46 research outputs found
The HERMES silicon project - The radiation protection system
No full textThe HERMES-detector has recently been upgraded with a silicon detector called the Lambda Wheels. This is the first detector following the interaction region. It consists of two disks of silicon detectors close to the beamline. This location makes it vulnerable to increased radiation levels which may be caused by beam instabilities. The Lambda Wheel detector, therefore, contains a system to detect these instabilities. This additional system triggers a kicker which dumps the HERA-lepton beam when the radiation level becomes too high. This contribution describes the radiation monitor which consists of two sets of three ionization chambers each, and the data-acquisition system which reads them out. The system has been installed and is operational since the summer of 2001. The HERA-accelerator was being commissioned after an upgrade during this time and several kinds of beam instabilities were observed with this protection system. The characteristics of some events will be described. © 2003 Elsevier B.V. All rights reserved.SCOPUS: cp.jinfo:eu-repo/semantics/publishe
Quark fragmentation to pi(+/-), pi(0), K-+/-, p and (p)over-bar in the nuclear environment
No full textThe influence of the nuclear medium on lepto-production of hadrons was studied in the HERMES experiment at DESY in semi- inclusive deep-inelastic scattering of 27.6 GeV positrons off deuterium, nitrogen and krypton targets. The differential multiplicity for krypton relative to that of deuterium has been measured for the first time for various identified hadrons (pi(+), pi(-), pi(0), K+, K-, p and (p) over bar) as a function of the virtual photon energy v, the fraction z of this energy transferred to the hadron, and the hadron transverse momentum squared p(t)(2). The multiplicity ratio is strongly reduced in the nuclear medium at low v and high z, with significant differences among the various hadrons. The distribution of the hadron transverse momentum is broadened towards high p(t)(2) in the nuclear medium, in a manner resembling the Cronin effect previously observed in collisions of heavy ions and protons with nuclei
Transverse Polarization of Lambda and Lambda-bar Hyperons in Quasi-Real Photon-Nucleon Scattering at HERMES
No full textThe HERMES experiment has measured the transverse polarization of Lambda and Lambda-bar hyperons produced inclusively in quasireal photoproduction at a positron beam energy of 27.6 GeV. The transverse polarization of the Lambda hyperon is found to be positive while the observed Lambda-bar polarization is compatible with zero. The transverse polarization values averaged over the kinematic acceptance of HERMES are 0.078 +/- 0.006(stat) +/- 0.012(syst) and -0.025 +/- 0.015(stat) +/- 0.018(syst) for Lambda and Lambda-bar hyperons, respectively. The dependences of Lambda and Lambda-bar polarizations on the fraction of the beam's light-cone momentum carried by the hyperon and on the hyperon's transverse momentum were investigated. The measured Lambda polarization rises linearly with and exhibits a different behavior for low and high values of , which approximately correspond to the backward and forward regions in the center-of-mass frame of the reaction
