Baoyi Chen

ϒ production as a probe for early state dynamics in high energy nuclear collisions at RHIC

Abstract ϒ production in heavy ion collisions at RHIC energy is investigated. While the transverse momentum spectra of the ground state ϒ ( 1 s ) are controlled by the initial state Cronin effect, the excited b b ¯ states are characterized by the competition between the cold and hot nuclear matter effects and sensitive to the dissociation temperatures determined by the heavy quark potential. We emphasize that it is necessary to measure the excited heavy quark states in order to extract the early stage information in high energy nuclear collisions at RHIC.

ψ′ production and B decay in heavy ion collisions at LHC

Abstract In comparison with J / ψ , the excited charmonium state ψ ′ is loosely bounded and its yield is dominantly from the B-hadron decay. Based on the transport approach, we study the double ratio of N ( ψ ′ ) / N ( J / ψ ) from A+A collisions to that from p+p collisions at LHC energy. We found that the primordial production in the initial stage and the regeneration in the hot medium are not significant for ψ ′ production in heavy ion collisions at LHC and the double ratio in semi-central and central collisions is controlled by the B decay.

The Outer Tracker detector of the HERA-B experiment. Part II: Front-end electronics

The HERA-B Outer Tracker is a large detector with 112674 drift chamber channels. It is exposed to a particle flux of up to 2x10^5/cm^2/s thus coping with conditions similar to those expected for the LHC experiments. The front-end readout system, based on the ASD-8 chip and a customized TDC chip, is designed to fulfil the requirements on low noise, high sensitivity, rate tolerance, and high integration density. The TDC system is based on an ASIC which digitizes the time in bins of about 0.5 ns within a total of 256 bins. The chip also comprises a pipeline to store data from 128 events which is required for a deadtime-free trigger and data acquisition system. We report on the development, installation, and commissioning of the front-end electronics, including the grounding and noise suppression schemes, and discuss its performance in the HERA-B experiment.

Mean Field Effect on

The mean field effect in quark-gluon plasma on J/\psi production in heavy ion collisions is perturbatively calculated in a transport approach. While the global nuclear modification factor R_{AA} is not sensitive to the mean field, the reduced threshold for J/\psi regeneration leads to a significant enhancement of R_{AA} at low transverse momentum at RHIC and LHC energies.

J/\psi

A new measurement of the b-bbar production cross section in 920 GeV proton-nucleus collisions is presented by the HERA-B collaboration. The b-bbar production is tagged via inclusive bottom quark decays into J/psi mesons, by exploiting the longitudinal separation of J/psi->ll decay vertices from the primary proton-nucleus interaction point. Both e+e- and mu+mu- channels are reconstructed, for a total of 83 +- 12 inclusive b->J/psi X events found. The combined analysis yields a b-bbar to prompt J/psi cross section ratio of

Production in Heavy Ion Collisions

{\frac{{\Delta\sigma(bbbar)}}{{\Delta\sigma_{\jpsi}}}} = 0.032\pm 0.005 \stat \pm 0.004 \sys

Improved measurement of the bb production cross section in 920 GeV fixed-target proton-nucleus collisions

measured in the x_f acceptance (-0.35 <x_f <0.15), extrapolated to

The Outer Tracker detector of the HERA-B experiment—Part I: Detector

\sigma(bbbar) = 14.9 \pm 2.2 \stat \pm 2.4 \sys

The outer tracker detector of the HERA-B experiment. Part III: Operation and performance

nb/nucleon in the total phase space.