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.
We present the first measurement of the jet pseudorapidity distribution in direct photon events from a sample of pp¯ collisions at s=1.8TeV, recorded with the Collider Detector at Fermilab. Quantum chromodynamics (QCD) predicts that these events are primarily from hard quark-gluon Compton scattering, qg→qγ, with the final state quark producing the jet of hadrons. The jet pseudorapidity distribution in this model is sensitive to parton momentum fractions between 0.015 and 0.15. We find that the shape of the measured pseudorapidity distribution agrees well with next-to-leading order QCD calculations.
The fully corrected shape of the pseudorapidity distribution normalised to the data in the absolute pseudorapidity bin from 0 to 0.7.
The reaction gamma p -> J/Psi p has been studied in ep interactions using the ZEUS detector at HERA. The cross section for elastic J/Psi photoproduction has been measured as a function of the photon-proton centre of mass energy W in the range 40 < W < 140 GeV at a median photon virtuality Q^2 of 5*10^{-5} GeV^2. The photoproduction cross section, sigma_{gamma p -> J/Psi p}, is observed to rise steeply with W. A fit to the data presented in this paper to determine the parameter $\delta$ in the form sigma_{gamma p -> J/Psi p} \propto W^{\delta} yields the value \delta = 0.92 \pm 0.14 \pm 0.10. The differential cross section dsigma/d|t| is presented over the range |t| < 1.0 GeV^2 where t is the square of the four-momentum exchanged at the proton vertex. d\sigma/d|t| falls exponentially with a slope parameter of 4.6 \pm 0.4 (+0.4-0.6) GeV^{-2}. The measured decay angular distributions are consistent with s-channel helicity conservation.
Data from the electron channel. Second systematic error is that attributed to the uncertainty in the modelof proton dissociation used for background subtraction.
Data from the muon channel. Second systematic error is that attributed to the uncertainty in the modelof proton dissociation used for background subtraction.
Data from the electron channel. Second systematic error is that attributed to the uncertainty in the modelof proton dissociation used for background subtraction.
Inclusive charged particle and event shape distributions are measured using 321 hadronic events collected with the DELPHI experiment at LEP at effective centre of mass energies of 130 to 136 GeV. These distributions are presented and compared to data at lower energies, in particular to the precise Z data. Fragmentation models describe the observed changes of the distributions well. The energy dependence of the means of the event shape variables can also be described using second order QCD plus power terms. A method independent of fragmentation model corrections is used to determine αs from the energy dependence of the mean thrust and heavy jet mass. It is measured to be: $$←pha _s(133 {⤪ GeV})={0.116}pm {0.007}_{exp-0.004theo}^{+0.005}$$ from the high energy data.
mean values for event shape variables.
Integral of event shape distribution over the specified interval.
Integral of event shape distribution over the specified interval.
Event shape and charged particle inclusive distributions are measured using 750000 decays of the Z to hadrons from the DELPHI detector at LEP. These precise data allow a decisive confrontation with models of the hadronization process. Improved tunings of the JETSET, ARIADNE and HERWIG parton shower models and the JETSET matrix element model are obtained by fitting the models to these DELPHI data as well as to identified particle distributions from all LEP experiments. The description of the data distributions by the models is critically reviewed with special importance attributed to identified particles.
Transverse momentum PTIN w.r.t. the Thrust axis. For the first table Thrust axis definition is from seen charged particles corrected to final state particles. For the second table Thrust axis definition is from seen charged plus neutral particles corrected to final state charged plus neutral particles.
Transverse momentum PTOUT w.r.t. the Thrust axis. For the first table Thrust axis definition is from seen charged particles corrected to final state particles. For the second table Thrust axis definition is from seen charged plus neutral particles corrected to final state charged plus neutral particles.
Transverse momentum PTIN w.r.t. the Sphericity axis. For the first table Sphericity axis definition is from seen charged particles corrected to final state particles. For the second table Sphericity axis definition is from seen charged plus neutral particles corrected to final state charged plus neutral particles.
A study of the production of strange octet and decuplet baryons in hadronic decays of the Z recorded by the DELPHI detector at LEP is presented. This includes the first measurement of the∑± average multiplicity. The total and differential cross sections, the event topology and the baryon-antibaryon correlations are compared with current hadronization models.
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The properties of two-, three-, four-, five-, and six-jet events with multijet masses >600 GeV /c2 are compared with QCD predictions. The shapes of the multijet-mass and leading-jet-angular distributions are approximately independent of jet multiplicity and are well described by the NJETS matrix element calculation and the HERWIG parton shower Monte Carlo predictions. The observed jet transverse momentum distributions for three- and four-jet events discriminate between the matrix element and parton shower predictions, the data favoring the matrix element calculation.
Exclusive 2-jet mass distribution.
Exclusive 3-jet mass distribution.
Exclusive 4-jet mass distribution.
The W+jet angular distribution is measured using W→eν events recorded with the Collider Detector at Fermilab (CDF) during the 1988-89 and 1992-93 Tevatron runs. The data agree well with both a leading order and a next-to-leading order theoretical prediction. The shape of the angular distribution is similar to that observed in photon + jet data and significantly different from that observed in dijet data.
Data normalized to 1 in the cos(theta) range -0.6 to 0.6.
Data normalized to 1 in the abs(cos(theta)) range <0.3.
Color coherence effects in pp¯ collisions are observed and studied with CDF, the Collider Detector at the Fermilab Tevatron collider. We demonstrate these effects by measuring spatial correlations between soft and leading jets in multijet events. Variables sensitive to interference are identified by comparing the data to the predictions of various shower Monte Carlo programs that are substantially different with respect to the implementation of coherence.
Observed normalised transverse energy distribution of the leading (highest ET) jet.. Data read from plot in the preprint.
Observed normalised transverse energy distribution of the second highest ET jet.. Data read from plot in the preprint.
Observed normalised pseudorapidity distribution of the third highest ET jet.. Data read from plot in the preprint.
An experiment has been performed with the Fermilab 30-inch bubble chamber and Downstream Particle Identifier to study inclusive charged pion production in the high energy interactions of π±,K+,p and\(\bar p\) with thin foils of magnesium, silver and gold. The laboratory rapidity and transverse momentum distributions are presented separately for π+ and π− production. Comparisons are made with data from hadron-proton interactions and theA dependence of the cross sections in the different kinematic regions is discussed. We investigate the dependence of the cross sections on the number of observed protons ejected from the nucleus. By using our π−A data from two different beam energies, we study the energy dependence of these spectra. Comparisons are made with the VENUS string model Monte Carlo.
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