
Submitted to Physical Review
Measurement of higher cumulants of net-charge multiplicity distributions in AuAu collisions at GeV
We report the measurement of cumulants () of the net-charge
distributions measured within pseudorapidity () in AuAu
collisions at GeV with the PHENIX experiment at the
Relativistic Heavy Ion Collider. The ratios of cumulants (e.g. ,
) of the net-charge distributions, which can be related to volume
independent susceptibility ratios, are studied as a function of centrality and
energy. These quantities are important to understand the quantum-chromodynamics
phase diagram and possible existence of a critical end point. The measured
values are very well described by expectation from negative binomial
distributions. We do not observe any nonmonotonic behavior in the ratios of the
cumulants as a function of collision energy. The measured values of and can be directly compared to lattice
quantum-chromodynamics calculations and thus allow extraction of both the
chemical freeze-out temperature and the baryon chemical potential at each
center-of-mass energy.Comment: 512 authors, 8 pages, 4 figures, 1 table. v2 is version accepted for
publication in Phys. Rev. C as a Rapid Communication. Plain text data tables
for the points plotted in figures for this and previous PHENIX publications
are (or will be) publicly available at http://www.phenix.bnl.gov/papers.htm
Inclusive cross section and double helicity asymmetry for pi^0 production in p+p collisions at sqrt(s) = 62.4 GeV
The PHENIX experiment presents results from the RHIC 2006 run with polarized
proton collisions at sqrt(s) = 62.4 GeV for inclusive pi^0 production at
mid-rapidity. Unpolarized cross section results are measured for transverse
momenta p_T = 0.5 to 7 GeV/c. Next-to-leading order perturbative quantum
chromodynamics calculations are compared with the data, and while the
calculations are consistent with the measurements, next-to-leading logarithmic
corrections improve the agreement. Double helicity asymmetries A_LL are
presented for p_T = 1 to 4 GeV/c and probe the higher range of Bjorken_x of the
gluon (x_g) with better statistical precision than our previous measurements at
sqrt(s)=200 GeV. These measurements are sensitive to the gluon polarization in
the proton for 0.06 < x_g < 0.4.Comment: 387 authors from 63 institutions, 10 pages, 6 figures, 1 table.
Submitted to Physical Review D. Plain text data tables for the points plotted
in figures for this and previous PHENIX publications are (or will be)
publicly available at http://www.phenix.bnl.gov/papers.htm
Inclusive cross section and single-transverse-spin asymmetry for very forward neutron production in polarized p+p collisions at sqrt(s)=200 GeV
The energy dependence of the single-transverse-spin asymmetry, A_N, and the
cross section for neutron production at very forward angles were measured in
the PHENIX experiment at RHIC for polarized p+p collisions at sqrt(s)=200 GeV.
The neutrons were observed in forward detectors covering an angular range of up
to 2.2 mrad. We report results for neutrons with momentum fraction of x_F=0.45
to 1.0. The energy dependence of the measured cross sections were consistent
with x_F scaling, compared to measurements by an ISR experiment which measured
neutron production in unpolarized p+p collisions at sqrt(s)=30.6--62.7 GeV. The
cross sections for large x_F neutron production for p+p collisions, as well as
those in e+p collisions measured at HERA, are described by a pion exchange
mechanism. The observed forward neutron asymmetries were large, reaching
A_N=-0.08+/-0.02 for x_F=0.8; the measured backward asymmetries, for negative
x_F, were consistent with zero. The observed asymmetry for forward neutron
production is discussed within the pion exchange framework, with interference
between the spin-flip amplitude due to the pion exchange and nonflip amplitudes
from all Reggeon exchanges. Within the pion exchange description, the measured
neutron asymmetry is sensitive to the contribution of other Reggeon exchanges
even for small amplitudes.Comment: 383 authors, 16 pages, 18 figures, 6 tables. Submitted to Phys. Rev.
D. Plain text data tables for the points plotted in figures for this and
previous PHENIX publications are (or will be) publicly available at
http://www.phenix.bnl.gov/papers.htm
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