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Production of π0 and η mesons in Cu+Au collisions at sNN =200 GeV
Production of π0 and η mesons has been measured at midrapidity in Cu+Au collisions at sNN=200GeV. Measurements were performed in π0(η)→γγ decay channel in the 1(2)-20GeV/c transverse momentum range. A strong suppression is observed for π0 and η meson production at high transverse momentum in central Cu+Au collisions relative to the p+p results scaled by the number of nucleon-nucleon collisions. In central collisions the suppression is similar to Au+Au with comparable nuclear overlap. The η/π0 ratio measured as a function of transverse momentum is consistent with mT-scaling parametrization down to pT=2GeV/c, its asymptotic value is constant and consistent with Au+Au and p+p and does not show any significant dependence on collision centrality. Similar results were obtained in hadron-hadron, hadron-nucleus, and nucleus-nucleus collisions as well as in e+e- collisions in a range of collision energies sNN=3-1800 GeV. This suggests that the quark-gluon-plasma medium produced in Cu+Cu collisions either does not affect the jet fragmentation into light mesons or it affects the π0 and η the same way
L\'evy-stable two-pion Bose-Einstein correlations in GeV AuAu collisions
We present a detailed measurement of charged two-pion correlation functions
in 0%-30% centrality GeV AuAu collisions by the
PHENIX experiment at the Relativistic Heavy Ion Collider. The data are well
described by Bose-Einstein correlation functions stemming from L\'evy-stable
source distributions. Using a fine transverse momentum binning, we extract the
correlation strength parameter , the L\'evy index of stability
and the L\'evy length scale parameter as a function of average
transverse mass of the pair . We find that the positively and the
negatively charged pion pairs yield consistent results, and their correlation
functions are represented, within uncertainties, by the same L\'evy-stable
source functions. The measurements indicate a decrease of the
strength of the correlations at low . The L\'evy length scale parameter
decreases with increasing , following a hydrodynamically
predicted type of scaling behavior. The values of the L\'evy index of stability
are found to be significantly lower than the Gaussian case of
, but also significantly larger than the conjectured value that may
characterize the critical point of a second-order quark-hadron phase
transition.Comment: 448 authors, 25 pages, 11 figures, 4 tables, 2010 data. v2 is version
accepted for publication in 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
Single electron yields from semileptonic charm and bottom hadron decays in AuAu collisions at GeV
The PHENIX Collaboration at the Relativistic Heavy Ion Collider has measured
open heavy-flavor production in minimum bias AuAu collisions at
GeV via the yields of electrons from semileptonic decays
of charm and bottom hadrons. Previous heavy-flavor electron measurements
indicated substantial modification in the momentum distribution of the parent
heavy quarks due to the quark-gluon plasma created in these collisions. For the
first time, using the PHENIX silicon vertex detector to measure precision
displaced tracking, the relative contributions from charm and bottom hadrons to
these electrons as a function of transverse momentum are measured in AuAu
collisions. We compare the fraction of electrons from bottom hadrons to
previously published results extracted from electron-hadron correlations in
collisions at GeV and find the fractions to be
similar within the large uncertainties on both measurements for
GeV/. We use the bottom electron fractions in AuAu and along
with the previously measured heavy flavor electron to calculate the
for electrons from charm and bottom hadron decays separately. We find
that electrons from bottom hadron decays are less suppressed than those from
charm for the region GeV/.Comment: 432 authors, 33 pages, 23 figures, 2 tables, 2011 data. v2 is version
accepted for publication by 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
Inclusive cross section and double-helicity asymmetry for production at midrapidity in collisions at GeV
PHENIX measurements are presented for the cross section and double-helicity
asymmetry () in inclusive production at midrapidity from
collisions at ~GeV from data taken in 2012 and 2013 at
the Relativistic Heavy Ion Collider. The next-to-leading-order
perturbative-quantum-chromodynamics theory calculation is in excellent
agreement with the presented cross section results. The calculation utilized
parton-to-pion fragmentation functions from the recent DSS14 global analysis,
which prefer a smaller gluon-to-pion fragmentation function. The
results follow an increasingly positive asymmetry trend with
and with respect to the predictions and are in excellent
agreement with the latest global analysis results. This analysis incorporated
earlier results on and jet , and suggested a positive
contribution of gluon polarization to the spin of the proton for the
gluon momentum fraction range . The data presented here extend to a
currently unexplored region, down to , and thus provide additional
constraints on the value of . The results confirm the evidence for
nonzero using a different production channel in a complementary
kinematic region.Comment: 413 authors, 8 pages, 4 figures. v2 is version accepted as PRD 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
Medium modification of jet fragmentation in Au+Au collisions at sqrt(s_NN)=200 GeV measured in direct photon-hadron correlations
The jet fragmentation function is measured with direct photon-hadron
correlations in p+p and Au+Au collisions at sqrt(s_NN)=200 GeV. The p_T of the
photon is an excellent approximation to the initial p_T of the jet and the
ratio z_T=p_T^h/p_T^\gamma is used as a proxy for the jet fragmentation
function. A statistical subtraction is used to extract the direct photon-hadron
yields in Au+Au collisions while a photon isolation cut is applied in p+p. I_
AA, the ratio of jet fragment yield in Au+Au to that in p+p, indicates
modification of the jet fragmentation function. Suppression, most likely due to
energy loss in the medium, is seen at high z_T. The fragment yield at low z_T
is enhanced at large angles. Such a trend is expected from redistribution of
the lost energy into increased production of low-momentum particles.Comment: 562 authors, 70 insitutions, 8 pages, and 3 figures. Submitted to
Phys. Rev. Lett. v2 has minor changes to improve clarity. 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
Production of and mesons in UU collisions at GeV
The PHENIX experiment at the Relativistic Heavy Ion Collider measured
and mesons at midrapidity in UU collisions at
GeV in a wide transverse momentum range. Measurements were performed in the
decay modes. A strong suppression of
and meson production at high transverse momentum was observed in
central UU collisions relative to binary scaled results. Yields of
and mesons measured in UU collisions show similar suppression
pattern to the ones measured in AuAu collisions at
GeV for similar numbers of participant nucleons. The / ratios do
not show dependence on centrality or transverse momentum, and are consistent
with previously measured values in hadron-hadron, hadron-nucleus,
nucleus-nucleus, and collisions.Comment: 403 authors from 72 institutions, 13 pages, 6 figures, 7 tables, 2012
data. v2 is version accepted by Physical Review 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
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