Search

The production of D±- and D0-mesons has been measured with the ZEUS detector at HERA using an integrated luminosity of 133.6 pb−1. The measurements cover the kinematic range 5< Q2<1000 GeV2, 0.02< y<0.7, 1.5< p<15 GeV and | η D|<1.6. Combinatorial background to the D-meson signals is reduced by using the ZEUS microvertex detector to reconstruct displaced secondary vertices. Production cross sections are compared with the predictions of next-to-leading-order QCD, which is found to describe the data well. Measurements are extrapolated to the full kinematic phase space in order to obtain the open-charm contribution, $F_{2}^{c\bar{c}}$ , to the proton structure function, F2. [ABSTRACT FROM AUTHOR]

The production of dijets in diffractive deep inelastic scattering has been measured with the ZEUS detector at HERA using an integrated luminosity of 61 pb-1. The dijet cross section has been measured for virtualities of the exchanged virtual photon, 5 < Q2 < 100 GeV2, and γ*p centre-of-mass energies, 100 < W < 250 GeV. The jets, identified using the inclusive kT algorithm in the γ*p frame, were required to have a transverse energy E* T,jet > 4 GeV and the jet with the highest transverse energy was required to have E* T,jet > 5 GeV. All jets were required to be in the pseudorapidity range -3.5<η* jet<0. The differential cross sections are compared to leading-order predictions and next-to-leading-order QCD calculations based on recent diffractive parton densities extracted from inclusive diffractive deep inelastic scattering data. [ABSTRACT FROM AUTHOR]

Forward jet cross sections have been measured in neutral current deep inelastic scattering at low Bjorken-x with the ZEUS detector at HERA using an integrated luminosity of 81.8 pb-1. Measurements are presented for inclusive forward jets as well as for forward jets accompanied by a dijet system. The explored phase space, with jet pseudorapidity up to 4.3 is expected to be particularly sensitive to the dynamics of QCD parton evolution at low x. The measurements are compared to fixed-order QCD calculations and to leading-order parton-shower Monte Carlo models. [ABSTRACT FROM AUTHOR]

The inelastic production of $J/\psi$ mesons in ep collisions has been studied with the ZEUS detector at HERA using an integrated luminosity of $109{ \text{pb}^{-1}}$. The $J/\psi$ mesons were identified using the decay channel $J/\psi\to\mu^{ + }\mu^{-}$. The measurements were performed in the kinematic range $2 < Q^2 < 80 {\rm GeV}^2$, $50 < W < 250 \text{GeV}$, 0.2 < z < 0.9 and $-1.6 < Y_{\text{lab}} < 1.3$, where Q2 is the virtuality of the exchanged photon, W is the photon-proton centre-of-mass energy, z is the fraction of the photon energy carried by the $J/\psi$ meson in the proton rest frame and $Y_{\text{lab}}$ is the rapidity of the $J/\psi$ in the laboratory frame. The measured cross sections are compared to theoretical predictions within the non-relativistic QCD framework including colour-singlet and colour-octet contributions, as well as to predictions based on the k T-factorisation approach. Calculations of the colour-singlet process generally agree with the data, whereas inclusion of colour-octet terms spoils this agreement. [ABSTRACT FROM AUTHOR]

Abstract: Inclusive-jet and dijet differential cross sections have been measured in neutral current deep inelastic ep scattering for exchanged boson virtualities with the ZEUS detector at HERA using an integrated luminosity of 82 pb−1. Jets were identified in the Breit frame using the cluster algorithm. Jet cross sections are presented as functions of several kinematic and jet variables. The results are also presented in different regions of . Next-to-leading-order QCD calculations describe the measurements well. Regions of phase space where the theoretical uncertainties are small have been identified. Measurements in these regions have the potential to constrain the gluon density in the proton when used as inputs to global fits of the proton parton distribution functions. [Copyright &y& Elsevier]

Abstract: A search for pentaquarks decaying to () and corresponding antiparticles has been performed with the ZEUS detector at HERA. The data sample consists of deep inelastic ep scattering events at centre-of-mass energies of 300 and 318 GeV, and corresponds to 121 pb−1 of integrated luminosity. A clear signal for was observed. However, no signal for any new baryonic state was observed at higher masses in either the or channels. The searches in the antiparticle channels were also negative. Upper limits on the ratio of a possible () signal to the signal were set in the mass range 1650–2350 MeV. [Copyright &y& Elsevier]

The azimuthal distribution of jets produced in the Breit frame in high-Q2 deep inelastic e+p scattering has been studied with the ZEUS detector at HERA using an integrated luminosity of 38.6 pb−1. The measured azimuthal distribution shows a structure that is well described by next-to-leading-order QCD predictions over the Q2 range considered, Q2>125 GeV2. [Copyright &y& Elsevier]

Inclusive jet differential cross sections have been measured in neutral current deep inelastic e+p scattering for boson virtualities Q2>125 GeV2. The data were taken using the ZEUS detector at HERA and correspond to an integrated luminosity of 38.6 pb−1. Jets were identified in the Breit frame using the longitudinally invariant kT cluster algorithm. Measurements of differential inclusive jet cross sections are presented as functions of jet transverse energy (EBT,jet), jet pseudorapidity and Q2, for jets with EBT,jet>8 GeV. Next-to-leading-order QCD calculations agree well with the measurements both at high Q2 and high EBT,jet. The value of αs(MZ), determined from an analysis of dσ/dQ2 for Q2>500 GeV2, is αs(MZ)=0.1212±0.0017(stat.)+0.0023−0.0031(syst.)+0.0028−0.0027(th.). [Copyright &y& Elsevier]

Diffractive production of D&ast;±(2010) mesons in deep inelastic scattering has been measured with the ZEUS detector at HERA using an integrated luminosity of 44.3 pb−1. Diffractive charm production is identified by the presence of a large rapidity gap in the final state of events in which a D&ast;±(2010) meson is reconstructed in the decay channel D&ast;+→(D0→K−π+)π+s (+ charge conjugate). Differential cross sections when compared with theoretical predictions indicate the importance of gluons in such diffractive interactions. [Copyright &y& Elsevier]

A search for physics beyond the Standard Model has been performed with high-Q2 neutral current deep inelastic scattering events recorded with the ZEUS detector at HERA. Two data sets, e+p→e+X and e-p→e-X, with respective integrated luminosities of 112 pb-1 and 16 pb-1, were analyzed. The data reach Q2 values as high as 40 000 GeV2. No significant deviations from Standard Model predictions were observed. Limits were derived on the effective mass scale in eeqq contact interactions, the ratio of leptoquark mass to the Yukawa coupling for heavy leptoquark models and the mass scale parameter in models with large extra dimensions. The limit on the quark charge radius, in the classical form factor approximation, is 0.85×10-16 cm. [Copyright &y& Elsevier]

A resonance search has been made in the K0Sp and K0S&pmacr; 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. [Copyright &y& Elsevier]

Inclusive Ks0Ks0 production in deep inelastic ep scattering at HERA has been studied with the ZEUS detector using an integrated luminosity of 120 pb−1. Two states are observed at masses of 1537+9−8 MeV and 1726±7 MeV, as well as an enhancement around 1300 MeV. The state at 1537 MeV is consistent with the well established f′2(1525). The state at 1726 MeV may be the glueball candidate f0(1710). However, it''s width of 38+20−14 MeV is narrower than 125±10 MeV observed by previous experiments for the f0(1710). [Copyright &y& Elsevier]