37 research outputs found
Measurement of -meson production in CuAu at GeV and UU at GeV
The PHENIX experiment reports systematic measurements at the Relativistic
Heavy Ion Collider of -meson production in asymmetric CuAu collisions
at =200 GeV and in UU collisions at =193
GeV. Measurements were performed via the decay
channel at midrapidity . Features of -meson production
measured in CuCu, CuAu, AuAu, and UU collisions were found to not
depend on the collision geometry, which was expected because the yields are
averaged over the azimuthal angle and follow the expected scaling with
nuclear-overlap size. The elliptic flow of the meson in CuAu,
AuAu, and UU collisions scales with second order participant eccentricity
and the length scale of the nuclear overlap region (estimated with the number
of participating nucleons). At moderate , -meson production measured
in CuAu and UU collisions is consistent with coalescence-model
predictions, whereas at high the production is in agreement with
expectations for in-medium energy loss of parent partons prior to their
fragmentation. The elliptic flow for mesons measured in CuAu and
UU collisions is well described by a (2+1)D viscous-hydrodynamic model with
specific-shear viscosity .Comment: 411 authors from 76 institutions, 16 pages, 12 figures, 9 tables,
2012 data. v1 is version submitted to 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
Measurement of nuclear modification at backward and forward rapidity in , Al, and Au collisions at GeV
Suppression of the nuclear-modification factor has been seen as a
trademark signature of final-state effects in large collision systems for
decades. In small systems, the nuclear modification was attributed to
cold-nuclear-matter effects until the observation of strong differential
suppression of the state in collisions suggested the
presence of final-state effects. Results of and
measurements in the dimuon decay channel are presented here for ,
Al, and Au collision systems at GeV. The
results are predominantly shown in the form of the nuclear-modification factor,
, the ratio of the invariant yield per nucleon-nucleon
collision in collisions of proton on target nucleus to that in
collisions. Measurements of the and nuclear-modification
factor are compared with shadowing and transport-model predictions, as well as
to complementary measurements at Large-Hadron-Collider energies.Comment: 315 authors from 69 institutions, 16 pages, 9 figures, 4 tables, 2015
data. v2 is version accepted for publication in 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
Improving constraints on gluon spin-momentum correlations in transversely polarized protons via midrapidity open-heavy-flavor electrons in collisions at GeV
Polarized proton-proton collisions provide leading-order access to gluons, presenting an opportunity to constrain gluon spin-momentum correlations within transversely polarized protons and enhance our understanding of the three-dimensional structure of the proton. Midrapidity open-heavy-flavor production at GeV is dominated by gluon-gluon fusion, providing heightened sensitivity to gluon dynamics relative to other production channels. Transverse single-spin asymmetries of electrons and positrons from heavy-flavor hadron decays are measured at midrapidity using the PHENIX detector at the Relativistic Heavy Ion Collider. These charge-separated measurements are sensitive to gluon correlators that can in principle be related to gluon orbital angular momentum via model calculations. Explicit constraints on gluon correlators are extracted for two separate models, one of which had not been constrained previously
Disentangling centrality bias and final-state effects in the production of high- using direct in Au collisions at GeV
International audiencePHENIX presents a simultaneous measurement of the production of direct and in Au collisions at GeV over a range of 7.5 to 18 GeV/ for different event samples selected by event activity, i.e. charged-particle multiplicity detected at forward rapidity. Direct-photon yields are used to empirically estimate the contribution of hard-scattering processes in the different event samples. Using this estimate, the average nuclear-modification factor is , consistent with unity for minimum-bias (MB) Au events. For event classes with moderate event activity, is consistent with the MB value within 5% uncertainty. These results confirm that the previously observed enhancement of high- production found in small-system collisions with low event activity is a result of a bias in interpreting event activity within the Glauber framework. In contrast, for the top 5% of events with the highest event activity, is suppressed by 20% relative to the MB value with a significance of , which may be due to final-state effects
Improving constraints on gluon spin-momentum correlations in transversely polarized protons via midrapidity open-heavy-flavor electrons in collisions at GeV
Polarized proton-proton collisions provide leading-order access to gluons,
presenting an opportunity to constrain gluon spin-momentum correlations within
transversely polarized protons and enhance our understanding of the
three-dimensional structure of the proton. Midrapidity open-heavy-flavor
production at GeV is dominated by gluon-gluon fusion, providing
heightened sensitivity to gluon dynamics relative to other production channels.
Transverse single-spin asymmetries of electrons and positrons from heavy-flavor
hadron decays are measured at midrapidity using the PHENIX detector at the
Relativistic Heavy Ion Collider. These charge-separated measurements are
sensitive to gluon correlators that can in principle be related to gluon
orbital angular momentum via model calculations. Explicit constraints on gluon
correlators are extracted for two separate models, one of which had not been
constrained previously.Comment: 315 authors from 69 institutions, 8 pages, 2 figures, 2015 data;
followed by ancillary material: 3 pages, 3 figures, 3 tables. 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