308 research outputs found
STAR inner tracking upgrade - A performance study
Anisotropic flow measurements have demonstrated development of partonic
collectivity in Au+Au collisions at RHIC. To understand the
partonic EOS, thermalization must be addressed. Collective motion of
heavy-flavor (c,b) quarks can be used to indicate the degree of thermalization
of the light-flavor quarks (u,d,s). Measurement of heavy-flavor quark
collectivity requires direct reconstruction of heavy-flavor hadrons in the low
\pt region. Measurement of open charm spectra to high \pt can be used to
investigate heavy-quark energy loss and medium properties. The Heavy Flavor
Tracker (HFT), a proposed upgrade to the STAR experiment at midrapidity, will
measure of open-charm hadrons to very low \pt by reconstructing their
displaced decay vertices. The innermost part of the HFT is the PIXEL detector
(made of two low mass monolithic active pixel sensor layers), which delivers a
high precision position measurement close to the collision vertex. The
Intermediate Silicon Tracker (IST), a 1-layer strip detector, is essential to
improve hit identification in the PIXEL detector when running at full RHIC-II
luminosity. Using a full GEANT simulation, open charm measurement capabilities
of STAR with the HFT will be shown. Its performance in a broad \pt range will
be demonstrated on (\pt > 0.5\mathrm{GeV}/c) and
(\pt < 10\mathrm{GeV}/c) measurements of \D meson. Results of
reconstruction of \Lc baryon in heavy-ion collisions are presented.Comment: to appear in EPJ C (Hot Quarks 2008 conference volume
Transverse Spin at PHENIX: Results and Prospects
The Relativistic Heavy Ion Collider (RHIC), as the world's first and only
polarized proton collider, offers a unique environment in which to study the
spin structure of the proton. In order to study the proton's transverse spin
structure, the PHENIX experiment at RHIC took data with transversely polarized
beams in 2001-02 and 2005, and it has plans for further running with transverse
polarization in 2006 and beyond. Results from early running as well as
prospective measurements for the future will be discussed.Comment: 6 pages, 2 figures, presented at Transversity 2005, Como, Ital
Does the Charm Flow at RHIC?
Recent PHENIX Au+Au -> e- + X data from open charm decay are shown to be
consistent with two extreme opposite dynamical scenarios of ultra-relativistic
nuclear reactions. Perturbative QCD without final state interactions was
previously shown to be consistent with the data. However, we show that the data
are also consistent with zero mean free path hydrodynamics characterized by a
common transverse flow velocity field. The surprising coincidence of both D and
B hydrodynamic flow spectra with pQCD up to p_T ~ 3 and 5 GeV, respectively,
suggests that heavy quarks may be produced essentially at rest in the rapidly
expanding gluon plasma. Possible implications and further tests of collective
heavy quark dynamics are discussed.Comment: 10 pages, 3 figures, submitted to Phys. Lett.
Antideuteron yield at the AGS and coalescence implications
We present Experiment 864's measurement of invariant antideuteron yields in
11.5A GeV/c Au + Pt collisions. The analysis includes 250 million triggers
representing 14 billion 10% central interactions sampled for events with high
mass candidates. We find (1/2 pi pt) d^(2)N/dydpt = 3.5 +/- 1.5 (stat.)
+0.9,-0.5 (sys.) x 10^(-8) GeV^(-2)c^(2) for 1.8=0.35 GeV/c
(y(cm)=1.6) and 3.7 +/- 2.7 (stat.) +1.4,-1.5 (sys.) x 10^(-8) GeV^(-2)c^(2)
for 1.4=0.26 GeV/c, and a coalescence parameter B2-bar of 4.1 +/-
2.9 (stat.) +2.3,-2.4 (sys.) x 10^(-3) GeV^(2)c^(-3). Implications for the
coalescence model and antimatter annihilation are discussed.Comment: 8 pages, 4 figures, Latex, submitted to Phys. Rev. Let
Mass dependence of light nucleus production in ultrarelativistic heavy ion collisions
Light nuclei can be produced in the central reaction zone via coalescence in
relativistic heavy ion collisions. E864 at BNL has measured the production of
ten light nuclei with nuclear number of A=1 to A=7 at rapidity and
. Data were taken with a Au beam of momentum of 11.5 A
on a Pb or Pt target with different experimental settings. The
invariant yields show a striking exponential dependence on nuclear number with
a penalty factor of about 50 per additional nucleon. Detailed analysis reveals
that the production may depend on the spin factor of the nucleus and the
nuclear binding energy as well.Comment: (6 pages, 3 figures), some changes on text, references and figures'
lettering. To be published in PRL (13Dec1999
Measurements of Light Nuclei Production in 11.5 A GeV/c Au+Pb Heavy-Ion Collisions
We report on measurements by the E864 experiment at the BNL-AGS of the yields
of light nuclei in collisions of Au(197) with beam momentum of 11.5 A GeV/c on
targets of Pb(208) and Pt(197). The yields are reported for nuclei with baryon
number A=1 up to A=7, and typically cover a rapidity range from y(cm) to
y(cm)+1 and a transverse momentum range of approximately 0.1 < p(T)/A < 0.5
GeV/c. We calculate coalescence scale factors B(A) from which we extract model
dependent source dimensions and collective flow velocities. We also examine the
dependences of the yields on baryon number, spin, and isospin of the produced
nuclei.Comment: 21 figures-to be published in Phys. Rev.
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Beam Energy and Centrality Dependence of Direct-Photon Emission from Ultrarelativistic Heavy-Ion Collisions.
The PHENIX collaboration presents first measurements of low-momentum (0.41 GeV/c) direct-photon yield dN_{γ}^{dir}/dη is a smooth function of dN_{ch}/dη and can be well described as proportional to (dN_{ch}/dη)^{α} with α≈1.25. This scaling behavior holds for a wide range of beam energies at the Relativistic Heavy Ion Collider and the Large Hadron Collider, for centrality selected samples, as well as for different A+A collision systems. At a given beam energy, the scaling also holds for high p_{T} (>5 GeV/c), but when results from different collision energies are compared, an additional sqrt[s_{NN}]-dependent multiplicative factor is needed to describe the integrated-direct-photon yield
The Ter-Mikayelian Effect on QCD Radiative Energy Loss
The color dielectric modification of the gluon dispersion relation in a dense
QCD medium suppresses both the soft and collinear gluon radiation associated
with jet production. We compute both the longitudinal and transverse plasmon
contributions to the zeroth order in opacity radiative energy loss. This QCD
analog of the Ter-Mikayelian effect in QED leads to reduction of the
energy loss of high transverse momentum charm quarks produced in a QCD plasma
with a characteristic Debye mass GeV.Comment: 18 Pages, 16 Figure
Deuteron and antideuteron production in Au+Au collisions at sqrt(s_NN)=200 GeV
The production of deuterons and antideuterons in the transverse momentum
range 1.1 < p_T < 4.3 GeV/c at mid-rapidity in Au + Au collisions at
sqrt(s_NN)=200 GeV has been studied by the PHENIX experiment at RHIC. A
coalescence analysis comparing the deuteron and antideuteron spectra with those
of protons and antiprotons, has been performed. The coalescence probability is
equal for both deuterons and antideuterons and increases as a function of p_T,
which is consistent with an expanding collision zone. Comparing (anti)proton
yields p_bar/p = 0.73 +/- 0.01, with (anti)deuteron yields: d_bar/d = 0.47 +/-
0.03, we estimate that n_bar/n = 0.64 +/- 0.04.Comment: 326 authors, 6 pages text, 5 figures, 1 Table. 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
Mid-Rapidity Direct-Photon Production in p+p Collisions at sqrt(s) = 200 GeV
A measurement of direct photons in p+p collisions at sqrt(s)=200 GeV is
presented. A photon excess above background from pi^0 --> gamma+gamma, eta -->
gamma+gamma, and other decays is observed in the transverse momentum range 5.5
< p_T < 7 GeV/c. The result is compared to a next-to-leading-order perturbative
QCD calculation. Within errors, good agreement is found between the QCD
calculation and the measured result.Comment: 330 authors, 7 pages text, RevTeX, 2 figures, 2 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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