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

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

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

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

Measurement of dijets in DIS and comparison to NLO calculations

We report a measurement of the dijet production cross section in neutral current deep inelastic scattering with the ZEUS detector at the HERA ep collider. Dijet events are identified with the cone algorithm and the results are compared to next-to-leading order perturbative QCD calculations. The systematic uncertainties of both the measurement and the calculation we discussed

Diffractive production of charm and jets at HERA

Measurements are presented of dijet cross sections in diffractive photoproduction and of D*(+/-) production in diffractive deep inelastic scattering at HERA. A combined QCD analysis of the diffractive dijet cross sections and diffractive structure function results leads to a picture in which the pomeron has a substantial gluon component with a hard momentum spectrum

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

Diffractive measurements from ZEUS

Recent results on diffraction from the ZEUS Collaboration at HERA are presented. Properties of the diffractive photon dissociation in photoproduction and deep inelastic scattering were studied and the intercept of the pomeron, alpha(IP)(0), was inferred

Forward transverse energy flow and forward jets at low x

Transverse energy flow and forward jet cross sections at low values of x(Bj) are measured with the ZEUS detector at HERA in order to study the underlying parton dynamics (DGLAP versus BFKL). The energy how has been compared to different model simulations, but hadronization effects are too large to draw a firm conclusion. The measured jet cross section for 10(-4) < x(Bj) < 5.10(-3) is for the lower x(Bj)-bins larger than that of NLO QCD DGLAP calculations but lies still below a more qualitative BFKL prediction

QCD fits to ZEUS and fixed target structure function data

Preliminary results are presented on the gluon density at low x obtained from a QCD analysis of ZEUS 1994 F-2 structure function data combined with those from NMC. Also given are estimates of the experimental error on the e(+) p NC Born cross section at large x and Q(2). This estimate is obtained from propagation of the statistical and systematic errors on fixed target structure functions