Recent photoproduction results from ZEUS

Recent results for inclusive jet cross sections, dijet cross sections and dijet angular distributions are compared with NLO perturbative QCD calculations. The observation of isolated high PT photons (prompt photons) is also reported

F-2(D(3)) measurements at ZEUS

Results on the diffractive structure function F-2(D(3)) in deep inelastic neutral current positron-proton scattering (DIS) have been obtained by the ZEUS collaboration using two different methods. Diffractive interactions are selected by either requiring a small, not exponentially suppressed invariant hadronic mass M-X in the main detector or by detecting a fast proton in the ZEUS leading proton spectrometer (LPS). The results of the two methods are compared

Leading baryons at low x(L) in DIS and photoproduction at ZEUS

Results obtained by the ZEUS collaboration on leading baryon production in the proton fragmentation region are presented. The reaction gamma p --> NX, with N a proton or a neutron, is examined both at low and high photon virtuality

Event shape analysis of multihadronic final states in deep inelastic rapidity gap events at HERA

A global event shape analysis of the multihadronic final states observed in deep inelastic scattering (DIS) with a large forward rapidity gap (LRG) is performed in the range Q(2) greater than or equal to 5 GeV2, 160 GeV less than or equal to W less than or equal to 250 GeV and eta(max) less than or equal to 1.8. Particular emphasis is paid to the dependence of these variables, measured in the gamma*-pomeron rest frame, upon M-X, the mass of the hadronic final state. With increasing M-X the multihadronic final states become planar. The broadening effects exhibited by the data can be described by including a gluon density in models where the pomeron has a partonic structure or alternatively by considering a direct coupling of the pomeron to quark and gluon pairs

Fragmentation functions at ZEUS

The scaled momentum spectra of final state charged hadrons produced in Deep Inelastic Scattering in the ranges 10 < Q(2) < 1280 GeV2 and 6 . 10(-4) < x(Bjorken) < 5 . 10(-2) have been measured in the current region of the Breit frame using the ZEUS detector. The evolution with Q(2) of the scaled momentum, x(p) = 2p(Breit)/Q, has been investigated and preliminary results are presented which show evidence for scaling violations and support for the universality of quark fragmentation

Measurement of the proton structure function F-2 and the total gamma*p cross-section at low Q(2) and low x

The ZEUS-experiment at HERA has significantly enhanced the kinematic coverage for low Q(2) and low x inelastic e(+)p --> e(+) X scattering with an upgrade of the ZEUS-detector in 1995 which extends the acceptance for small positron scattering angles. The upgrade included the modification of the beam pipe with low mass exit windows and the installation of a small electromagnetic sampling calorimeter, the Beam Pipe Calorimeter (BPC), to explore the region in Q(2) of 0.11 less than or equal to Q(2) less than or equal to 0.65 GeV2. A shift of two rear uranium calorimeter (RCAL) modules and the small rear tracking detector (SRTD) closer to the beam together with a data sample taken with a shifted event vertex extended the Q(2) coverage of the main detector down to 0.6 GeV2. Both data sets have been used to measure the proton structure function F-2 and the total virtual photonproton gamma*p cross-section. Results are presented for 0.11 less than or equal to Q(2) less than or equal to 6.10 GeV2 and 2.10(-6) less than or equal to x less than or equal to 7.10(-4) along with a comparison to various models

Jet shapes at HERA

The shape of jets produced in quasi-real photon-proton interactions and deep inelastic positron-proton scattering (DIS) at high Q(2) (Q(2) > 100 GeV2) has been measured with the ZEUS detector at HERA. Jets with transverse energies E-T(jet) > 14 GeV and pseudorapidities (eta(jet)) in the range -1 collisions, and are similar to those in e(+)e(-) interactions

D* and J/psi inelastic photoproduction at HERA

Cross sections of D* and J/Psi inelastic photoproduction were measured by the ZEUS detector at HERA collider. Comparisons of the data with calculations in NLO pQCD and SHA QCD approaches were made

Searches at HERA for excited fermions, contact interactions, a heavy neutrino, and: a HERA excess?

Results are presented on a number of searches for new physics in ep collisions at HERA using the ZEUS and HI detectors. Limits are presented on the production of elicited fermions, contact interactions, as well as a heavy right handed neutrino and W-R boson. Also presented are ZEUS results on the excess of events at high x and Q(2)

High Q(2) events in ep collisions

Using the ZEUS detector at HERA, we have studied the reaction e(+) p --> e(+) X for Q(2) > 5000 GeV2 with a 20.1 pb(-1) data sample collected during the years 1994 to 1996. For Q(2) below 15000 GeV2, the data are in good agreement with Standard Model expectations. For Q(2) > 35000 GeV2, two events are observed while 0.145 +/- 0.013 events are expected. For x > 0.55 and y > 0.25, four events are observed where 0.91 +/- 0.08 events are expected. The observed excess above Standard Model expectations is particularly interesting because it occurs in a previously unexplored kinematic region