Showing papers by "Christophe Royon published in 1997"

The H1 detector at HERA

Abstract: General aspects of the H1 detector at the electron-proton storage ring HERA as well as technical descriptions of the magnet, luminosity system, trigger, slow-control, data acquisition and off-line data handling are given. The three major components of the detector, the tracking, calorimeter and muon detectors, will be described in a forthcoming article. The present paper describes the detector that was used from 1992 to the end of 1994. After this a major upgrade of some components was undertaken. Some performance figures from luminosity runs at HERA during 1993 and 1994 are given.

The tracking calorimeter and muon detectors of the H1 experiment at Hera

Abstract: Technical aspects of the three major components of the H1 detector at the electron-proton storage ring HERA are described. This paper covers the detector status up to the end of 1994 when a major upgrading of some of its elements was undertaken. A description of the other elements of the detector and some performance figures from luminosity runs at HERA during 1993 and 1994 are given in a paper previously published in this journal.

The H1 lead/scintillating-fibre calorimeter

Abstract: The backward region of the H1 detector has been upgraded in order to provide improved measurement of the scattered electron in deep inelastic scattering events. The centerpiece of the upgrade is a high-resolution lead/scintillating-fibre calorimeter. The main design goals of the calorimeter are: good coverage of the region close to the beam pipe, high angular resolution and energy resolution of better than 2% for 30 GeV electrons. The calorimeter should be capable of providing coarse hadronic energy measurement and precise time information to suppress out-of-time background events at the first trigger level. It must be compact due to space restrictions. These requirements were fulfilled by constructing two separate calorimeter sections. The inner electromagnetic section is made of 0.5 mm scintillating plastic fibres embedded in a lead matrix. Its lead-to-fibre ratio is 2.3:1 by volume. The outer hadronic section consists of 1.0 mm diameter fibres with a lead-to-fibre ratio of 3.4:1. The mechanical construction of the new calorimeter and its assembly in the H1 detector are described.

Observation of events at very high $Q^{2}$ in $e p$ collisions at HERA

Abstract: Measurements of ep scattering with squared 4—momentum transfer Q2 up to 35000 GeV2 are compared with the expectation of the standard deep-inelastic model of lepton—nucleon scattering (DIS). For Q2 > 15000 GeV2, N obs = 12 neutral current candidate events are observed where the expectation is N DIS = 4.71 ± 0.76 events. In the same Q2 range, N obs = 4 charged current candidates are observed where the expectation is N DIS = 1.77 ± 0.87 events. The probability P(N ≥ N obs) that the DIS model signal N fluctuates to N ≥ N obs in a random set of experiments is 6 × 10−3 for neutral current and 0.14 for charged current. The difference in the observed and expected number of Neutral Current events is mostly due to events at large masses $M = \sqrt {xs}$ in which the positron is backscattered at large y = Q2/M2.

Diffraction dissociation in photoproduction at HERA

Abstract: A study is presented of the process γp → XY, where there is a large rapidity gap between the systems X and Y. Measurements are made of the differential cross section as a function of the invariant mass MX of the system produced at the photon vertex. Results are presented at centre of mass energies of 〈W〉 = 187 GeV and 〈W〉 =231 GeV, both where the proton dominantly remains intact and, for the first time, where it dissociates. Both the centre of mass energy and the \(M_X^2\) dependence of HERA data and those from a fixed target experiment may simultaneously be described in a triple-Regge model. The low mass photon dissociation process is found to be dominated by diffraction, though a sizable subleading contribution is present at larger masses. The pomeron intercept is extracted and found to be αP(0) = 1.068 ± 0.016 (stat.) ± 0.022 (syst.) ± 0.041 (model), in good agreement with values obtained from total and elastic hadronic and photoproduction cross sections. The diffractive contribution to the process γp → Xp with \(M_X^2/{W^2} < 0.05\) is measured to be 22.2 ± 0.6 (stat.) ± 2.6 (syst.) ± 1.7 (model)% of the total γp cross section at 〈W〉 = 187 GeV.