Pierre Darriulat

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.

Study of the surface resistance of superconducting niobium films at 1.5 GHz

Abstract A systematic study of superconducting properties of niobium films sputtered on the inner wall of radiofrequency cavities is presented. The measured quantities include in particular the response to 1.5 GHz microwaves, the critical temperature, the penetration depth and the magnetic penetration field. In addition to films grown in different gas discharges (Xe, Kr, Ar and Ar/Ne mixtures) and to films grown on substrates prepared under different conditions, the study also includes bulk niobium cavities. The surface resistance is analysed in terms of its dependence on temperature, on RF field and, when relevant, on the density of trapped fluxons. A simple parameterisation is found to give a good fit to the data. Once allowance for the presence of impurities and defects is made by means of a single parameter, the electron mean free path, good agreement with BCS theory is observed. The fluxon-induced losses are studied in detail and their dependence on RF field, on temperature and on the density of trapped fluxons is analysed. The residual resistance is observed to be essentially uncorrelated with the other variables, suggesting that it is dominantly extragranular. In occasions very low residual resistances, in the nΩ range, have been maintained over a broad range of RF field, indicating the absence of significant fundamental limitations specific to the film technology in practical applications such as the production of accelerating cavities for particle accelerators.

Direct photon production at the CERN p̄p collider

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.

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.

Superconducting niobium cavities, a case for the film technology

Abstract Evidence is presented for niobium film cavities performing as well as niobium bulk cavities, at variance with a widespread belief that their much smaller grain size should be a fundamental limitation preventing high quality factors to be maintained over a wide range of accelerating fields. By comparing the relative merits of the bulk and film technologies, a strong case is presented in favour of the latter.

Study of the residual surface resistance of niobium films at 1.5 GHz

Potential contributions to the residual surface resistance of niobium films exposed to 1.5 GHz microwaves are reviewed and studied. These include the oxidation of the film surface, the formation of hydride precipitates, the contamination by noble gas atoms and the presence of macroscopic film defects such as those resulting from the roughness of the substrate. Particular attention is given to the dependence of the residual resistance on the amplitude of the microwave. Results similar to those obtained for bulk niobium provide strong evidence against the conjecture that the small size of the film grains should be a fundamental limitation to the production of films having a low residual resistance.

Experimental study of the emergence of two-jet dominance in pp collisions at √s = 630 GeV

Abstract A heuristic model is used to describe data collected by the UA2 experiment at √ s = 630 GeV . Distributions of the energy sharing between the leading clusters and the rest of the event are examined. The main features of these distributions can be described by a two-component model with soft, collective interactions dominating at low transverse energy and hard, constituent interactions dominating at high transverse energy. This model provides a simple picture of the emergence of two-jet dominance at SPS p p Collider energies.

Fluxon pinning in niobium films

Resistive losses induced by the presence of trapped magnetic flux in niobium superconducting films have been studied using 1.5 GHz microwaves. They are measured to span a very broad spectrum depending on the film-substrate interface and on the gas used in the sputtering discharge. An interpretation in terms of pinning by noble gas clusters is considered.

Studies of RF-superconductivity properties of niobium film-coated cavities at cern

Extensive tests have been performed on several cavities, operated at 1.5 GHz in the TMoio mode, obtained by sputter-coating niobium on copper, in order to study the physical phenomena responsible for their ultimate performance. Cavities manufactured with the same technique, but resonating at 352 MHz, are in current operation in the CERN Large Electron-Positron Collider LEP.

Revealing Partons in Hadrons: From the ISR to the SPS Collider

Our understanding of the structure of hadrons has developed during the seventies and early eighties from a few vague ideas to a precise theory, Quantum Chromodynamics, that describes hadrons as made of elementary partons (quarks and gluons). Deep inelastic scattering of electrons and neutrinos on nucleons and electron–positron collisions have played a major role in this development. Less well known is the role played by hadron collisions in revealing the parton structure, studying the dynamic of interactions between partons and offering an exclusive laboratory for the direct study of gluon interactions. The present article recalls the decisive contributions made by the CERN Intersecting Storage Rings and, later, the proton–antiproton SPS Collider to this chapter of physics. 1. Preamble In the mid-sixties, when the ISR were being born, the idea that hadrons could be composite particles was still far from being generally accepted. Summer school lectures were giving as much weight to bootstrap ideas 1 as to the newly born quark model. 2 We remember a seminar by C. N. Yang 3 at CERN, just before the ISR first collisions, introducing the concept of limiting fragmentation, which we were religiously listening to in the hope that it could give us an idea of what to expect from our imminent exploration of the high energy territory. In spite of the spectacular success of Gell-Mann’s eightfold way, the quark model had to face two very strong counter-arguments: the failure of many quark search experiments to find any hint for fractional charges and the apparent incompatibility of the quark model with Fermi–Dirac statistics. Indeed, we did not know about colour, nor about the peculiar behavior of the strong force to get weaker at short distances. The light would come from SLAC at the very end of the decade, with deep inelastic electron scattering soon followed by SPEAR and its harvest of revolutionary results. If hadrons are composite, it should be possible to understand hadron collisions in terms of interactions and rearrangements of the constituents, the so-called partons, and, in particular, to eject one of them, as in nuclear physics with (p,2p )o r (p,pn) reactions. It is indeed possible, but it took a decade to reach this goal. Hadrons are very different from nuclei, which can be qualitatively described classically in