The three different helicity states of W bosons, produced in the reaction e+e- -> W+W- -> l nu q q~ are studied using leptonic and hadronic W decays at sqrt{s}=183GeV and 189GeV. The W polarisation is also measured as a function of the scattering angle between the W- and the direction of the e- beam. The analysis demonstrates that W bosons are produced with all three helicities, the longitudinal and the two transverse states. Combining the results from the two center-of-mass energies and with leptonic and hadronic W decays, the fraction of longitudinally polarised W bosons is measured to be 0.261 +/- 0.051(stat.) +/- 0.016(syst.) in agreement with the expectation from the Standard Model.
Fraction of longitudinally polarized W bosons. Combined results from 183 and 189 GeV.
We have reconstructed the radiative decays $\chi_{b}(1P) \to \Upsilon(1S) \gamma $ and $\chi_{b}(2P) \to \Upsilon(1S) \gamma $ in $p \bar{p}$ collisions at $\sqrt{s} = 1.8$ TeV, and measured the fraction of $\Upsilon(1S)$ mesons that originate from these decays. For $\Upsilon(1S)$ mesons with $p^{\Upsilon}_{T}>8.0$ GeV/$c$, the fractions that come from $\chi_{b}(1P)$ and $\chi_{b}(2P)$ decays are $(27.1\pm6.9(stat)\pm4.4(sys))%$ and $(10.5\pm4.4(stat)\pm1.4(sys))%$, respectively. We have derived the fraction of directly produced $\Upsilon(1S)$ mesons to be $(50.9\pm8.2(stat)\pm9.0(sys))%$.
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The production of the J/ ψ and ψ ′ charmonia states has been studied, through their dimuon decay, in proton, Oxygen and Sulphur induced reactions, by the NA38 experiment at the CERN SPS. The proton data was collected with beams of 200 and 450 GeV, while the ion beams had an energy of 200 GeV per incident nucleon. The J/ ψ production cross-section per nucleon-nucleon collision exhibits a remarkably continuous pattern, as a function of the product of the mass numbers of the interacting nuclei, from pp up to S-U reactions. The same pattern is observed within S-U collisions, as a function of the collision centrality. While in p-A interactions both charmonia states exhibit the same A-dependence, in S-U collisions the ψ ′ production is very strongly suppressed.
Results of fitting the 200 and 450 GeV J/PSI data separately with a power law parametrization SIG=SIG0*(A*B)**POWER, where A and B are the beam and targetmass numbers. The value obtained from a combined fit is also given, as well as the ratio between the values of SIG0 for the 200 and 450 GeV data sets.
The J/PSI cross sections per nucleon (times the BR to di-muons) rescaled to 200 GeV/nucleon, using the SIG0 ratio detemined in the previous table, and to the cm rapidity window 0 to 1. The errors are combined statistical and systematic.
The ratio between the PSI(3685) and the J/PSI production cross section, times their BR into di-muons, at an incident beam energy of 450 GeV per nucleon. The errors are combined statistical and systematic.
The cross sections and forward-backward asymmetries of hadronic and leptonic events produced in e+e- collisions at centre-of-mass energies of 130-183 GeV are presented. Results for ee, mumu, tautau, qq, bb and cc production show no significant deviation from the Standard Model predictions. This enable constraints to be set upon physics beyond the Standard Model such as four-fermion contact interactions, leptoquarks, Z' bosons and R-parity violating squarks and sneutrinos. Limits on the energy scale Lambda of eeff contact interactions are typically in the range from 2-10 TeV. Limits on R-parity violating sneutrinos reach masses of a few hundred GeV for large values of their Yukawa couplings.
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DO has measured the inclusive production cross section of W and Z bosons in a sample of 13 pb$^{-1}$ of data collected at the Fermilab Tevatron. The cross sections, multiplied by their leptonic branching fractions, for production in pbar-p collisions at sqrt{s}=1.8 TeV are sigma_W*B(W->e nu) = 2.36+-0.02+-0.08+-0.13 nb, sigma_W*B(W->mu nu) = 2.09+-0.06+-0.22+-0.11 nb, sigma_Z*B(Z->e+ e-) = 0.218+-0.008+-0.008+-0.012 nb, and sigma_Z*B(Z->mu+ mu-) = 0.178+-0.022+-0.021+-0.009 nb, where the first uncertainty is statistical and the second systematic; the third reflects the uncertainty in the integrated luminosity. For the combined electron and muon analyses, we find sigma_W*B(W->l mu)/sigma_Z*B(Z->l+ l-) = 10.90+-0.52. Assuming standard model couplings, we use this result to determine the width of the W boson, and obtain Gamma(W) = 2.044+-0.097 GeV.
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Combined electron and muon analysis.
The fraction of Z to bbbar events in hadronic Z decays has been measured by the OPAL experiment using the data collected at LEP between 1992 and 1995. The Z to bbbar decays were tagged using displaced secondary vertices, and high momentum electrons and muons. Systematic uncertainties were reduced by measuring the b-tagging efficiency using a double tagging technique. Efficiency correlations between opposite hemispheres of an event are small, and are well understood through comparisons between real and simulated data samples. A value of Rb = 0.2178 +- 0.0011 +- 0.0013 was obtained, where the first error is statistical and the second systematic. The uncertainty on Rc, the fraction of Z to ccbar events in hadronic Z decays, is not included in the errors. The dependence on Rc is Delta(Rb)/Rb = -0.056*Delta(Rc)/Rc where Delta(Rc) is the deviation of Rc from the value 0.172 predicted by the Standard Model. The result for Rb agrees with the value of 0.2155 +- 0.0003 predicted by the Standard Model.
Second systematic error depends on Rc=Delta(R_c)/R_c ratio, where Delta(R_c) is the deviation of R_c from the value 0.172 predicted by the Standard Model.
Di-jet event rates have been measured for deep-inelastic scattering in the kinematic domain ~5 < Q^2 < ~100 GeV^2 and ~10^(-4) < x_Bj < ~10^(-2), and for jet transverse momenta squared p_t^2 > ~Q^2. The analysis is based on data collected with the H1 detector at HERA in 1994 corresponding to an integrated luminosity of about 2 pb^(-1). Jets are defined using a cone algorithm in the photon-proton centre of mass system requiring jet transverse momenta of at least 5 GeV. The di-jet event rates are shown as a function of Q^2 and x_Bj. Leading order models of point-like interacting photons fail to describe the data. Models which add resolved interacting photons or which implement the colour dipole model give a good description of the di-jet event rate. This is also the case for next-to-leading order calculations including contributions from direct and resolved photons.
Di-jet rates for 'Symmetric' and 'Asymmetric' scenarios for jet energy cuts.
Di-jet rates for 'Sum' scenario for jet energy cuts.
Di-jet rates for 'Symmetric' and 'Asymmetric' scenarios for jet energy cuts.
The reaction pp -> pf (pi+pi-pi0) ps has been studied at 450 GeV/c in an experiment designed to search for gluonic states. A spin analysis has been performed and the dPT filter applied. The analysis confirms the previous observation that all undisputed qqbar states are suppressed at small dPT. In addition, a clear difference is observed in the production mechanism for the eta and omega.
SIG(C=TOT) denotes the total cross section for each resonance. The variable ABS(PT(P=3)-PT(P=4)) is used as a glueball-QUARK QUARKBAR filter (see F.E.Close and A.Krik, PL 397B, 333 (1997)).
The NA50 collaboration has measured J/ψ , ψ′ and Drell Yan pair production in Pb Pb interactions at 158 GeV/ c per nucleon at the CERN SPS. Final results from the 1995 run and preliminary ones from the higher statistics 1996 run are presented. A anomalous J/ψ suppression (relative to the Drell-Yan process) has been observed with respect to the suppression pattern established in experiments NA38 and NA51 with proton, oxygen and sulfur beams. The 1996 data allow a detailed study of the suppression pattern in the Pb Pb sample itself, showing a discontinuity around an E T value (the neutral transverse electromagnetic energy) of 50 GeV. The ψ′ is also suppressed relative to Drell-Yan, with a pattern very similar to the one observed in S U collisions. Finally, the p T distributions of dimuons are presented. The average p T 2 of the J/ψ in Pb Pb collisions does not increase any more with E T above 100 GeV.
ET - neutral transverse energy in the electromagnetic calorimeter, etarap=1.1-2.3.
Enhanced production of strange baryons and anti-baryons at central rapidity in S-W and S-z.sbnd;S with respect to p-A reactions has been reported by the CERN experiments WA85 and WA94. The WA97 experiment is extending such a study to Pb Pb collisions making use of the newly developed silicon pixel detectors. Results on Λ, Ξ − and Ω − production in Pb Pb collisions at 158 A GeV/ c at central rapidity are presented. Transverse mass spectra and particle ratios are presented. Hyperon yields are given as a function of the collision centrality and compared with those obtained from p-Pb collisions using the same experimental setup.
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