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

MEASUREMENT OF MULTIPLICITY AND MOMENTUM SPECTRA IN THE CURRENT FRAGMENTATION REGION OF THE BREIT FRAME AT HERA

Charged particle production has been measured in Deep Inelastic Scattering (DIS) events using the ZEUS detector over a large range of Q(2) from 10 to 1280 GeV2 The evolution with Q of the charged multiplicity and scaled momentum has been investigated in the current fragmentation region of the Breit frame. The data are used to study QCD coherence effects in DIS and are compared with corresponding e(+)e(-) data in order to test the universality of quark fragmentation

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

MEASUREMENT OF MULTIPLICITY AND MOMENTUM SPECTRA IN THE CURRENT FRAGMENTATION REGION OF THE BREIT FRAME AT HERA RID B-9165-2008 RID C-5889-2009 RID A-4818-2008 RID C-1693-2008

Charged particle production has been measured in Deep Inelastic Scattering (DIS) events using the ZEUS detector over a large range of Q(2) from 10 to 1280 GeV2 The evolution with Q of the charged multiplicity and scaled momentum has been investigated in the current fragmentation region of the Breit frame. The data are used to study QCD coherence effects in DIS and are compared with corresponding e(+)e(-) data in order to test the universality of quark fragmentation

MEASUREMENT OF THE PROTON STRUCTURE-FUNCTION F2 FROM THE 1993 HERA DATA RID B-9165-2008 RID C-5889-2009 RID A-4818-2008 RID C-1693-2008

The ZEUS detector has been used to measure the proton structure function F-2. During 1993 HERA collided 26.7 GeV electrons on 820 GeV protons. The data sample corresponds to an integrated luminosity of 0.54 pb(-1), representing a twenty fold increase in statistics compared to that of 1992. Results are presented for 7 < Q(2) < 10(4) GeV2 and x values as low as 3 x 10(-4). The rapid rise in F-2 as x decreases observed previously is now studied in greater detail and persists for Q(2) values up to 500 GeV2

A SEARCH FOR EXCITED FERMIONS IN ELECTRON-PROTON COLLISIONS AT HERA RID B-9165-2008 RID C-5889-2009 RID A-4818-2008 RID C-1693-2008

A search for excited states of the standard model fermions was performed using the ZEUS detector at the HERA electron-proton collider, operating at a centre of mass energy of 296 GeV. In a sample corresponding to an integrated luminosity of 0.55 pb(-1), no evidence was found for any resonant state decaying into final states composed of a fermion and a gauge boson. Limits on the coupling strength times branching ratio of excited fermions are presented for masses between 50 GeV and 250 GeV, extending previous search regions significantly

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