C. Conta

Observation of single isolated electrons of high transverse momentum in events with missing transverse energy at the CERN pp collider

Abstract We report the results of a search for single isolated electrons of high transverse momentum at the CERN p p collider. Above 15 GeV/c, four events are found having large missing transverse energy along a direction opposite in azimuth to that of the high-pT electron. Both the configuration of the events and their number are consistent with the expectations from the process p + p → W ± + anything , with W→e+ν, where W± is the charged Intermediate Vector Boso postulated by the unified electroweak theory.

Evidence for Z0→e+e− at the CERN p collider

Abstract From a search for electron pairs produced in p p collisions at s = 550 GeV we report the observation of eight events which we interpret as resulting from the process p +p→Z 0 + anything, followed by the decay Z0→e++e− or Z0→e++e−+γ, where Z0 is the neutral Intermediate Vector Boson postulated by the unified electroweak theory. We use four of these events to measure the Z0 mass M Z = 91.9 ± 1.3 ± 1.4 (systematic) GeV /c 2 .

Observation of very large transverse momentum jets at the CERN pp collider

The distribution of total tranverse energy ΣET over the pseudorapidity interval −1 < η < 1 and an azimuthal range Δφ=300° has been measured in the UA2 experiment at the CERN pp collider (s = 540 GeV) using a highly segmented total absorption caloriter. In the events with very large ΣET (ΣET⪆60 GeV) most of the transverse energy is found to be contained in small angular regions as expected for high transverse momentum hadron jets. We discuss the properties of a sample of two-jet events with invariant two-jet masses up to 140 GeVc2 and we measure the cross section for inclusive jet production in the range of jet transverse momenta between 15 and 60 GeVc.

Observation of Electrons Produced in Association with Hard Jets and Large Missing Transverse Momentum in p anti-p Collisions at s**(1/2) = 540-GeV

Abstract Using a sample of events collected by UA2 and corresponding to an integrated luminosity of 116 nb −1 . we have searched for electron-“neutrino” pairs in which the transverse momenta of the electron and of the “neutrino” exceed 15 GeV/c and 25 GeV/c respectively. A total of 35 events are observed in low background conditions. Most events can be interpreted in terms of W ± production from QCD processes. Events in which the observation of hard jets makes this interpretation unlikely are described in detail. Possible sources of background contamination are considered.

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

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).

\sqrt s

Transverse momentum distributions of pions, kaons and protons have been measured around 90° in the UA2 detector at the SPS p p collider, at a CM energy of 540 GeV. All the cross sections have increased by more than a factor of 2 over those measured at ISR energies and exhibit a flatter behaviour with respect to transverse momentum.

dependence of jet production at the Cern

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).

\bar pp

We present the results of a search for nu_mu → nu_e oscillations in the NOMAD experiment at Cern. The experiment looked for the appearance of nu_e in a predominantly nu_mu wide-band neutrino beam at the CERN SPS. No evidence for oscillations was found. The 90% confidence limits obtained are Delta m^2 ~ 10 eV^2.

collider

Abstract A description is given of the NOMAD electromagnetic calorimeter, consisting of 875 lead-glass counters read out by two-stage photomultipliers and a low noise electronic chain. The detector operates in a 0.4 T magnetic field transverse to the counter axis. The paper discusses the design criteria, the lead-glass characteristics, the properties of the read out chain and provides a summary of the calorimeter performance.