Three-jet production is studied for the first time in deep-inelastic positron-proton scattering. The measurement carried out with the H1 detector at HERA covers a large range of four-momentum transfer squared 5 < Q^2 < 5000 GeV^2 and invariant three-jet masses 25 < M_(3jet) < 140 GeV. Jets are defined by the inclusive k_T algorithm in the Breit frame. The size of the three-jet cross section and the ratio of the three-jet to the dijet cross section R_(3/2) are described over the whole phase space by the predictions of perturbative QCD in next-to-leading order. The shapes of angular jet distributions deviate significantly from a uniform population of the available phase space but are well described by the QCD calculation.
The inclusive 3-Jet cross section as a function of Q**2.
The ratio of 3 jets to 2 jets as a function of Q**2.
The inclusive 3-JET cross section as a function of Bjorken scaling variableX for the Q**2 range 5 to 100 GeV**2.
We have studied inclusive muon events using all the data collected by the TOPAZ detector at sqrt(s)=58 GeV with an integrated luminosity of 273pb-1. From 1328 inclusive muon events, we measured the ratio R_qq of the cross section for qq-bar production to the total hadronic cross section and forward-backward asymmetry A^q_FB for b and c quarks. The obtained results are R_bb = 0.13+-0.02(stat)+-0.01(syst), R_cc = 0.36+-0.05(stat)+-0.05(syst), A^b_FB = -0.20+-0.16(stat)+-0.01(syst) and A^c_FB = -0.17+-0.14(stat)+-0.02(syst), in fair agreement with a prediction of the standard model.
Differential cross section with respect to cos(theta).
Cross section deduced from a four-parameter fit.
Forward-backward asymmetry for a four-parameter fit.
Jet production in charged and neutral current events in the kinematic range of Q^2 from 640 to 35000 GeV^2 is studied in deep-inelastic positron-proton scattering at HERA. The measured rate of multi-jet events and distributions of jet polar angle, transverse energy, dijet mass, and other dijet variables are presented. Using parton densities derived from inclusive DIS cross sections, perturbative QCD calculations in NLO are found to give a consistent description of both the neutral and charged current dijet production. A direct, model independent comparison of the jet distributions in charged and neutral current events confirms that the QCD dynamics of the hadronic final state is independent of the underlying electroweak scattering process.
Rates of charged current events as a function of Q**2.
Rates of neutral current events as a function of Q**2.
Normalised distribution in Y2 for NC and CC dijet events. Y2 is the smallest scaled value of KT (KTJET**2/W**2) given by the combination of (2+1) jets. The +1 refers to the proton remnant jet.
An analysis of the data collected in 1997 and 1998 with the DELPHI detector at e+e- collision energies close to 183 and 189 GeV was performed in order to extract the hadronic and leptonic fermion-pair cross-sections, as well as the leptonic forward-backward asymmetries and angular distributions. The data are used to put limit on contact interactions between fermions, the exchange of R-parity violating SUSY sneutrinos, Z' bosons and the existence of gravity in extra dimensions.
No description provided.
No description provided.
No description provided.
We report on measurements of e+e- annihilation into hadrons and lepton pairs. The data have been collected with the L3 detector at LEP at centre-of-mass energies between 130 and 189 GeV. Using a total integrated luminosity of 243.7 pb^-1, 25864 hadronic and 8573 lepton-pair events are selected for the measurement of cross sections and leptonic forward-backward asymmetries. The results are in good agreement with Standard Model predictions.
Measured cross sections for the hadronic events.
Measured cross sections for the muon-pair events.
Measured cross sections for the tau-pair events.
We report on the production of J/psi mesons in 530 and 800 GeV/c proton - Be collisions in the Feynman-x range 0.0 < xf < 0.6. The J/psi mesons were detected via decays into opposite sign muon pairs. Differential distributions for J/psi production have been measured as functions of xf, pT^2, and cosine of the Gottfried-Jackson decay angle. These distributions are compared with results on J/psi production obtained in 515 GeV/c pion - Be collisions, measured by the same experiment, as well as with results from other experiments using incident protons.
Differential XL distribution for J/PSI production in 530 GeV pBe collisions. Errors are combined statistics and systematics.
Differential PT**2 distribution for J/PSI production in 530 GeV pBe collisions. Errors are combined statistics and systematics.
Differential COS(THETA) distribution for J/PSI production in 530 GeV pBe collisions. Errors are combined statistics and systematics.
Cross-sections and angular distributions for hadronic and lepton pair final states in e+e- collisions at a centre-of-mass energy near 189 GeV, measured with the OPAL detector at LEP, are presented and compared with the predictions of the Standard Model. The results are used to measure the energy dependence of the electromagnetic coupling constant alpha_em, and to place limits on new physics as described by four-fermion contact interactions or by the exchange of a new heavy particle such as a sneutrino in supersymmetric theories with R-parity violation. A search for the indirect effects of the gravitational interaction in extra dimensions on the mu+mu- and tau+tau- final states is also presented.
Hadronic cross section.
The cross sections for hadronic, and muon- and tau-pair production in the two sprime/s regions.
The cross sections for electron -pair production with various angular cuts.
The cross section for the photoproduction of events containing three jets with a three-jet invariant mass of M_3J > 50 GeV has been measured with the ZEUS detector at HERA. The three-jet angular distributions are inconsistent with a uniform population of the available phase space but are well described by parton shower models and O(alpha alpha_s^2) pQCD calculations. Comparisons with the parton shower model indicate a strong contribution from initial state radiation as well as a sensitivity to the effects of colour coherence.
Cross section in the specified kinematic range.
The measured 3-jet cross-section w.r.t. the 3-jet invariant mass.
The measured distribution in THETA(P=3).
The correlated production of Lambda and Lambdabar baryons has been studied using 4.3 million multihadronic Zo decays recorded with the OPAL detector at LEP. Di-lambda pairs were investigated in the full data sample and for the first time also in 2-jet and 3-jet events selected with the k_t algorithm. The distributions of rapidity differences from correlated Lambda-Lambdabar pairs exhibit short-range, local correlations and prove to be a sensitive tool to test models, particularly for 2-jet events. The JETSET model describes the data best but some extra parameter tuning is needed to improve agreement with the experimental results in the rates and the rapidity spectra simultaneously. The recently developed modification of JETSET, the MOdified Popcorn Scenarium (MOPS), and also HERWIG do not give satisfactory results. This study of di-lambda production in 2- and 3-jet events supports the short-range compensation of quantum numbers.
Average multipicity of LAMBDA pairs in hadronic events.
Average multipicity of LAMBDA pairs in 2-Jet events.
Average multipicity of LAMBDA pairs in 3-Jet events.
Cross-sections for hadronic, b-bbar and lepton pair final states in e+e- collisions at sqrt(s) = 183 GeV, measured with the OPAL detector at LEP, are presented and compared with the predictions of the Standard Model. Forward-backward asymmetries for the leptonic final states have also been measured. Cross-sections and asymmetries are also presented for data recorded in 1997 at sqrt(s) = 130 and 136 GeV. The results are used to measure the energy dependence of the electromagnetic coupling constant alpha_em, and to place limits on new physics as described by four-fermion contact interactions or by the exchange of a new heavy particle such as a leptoquark, or of a squark or sneutrino in supersymmetric theories with R-parity violation.
No description provided.
The contribution of interference between initial- and final-state radiationhas been removed.
The contribution of interference between initial- and final-state radiationhas been removed.
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