2,591 research outputs found
suppression in the threshold model at RHIC and LHC energy
In the QGP based threshold model \cite{Blaizot:2000ev,Blaizot:1996nq}, in
addition to the normal nuclear absorption, 's are subjected to an
'anomalous' suppression such that above a threshold density , all
the 's are melted. In the threshold model we have analysed the recent
PHENIX data on the centrality dependence of suppression in Au+Au
collisions at RHIC. Feedback from decay of the state is accounted for.
's are anomalously suppressed above a threshold density,
. Threshold density for anomalous
suppression of the state is uncertain to a large extent, . The fraction of the state can not be determined
unambiguously, depending on the nuclear absorption, it can vary from 20% to
40%. We have also predicted for the suppression in Pb+Pb collisions at LHC
energy. In central Pb+Pb collisions, 's are suppressed by a factor of
3-4. Suppression pattern is rather similar to that in Au+Au collisions, if not
slighty less in central collisions. Using the PHENIX data on the participant
number dependence of the Bjorken energy density, we have also estimated the QGP
formation time. For critical temperature =192 MeV, estimated QGP formation
time ranges between 0.07-0.09 fm/c.Comment: 9 pages, 9 figure
Recent Heavy-Flavor results at STAR
We present the recent results on non-photonic electron (NPE) yields from RHIC
run8 p+p collisions. The ratio as a function of in run8 with a
factor of 10 reduction of the inner detector material at STAR is found to be
consistent with those results from run3 taking into account the NPE from charm
leptonic decay and the difference of photonic electron yield from photon
conversion in detector material. \Jpsi spectra in \pp and \cucu collisions at
\sNN = 200 GeV with high sampled luminosity \Jpsi spectrum at high-\pT follows
scaling, but the scaling is violated at low \pT. -hadron
correlations in \pp collisions are studied to understand the \Jpsi production
mechanism at high . We observed an absence of charged hadrons accompanying
\Jpsi on the near-side, in contrast to the strong correlation peak in the
di-hadron correlations. This constrains the -meson contribution and jet
fragmentation to inclusive \Jpsi to be . Yields in
minimum-bias \cucu collisions are consistent with those in \pp collisions
scaled by the underlying binary nucleon-nucleon collisions in the measured \pT
range. Other measurements and future projects related to heavy-flavors are
discussed.Comment: 8 pages 4 figures, proceedings of the International Conference on
Strangeness in Quark Matter 2008 - Beijing, China, Oct. 6-10, 200
ASCA Detection of Pulsed X-ray Emission from PSR J0631+1036
ASCA's long look at the 288 millisecond radio pulsar, PSR J0631+1036, reveals
coherent X-ray pulsation from this source for the first time. The source was
first detected in the serendipitous Einstein observation and later identified
as a radio pulsar. Possible pulsation in the gamma-ray band has been detected
from the CGRO EGRET data (Zepka, et al. 1996). The X-ray spectrum in the ASCA
band is characterized by a hard power-law type emission with a photon index of
about 2.3, when fitted with a single power-law function modified with
absorption. An additional blackbody component of about 0.14 keV increases the
quality of the spectral fit. The observed X-ray flux is 2.1e-13 ergs/s/cm2 in
the 1-10 keV band. We find that many characteristics of PSR J0631+1036 are
similar to those of middle-aged gamma-ray pulsars such as PSR B1055-52, PSR
B0633+17 (Geminga), and PSR B0656+14.Comment: To appear in ApJ Letter
Strict Limit on CPT Violation from Polarization of Gamma-Ray Bursts
We report the strictest observational verification of CPT invariance in the
photon sector, as a result of gamma-ray polarization measurement of distant
gamma-ray bursts (GRBs), which are brightest stellar-size explosions in the
universe. We detected the gamma-ray polarization of three GRBs with high
significance, and the source distances may be constrained by a well-known
luminosity indicator for GRBs. For the Lorentz- and CPT-violating dispersion
relation E_{\pm}^2=p^2 \pm 2\xi p^3/M_{Pl}, where \pm denotes different
circular polarization states of the photon, the parameter \xi is constrained as
|\xi|<O(10^{-15}). Barring precise cancellation between quantum gravity effects
and dark energy effects, the stringent limit on the CPT-violating effect leads
to the expectation that quantum gravity presumably respects the CPT invariance.Comment: 4 pages; accepted for publication in Physical Review Letters;
redshift estimates of GRBs changed (i.e z=0.382 was wrong for GRB 110721A)
and calculations of \xi limit improved from the previous versio
Development of a Time Projection Chamber Using Gas Electron Multipliers (GEM-TPC)
We developed a prototype time projection chamber using gas electron
multipliers (GEM-TPC) for high energy heavy ion collision experiments. To
investigate its performance, we conducted a beam test with 3 kinds of gases
(Ar(90%)-CH4(10%), Ar(70%)-C2H6(30%) and CF4). Detection efficiency of 99%, and
spatial resolution of 79 m in the pad-row direction and 313 m in the
drift direction were achieved. The test results show that the GEM-TPC meets the
requirements for high energy heavy ion collision experiments. The configuration
and performance of the GEM-TPC are described.Comment: 18 pages, 12 figures, published online in Nucl. Instr. and Meth.
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