H1 alignement experience

This report describes the experience gained during alignment of the tracking system of the H1 detector. It concentrates on the alignment and calibration of the central trackers using the Millepede method for the reprocessing of the HERA I data in 2001/2002 and recent improvements for the HERA II data taking. The methods used by the other tracking detectors of H1 are mentioned only briefly

Probing the parton densities of virtual photons with the reaction gamma^*gamma->jets at LEP

We present a next-to-leading order calculation of jet production in gamma^*gamma collisions from e+e- scattering in a region where the virtuality Q^2 of the probing virtual photon is small compared to the transverse jet energy. The calculation is based on the phase-space slicing method. The initial state singularity of the virtual photon is factorized into the structure function of the virtual photon, using the MS-bar factorization scheme for virtual photons. Numerical results are presented for LEP2 conditions. The perturbative stability of the pure direct virtual photon approach is compared to that of including resolved virtual photons in different regions of Q^2. We make predictions for cross sections which suggest that different parametrizations of virtual photon parton densities should be distinguishable by measurements of jet cross sections at LEP.Comment: 19 pages, 8 eps figue

Inclusive One- and Two-Jet Cross sections in γγ\gamma\gamma Reactions at e+e−e^+e^- Colliders

We have calculated inclusive one-- and two--jet production in photon--photon collisions superimposing direct, single resolved and double resolved cross sections for center of mass energies of the LEP1, LEP2 and NLC range. The direct and single resolved cross sections are calculated up to next--to--leading order. The double resolved two--jet cross section is calculated only in LO with a $k$ factor estimated from the NLO one--jet cross section. Various differential cross sections as functions of transverse momenta and rapidities of the jets are evaluated.Comment: 25 pages, latex, 15 figures appended as uuencoded fil

Installing, Running and Maintaining Large Linux Clusters at CERN

Having built up Linux clusters to more than 1000 nodes over the past five years, we already have practical experience confronting some of the LHC scale computing challenges: scalability, automation, hardware diversity, security, and rolling OS upgrades. This paper describes the tools and processes we have implemented, working in close collaboration with the EDG project [1], especially with the WP4 subtask, to improve the manageability of our clusters, in particular in the areas of system installation, configuration, and monitoring. In addition to the purely technical issues, providing shared interactive and batch services which can adapt to meet the diverse and changing requirements of our users is a significant challenge. We describe the developments and tuning that we have introduced on our LSF based systems to maximise both responsiveness to users and overall system utilisation. Finally, this paper will describe the problems we are facing in enlarging our heterogeneous Linux clusters, the progress we have made in dealing with the current issues and the steps we are taking to gridify the clustersComment: 5 pages, Proceedings for the CHEP 2003 conference, La Jolla, California, March 24 - 28, 200

Jet Production in Deep Inelastic Electron-Photon Scattering at e+e- Colliders in Next-to-Leading Order QCD

A complete next-to-leading order QCD calculation of deep inelastic electron-photon scattering including direct and resolved real photon components is presented. Soft and collinear singularities are extracted using the phase space slicing method. Application of the results for the prediction of single- and dijet cross sections at the LEP e+e- collider are presented, using the Snowmass jet definition. The dependence of the cross sections on the transverse momentum and on the rapidities of the jets are discussed.Comment: 28 pages, LaTeX, 10 eps figure