Measurement of the diffractive structure function in deep inelastic scattering at HERA

This paper presents an analysis of the inclusive properties of diffractive deep inelastic scattering events produced in $ep$ interactions at HERA. The events are characterised by a rapidity gap between the outgoing proton system and the remaining hadronic system. Inclusive distributions are presented and compared with Monte Carlo models for diffractive processes. The data are consistent with models where the pomeron structure function has a hard and a soft contribution. The diffractive structure function is measured as a function of \xpom, the momentum fraction lost by the proton, of $\beta$, the momentum fraction of the struck quark with respect to \xpom, and of $Q^2$. The \xpom dependence is consistent with the form \xpoma where $a~=~1.30~\pm~0.08~(stat)~^{+~0.08}_{-~0.14}~(sys)$ in all bins of $\beta$ and $Q^2$. In the measured $Q^2$ range, the diffractive structure function approximately scales with $Q^2$ at fixed $\beta$. In an Ingelman-Schlein type model, where commonly used pomeron flux factor normalisations are assumed, it is found that the quarks within the pomeron do not saturate the momentum sum rule.Comment: 36 pages, latex, 11 figures appended as uuencoded fil

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 ofαs, 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

Measurement of total and partial photon proton cross sections at 180 GeV center of mass energy

Photon proton cross sections for elastic light vector meson production, σelνp, inelastic diffractive production, σndνp, non-diffractive production, σdνp, as well as the total cross section, σtotνp, have been measured at an average υp center of mass energy of 180 GeV with the ZEUS detector at HERA. The resulting values are σelνp = 18 ± 7 μb, σdνp = 33 ± 8 μb, σndνp = 91 ± 11 μb, and σtotνp 143 ± 17 μb, where the errors include statistical and systematic errors added in quadrature

Inclusive transverse momentum distributions of charged particles in diffractive and nondiffractive photoproduction at HERA

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 \langle W \rangle = 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 $\langle M_{X} \rangle = 5$ GeV and $10$ GeV. The inclusive transverse momentum spectra fall exponentially in the low $p_{T}$ region. The non--diffractive data 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.Comment: 23 pages, latex, 4 figures appended as uuencoded fil

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

Measurement of total and partial photon proton cross-sections at 180-GeV center-of-mass energy

Photon proton cross sections for elastic light vector meson production, sigma(el)gammap, inelastic diffractive production, sigma(d)gammap, non-diffractive production, sigma(nd)gammap, as well as the total cross section, sigma(tot)gammap, have been measured at an average gammap center of mass energy of 180 GeV with the ZEUS detector at HERA. The resulting values are sigma(el)gammap = 18 +/- 7 mub, sigma(d)gammap = 33 +/- 8 mub, sigma(nd)gammap = 91 +/- 11 mub, and sigma(tot)gammap = 143 +/- 17 mub, where the errors include statistical and systematic errors added in quadrature

Jet production in highQ 2 deep-inelastic ep scattering at HERA

Two-jet production in deep-inelastic electron-proton scattering has been studied for $160<Q^2<1280$~GeV$^2$, $0.01<x<0.1$ 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.Comment: 26 pages, latex, 9 figures appended as uuencoded fil

Inclusive charged particle distributions in deep inelastic scattering events at HERA

A measurement of inclusive charged particle distributions in deep inelastic $ep$ scattering for $\gamma^* p$ centre-of-mass energies $75< W < 175$~GeV and momentum transfer squared $10< Q^2 < 160$~GeV$^2$ from the ZEUS detector at HERA is presented. The differential charged particle rates in the $\gamma^* p$ centre-of-mass system as a function of the scaled longitudinal momentum, $x_F$, and of the transverse momentum, $p_t^*$ and $\,\,$ , as a function of $x_F$, $W$ and $Q^2$ are given. Separate distributions are shown for events with (LRG) and without (NRG) a rapidity gap with respect to the proton direction. The data are compared with results from experiments at lower beam energies, with the naive quark parton model and with parton models including perturbative QCD corrections. The comparison shows the importance of the higher order QCD processes. Significant differences of the inclusive charged particle rates between NRG and LRG events at the same $W$ are observed. The value of $\,\,$ for LRG events with a hadronic mass $M_X$, which excludes the forward produced baryonic system, is similar to the $\,\,$ value observed in fixed target experiments at $W \approx M_X$.Comment: 34 pages, latex, 9 figures appended as uuencoded file. Author list correcte

Measurement of the proton structure function F2 from the 1993 HERA data

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

Neutral strange particle production in deep inelastic scattering at HERA

This paper presents measurements of \k\ and \lam\ 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\ and \lam\ production are determined for transverse momenta \ \ptr\ $> 0.5$ GeV and pseudorapidities $\left| \eta \right| < 1.3$. 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's in events with and without a large rapidity gap with respect to the proton direction are compared. The ratio of neutral \k's to charged particles per event in the measured kinematic range is, within the present statistics, the same in both samples.Comment: 27 pages, latex 8 figures appended as uuencoded fil