56 research outputs found
Cold Nuclear Matter Effects on J/psi Yields as a Function of Rapidity and Nuclear Geometry in Deuteron-Gold Collisions at sqrt(s_NN) = 200 GeV
We present measurements of J/psi yields in d+Au collisions at sqrt(s_NN) =
200 GeV recorded by the PHENIX experiment and compare with yields in p+p
collisions at the same energy per nucleon-nucleon collision. The measurements
cover a large kinematic range in J/psi rapidity (-2.2 < y < 2.4) with high
statistical precision and are compared with two theoretical models: one with
nuclear shadowing combined with final state breakup and one with coherent gluon
saturation effects. To remove model dependent systematic uncertainties we also
compare the data to a simple geometric model. We find that calculations where
the nuclear modification is linear or exponential in the density weighted
longitudinal thickness are difficult to reconcile with the forward rapidity
data.Comment: 449 authors from 66 institutions, 6 pages, 3 figures. Submitted to
Physical Review Letters. 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
Upsilon (1S+2S+3S) production in d+Au and p+p collisions at sqrt(s_NN)=200 GeV and cold-nuclear matter effects
The three Upsilon states, Upsilon(1S+2S+3S), are measured in d+Au and p+p
collisions at sqrt(s_NN)=200 GeV and rapidities 1.2<|y|<2.2 by the PHENIX
experiment at the Relativistic Heavy-Ion Collider. Cross sections for the
inclusive Upsilon(1S+2S+3S) production are obtained. The inclusive yields per
binary collision for d+Au collisions relative to those in p+p collisions
(R_dAu) are found to be 0.62 +/- 0.26 (stat) +/- 0.13 (syst) in the gold-going
direction and 0.91 +/- 0.33 (stat) +/- 0.16 (syst) in the deuteron-going
direction. The measured results are compared to a nuclear-shadowing model,
EPS09 [JHEP 04, 065 (2009)], combined with a final-state breakup cross section,
sigma_br, and compared to lower energy p+A results. We also compare the results
to the PHENIX J/psi results [Phys. Rev. Lett. 107, 142301 (2011)]. The rapidity
dependence of the observed Upsilon suppression is consistent with lower energy
p+A measurements.Comment: 495 authors, 11 pages, 9 figures, 5 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
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
Measurements of elliptic and triangular flow in high-multiplicity HeAu collisions at GeV
We present the first measurement of elliptic () and triangular ()
flow in high-multiplicity HeAu collisions at
GeV. Two-particle correlations, where the particles have a large separation in
pseudorapidity, are compared in HeAu and in collisions and
indicate that collective effects dominate the second and third Fourier
components for the correlations observed in the HeAu system. The
collective behavior is quantified in terms of elliptic and triangular
anisotropy coefficients measured with respect to their corresponding
event planes. The values are comparable to those previously measured in
Au collisions at the same nucleon-nucleon center-of-mass energy.
Comparison with various theoretical predictions are made, including to models
where the hot spots created by the impact of the three He nucleons on the
Au nucleus expand hydrodynamically to generate the triangular flow. The
agreement of these models with data may indicate the formation of low-viscosity
quark-gluon plasma even in these small collision systems.Comment: 630 authors, 9 pages, 4 figures, 2 tables. v2 is the version accepted
for publication by Physical Review Letters. 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 away-side jet fragments with respect to the reaction plane in Au+Au collisions at sqrt(s_NN) = 200 GeV
Pair correlations between large transverse momentum neutral pion triggers
(p_T=4--7 GeV/c) and charged hadron partners (p_T=3--7 GeV/c) in central
(0--20%) and midcentral (20--60%) Au+Au collisions are presented as a function
of trigger orientation with respect to the reaction plane. The particles are at
larger momentum than where jet shape modifications have been observed, and the
correlations are sensitive to the energy loss of partons traveling through hot
dense matter. An out-of-plane trigger particle produces only 26+/-20% of the
away-side pairs that are observed opposite of an in-plane trigger particle. In
contrast, near-side jet fragments are consistent with no suppression or
dependence on trigger orientation with respect to the reaction plane. These
observations are qualitatively consistent with a picture of little near-side
parton energy loss either due to surface bias or fluctuations and increased
away-side parton energy loss due to a long path through the medium. The
away-side suppression as a function of reaction-plane angle is shown to be
sensitive to both the energy loss mechanism in and the space-time evolution of
heavy-ion collisions.Comment: 427 authors, 15 pages, 14 figures, 1 table. 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
Transverse energy production and charged-particle multiplicity at midrapidity in various systems from to 200 GeV
Measurements of midrapidity charged particle multiplicity distributions,
, and midrapidity transverse-energy distributions,
, are presented for a variety of collision systems and energies.
Included are distributions for AuAu collisions at ,
130, 62.4, 39, 27, 19.6, 14.5, and 7.7 GeV, CuCu collisions at
and 62.4 GeV, CuAu collisions at
GeV, UU collisions at GeV,
Au collisions at GeV, HeAu collisions at
GeV, and collisions at
GeV. Centrality-dependent distributions at midrapidity are presented in terms
of the number of nucleon participants, , and the number of
constituent quark participants, . For all collisions
down to GeV, it is observed that the midrapidity data
are better described by scaling with than scaling with . Also presented are estimates of the Bjorken energy density,
, and the ratio of to ,
the latter of which is seen to be constant as a function of centrality for all
systems.Comment: 706 authors, 32 pages, 20 figures, 34 tables, 2004, 2005, 2008, 2010,
2011, and 2012 data. v2 is version accepted for publication in Phys. Rev.
Direct photon production in d+Au collisions at sqrt(s_NN)=200 GeV
Direct photons have been measured in sqrt(s_NN)=200 GeV d+Au collisions at
midrapidity. A wide p_T range is covered by measurements of nearly-real virtual
photons (1<p_T<6 GeV/c) and real photons (5<p_T<16 GeV/c). The invariant yield
of the direct photons in d+Au collisions over the scaled p+p cross section is
consistent with unity. Theoretical calculations assuming standard cold nuclear
matter effects describe the data well for the entire p_T range. This indicates
that the large enhancement of direct photons observed in Au+Au collisions for
1.0<p_T<2.5 GeV/c is due to a source other than the initial-state nuclear
effects.Comment: 547 authors, 7 pages, 4 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
Measurement of Transverse Single-Spin Asymmetries for J/psi Production in Polarized p+p Collisions at sqrt(s) = 200 GeV
We report the first measurement of transverse single-spin asymmetries in
production from transversely polarized collisions at GeV with data taken by the PHENIX experiment in 2006 and 2008. The
measurement was performed over the rapidity ranges and for transverse momenta up to 6 GeV/. production at RHIC is
dominated by processes involving initial-state gluons, and transverse
single-spin asymmetries of the can provide access to gluon dynamics
within the nucleon. Such asymmetries may also shed light on the long-standing
question in QCD of the production mechanism. Asymmetries were obtained
as a function of transverse momentum and Feynman-, with a value of
in the forward region. This
result suggests possible nonzero trigluon correlation functions in transversely
polarized protons and, if well defined in this reaction, a nonzero gluon Sivers
distribution function.Comment: 431 authors from 62 institutions, 13 pages, 5 figures, and 5 tables.
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
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