J. J. Wang

Polarization of Lambda and (Lambda)over-bar in 920 GeV fixed-target proton-nucleus collisions

A measurement of the polarization of Lambda and Anti-Lambda baryons produced in pC and pW collisions at sqrt(s)=41.6 GeV has been performed with the HERA-B spectrometer. The measurements cover the kinematic range of 0.6 GeV/c<p_T<1.2 GeV/c in transverse momentum and -0.15<x_F<0.01 in Feynman-x. The polarization results from the two different targets agree within the statistical error. In the combined data set, the largest deviation from zero, +0.054 +- 0.029, is measured for x_F<-0.07. Zero polarization is expected at x_F=0 in the absence of nuclear effects. The polarization results for the Lambda agree with a parametrization of previous measurements which were performed at positive x_F values, where the Lambda polarization is negative. Results of Anti-Lambda polarization measurements are consistent with zero.

Measurement of the Upsilon production cross section in 920 GeV fixed-target proton-nucleus collisions

Abstract The cross section ratio R J / ψ = Br ( ϒ → l + l − ) ⋅ d σ ( ϒ ) / d y | y = 0 / σ ( J / ψ ) has been measured with the HERA-B spectrometer in fixed-target proton–nucleus collisions at 920 GeV proton beam energy corresponding to a proton–nucleon c.m.s. energy of s = 41.6 GeV . The combined results for the decay channels ϒ → e + e − and ϒ → μ + μ − yield a ratio R J / ψ = ( 9.0 ± 2.1 ) × 10 −6 . The corresponding ϒ production cross section per nucleon at mid-rapidity ( y = 0 ) has been determined to be Br ( ϒ → l + l − ) ⋅ d σ ( ϒ ) / d y | y = 0 = 4.5 ± 1.1 pb / nucleon .

A realistic design of the CBM-TOF wall based on modules commissioned in-beam

The Compressed Baryonic Matter experiment at the future Facility for Antiproton and Ion Research will use a time-of-flight (TOF) wall for hadron identification, which is at the moment planned to be based on the Multi-gap Resistive Plate Chamber (MRPC) technology. The wall will be placed at 10m distance from the target, covering an area of the order of 150 m2. Over such an area, it will provide a time-of-flight resolution of 80 ps, by resorting to ca. 50000 RPC cells (in multi-strip or multi-pad configuration). Fluxes of quasi-minimum ionizing particles (γβ≥3) as high as 20 kHz/cm2 can be reached in the central region, corresponding to the low polar angle/high rapidity section. We propose here a realistic design for building the TOF wall by resorting to a single technology based on low-resistivity doped glass and relying on small structural modifications of the modules developed and tested during the last two years. Latest results from the modules are summarized. A comprehensive analytic discussion on the counter performance under non-uniform beams, when neglecting non-local effects, is also presented.

Monte Carlo simulation of image properties of an X-ray intensifying screen

Abstract A Monte Carlo simulation program named MCPEP has been developed. Based on the existing simulation program that simulates the transfer of X-ray photons and the secondary electrons, MCPEP also simulates the light photons in the screen. The performances of an intensifying screen ( Gd 2 O 2 S : Tb ) with different thickness and different X-ray energies have been analyzed by MCPEP. The calculated light photon probability distribution, average light photon number per absorbed X-ray photon, statistical factor for light emission, X-ray detection efficiency, detective quantum efficiency (DQE) and point spread function (PSF) of the screen are presented.

Development of a large-area Multigap RPC with adequate spatial resolution for muon tomography

We study the performance of a large-area 2-D Multigap Resistive Plate Chamber (MRPC) designed for muon tomography with high spatial resolution. An efficiency up to 98% and a spatial resolution of around 270 μ m are obtained in cosmic ray and X-ray tests. The performance of the MRPC is also investigated for two working gases: standard gas and pure Freon. The result shows that the MRPC working in pure Freon can provide higher efficiency and better spatial resolution.

Improved measurement of the b(b)over-bar production cross section in 920 GeV fixed-target proton-nucleus collisions

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

MTF and DQE analysis of x-ray intensifying screens

{frac{{Deltasigma(bbbar)}}{{Deltasigma_{jpsi}}}} = 0.032pm 0.005 stat pm 0.004 sys

Development and evaluation of a CCD-based portable digital flash x-ray imager

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

A theoretical model of a fast waveform sampling switch

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

The CBM time-of-flight wall

nb/nucleon in the total phase space.