Professor Brian Foster OBE, FRS

Abstract:

Charged particle production has been measured in deep inelastic scattering (DIS) events over a large range of x and Q2 using the ZEUS detector. The evolution of the scaled momentum, xp, with Q2, in the range 10 to 1280 GeV2, has been investigated in the current fragmentation region of the Breit frame. The results show clear evidence, in a single experiment, for scaling violations in scaled momenta as a function of Q2. © 1997 Elsevier Science B.V.

Abstract:

Events containing an isolated prompt photon with high transverse energy, together with a balancing jet, have been observed for the first time in photoproduction at HERA. The data were taken with the ZEUS detector, in a γp centre of mass energy range 120-250 GeV. The fraction of the incoming photon energy participating in the production of the prompt photon and the jet, xγ, shows a strong peak near unity, consistent with LO QCD Monte Carlo predictions. In the transverse energy and pseudorapidity range 5 ≤ EγT < 10 GeV, -0.7 ≤ ηγ < 0.8, EjetT ≥ 5 GeV, and -1.5 ≤ ηjet ≤ 1.8, with xOBSγ > 0.8, the measured cross section is 15.3 ± 3.8 ± 1.8 pb, in good agreement with a recent NLO calculation. © 1997 Elsevier Science B.V.

Abstract:

The ZEUS Central Tracking Detector utilizes a time difference measurement to provide a fast determination of the z coordinate of each hit. The z-by-timing measurement is achieved by using a Time-to-Amplitude Converter which has an intrinsic timing resolution of 36 ps, has pipelined readout, and has a multihit capability of 48 ns. In order to maintain the required sub-nanosecond timing accuracy, the technique incorporates an automated self-calibration system. The readout of the z-by-timing data utilizes a fully customized timing control system which runs synchronously with the HERA beam-crossing clock, and a data acquisition system implemented on a network of Transputers. Three dimensional space-points provided by the z-by-timing system are used as input to all three levels of the ZEUS trigger and for offline track reconstruction. The average z resolution is determined to be 4.4 cm for multi-track events from positron-proton collisions in the ZEUS detector.

Abstract:

This paper presents measurements of D*f± production in deep inelastic scattering from collisions between 27.5GeV positrons and 820GeV protons. The data have been taken with the ZEUS detector at HERA. The decay channel D*+ → (D0 → K-π+)π+ (+c.c.) has been used in the study. The e+p cross section for inclusive D*± production with 5 < Q2 < 100GeV2 and y < 0.7 is 5.3±1.0±0.8nb in the kinematic region 1.3 < pT(D*±) < 9.0GeV and |η(D*±) | < 1.5. Differential cross sections as functions of pT(D*±), η(D*±), W and Q2 are compared with next-to-leading order QCD calculations based on the photon-gluon fusion production mechanism. After an extrapolation of the cross section to the full kinematic region in pT(D*±) and η(D*±), the charm contribution Fcc̄2(x,Q2) to the proton structure function is determined for Bjorken x between 2 · 10-4 and 5 · 10-3. © 1997 Elsevier Science B.V.