Angular and Current-Target Correlations in Deep Inelastic Scattering at HERA

Correlations between charged particles in deep inelastic ep scattering have been studied in the Breit frame with the ZEUS detector at HERA using an integrated luminosity of 6.4 pb-1. Short-range correlations are analysed in terms of the angular separation between current-region particles within a cone centred around the virtual photon axis. Long-range correlations between the current and target regions have also been measured. The data support predictions for the scaling behaviour of the angular correlations at high Q2 and for anti-correlations between the current and target regions over a large range in Q2 and in the Bjorken scaling variable x. Analytic QCD calculations and Monte Carlo models correctly describe the trends of the data at high Q2, but show quantitative discrepancies. The data show differences between the correlations in deep inelastic scattering and e+e- annihilation.Comment: 26 pages including 10 figures (submitted to Eur. J. Phys. C

Angular and Current-target Correlations in Deep Inelastic Scattering at HERA

Correlations between charged particles in deep inelastic e+ p scattering have been studied in the Breit frame with the ZEUS detector at HERA using an integrated luminosity of 6.4pb-1. Short-range correlations are analysed in terms of the angular separation between current-region particles within a cone centred around the virtual photon axis. Long-range correlations between the current and target regions have also been measured. The data support predictions for the scaling behaviour of the angular correlations at high Q2 and for anti-correlations between the current and target regions over a large range in Q2 and in the Bjorken scaling variable x. Analytic QCD calculations and Monte Carlo models correctly describe the trends of the data at high Q2, but show quantitative discrepancies. The data show differences between the correlations in deep inelastic scattering and e+e- annihilation

Measurement of D*(+/-) production and the charm contribution to F-2 in deep inelastic scattering at HERA

The production of D*(+/-)(2010) mesons in deep inelastic scattering has been measured in the ZEUS detector at HERA using an integrated luminosity of 37 pb(-1). The decay channels D*(+) --> D(0)pi(+) (+ c.c.), with D-0 --> K(-)pi(+) or D-0 --> K(-)pi(-)pi(+)pi(+), have been used to identify the D mesons. The e(+)p cross section for inclusive D*(+/-) production with 1 < Q(2) < 600 GeV2 and 0.02 < y < 0.7 is 8.31+/-0.31(stat.)(+0.30)(-0.50) (syst.) nb in the kinematic region 1.5 < pT(D*(+/-)) < 15GeV and eta(D*(+/-)) < 1.5. Differential cross sections are consistent with a next-to-leading-order perturbative-QCD calculation when using charm-fragmentation models which take into account the interaction of the charm quark with the proton remnant. The observed cross section is extrapolated to the full kinematic region in pr(D*(+/-)) and eta(D*(+/-)) in order to determine the charm contribution, F-2(c (c) over bar)(x,Q(2)), to the proton structllre function. The ratio F-2(c (c) over bar)/F-2 rises from similar or equal to 10% at Q(2) similar or equal to 1.8 GeV2 to similar or equal to 30% at Q(2) similar or equal to 130 GeV2 for x values in the rarlge 10(-4) to 10(-3)

Measurement of inclusive prompt photon photoproduction at HERA

First inclusive measurements of isolated prompt photons in photoproduction at the HERA ep collider have been made with the ZEUS detector, using an integrated luminosity of 38.4 pb/sup -1/. Cross sections are given as a function of the pseudorapidity and the transverse energy ( eta /sup gamma /, E/sub T//sup gamma /) of the photon, for E/sub T//sup gamma / gt 5 GeV in the gamma p centre-of-mass energy range 134-285 GeV. Comparisons are made with predictions from Monte Carlo models having leading-logarithm parton showers, and with next-to-leading-order QCD calculations, using currently available parameterisations of the photon structure. For forward eta /sup gamma / (proton direction) good agreement is found, but in the rear direction all predictions fall below the data

Search for contact interactions in deep inelastic e(+)p -> e(+)X scattering at HERA

In a search for signatures of physics processes beyond the Standard Model, various eeqq vector contact-interaction hypotheses have been tested using the high-Q(2) deep inelastic neutral-current e(+)p scattering data collected with the ZEUS detector at HERA. The data correspond to an integrated luminosity of 47.7pb(-1) of e(+)p interactions at 300 GeV center-of-mass energy. No significant evidence of a contact-interaction signal has been found. Limits at the 95% confidence level are set on the contact-interaction amplitudes. The effective mass scales Lambda corresponding to these limits range from 1.7 TeV to 5 TeV for the contact-interaction scenarios considered

Measurement of high-Q(2) neutral-current e(+)p deep inelastic scattering cross-sections at HERA

The e(+)p neutral-current deep inelastic scattering differential cross-sections d sigma/dQ(2), for Q(2) > 400 GeV2, d sigma/dx and d sigma/dy, for Q(2) > 400, 2500 and 10000 GeV2, have been measured with the ZEUS detector at HERA. The data sample of 47.7 pb(-1) was collected at a center-of-mass energy of 300 GeV. The cross-section, d sigma/dQ(2), falls by six orders of magnitude between Q(2) = 400 and 40000 GeV2. The predictions of the Standard Model are in very good agreement with the data. Complementing the observations of time-like Z(0) contributions to fermion-antifermion annihilation! the data provide direct evidence for the presence of Z(0) exchange in the space-like region explored by deep inelastic scattering