P. Cenci

MEASUREMENT OF THE STANDARD MODEL PARAMETERS FROM A STUDY OF W AND Z BOSONS

Abstract A study has been made of the decays W → ev and Z → e + e − , using the UA2 detector at the CERN pp Collider. The data correspond to an integrated luminosity of 142 nb −1 at a centre-of-mass collision energy √ s =546 GeV, and 768 nb −1 at √ s =630 GeV. Measurements of the standard model parameters from samples of 251 W decay and 39 Z decay candidates are compared with expectations of the standard electroweak model.

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).

Search for exotic processes at the CERN pp̄ collider

Abstract The total UA2 data sample at the CERN pp Collider corresponds to an integrated luminosity of 910 nb −1 . Limits on various hypothetical processes, such as production of excited electrons, additional charged or neutral vector bosons, or supersymmetric particles, are presented from the analysis of this sample.

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 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.

Collider

Abstract Fragmentation properties of a sample of two-jet events measured by the UA2 detector at the CERN p p Collider are described. The energy flow is compared with different model predictions. The charged particle multiplicity in jets is found to exceed extrapolations from lower energy e + e − jet data.

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

Abstract A prototype electromagnetic calorimeter containing 180 litres of liquid krypton has been tested in electron and muon beams at the CERN SPS. The main features of this detector are its active shower medium, a granularity of 2 cm with tower readout, and the use of the initial current readout technique with an effective shaping time of about 60 ns. An energy resolution for electrons of 4.1% √E[ GeV ] with a constant term of 0.4% and a noise contribution of 50 MeV has been achieved. The calorimeter has a spatial resolution of 4.5 mm √E[ GeV ] with a constant term of 0.3 mm and a time resolution of about 0.5 ns for energies larger than 10 GeV.

Measurement of jet fragmentation properties at the CERN pp Collider

Abstract The UA2 experiment at the CERN p p Collider has identified a total sample of 251 W→eν events. Among this sample 221 events are found without jets and 29 with one jet. The yield of one-jet events relative to that of zero-jet events provides a measurement of the strong coupling constant: αs(Mw2)=0.13±0.03(stat)±0.03±(syst1)±0.02(syst2), where syst1 represents the experimental systematic error and syst2 is an estimate of the theoretical uncertainty.

PERFORMANCE OF AN ELECTROMAGNETIC LIQUID KRYPTON CALORIMETER

AbstractA measurement of the direct production of photons with high transverse momentum from