We present results on dijet production via hard color-singlet exchange in proton-antiproton collisions at root-s = 630 GeV and 1800 GeV using the DZero detector. The fraction of dijet events produced via color-singlet exchange is measured as a function of jet transverse energy, separation in pseudorapidity between the two highest transverse energy jets, and proton-antiproton center-of-mass energy. The results are consistent with a color-singlet fraction that increases with an increasing fraction of quark-initiated processes and inconsistent with two-gluon models for the hard color-singlet.
Colour-singlet fraction at 1.8 TeV.
Ratio of colour-singlet fractions between 630 and 1800 GeV.
The splitting processes in identified quark and gluon jets are investigated using longitudinal and transverse observables. The jets are selected from symmetric three-jet events measured in Z decays with the Delphi detector in 1991-1994. Gluon jets are identified using heavy quark anti-tagging. Scaling violations in identified gluon jets are observed for the first time. The scale energy dependence of the gluon fragmentation function is found to be about two times larger than for the corresponding quark jets, consistent with the QCD expectation CA/CF. The primary splitting of gluons and quarks into subjets agrees with fragmentation models and, for specific regions of the jet resolution y, with NLLA calculations. The maximum of the ratio of the primary subjet splittings in quark and gluon jets is 2.77±0.11±0.10. Due to non-perturbative effects, the data are below the expectation at small y. The transition from the perturbative to the non-perturbative domain appears at smaller y for quark jets than for gluon jets. Combined with the observed behaviour of the higher rank splittings, this explains the relatively small multiplicity ratio between gluon and quark jets.
Scaled energy distribution of charged hadrons produced in Quark jets in 'Y'topology 3-JET events.
Scaled energy distribution of charged hadrons produced in Gluon jets in 'Y'topology 3-JET events.
Scaled energy distribution of charged hadrons produced in Quark jets in 'Mercedes' topology 3-JET events.
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.
Deep inelastic charged--current reactions have been studied in $e~+p$ and $e~-p$ collisions at a center of mass energy of about $300\,\gev$ in the kinematic region $Q~2\greater200\,\gev~2$ and $x\greater0.006$ using the ZEUS detector at HERA. The integrated cross sections for $Q~2\greater200\,\gev~2$ are found to be $\sigep=30.3\,{}~{+5.5}_{\mns4.2}\,{}~{+1.6}_{\mns2.6}\,{\rm pb}$ and $\sigem=54.7\,{}~{+15.9}_{\mns\chax 9.8}\,{}~{+2.8}_{\mns3.4}\,{\rm pb}$. Differential cross sections have been measured as functions of the variables $x$, $y$ and $Q~2$. From the measured differential cross sections $d\sigma/dQ~2$, the $W$ boson mass is determined to be $M_W=79\,{}~{+8} _{-7}{}~{+4}_{-4}\,\gev$. Measured jet rates and transverse energy profiles agree with model predictions. A search for charged--current interactions with a large rapidity gap yielded one candidate event, corresponding to a cross section of $\sigep(Q~2\greater200\,\gev~2;\eta_{\rm max}<2.5)=0.8\,{}_{-0.7}~ {+1.8}\,\pm0.1\,{\rm pb}$.
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We measure an inclusive branching fraction of (13.9 ± 2.0−2.2+1.9)% for the decay τ−→ντπ−π0+nh0(n>~1), where h0 is a π0 or an η. The data sample, obtained with the time-projection-chamber detector facility at the SLAC e+e− storage ring PEP, corresponds to an integrated luminosity of 72 pb−1 at 29 GeV center-of-mass energy. The measured branching fraction is somewhat greater than the theoretical prediction and, with errors taken into account, could resolve the present difference between the inclusive and the sum of the exclusive τ± branching fractions into one charged prong.
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We report on the first search with virtual photon-photon collisions for narrow, neutral resonances with even C parity in the mass range 4.5
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Direct electrons are observed in baryon events produced in e+e− annihilation at center-of-mass energies above the ΛcΛ¯c threshold. These events are attributed to charmed-baryon pair production and subsequent Λc semileptonic decay. Various semileptonic branching ratios of the Λc are determined, including B(Λc→e+X)=(4.5±1.7)%.
ELECTRON-BARYON RATIO ABOVE AND BELOW LAMBDA/C THRESHOLD.
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We present results on the jet structure observed in multihadronic events produced by e+e− annihilation in the Mark I magnetic detector at SPEAR. The evidence for jet structure and the jet-axis angular distribution are reported. We give inclusive distributions of the hadrons in Feynman x, rapidity, and transverse momentum relative to the jet axis.
Observed particle PT with respect to jet axis for events with three or more detected charged particles.
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292+-7 MUB - CORRECTED VALUE FOR FIRST REACTION (SLOW PROTONS). M(P 4PI) <= 3.5 GEV FOR REACTIONS WITH FOUR PIONS.
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