41 research outputs found
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
Measurement of jet-medium interactions via direct photon-hadron correlations in AuAu and Au collisions at GeV
We present direct photon-hadron correlations in 200 GeV/A AuAu, Au
and collisions, for direct photon from 5--12 GeV/, collected
by the PHENIX Collaboration in the years from 2006 to 2011. We observe no
significant modification of jet fragmentation in Au collisions,
indicating that cold nuclear matter effects are small or absent. Hadrons
carrying a large fraction of the quark's momentum are suppressed in AuAu
compared to and Au. As the momentum fraction decreases, the
yield of hadrons in AuAu increases to an excess over the yield in
collisions. The excess is at large angles and at low hadron and is most
pronounced for hadrons associated with lower momentum direct photons.
Comparison to theoretical calculations suggests that the hadron excess arises
from medium response to energy deposited by jets.Comment: 578 authors from 80 institutions, 11 pages, 7 figures, data from
2007, 2008, 2010, and 2011. 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
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
Confirmation of the existence of the X17 particle
In a 2016 paper, an anomaly in the internal pair creation on the M1 transition depopulating the 18.15 MeV isoscalar 1+ state on 8Be was observed. This could be explained by the creation and subsequent decay of a new boson, with mass mXc2 = 16.70 MeV. Further experiments of the same transition with an improved and independent setup were performed, which constrained the mass of the X17 boson (mXc2) and its branching ratio relative to the γ-decay of the 8Be excited state (BX), to mXc2 = 17.01(16) MeV and BX = 6(1) 10−6, respectively. Using the latter setup, the e+e− pairs depopulating the 21 MeV Jπ = 0− 0+ transition in 4He were investigated and a resonance in the angular correlation of the pairs was observed, which could be explained by the same X17 particle, with mass mXc2 = 16.98 ± 0.16(stat) ± 0.20(syst) MeV
A new anomaly observed in He supporting the existence of the hypothetical X17 particle
Recently, we observed an anomalous peak-like excess of internal pairs at around 140° for the M1 transition depopulating the 18.15 MeV isoscalar state in Be. The deviation from the theoretical prediction can be described by GEANT simulations assuming the creation and subsequent decay of a new, light boson with a mass of 16.7 MeV/. In order to reduce the possible systematic errors from the experimenntal data, we re-investigated the Be anomaly with an improved setup and confirmed the anomaly within the statistical uncertainties. We also studied the angular correlation of the electron-positron pairs created in the M0 transition depopulating the 21.01 MeV 0 state in He, and observed an anomalous excess of pairs at a significantly smaller angle of 115°. Since the transition energy was higher in this case, the observed anomaly could be described by assuming the creation and subsequent decay of the same light particle in the simulations
Confirmation of the existence of the X17 particle
In a 2016 paper, an anomaly in the internal pair creation on the M1 transition depopulating the 18.15 MeV isoscalar 1+ state on 8Be was observed. This could be explained by the creation and subsequent decay of a new boson, with mass mXc2 = 16.70 MeV. Further experiments of the same transition with an improved and independent setup were performed, which constrained the mass of the X17 boson (mXc2) and its branching ratio relative to the γ-decay of the 8Be excited state (BX), to mXc2 = 17.01(16) MeV and BX = 6(1) 10−6, respectively. Using the latter setup, the e+e− pairs depopulating the 21 MeV Jπ = 0− 0+ transition in 4He were investigated and a resonance in the angular correlation of the pairs was observed, which could be explained by the same X17 particle, with mass mXc2 = 16.98 ± 0.16(stat) ± 0.20(syst) MeV