156 research outputs found
Production of phi mesons at mid-rapidity in sqrt(s_NN) = 200 GeV Au+Au collisions at RHIC
We present the first results of meson production in the K^+K^- decay channel
from Au+Au collisions at sqrt(s_NN) = 200 GeV as measured at mid-rapidity by
the PHENIX detector at RHIC. Precision resonance centroid and width values are
extracted as a function of collision centrality. No significant variation from
the PDG accepted values is observed. The transverse mass spectra are fitted
with a linear exponential function for which the derived inverse slope
parameter is seen to be constant as a function of centrality. These data are
also fitted by a hydrodynamic model with the result that the freeze-out
temperature and the expansion velocity values are consistent with the values
previously derived from fitting single hadron inclusive data. As a function of
transverse momentum the collisions scaled peripheral.to.central yield ratio RCP
for the is comparable to that of pions rather than that of protons. This result
lends support to theoretical models which distinguish between baryons and
mesons instead of particle mass for explaining the anomalous proton yield.Comment: 326 authors, 24 pages text, 23 figures, 6 tables, RevTeX 4. To be
submitted to Physical Review C as a regular article. 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
Effective Rheology of Bubbles Moving in a Capillary Tube
We calculate the average volumetric flux versus pressure drop of bubbles
moving in a single capillary tube with varying diameter, finding a square-root
relation from mapping the flow equations onto that of a driven overdamped
pendulum. The calculation is based on a derivation of the equation of motion of
a bubble train from considering the capillary forces and the entropy production
associated with the viscous flow. We also calculate the configurational
probability of the positions of the bubbles.Comment: 4 pages, 1 figur
Ca2+ Extrusion by NCX Is Compromised in Olfactory Sensory Neurons of OMP−/− Mice
The role of olfactory marker protein (OMP), a hallmark of mature olfactory sensory neurons (OSNs), has been poorly understood since its discovery. The electrophysiological and behavioral phenotypes of OMP knockout mice indicated that OMP influences olfactory signal transduction. However, the mechanism by which this occurs remained unknown.We used intact olfactory epithelium obtained from WT and OMP(-/-) mice to monitor the Ca(2+) dynamics induced by the activation of cyclic nucleotide-gated channels, voltage-operated Ca(2+) channels, or Ca(2+) stores in single dendritic knobs of OSNs. Our data suggested that OMP could act to modulate the Ca(2+)-homeostasis in these neurons by influencing the activity of the plasma membrane Na(+)/Ca(2+)-exchanger (NCX). Immunohistochemistry verifies colocalization of NCX1 and OMP in the cilia and knobs of OSNs. To test the role of NCX activity, we compared the kinetics of Ca(2+) elevation by stimulating the reverse mode of NCX in both WT and OMP(-/-) mice. The resulting Ca(2+) responses indicate that OMP facilitates NCX activity and allows rapid Ca(2+) extrusion from OSN knobs. To address the mechanism by which OMP influences NCX activity in OSNs we studied protein-peptide interactions in real-time using surface plasmon resonance technology. We demonstrate the direct interaction of the XIP regulatory-peptide of NCX with calmodulin (CaM).Since CaM also binds to the Bex protein, an interacting protein partner of OMP, these observations strongly suggest that OMP can influence CaM efficacy and thus alters NCX activity by a series of protein-protein interactions
J/psi production from proton-proton collisions at sqrt(s) = 200 GeV
J/psi production has been measured in proton-proton collisions at sqrt(s)=
200 GeV over a wide rapidity and transverse momentum range by the PHENIX
experiment at RHIC. Distributions of the rapidity and transverse momentum,
along with measurements of the mean transverse momentum and total production
cross section are presented and compared to available theoretical calculations.
The total J/psi cross section is 3.99 +/- 0.61(stat) +/- 0.58(sys) +/-
0.40(abs) micro barns. The mean transverse momentum is 1.80 +/- 0.23(stat) +/-
0.16(sys) GeV/c.Comment: 326 authors, 6 pages text, 4 figures, 1 table, RevTeX 4. To be
submitted to PRL. 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 Single Electron Event Anisotropy in Au+Au Collisions at sqrt(s_NN) = 200 GeV
The transverse momentum dependence of the azimuthal anisotropy parameter v_2,
the second harmonic of the azimuthal distribution, for electrons at
mid-rapidity (|eta| < 0.35) has been measured with the PHENIX detector in Au+Au
collisions at sqrt(s_NN) = 200 GeV. The measurement was made with respect to
the reaction plane defined at high rapidities (|eta| = 3.1 -- 3.9). From the
result we have measured the v_2 of electrons from heavy flavor decay after
subtraction of the v_2 of electrons from other sources such as photon
conversions and Dalitz decay from light neutral mesons. We observe a non-zero
single electron v_2 with a 90% confidence level in the intermediate p_T region.Comment: 330 authors, 11 pages text, RevTeX4, 9 figures, 1 tables. 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
Systematic Studies of the Centrality and sqrt(s_NN) Dependence of dE_T/deta and dN_ch/deta in Heavy Ion Collisions at Mid-rapidity
The PHENIX experiment at RHIC has measured transverse energy and charged
particle multiplicity at mid-rapidity in Au+Au collisions at sqrt(s_NN) = 19.6,
130 and 200 GeV as a function of centrality. The presented results are compared
to measurements from other RHIC experiments, and experiments at lower energies.
The sqrt(s_NN) dependence of dE_T/deta and dN_ch/deta per pair of participants
is consistent with logarithmic scaling for the most central events. The
centrality dependence of dE_T/deta and dN_ch/deta is similar at all measured
incident energies. At RHIC energies the ratio of transverse energy per charged
particle was found independent of centrality and growing slowly with
sqrt(s_NN). A survey of comparisons between the data and available theoretical
models is also presented.Comment: 327 authors, 25 pages text, 19 figures, 17 tables, RevTeX 4. To be
submitted to Physical Review C as a regular article. 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
Centrality Dependence of Charm Production from Single Electrons in Au+Au Collisions at sqrt(s_NN) = 200 GeV
The PHENIX experiment has measured mid-rapidity transverse momentum spectra
(0.4 < p_T < 4.0 GeV/c) of single electrons as a function of centrality in
Au+Au collisions at sqrt(s_NN) = 200 GeV. Contributions to the raw spectra from
photon conversions and Dalitz decays of light neutral mesons are measured by
introducing a thin (1.7% X_0) converter into the PHENIX acceptance and are
statistically removed. The subtracted ``non-photonic'' electron spectra are
primarily due to the semi-leptonic decays of hadrons containing heavy quarks
(charm and bottom). For all centralities, charm production is found to scale
with the nuclear overlap function, T_AA. For minimum-bias collisions the charm
cross section per binary collision is N_cc^bar/T_AA = 622 +/- 57 (stat.) +/-
160 (sys.) microbarns.Comment: 326 authors, 4 pages text, 3 figures, 1 table, RevTeX 4. To be
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
Alignment of the ALICE Inner Tracking System with cosmic-ray tracks
37 pages, 15 figures, revised version, accepted by JINSTALICE (A Large Ion Collider Experiment) is the LHC (Large Hadron Collider) experiment devoted to investigating the strongly interacting matter created in nucleus-nucleus collisions at the LHC energies. The ALICE ITS, Inner Tracking System, consists of six cylindrical layers of silicon detectors with three different technologies; in the outward direction: two layers of pixel detectors, two layers each of drift, and strip detectors. The number of parameters to be determined in the spatial alignment of the 2198 sensor modules of the ITS is about 13,000. The target alignment precision is well below 10 micron in some cases (pixels). The sources of alignment information include survey measurements, and the reconstructed tracks from cosmic rays and from proton-proton collisions. The main track-based alignment method uses the Millepede global approach. An iterative local method was developed and used as well. We present the results obtained for the ITS alignment using about 10^5 charged tracks from cosmic rays that have been collected during summer 2008, with the ALICE solenoidal magnet switched off.Peer reviewe
First measurement of the |t|-dependence of coherent J/ψ photonuclear production
The first measurement of the cross section for coherent J/ψ photoproduction as a function of |t|, the square of the momentum transferred between the incoming and outgoing target nucleus, is presented. The data were measured with the ALICE detector in ultra-peripheral Pb–Pb collisions at a centre-of-mass energy per nucleon pair sNN=5.02TeV with the J/ψ produced in the central rapidity region |y|<0.8, which corresponds to the small Bjorken-x range (0.3−1.4)×10−3.
The measured |t|-dependence is not described by computations based only on the Pb nuclear form factor, while the photonuclear cross section is better reproduced by models including shadowing according to the leading-twist approximation, or gluon-saturation effects from the impact-parameter dependent Balitsky–Kovchegov equation. These new results are therefore a valid tool to constrain the relevant model parameters and to investigate the transverse gluonic structure at very low Bjorken-x.publishedVersio
Resolving the strange behavior of extraterrestrial potassium in the upper atmosphere
It has been known since the 1960s that the layers of Na and K atoms, which occur between 80 and 105 km in the Earth's atmosphere as a result of meteoric ablation, exhibit completely different seasonal behavior. In the extratropics Na varies annually, with a pronounced wintertime maximum and summertime minimum. However, K varies semiannually with a small summertime maximum and minima at the equinoxes. This contrasting behavior has never been satisfactorily explained. Here we use a combination of electronic structure and chemical kinetic rate theory to determine two key differences in the chemistries of K and Na. First, the neutralization of K+ ions is only favored at low temperatures during summer. Second, cycling between K and its major neutral reservoir KHCO3 is essentially temperature independent. A whole atmosphere model incorporating this new chemistry, together with a meteor input function, now correctly predicts the seasonal behavior of the K layer
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