230 research outputs found
Cold Nuclear Matter Effects and Heavy Quark Production in PHENIX
The PHENIX experiment uses semileptonic decay channels to measure open and
closed heavy flavor cross sections across the rapidity range .
High luminosity data are now available for p+p, d+Au, Cu+Cu and Au+Au
collisions at =200 GeV, and for Au+Au collisions at
= 62 GeV. We discuss recent d+Au results for open heavy flavor
and production, and discuss their implications for the cold nuclear
matter contributions to heavy flavor production in heavy ion collisions.Comment: 8 pages, 9 figures. Proceedings for talk at Hard Probes 201
Quarkonia Measurements with STAR
We report results on quarkonium production from the STAR experiment at the
Relativistic Heavy-Ion Collider (RHIC). J/psi spectra in p+p and Cu+Cu
collisions at sqrt(s) = 200 GeV with transverse momenta in the range of 0.5-14
GeV/c and 5-8 GeV/c, respectively, are presented. We find that for p_T > 5
GeV/c yields in p+p collisions are consistent with those in minimum-bias Cu+Cu
collisions scaled with the respective number of binary nucleon-nucleon
collisions. In this range the nuclear modification factor, R_AA, is measured to
be 0.9+-0.2(stat). For the first time at RHIC, high-p_T J/psi-hadron
correlations were studied in p+p collisions. Implications from our measurements
on J/psi production mechanisms, constraints on open bottom yields, and J/psi
dissociation mechanisms at high-p_T are discussed. In addition, we give a brief
status of measurements of Upsilon production in p+p and Au+Au collisions and
present projections of future quarkonia measurements based on an upgrades to
the STAR detector and increased luminosity achieved through stochastic cooling
of RHIC.Comment: 5 pages, 5 figures. Prepared for 3rd International Conference on Hard
and Electromagnetic Probes of High-Energy Nuclear Collisions (Hard Probes
2008), A Toxa, Spain, June 8-14, 200
C10 and 11B+ 12C reactions from 4 to 9 MeV/nucleon
Reaction products arising from the interaction of 11B+ 12C and 10B+ 13C have been studied in the energy range 4<Elab(B)<9 MeV/nucleon. From the total fusion cross sections for the two entrance channels, the critical angular momenta have been extracted and then compared as a function of compound nucleus excitation energy. Even though a limitation in the fusion cross section was observed, no common limitation was found in the critical angular momenta for these two systems up to at least a Na23 excitation energy of 60 MeV. Above this excitation energy, the experimental uncertainties make this point less clear. Up to an excitation energy of 60 MeV in Na23, a fusion limitation based on reaching a critical density of compound nucleus states like the yrast or ''statistical'' yrast line cannot be responsible for the fusion cross section limitations observed for these entrance channels. The present data suggest that competing entrance channel processes are responsible for the observed fusion cross section limitations
Energy dependence of fusion evaporation-residue cross sections in the Si28+12C reaction
Fusion evaporation-residue cross sections for the Si28+12C reaction have been measured in the energy range 18≤Ec.m.≤136 MeV using time-of-flight techniques. Velocity distributions of mass-identified reaction products were used to identify evaporation residues and to determine the complete-fusion cross sections at high energies. The data are in agreement with previously established systematics which indicate an entrance-channel mass-asymmetry dependence of the incomplete-fusion evaporation-residue process. The complete-fusion evaporation-residue cross sections and the deduced critical angular momenta are compared with earlier measurements and the predictions of existing models
Nuclear effects on J/{\psi} production in proton-nucleus collisions
The study of nuclear effects for J/{\psi} production in proton-nucleus
collisions is crucial for a correct interpretation of the J/{\psi} suppression
patterns experimentally observed in heavy-ion collisions. By means of three
representative sets of nuclear parton distribution, the energy loss effect in
the initial state and the nuclear absorption effect in the final state are
taken into account in the uniform framework of the Glauber model. A leading
order phenomenological analysis is performed on J/{\psi} production
cross-section ratios RW/Be(xF) for the E866 experimental data. The J/{\psi}
suppression is investigated quantitatively due to the different nuclear
effects. It is shown that the energy loss effect with resulting in the
suppression on RW/Be(xF) is more important than the nuclear effects on parton
distributions in high xF region. The E866 data in the small xF keep out the
nuclear gluon distribution with a large anti-shadowing effect. However, the new
HERA-B measurement is not in support of the anti-shadowing effect in the
nuclear gluon distribution. It is found that the J/{\psi}-nucleon inelastic
cross section {\sigma} J/{\psi} abs depends on the kinematical variable xF, and
increases as xF in the region xF > 0.2. 1 Introductio
Proximity effect at superconducting Sn-Bi2Se3 interface
We have investigated the conductance spectra of Sn-Bi2Se3 interface junctions
down to 250 mK and in different magnetic fields. A number of conductance
anomalies were observed below the superconducting transition temperature of Sn,
including a small gap different from that of Sn, and a zero-bias conductance
peak growing up at lower temperatures. We discussed the possible origins of the
smaller gap and the zero-bias conductance peak. These phenomena support that a
proximity-effect-induced chiral superconducting phase is formed at the
interface between the superconducting Sn and the strong spin-orbit coupling
material Bi2Se3.Comment: 7 pages, 8 figure
Centrality Dependence of the High p_T Charged Hadron Suppression in Au+Au collisions at sqrt(s_NN) = 130 GeV
PHENIX has measured the centrality dependence of charged hadron p_T spectra
from central Au+Au collisions at sqrt(s_NN)=130 GeV. The truncated mean p_T
decreases with centrality for p_T > 2 GeV/c, indicating an apparent reduction
of the contribution from hard scattering to high p_T hadron production. For
central collisions the yield at high p_T is shown to be suppressed compared to
binary nucleon-nucleon collision scaling of p+p data. This suppression is
monotonically increasing with centrality, but most of the change occurs below
30% centrality, i.e. for collisions with less than about 140 participating
nucleons. The observed p_T and centrality dependence is consistent with the
particle production predicted by models including hard scattering and
subsequent energy loss of the scattered partons in the dense matter created in
the collisions.Comment: 7 pages text, LaTeX, 6 figures, 2 tables, 307 authors, resubmitted to
Phys. Lett. B. Revised to address referee concerns. Plain text data tables
for the points plotted in figures for this and previous PHENIX publications
are publicly available at
http://www.phenix.bnl.gov/phenix/WWW/run/phenix/papers.htm
Heavy Quarks and Heavy Quarkonia as Tests of Thermalization
We present here a brief summary of new results on heavy quarks and heavy
quarkonia from the PHENIX experiment as presented at the "Quark Gluon Plasma
Thermalization" Workshop in Vienna, Austria in August 2005, directly following
the International Quark Matter Conference in Hungary.Comment: 8 pages, 5 figures, Quark Gluon Plasma Thermalization Workshop
(Vienna August 2005) Proceeding
Single Electrons from Heavy Flavor Decays in p+p Collisions at sqrt(s) = 200 GeV
The invariant differential cross section for inclusive electron production in
p+p collisions at sqrt(s) = 200 GeV has been measured by the PHENIX experiment
at the Relativistic Heavy Ion Collider over the transverse momentum range $0.4
<= p_T <= 5.0 GeV/c at midrapidity (eta <= 0.35). The contribution to the
inclusive electron spectrum from semileptonic decays of hadrons carrying heavy
flavor, i.e. charm quarks or, at high p_T, bottom quarks, is determined via
three independent methods. The resulting electron spectrum from heavy flavor
decays is compared to recent leading and next-to-leading order perturbative QCD
calculations. The total cross section of charm quark-antiquark pair production
is determined as sigma_(c c^bar) = 0.92 +/- 0.15 (stat.) +- 0.54 (sys.) mb.Comment: 329 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
Nuclear Modification of Electron Spectra and Implications for Heavy Quark Energy Loss in Au+Au Collisions at sqrt(s_NN)=200 GeV
The PHENIX experiment has measured mid-rapidity transverse momentum spectra
(0.4 < p_T < 5.0 GeV/c) of electrons as a function of centrality in Au+Au
collisions at sqrt(s_NN)=200 GeV. Contributions from photon conversions and
from light hadron decays, mainly Dalitz decays of pi^0 and eta mesons, were
removed. The resulting non-photonic electron spectra are primarily due to the
semi-leptonic decays of hadrons carrying heavy quarks. Nuclear modification
factors were determined by comparison to non-photonic electrons in p+p
collisions. A significant suppression of electrons at high p_T is observed in
central Au+Au collisions, indicating substantial energy loss of heavy quarks.Comment: 330 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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