L. Fayard

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).

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

Abstract A prototype lead-liquid-argon electromagnetic calorimeter with parallel plates and Accordion geometry has been equipped with high speed readout electronics and tested with electron and muon beams at the CERN SPS. For a response peaking time of about 35 ns, fast enough for operation at the future hadron colliders, the energy resolution for electrons is 9.6%/√E[GeV] with a local constant term of 0.3% and a noise contribution of 0.33 E[ GeV ] . The spatial accuracy achieved with a detector granularity of 2.7 cm is 3.7 mm E[ GeV ] and the angular resolution 12 mrad at 60 GeV.

Collider

Abstract The invariant mass distribution of jet pairs observed in the UA2 central calorimeter is examined in the search for an excess of events in the region of the W ± and Z bosons, which would reveal their decays into quark-antiquark pairs. We give a detailed account of the methods of analysis used to optimize the mass resolution achieving ≅±10%. A structure is observed at the level of ≅ 3 standard deviations in the mass region of W ± and Z with shape and position consistent with expectation from their qqdecays. It contains 632 ± 190 events, 1.4 standard deviations above the standard model prediction of 340 ± 80 events.

Performance of a liquid argon Accordion calorimeter with fast readout

Abstract A prototype liquid argon preshower detector with a strip granularity of 2.5 mm has been tested at the CERN SPS in front of a liquid argon Accordion calorimeter. For charged tracks a signal-to-noise ratio of 9.4 and a space resolution of 340 μm were measured; the rejection power against overlapping photons produced in the decay of 50 GeV π 0 s is larger than 3; the precision on

Search for decays of the W± and Z bosons into quark-antiquark pairs

Abstract A prototype of a lead liquid argon accordion calorimeter with two types of cylindrical geometry was constructed and equipped with high speed readout electronics. The energy resolution for electrons is 10%/√E (GeV) with a local constant term of 0.65%. The resolutions obtained for position and angular measurements are given.

Performance of a liquid argon preshower detector integrated with an Accordion calorimeter

Summary form only given. A research and development program is being conducted in view of realizing an electromagnetic and hadronic calorimeter for the Large Hadron Collider (LHC). The authors report on tests on fast electronics, coupled to an electromagnetic prototype calorimeter built with an accordion structure. Three different types of preamplifiers have been used. In two (Si and GaAs hybrids), the preamplifier is operated in liquid argon. In the third one, a common based (Si JFET or GaAs) transistor is in the liquid, the charge preamplifier being outside the cryostat, after about 6 m of 50- Omega cable. The shaping amplifier uses RC-CR filtering. The response to a short current pulse peaks after about 20 ns. When the system is connected to the calorimeter, the liquid argon signals peak, as expected, after 30 ns. Noise, linearity, and cross-talk between channels were investigated. First results from an exposure of the calorimeter to electrons of energy 30 to 175 GeV were obtained.<<ETX>>