Measurement of the reaction gamma*p->phi p in deep, inelastic e(+)p scattering at HERA

The production of phi mesons in the reaction e(+)p --> e(+)phi p (phi --> K+K-), for 7 phi p cross section rises strongly with W. This behaviour is similar to that previously found for the gamma*p --> rho(0)p cross section. This strong dependence cannot be explained by production through soft pomeron exchange, It is, however, consistent with perturbative QCD expectations, where it reflects the rise of the gluon momentum density in the proton at small x. The ratio of sigma(phi)/sigma(rho(0)), which has previously been determined by ZEUS to be 0.065 +/- 0.013 (stat.) in photoproduction at a mean W of 70 GeV, is measured to be 0.18 +/- 0.05 (stat.) +/- 0.03 (syst.) at a mean Q(2) of 12.3 GeV2 and mean W of approximate to 100 GeV and is thus approaching at large Q(2) the value of 2/9 predicted from the quark charges of the vector mesons and a flavour independent production mechanism

Extraction of the Gluon Density of the Proton At X

The gluon momentum density xg(x, Q(2)) of the proton was extracted at Q(2) = 20 GeV2 for small values of x between 4 x 10(-4) and 10(-2) from the scaling violations of the proton structure function F-2 measured recently by ZEUS in deep inelastic neutral current ep scattering at HERA. The extraction was performed in two ways. Firstly, using a global NLO fit to the ZEUS data on F-2 at low x constrained by measurements from NMC at larger x; and secondly using published approximate methods for the solution of the GLAP QCD evolution equations. Consistent results are obtained. A substantial increase of the gluon density is found at small x in comparison with the NMC result obtained at larger values of x

EXTRACTION OF THE GLUON DENSITY OF THE PROTON AT X RID B-9165-2008 RID C-5889-2009 RID A-4818-2008 RID C-1693-2008

The gluon momentum density xg(x, Q(2)) of the proton was extracted at Q(2) = 20 GeV2 for small values of x between 4 x 10(-4) and 10(-2) from the scaling violations of the proton structure function F-2 measured recently by ZEUS in deep inelastic neutral current ep scattering at HERA. The extraction was performed in two ways. Firstly, using a global NLO fit to the ZEUS data on F-2 at low x constrained by measurements from NMC at larger x; and secondly using published approximate methods for the solution of the GLAP QCD evolution equations. Consistent results are obtained. A substantial increase of the gluon density is found at small x in comparison with the NMC result obtained at larger values of x

HADRONIC ENERGY-DISTRIBUTIONS IN DEEP-INELASTIC ELECTRON-PROTON SCATTERING

This paper presents energy distributions of the hadronic system produced in neutral-current electron-proton deep-inelastic scattering at a centre of mass energy of 296 GeV. Comparison of the results with QCD Monte Carlo models shows that QCD radiation has a strong influence on the characteristics of the final state. The data are reasonably reproduced by the Lund model based on a matrix element calculation in first order of alpha(s), followed by appropriate parton showers, as well as by the colour dipole model. The HERWIG parton shower model also gives a reasonable representation of the data. Neither the first order matrix elements alone nor the Lund parton shower model, without the matrix element calculation, reproduce the data

OBSERVATION OF 2-JET PRODUCTION IN DEEP-INELASTIC SCATTERING AT HERA

A sample of events with two distinct jets, in addition to the proton remnant, has been identified in deep inelastic, neutral current ep interactions recorded at HERA by the ZEUS experiment. For these events, the mass of the hadronic system ranges from 40 to 260 GeV. The salient features of the observed jet production agree with the predictions of higher order QCD

JET PRODUCTION IN HIGH Q(2) DEEP-INELASTIC EP SCATTERING AT HERA RID B-9165-2008 RID C-5889-2009 RID A-4818-2008 RID C-1693-2008

Two-jet production in deep-inelastic electron-proton scattering has been studied for 160 < Q(2) < 1280 GeV2 0.01 < x < 0.1 and 0.04 < y < 0.95 with the ZEUS detector at HERA. The kinematic properties of the jets and the jet production rates are presented. The partonic scaling variables of the two-jet system and the rate of two-jet production are compared to perturbative next-to-leading order QCD calculations

NEUTRAL STRANGE PARTICLE-PRODUCTION IN DEEP-INELASTIC SCATTERING AT HERA RID B-9165-2008 RID C-5889-2009 RID A-4818-2008 RID C-1693-2008

This paper presents measurements of K-0 and Lambda production in neutral current, deep inelastic scattering of 26.7 GeV electrons and 820 GeV protons in the kinematic range 10 0.04. Average multiplicities for K-0 and Lambda production are determined for transverse momenta p(T) > 0.5 GeV and pseudorapidities \eta\ < 1.3. The multiplicities favour a stronger strange to light quark suppression in the fragmentation chain than found in e(+)e(-) experiments. The production properties of K-0's in events with and without a large rapidity gap with respect to the proton direction are compared. The ratio of neutral K-0's to charged particles per event in the measured kinematic range is, within the present statistics, the same in both samples

INCLUSIVE TRANSVERSE-MOMENTUM DISTRIBUTIONS OF CHARGED-PARTICLES IN DIFFRACTIVE AND NON-DIFFRACTIVE PHOTOPRODUCTION AT HERA RID B-9165-2008 RID C-5889-2009 RID A-4818-2008 RID C-1693-2008

Inclusive transverse momentum spectra of charged particles in photoproduction events in the laboratory pseudorapidity range -1.2 < eta < 1.4 have been measured up to P-T = 8 GeV using the ZEUS detector. Diffractive and non-diffractive reactions have been selected with an average gamma p centre of mass (c.m.) energy of (W) = 180 GeV. For diffractive reactions, the p(T) spectra of the photon dissociation events have been measured in two intervals of the dissociated photon mass with mean values (M(X)) = 5 GeV and 10 GeV. The inclusive transverse momentum spectra fall exponentially in the low p(T) region. The non-diffractive data p show a pronounced high p(T) tail departing from the exponential shape. The p(T) 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