Study of the Pion Trajectory in the Photoproduction of Leading Neutrons at HERA

Energetic neutrons produced in ep collisions at HERA have been studied with the ZEUS detector in the photoproduction regime at a mean photon-proton center-of-mass energy of 220 GeV. The neutrons carry a large fraction 0.6

Observation of Isolated High-E\u3csub\u3eT\u3c/sub\u3e Photons in Deep Inelastic Scattering

First measurements of cross sections for isolated prompt photon production in deep inelastic ep scattering have been made using the ZEUS detector at the HERA electron-proton collider using an integrated luminosity of 121 pb -1. A signal for isolated photons in the transverse energy and rapidity ranges

Evidence for a Narrow Baryonic State Decaying to K\u3csub\u3eS\u3c/sub\u3e\u3csup\u3e0\u3c/sup\u3ep and K\u3csub\u3eS\u3c/sub\u3e\u3csup\u3e0\u3c/sup\u3ep̄ in Deep Inelastic Scattering at HERA

A resonance search has been made in the K0Sp and K0Sp̄ invariant-mass spectrum measured with the ZEUS detector at HERA using an integrated luminosity of 121 pb-1. The search was performed in the central rapidity region of inclusive deep inelastic scattering at an ep centre-of-mass energy of 300-318 GeV for exchanged photon virtuality, Q2, above 1 GeV2. Recent results from fixed-target experiments give evidence for a narrow baryon resonance decaying to K+n and K0Sp, interpreted as a pentaquark. The results presented here support the existence of such state, with a mass of 1521.5±1.5(stat.)+2.8-1.7(syst.) MeV and a Gaussian width consistent with the experimental resolution of 2 MeV. The signal is visible at high Q2 and, for Q2\u3e20 GeV2, contains 221±48 events. The probability of a similar signal anywhere in the range 1500-1560 MeV arising from fluctuations of the background is below 6×10-5. © 2004 Elsevier B.V. All rights reserved

Bose-Einstein Correlations in One and Two Dimensions in Deep Inelastic Scattering

Bose-Einstein correlations in one and two dimensions have been studied in deep inelastic ep scattering events measured with the ZEUS detector at HERA using an integrated luminosity of 121 pb-1. The correlations are independent of the virtuality of the exchanged photon, Q2, in the range 0.1 \u3c Q2 \u3c 8000 GeV2. There is no significant difference between the correlations in the current and target regions of the Breit frame for Q2 \u3e 100 GeV2. The two-dimensional shape of the particle-production source was investigated, and a significant difference between the transverse and the longitudinal dimensions of the source is observed. This difference also shows no Q2 dependence. The results demonstrate that Bose-Einstein interference, and hence the size of the particle-production source, is insensitive to the hard subprocess. © 2004 Published by Elsevier B.V

Evidence for a narrow baryonic state decaying to K0Sp and KOSp in deep inelastic scattering at HERA

A resonance search has been made in the K0Sp and KOSp invariant-mass spectrum measured with the ZEUS detector at HERA using an integrated luminosity of 121 pb−1. The search was performed in the central rapidity region of inclusive deep inelastic scattering at an ep centre-of-mass energy of 300–318 GeV for exchanged photon virtuality, Q2, above 1 GeV2. Recent results from fixed-target experiments give evidence for a narrow baryon resonance decaying to K+n and K0Sp, interpreted as a pentaquark. The results presented here support the existence of such state, with a mass of 1521.5±1.5(stat.)+2.8−1.7(syst.) MeV and a Gaussian width consistent with the experimental resolution of 2 MeV. The signal is visible at high Q2 and, for Q2>20 GeV2, contains 221±48 events. The probability of a similar signal anywhere in the range 1500–1560 MeV arising from fluctuations of the background is below 6×10−5

Search for QCD-instanton Induced Events in Eeep Inelastic ep Scattering at HERA

A search for QCD-instanton-induced events in deep inelastic ep scattering has been performed with the ZEUS detector at the HERA collider, using data corresponding to an integrated luminosity of 38 pb-1. A kinematic range defined by cuts on the photon virtuality, Q2 \u3e 120 GeV 2, and on the Bjorken scaling variable, x \u3e 10-3, has been investigated. The QCD-instanton induced events were modelled by the Monte Carlo generator QCDINS. A background-independent, conservative 95% confidence level upper limit for the instanton cross section of 26 pb is obtained, to be compared with the theoretically expected value of 8.9pb

Multijet Production in Neutral Current Deep Inelastic Scattering at HERA and Determination of α\u3csub\u3es\u3c/sub\u3e

Multijet production rates in neutral current deep inelastic scattering have been measured in the range of exchanged boson virtualities 10 \u3c Q 2 \u3c 5000 GeV2. The data were taken at the ep collider HERA with centre-of-mass energy √s = 318 GeV using the ZEUS detector and correspond to an integrated luminosity of 82.2pb-1. Jets were identified in the Breit frame using the kT cluster algorithm in the longitudinally invariant inclusive mode. Measurements of differential dijet and trijet cross sections are presented as functions of jet transverse energy (ET,Bjet), pseudorapidity (ηLABjet) and Q2 with ET,Bjet \u3e 5 GeV and -1 \u3c ηLABjet \u3c 2.5. Next-to-leading-order QCD calculations describe the data well. The value of the strong coupling constant αs(MZ), determined from the ratio of the trijet to dijet cross sections, is αs(MZ) = 0.1179 ± 0.0013 (stat.)-0.0046-0.0028 (exp.) -0.0046+0.0064 (th.). © Springer-Verlag / Società Italiana di Fisica 2005

Propagation in 3D spiral-arm cosmic-ray source distribution models and secondary particle production using PICARD

We study the impact of possible spiral-arm distributions of Galactic cosmic-ray sources on the flux of various cosmic-ray nuclei throughout our Galaxy. We investigate model cosmic-ray spectra at the nominal position of the sun and at different positions within the Galaxy. The modelling is performed using the recently introduced numerical cosmic ray propagation code \textsc{Picard}. Assuming non-axisymmetric cosmic ray source distributions yields new insights on the behaviour of primary versus secondary nuclei. We find that primary cosmic rays are more strongly confined to the vicinity of the sources, while the distribution of secondary cosmic rays is much more homogeneous compared to the primaries. This leads to stronger spatial variation in secondary to primary ratios when compared to axisymmetric source distribution models. A good fit to the cosmic-ray data at Earth can be accomplished in different spiral-arm models, although leading to decisively different spatial distributions of the cosmic-ray flux. This results in very different cosmic ray anisotropies, where even a good fit to the data becomes possible. Consequently, we advocate directions to seek best fit propagation parameters that take into account the higher complexity introduced by the spiral-arm structure on the cosmic-ray distribution. We specifically investigate whether the flux at Earth is representative for a large fraction of the Galaxy. The variance among possible spiral-arm models allows us to quantify the spatial variation of the cosmic-ray flux within the Galaxy in presence of non-axisymmetric source distributions.Comment: 38 pages, 16 figures, accepted for publication in Astroparticle Physic

Observation of isolated high-E_T photons in deep inelastic scattering

First measurements of cross sections for isolated prompt photon production in deep inelastic ep scattering have been made using the ZEUS detector at the HERA electron-proton collider using an integrated luminosity of 121 pb^-1. A signal for isolated photons in the transverse energy and rapidity ranges 5 < E_T^gamma < 10 GeV and -0.7 < eta^gamma < 0.9 was observed for virtualities of the exchanged photon of Q^2 > 35 GeV^2. Cross sections are presented for inclusive prompt photons and for those accompanied by a single jet in the range E_T^jet \geq 6 GeV and -1.5 \leq eta^jet < 1.8. Calculations at order alpha^3alpha_s describe the data reasonably well.Comment: 16 pages, 5 figure

An NLO QCD Analysis of Inclusive Cross-section and Jet-production Fata from the ZEUS Experiment

The ZEUS inclusive differential cross-section data from HERA, for charged and neutral current processes taken with e + and e - beams, together with differential cross-section data on inclusive jet production in e + p scattering and dijet production in γp scattering, have been used in a new NLO QCD analysis to extract the parton distribution functions of the proton. The input of jet-production data constrains the gluon and allows an accurate extraction of alpha s(MZ) at NLO; alphas = 0.1183±0.0028(exp.)±0.0008(model). An additional uncertainty from the choice of scales is estimated as ±0.005. This is the first extraction of alphas(MZ) from HERA data alone. © Springer-Verlag/Società Italiana de Fisica 2005