Plasma-Wakefield Accelerator Group

Abstract:

Inclusive transverse momentum spectra of charged particles in photoproduction events in the laboratory pseudorapidity range -1.2<η<1.4 have been measured up to pT=8 GeV usign the ZEUS detector. Diffractive and non-diffractive reactions have been selected with an average γp centre of mass (c.m.) energy of 〈W〉=180 GeV. For diffractive reactions, the pT spectra of the photon dissociation events have been measured in two intervals of the dissociated photon mass with mean values 〈MX〉=5 GeV and 10 GeV. The inclusive transverse momentum spectra fall exponentially in the low pT region. The non-diffractive data show a pronounced high pT tail departing from the exponential shape. The pT distributions are compared to lower energy photoproduction data and to hadron-hadron collisions at a similar c.m. energy. The data are also compared to the results of a next-to-leading order QCD calculation. © 1995 Springer-Verlag.

Abstract:

The design of the second level trigger for the inner silicon tracking detector of the SDC experiment at the Superconducting Super Collider (SSC) is outlined. The main purpose of the trigger is to recognise with high efficiency high transverse momentum tracks in both the barrel and end-cap. By means of a two-stage analysis it is possible to measure track momentum with the full precision of the silicon tracker. An outline of a possible hardware implementation is presented.

Abstract:

We report the first observation of charmed mesons with the ZEUS detector at HERA using the decay channel D^*+→ (D⁰→ K^-π⁺)π⁺(+c.c.). Clear signals in the mass difference ΔM=M(D^*)-M(D⁰) as well as in the M(Kπ) distribution at the D⁰mass are found. The ep cross section for inclusive D^*±production with Q²< 4 GeV²in the γp centre-of-mass energy range 115 < W < 275 GeV has been determined to be (32±7-7 ⁺⁴) nb in the kinematic regionpt(D^*) ≥ 1.7 GeV, |η(D^*)| < 1.5. Extrapolating outside this region, assuming a mass of the charm quark of 1.5 GeV, we estimate the ep charm cross section to be σ(ep → ccX) = (0.45 ± 0.11-0.22 ^+0.37) μb at s=296 GeV and 〈W〉 = 198 GeV. The average γp charm cross section σ(γp → ccX) is found to be (6.3 ± 2.2-3.0 ^+6.3) μb at 〈W〉 = 163 GeV and (16.9 ± 5.2-8.5 ^+13.9) μb at 〈W〉 = 243 GeV. The increase of the total charm photoproduction cross section by one order of magnitude with respect to low energy data experiments is well described by QCD NLO calculations using singular gluon distributions in the proton. © 1995.

Abstract:

Dijet production by almost real photons has been studied at HERA with the ZEUS detector. Jets have been identified using the cone algorithm. A cut on xγ ^OBS, the fraction of the photon energy participating in the production of the two jets of highest transverse energy, is used to define cross sections sensitive to the parton distributions in the proton and in the photon. The dependence of the dijet cross sections on pseudorapidity has been measured for xγ ^OBS ≥ 0.75 and xγ ^OBS < 0.75. The former is sensitive to the gluon momentum density in the proton. The latter is sensitive to the ginon in the photon. The cross sections are corrected for detector acceptance and compared to leading order QCD calculations. © 1995.

Abstract:

Two-jet production in deep-inelastic electron-proton scattering has been studied for 160

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