J. R. Hansen

Measurement of the s**(1/2) Dependence of Jet Production at the CERN anti-p p Collider

Abstract The production of very large transverse momentum ( p T ) hadron jets has been measured in the UA2 experiment at the CERN p p Collider for s =630 GeV . The inclusive jet production cross sections exhibit a p T -dependent increase with respect to the s =546 GeV data from previous Collider runs. This increase can be described both by QCD calculations and by approximate x T =2 p T /√ s scaling. No significant deviation of the data from QCD predictions is observed at very large p T , placing a lower limit on the characteristic scale Λ c of a hypothetical superstrong contact interaction responsible for the binding of preons in the quark ( Λ c >370 GeV at 95% CL).

Particle identification using the time-over-threshold method in the ATLAS Transition Radiation Tracker

Abstract Test-beam studies of the ATLAS Transition Radiation Tracker (TRT) straw tube performance in terms of electron–pion separation using a time-over-threshold method are described. The test-beam data are compared with Monte Carlo simulations of charged particles passing through the straw tubes of the TRT. For energies below 10 GeV , the time-over-threshold method combined with the standard transition-radiation cluster-counting technique significantly improves the electron–pion separation in the TRT. The use of the time-over-threshold information also provides some kaon–pion separation, thereby significantly enhancing the B-physics capabilities of the ATLAS detector.

Direct Photon Production at the {CERN}

Abstract Using the UA2 apparatus, the inclusive cross section has been measured for production of high- p T direct photons in pp collisions at s =546 GeV and s =630 GeV . The results are in good agreement with QCD predictions.

\bar{p} p

The techniques to measure the position of sense wires and field wires, the gas gain and the gas flow rate inside wire chambers using a collimated and filtered X-ray beam are reported. Specific examples are given using barrel modules of the Transition Radiation Tracker of the ATLAS experiment.

Collider

The Level-2 Trigger Pilot Project of ATLAS, one of the two general purpose LHC experiments, is part of the on-going programme to develop the ATLAS High Level Triggers (HLT). The Level-2 Trigger will receive events at up to 100 kHz, which has to be reduced to a rate suitable for full event-building of the order of 1 kHz. To reduce the data collection bandwidth and processing power required for the challenging Level-2 task it is planned to use Region of Interest guidance (from Level-1) and sequential processing. The Pilot Project included the construction and use of testbeds of up to 48 processing nodes, development of optimised components and computer simulations of a full system. It has shown how the required performance can be achieved, using largely commodity components and operating systems, and validated an architecture for the Level-2 system. This paper describes the principal achievements and conclusions of this project.