This paper presents the first analysis of diffractive photon dissociation events in deep inelastic positron-proton scattering at HERA in which the proton in the final state is detected and its momentum measured. The events are selected by requiring a scattered proton in the ZEUS leading proton spectrometer (LPS) with $\xl>0.97$, where $\xl$ is the fraction of the incoming proton beam momentum carried by the scattered proton. The use of the LPS significantly reduces the contamination from events with diffractive dissociation of the proton into low mass states and allows a direct measurement of $t$, the square of the four-momentum exchanged at the proton vertex. The dependence of the cross section on $t$ is measured in the interval $0.073<|t|<0.4$~$\gevtwo$ and is found to be described by an exponential shape with the slope parameter $b=\tslopeerr$. The diffractive structure function $\ftwodfour$ is presented as a function of $\xpom \simeq 1-\xl$ and $\beta$, the momentum fraction of the struck quark with respect to $\xpom$, and averaged over the $t$ interval $0.073<|t|<\ftwodfourtmax$~$\gevtwo$ and the photon virtuality range $5
The measured distribution of T, the squared momentum transfer to the virtual pluton.
Slope of the T distribution.
The structure function F2(NAME=D4).
Charged particle production has been measured in deep inelastic scattering (DIS) events over a large range of $x$ and $Q^2$ using the ZEUS detector. The evolution of the scaled momentum, $x_p$, with $Q^2,$ in the range 10 to 1280 $GeV^2$, has been investigated in the current fragmentation region of the Breit frame. The results show clear evidence, in a single experiment, for scaling violations in scaled momenta as a function of $Q^2$.
No description provided.
No description provided.
No description provided.
We have searched for first generation scalar leptoquark (LQ) pairs in the enu+jets channel using ppbar collider data (integrated luminosity= 115 pb^-1) collected by the DZero experiment at the Fermilab Tevatron during 1992-96. The analysis yields no candidate events. We combine the results with those from the ee+jets and nunu+jets channels to obtain 95% confidence level (CL) upper limits on the LQ pair production cross section as a function of mass and of beta, the branching fraction to a charged lepton. Comparing with the next-to-leading order theory, we set 95% CL lower limits on the LQ mass of 225, 204, and 79 GeV/c^2 for beta=1, 1/2, and 0, respectively.
The cross section values are extracted with the assumption that BR(LQ --> EQUARK) = 1/2.
A global event shape analysis of the multihadronic final states observed in neutral current deep inelastic scattering events with a large rapidity gap with respect to the proton direction is presented. The analysis is performed in the range $5 \leq Q^2 \leq 185\gev^2$ and $160 \leq W \leq 250\gev$, where $Q^2$ is the virtuality of the photon and $W$ is the virtual-photon proton centre of mass energy. Particular emphasis is placed on the dependence of the shape variables, measured in the $\gamma^*-$pomeron rest frame, on the mass of the hadronic final state, $M_X$. With increasing $M_X$ the multihadronic final state becomes more collimated and planar. The experimental results are compared with several models which attempt to describe diffractive events. The broadening effects exhibited by the data require in these models a significant gluon component of the pomeron.
Measured (uncorrected) polar distribution of the sphericity axis w.r.t. thevirtual photon direction in the (gamma*-pomeron)rest frame Data are in bins of the mass of the final state hadronic system.
Measured (uncorrected) polar distribution of the sphericity axis w.r.t. thevirtual photon direction in the (gamma*-pomeron)rest frame Data are in bins of the mass of the final state hadronic system.
Measured (uncorrected) polar distribution of the sphericity axis w.r.t. thevirtual photon direction in the (gamma*-pomeron)rest frame Data are in bins of the mass of the final state hadronic system.
The shape of jets produced in quasi-real photon-proton collisions at centre-of-mass energies in the range $134-277$ GeV has been measured using the hadronic energy flow. The measurement was done with the ZEUS detector at HERA. Jets are identified using a cone algorithm in the $\eta - \phi$ plane with a cone radius of one unit. Measured jet shapes both in inclusive jet and dijet production with transverse energies $E^{jet}_T>14$ GeV are presented. The jet shape broadens as the jet pseudorapidity ($\eta^{jet}$) increases and narrows as $E^{jet}_T$ increases. In dijet photoproduction, the jet shapes have been measured separately for samples dominated by resolved and by direct processes. Leading-logarithm parton-shower Monte Carlo calculations of resolved and direct processes describe well the measured jet shapes except for the inclusive production of jets with high $\eta^{jet}$ and low $E^{jet}_T$. The observed broadening of the jet shape as $\eta^{jet}$ increases is consistent with the predicted increase in the fraction of final state gluon jets.
Inclusive jet production. Data in different pseudorapidity ranges.
Inclusive jet production. Data in different pseudorapidity ranges.
Inclusive jet production. Data in different pseudorapidity ranges.
Dijet cross sections are presented using photoproduction data obtained with the ZEUS detector during 1994. These measurements represent an extension of previous results, as the higher statistics allow cross sections to be measured at higher jet transverse energy (ETJ). Jets are identified in the hadronic final state using three different algorithms, and the cross sections compared to complete next-to-leading order QCD calculations. Agreement with these calculations is seen for the pseudorapidity dependence of the direct photon events with ETJ > 6 GeV and of the resolved photon events with ETJ > 11 GeV. Calculated cross sections for resolved photon processes with 6 GeV < ETJ < 11 GeV lie below the data.
Dijet cross section using the KTCLUS jet alogrithm with a minimum ET for each jet of 6 GeV and a requirement on X(NAME=GAMMA_OBS) to be 0.0 TO 1.0. The second DSYS errors are the correlated uncertainties.
Dijet cross section using the KTCLUS jet alogrithm with a minimum ET for each jet of 8 GeV and a requirement on X(NAME=GAMMA_OBS) to be 0.0 TO 1.0. The second DSYS errors are the correlated uncertainties.
Dijet cross section using the KTCLUS jet alogrithm with a minimum ET for each jet of 11 GeV and a requirement on X(NAME=GAMMA_OBS) to be 0.0 TO 1.0. The second DSYS errors are the correlated uncertainties.
Photon diffractive dissociation, $\gamma p \to Xp$, has been studied at HERA with the ZEUS detector using $ep$ interactions where the virtuality $Q^2$ of the exchanged photon is smaller than 0.02 GeV$^2$. The squared four-momentum $t$ exchanged at the proton vertex was determined in the range $0.073<|t|<0.40$ GeV$^2$ by measuring the scattered proton in the ZEUS Leading Proton Spectrometer. In the photon-proton centre-of-mass energy interval $176
T is the squared four momentum transfer at the proton vertex.
SLOPE of the DN/DT distribution.
Charged particles ($h^\pm$) and \kz mesons have been studied in photoproduced events containing at least one jet of $E_T > 8$ GeV in a pseudorapidity interval (--0.5, 0.5) in the ZEUS laboratory frame. Distributions are presented in terms of transverse momentum, pseudorapidity and distance of the particle from the axis of a jet. The properties of \hpm within the jet are described well using the standard settings of PYTHIA, but the use of the multiparton interaction option improves the description outside the jets. A reasonable overall description of the \kz behaviour is possible with PYTHIA using a reduced value of the strangeness suppression parameter. The numbers of $h^\pm$ and \kz within a jet as defined above are measured to be $3.25\pm0.02\pm0.28$ and $0.431\pm0.013\pm0.088$ respectively. Fragmentation functions are presented for $h^\pm$ and \kz in photoproduced jets; agreement is found with calculations of Binnewies et al. and, at higher momenta, with $p\bar p$ scattering and with standard PYTHIA. Fragmentation functions in direct photoproduced events are extracted, and at higher momenta give good agreement with data from related processes in $e^+e^-$ annihilation and deep inelastic $ep$ scattering.
Corrected multiplicities of charged particles and neutral K0 mesons per photoproduced jet.
Corrected distribution of charged particles per jet in events containing a hadron jet.
Corrected distribution of charged particles per jet in events containing a hadron jet.
Elastic and proton-dissociative rho0 photoproduction (gamma p-->rho0 p,gamma p -->rho0 N,with rho0-->pi+pi-) has been studied in ep interactions at HERA for gamma-p centre-of-mass energies in the range 50
Integrated elastic rho0 photoproduction cross section.
Integrated elastic pi+ pi- photoproduction cross section.
Differential T distribution. Statistical errors only.
We determine the top quark mass m_t using t-tbar pairs produced in the D0 detector by \sqrt{s} = 1.8 TeV p-pbar collisions in a 125 pb^-1 exposure at the Fermilab Tevatron. We make a two constraint fit to m_t in t-tbar -> b W^+bbar W^- final states with one W boson decaying to q-qbar and the other to e-nu or mu-nu. Likelihood fits to the data yield m_t(l+jets) = 173.3 +- 5.6 (stat) +- 5.5 (syst) GeV/c^2. When this result is combined with an analysis of events in which both W bosons decay into leptons, we obtain m_t = 172.1 +- 5.2 (stat) +- 4.9 (syst) GeV/c^2. An alternate analysis, using three constraint fits to fixed top quark masses, gives m_t(l+jets) = 176.0 +- 7.9 (stat) +- 4.8 (syst) GeV/C^2, consistent with the above result. Studies of kinematic distributions of the top quark candidates are also presented.
No description provided.
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