Showing papers by "Hermann Kolanoski published in 2003"

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

Abstract: Using the HERA - B detector, the $b\overline{b}$ production cross section has been measured in 920 GeV proton collisions on carbon and titanium targets. The $b\overline{b}$ production was tagged via inclusive bottom quark decays into $J/\psi$ by exploiting the longitudinal separation of $J/\psi\to l^+l^-$ decay vertices from the primary proton-nucleus interaction. Both e + e - and $\mu^+\mu^-$ channels have been reconstructed and the combined analysis yields the cross section $\sigma(b\overline{b}) = 32 ^{+14} _{-12} (stat) ^{+6} _{-7} (sys) nb/nucleon$ .

Undulator-Based Production of Polarized Positrons, A Proposal for the 50-GeV Beam in the FFTB

Abstract: The full exploitation of the physics potential of future linear colliders such as the JLC, NLC, and TESLA will require the development of polarized positron beams. In the proposed scheme of Balakin and Mikhailichenko [1] a helical undulator is employed to generate photons of several MeV with circular polarization which are then converted in a relatively thin target to generate longitudinally polarized positrons. This experiment, E-166, proposes to test this scheme to determine whether such a technique can produce polarized positron beams of sufficient quality for use in future linear colliders. The experiment will install a meter-long, short-period, pulsed helical undulator in the Final Focus Test Beam (FFTB) at SLAC. A low-emittance 50-GeV electron beam passing through this undulator will generate circularly polarized photons with energies up to 10 MeV. These polarized photons are then converted to polarized positrons via pair production in thin targets. Titanium and tungsten targets, which are both candidates for use in linear colliders, will be tested. The experiment will measure the flux and polarization of the undulator photons, and the spectrum and polarization of the positrons produced in the conversion target, and compare the measurement results to simulations. Thus the proposed experiment directly tests formore » the first time the validity of the simulation programs used for the physics of polarized pair production in finite matter, in particular the effects of multiple scattering on polarization. Successful comparison of the experimental results to the simulations will lead to greater confidence in the proposed designs of polarized positrons sources for the next generation of linear colliders. This experiment requests six-weeks of time in the FFTB beam line: three weeks for installation and setup and three weeks of beam for data taking. A 50-GeV beam with about twice the SLC emittance at a repetition rate of 30 Hz is required.« less

Inclusive V-0 production cross sections from 920 GeV fixed target proton-nucleus collisions

Abstract: Inclusive differential cross sections dsigma(pA)/dx(F) and dsigma(pA)/dp(t)(2) for the production of K-S(0), Lambda, and (U) over bar particles are measured at HERA in proton-induced reactions on C, Al, Ti, and W targets. The incident beam energy is 920 GeV, corresponding to roots = 41.6 GeV in the proton-nucleon system. The ratios of differential cross sections dsigma(pA)(K-S(0))/dsigma(pA)(Lambda) and dsigma(pA)((U) over bar)/dsigma(pA) (Lambda) are measured to be 6.2 +/- 0.5 and 0.66 +/- 0.07, respectively, for x(F) approximate to -0.06. No significant dependence upon the target material is observed. Within errors, the slopes of the transverse momentum distributions da,Ald t also show no significant dependence upon the target material. The dependence of the extrapolated total cross sections sigma(pA) on the atomic mass A of the target material is discussed, and the deduced cross sections per nucleon sigma(pN) are compared with results obtained at other energies.

Aging studies for the large honeycomb drift tube system of the outer tracker of HERA-B

Abstract: The HERA-B Outer Tracker consists of drift tubes folded from polycarbonate foil and is operated with Ar/CF4/CO2 as drift gas. The detector has to stand radiation levels which are similar to LHC conditions. The first prototypes exposed to radiation in HERA-B suffered severe radiation damage due to the development of self-sustaining currents (Malter effect). In a subsequent extended R&D program major changes to the original concept for the drift tubes (surface conductivity, drift gas, production materials) have been developed and validated for use in harsh radiation environments. In the test program various aging effects (such as Malter currents, gain loss due to anode aging and etching of the anode gold surface) were observed, and cures by tuning of operation parameters were developed.

Humidity dependence of anode corrosion in HERA-B Outer Tracker chambers operated with Ar/CF4/CO2

Abstract: The Outer Tracker of the HERA-B experiment consists of drift tubes folded from gold-coated polycarbonate foils (honeycomb) and is operated with the gas mixture Ar/CF 4 /CO 2 . The choice of the materials and the drift gas was the result of an extended R&D program launched to avoid both anode aging (gain loss) and cathode aging (Malter effect). However, other aging effects were observed at high irradiation doses: rising conductivity of the wire-supporting strips and wire corrosion. In this paper, we show that these two aging effects could also be prevented by keeping water at a proper concentration (about 300 ppm ). In an attempt to interpret the test results, the production and reaction probability of molecular species produced via CF 4 dissociation in the avalanche are semi-quantitatively estimated.

Observations on cathode aging (Malter effect) in honeycomb drift chambers under high irradiation load

Abstract: The Outer Tracking (OTR) system for the HERA-B detector at DESY consists of honeycomb drift tubes with cathodes folded from Pokalon-C foil, a soot-containing polycarbonate, operating with CF 4 -containing drift gas. The first prototypes, exposed to radiation in HERA-B, suffered radiation damage ascribed to the Malter effect (ignition of self-sustaining discharges). We present the results of investigations of cathode surface properties and include a semiquantitative discussion of the ion-layer formation process. The achieved understanding was important for the development of a radiation-hard detector.