Professor Brian Foster OBE, FRS

Abstract:

Inclusive jet cross sections for events with a large rapidity gap with respect to the proton direction from the reaction ep → jet + X with quasi-real photons have been measured with the ZEUS detector. The cross sections refer to jets with transverse energies ETjet> 8 GeV. The data show the characteristics of a diffractive process mediated by pomeron exchange. Assuming that the events are due to the exchange of a pomeron with partonic structure, the quark and gluon content of the pomeron is probed at a scale ∼ (ETjet)2. A comparison of the measurements with model predictions based on QCD plus Regge phenomenology requires a contribution of partons with a hard momentum density in the pomeron. A combined analysis of the jet cross sections and recent ZEUS measurements of the diffractive structure function in deep inelastic scattering gives the first experimental evidence for the gluon content of the pomeron in diffractive hard scattering processes. The data indicate that between 30% and 80% of the momentum of the pomeron carried by partons is due to hard gluons. © 1995.

Abstract:

Photoproduction at HERA is studied in ep collisions, with the ZEUS detector, for γp centre-of-mass energies ranging from 130-270 GeV. A sample of events with two high-pTjets (pT> 6 GeV, η < 1.6) and a third cluster in the approximate direction of the electron beam is isolated using a clustering algorithm. These events are mostly due to resolved photoproduction. The third cluster is identified as the photon remnant. Its properties, such as the transverse and longitudinal energy flows around the axis of the cluster, are consistent with those commonly attributed to jets, and in particular with those found for the two jets in these events. The mean value of the photon remnant pTwith respect to the beam axis is measured to be 2.1 ± 0.2 GeV, which demonstrates substantial mean transverse momenta for the photon remnant. © 1995.

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.