377 research outputs found
Three-Particle Correlations from Parton Cascades in Au+Au Collisions
We present a study of three-particle correlations among a trigger particle
and two associated particles in Au + Au collisions at = 200 GeV
using a multi-phase transport model (AMPT) with both partonic and hadronic
interactions. We found that three-particle correlation densities in different
angular directions with respect to the triggered particle (`center', `cone',
`deflected', `near' and `near-away') increase with the number of participants.
The ratio of `deflected' to `cone' density approaches to 1.0 with the
increasing of number of participants, which indicates that partonic Mach-like
shock waves can be produced by strong parton cascades in central Au+Au
collisions.Comment: 9 pages, 6 figures; Final version to appear in Physics Letters
Di-hadron azimuthal correlation and Mach-like cone structure in parton/hadron transport model
In the framework of a multi-phase transport model (AMPT) with both partonic
and hadronic interactions, azimuthal correlations between trigger particles and
associated scattering particles have been studied by the mixing-event
technique. The momentum ranges of these particles are
GeV/ and GeV/ (soft), or 4
GeV/ and GeV/ (hard) in Au + Au collisions at
= 200 GeV. A Mach-like structure has been observed in
correlation functions for central collisions. By comparing scenarios with and
without parton cascade and hadronic rescattering, we show that both partonic
and hadronic dynamical mechanisms contribute to the Mach-like structure of the
associated particle azimuthal correlations. The contribution of hadronic
dynamical process can not be ignored in the emergence of Mach-like correlations
of the soft scattered associated hadrons. However, hadronic rescattering alone
cannot reproduce experimental amplitude of Mach-like cone on away-side, and the
parton cascade process is essential to describe experimental amplitude of
Mach-like cone on away-side. In addition, both the associated multiplicity and
the sum of decrease, whileas the increases, with the impact
parameter in the AMPT model including partonic dynamics from string melting
scenario.Comment: 9 pages, 5 figures; Physics Letters B 641, 362-367 (2006
The Vacuum System of HIRFL
AbstractThe vacuum system of Heavy Ion Research Facility in Lanzhou (HIRFL) is a large and complex system. HIRFL consists of two ECR ion sources, a sector focus cyclotron (SFC), a separate sector cyclotron (SSC) and a multi-purpose cooling storage ring system which has a main ring (CSRm) and an experiment ring (CSRe). Several beam lines connect these accelerators together and transfer various heavy ion beams to more than 10 experiment terminals. According to the requirements of the ion acceleration and ion lifetime, the working pressure in each accelerator is different. SFC is nearly 50 years old. After upgrade, the working pressure in SFC is improved from 10-6mbar to 10-8mbar. The pressure in SSC which was built in the 1980s reaches the same level. The cooling storage ring system with a length of 500m came into operation in 2007. The average pressures in CSRm and CSRe are 5×10-12mbar and 8×10-12mbar respectively. Different designs were adopt for vacuum system of a dozen beam lines to meet specific requirement of each experiment terminal. Along with the extensive development of the heavy ion researches and applications, new accelerators of HIRFL are under construction. The vacuum system of the new machines will be designed and constructed followed the overall schedule
Search for the Lepton Flavor Violation Processes and
The lepton flavor violation processes and are
searched for using a sample of 5.8 events collected with
the BESII detector. Zero and one candidate events, consistent with the
estimated background, are observed in and
decays, respectively. Upper limits on the branching ratios are determined to be
and at the 90% confidence level (C.L.).Comment: 9 pages, 2 figure
The pole in
Using a sample of 58 million events recorded in the BESII detector,
the decay is studied. There are conspicuous
and signals. At low mass, a large
broad peak due to the is observed, and its pole position is determined
to be - MeV from the mean of six analyses.
The errors are dominated by the systematic errors.Comment: 15 pages, 6 figures, submitted to PL
Observation of the decay \psip\rar\kstark
Using 14 million events collected with the BESII detector,
branching fractions of \psip\rar\kstarkpm and \kstarknn are determined to
be: \calB(\psip\rar\kstarkpm)=(2.9^{+1.3}_{-1.7}\pm0.4)\times 10^{-5} and
\calB(\psip\rar\kstarknn)=(13.3^{+2.4}_{-2.7}\pm1.9)\times 10^{-5}. The
results confirm the violation of the "12%" rule for these two decay channels
with higher precision. A large isospin violation between the charged and
neutral modes is observed.Comment: 5 pages, 3 figure
Direct Measurements of the Branching Fractions for and and Determinations of the Form Factors and
The absolute branching fractions for the decays and
are determined using singly
tagged sample from the data collected around 3.773 GeV with the
BES-II detector at the BEPC. In the system recoiling against the singly tagged
meson, events for and events for decays are observed. Those yield
the absolute branching fractions to be and . The
vector form factors are determined to be
and . The ratio of the two form
factors is measured to be .Comment: 6 pages, 5 figure
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