352 research outputs found
First axion dark matter search with toroidal geometry
We firstly report an axion haloscope search with toroidal geometry. In this
pioneering search, we exclude the axion-photon coupling
down to about GeV over the axion mass range from 24.7
to 29.1 eV at a 95\% confidence level. The prospects for axion dark matter
searches with larger scale toroidal geometry are also considered.Comment: 5 pages, 5 figures, 1 table and to appear in PRD-R
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
Quadrupole Anisotropy in Dihadron Azimuthal Correlations in Central Au Collisions at =200 GeV
The PHENIX collaboration at the Relativistic Heavy Ion Collider (RHIC)
reports measurements of azimuthal dihadron correlations near midrapidity in
Au collisions at =200 GeV. These measurements
complement recent analyses by experiments at the Large Hadron Collider (LHC)
involving central Pb collisions at =5.02 TeV, which
have indicated strong anisotropic long-range correlations in angular
distributions of hadron pairs. The origin of these anisotropies is currently
unknown. Various competing explanations include parton saturation and
hydrodynamic flow. We observe qualitatively similar, but larger, anisotropies
in Au collisions compared to those seen in Pb collisions at the
LHC. The larger extracted values in Au collisions at RHIC are
consistent with expectations from hydrodynamic calculations owing to the larger
expected initial-state eccentricity compared with that from Pb
collisions. When both are divided by an estimate of the initial-state
eccentricity the scaled anisotropies follow a common trend with multiplicity
that may extend to heavy ion data at RHIC and the LHC, where the anisotropies
are widely thought to arise from hydrodynamic flow.Comment: 375 authors, 7 pages, 5 figures. Published in Phys. Rev. Lett. v2 has
minor changes to text and figures in response to PRL referee suggestions.
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
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
Double Spin Asymmetry of Electrons from Heavy Flavor Decays in p+p Collisions at sqrt(s)=200 GeV
We report on the first measurement of double-spin asymmetry, A_LL, of
electrons from the decays of hadrons containing heavy flavor in longitudinally
polarized p+p collisions at sqrt(s)=200 GeV for p_T= 0.5 to 3.0 GeV/c. The
asymmetry was measured at mid-rapidity (|eta|<0.35) with the PHENIX detector at
the Relativistic Heavy Ion Collider. The measured asymmetries are consistent
with zero within the statistical errors. We obtained a constraint for the
polarized gluon distribution in the proton of |Delta g/g(log{_10}x=
-1.6^+0.5_-0.4, {mu}=m_T^c)|^2 < 0.033 (1 sigma), based on a leading-order
perturbative-quantum-chromodynamics model, using the measured asymmetry.Comment: 385 authors, 17 pages, 15 figures, 5 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
Cross section for production via dielectrons in dAu collisions at GeV
We report a measurement of pairs from semileptonic heavy-flavor
decays in Au collisions at GeV. Exploring the mass
and transverse-momentum dependence of the yield, the bottom decay contribution
can be isolated from charm, and quantified by comparison to {\sc pythia} and
{\sc mc@nlo} simulations. The resulting -production cross section is
~mb, which is equivalent to a nucleon-nucleon cross section of
b.Comment: 375 authors, 16 pages, 8 figures, 7 tables, 2008 data. 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
Suppression of back-to-back hadron pairs at forward rapidity in d+Au Collisions at sqrt(s_NN)=200 GeV
Back-to-back hadron pair yields in d+Au and p+p collisions at sqrt(s_NN)=200
GeV were measured with the PHENIX detector at the Relativistic Heavy Ion
Collider. Rapidity separated hadron pairs were detected with the trigger hadron
at pseudorapidity |eta|<0.35 and the associated hadron at forward rapidity
(deuteron direction, 3.0<eta<3.8). Pairs were also detected with both hadrons
measured at forward rapidity; in this case the yield of back-to-back hadron
pairs in d+Au collisions with small impact parameters is observed to be
suppressed by a factor of 10 relative to p+p collisions. The kinematics of
these pairs is expected to probe partons in the Au nucleus with low fraction x
of the nucleon momenta, where the gluon densities rise sharply. The observed
suppression as a function of nuclear thickness, p_T, and eta points to cold
nuclear matter effects arising at high parton densities.Comment: 381 authors, 6 pages, 4 figures. Published in Phys. Rev. Lett.
(http://link.aps.org/doi/10.1103/PhysRevLett.107.172301). v3 has minor
changes to match published version
(http://www.phenix.bnl.gov/phenix/WWW/info/pp1/128/PhysRevLett.107.172301)
Plain text data tables for points plotted in figures are publicly available
at http://www.phenix.bnl.gov/phenix/WWW/info/data/ppg128_data.htm
Azimuthal anisotropy of neutral pion production in Au+Au collisions at sqrt(s_NN) = 200 GeV: Path-length dependence of jet quenching and the role of initial geometry
We have measured the azimuthal anisotropy of pi0's for 1 < pT < 18 GeV/c for
Au+Au collisions at sqrt s_NN = 200 GeV. The observed anisotropy shows a
gradual decrease in 3 < pT < 7 - 10 GeV/c, but remains positive beyond 10
GeV/c. The magnitude of this anisotropy is under-predicted, up to at least 10
GeV/c, by current perturbative QCD (pQCD) energy-loss model calculations. An
estimate of the increase in anisotropy expected from initial-geometry
modification due to gluon saturation effects and initial-geometry fluctuations
is insufficient to account for this discrepancy. Calculations which implement a
path length dependence steeper than what is implied by current pQCD energy-loss
models, show reasonable agreement with the data.Comment: 384 authors, 6 pages text, 3 figures. Submitted to 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
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