Cross-section and angular distributions for hadronic and lepton-pair final states in e+e- collisions at centre-of-mass energies between 189 GeV and 209 GeV, measured with the OPAL detector at LEP, are presented and compared with the predictions of the Standard Model. The measurements are used to determine the electromagnetic coupling constant alphaem at LEP2 energies. In addition, the results are used together with OPAL measurements at 91-183 GeV within the S-matrix formalism to determine the gamma-Z interference term and to make an almost model-independent measurement of the Z mass. Limits on extensions to the Standard Model described by effective four-fermion contact interactions or the addition of a heavy Z boson are also presented.
CM energy values.
Measured cross section for QUARK QUARKBAR (HADRON) production. The data are corrected to no interference between initial and final state radiation.
Measured cross section for MU+ MU- production. The data are corrected to no interference between initial and final state radiation.
We search for lepton flavour violating events (e mu, e tau and mu tau) that could be directly produced in e+e- annihilations, using the full available data sample collected with the OPAL detector at centre-of-mass energies between 189 GeV and 209 GeV. In general, the Standard Model expectations describe the data well for all the channels and at each sqrt(s). A single e mu event is observed where according to our Monte Carlo simulations only 0.019 events are expected from Standard Model processes. We obtain the first limits on the cross-sections sigma(e+e- -> e mu, e tau and mu tau) as a function of sqrt(s) at LEP2 energies.
No description provided.
Measurements are presented of the polarisation of W+W- boson pairs produced in e+e- collisions, and of CP-violating WWZ and WWGamma trilinear gauge couplings. The data were recorded by the OPAL experiment at LEP during 1998, where a total integrated luminosity of 183 pb^-1 was obtained at a centre-of-mass energy of 189 GeV. The measurements are performed through a spin density matrix analysis of the W boson decay products. The fraction of W bosons produced with longitudinal polarisation was found to be sigma_L/sigma_total = (21.0 +- 3.3 +- 1.6)% where the first error is statistical and the second systematic. The joint W boson pair production fractions were found to be sigma_TT/sigma_total = (78.1 +- 9.0 +- 3.2) %, sigma_LL/sigma_total = (20.1 +- 7.2 +- 1.8) % and sigma_TL/sigma_total = (1.8 +- 14.7 +- 3.8) %. In the CP-violating trilinear gauge coupling sector we find kappa_z = -0.20 +0.10 -0.07, g^z_4 = -0.02 +0.32 -0.33 and lambda_z = -0.18 +0.24 -0.16, where errors include both statistical and systematic uncertainties. In each case the coupling is determined with all other couplings set to their Standard Model values except those related to the measured coupling via SU(2)_LxU(1)_Y symmetry. These results are consistent with Standard Model expectations.
Individual W-boson transverse polarised cross-sections.
Individual W-boson longitudinal polarised cross-sections.
W pair polarized cross-sections. (C=TT), (C=LL), and (C=TL) stand for both W transversely polarised, for both W longitudinally polarised, and for transversely and longitudinally polarisedW-bosons, respectively.
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.
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.
Production of events with hadronic and leptonic final states has been measured in e^+e^- collisions at centre-of-mass energies of 130-172 GeV, using the OPAL detector at LEP. Cross-sections and leptonic forward-backward asymmetries are presented, both including and excluding the dominant production of radiative Z \gamma events, and compared to Standard Model expectations. The ratio R_b of the cross-section for bb(bar) production to the hadronic cross-section has been measured. In a model-independent fit to the Z lineshape, the data have been used to obtain an improved precision on the measurement of \gamma-Z interference. The energy dependence of \alpha_em has been investigated. The measurements have also been used to obtain limits on extensions of the Standard Model described by effective four-fermion contact interactions, to search for t-channel contributions from new massive particles and to place limits on chargino pair production with subsequent decay of the chargino into a light gluino and a quark pair.
SIG(C=MEAS) and SIG(C=CORR) stand for measured values without (C=MEAS) and with (C=CORR) correction for interference between initial- and final-state radiation.
The angular distribution of the thrust axis. Errors include statistical and systematic effects combined, with the former dominant.
The measured values include the effect of interference between initial- andfinal-state radiation.
We present the results of a search for third generation leptoquark (LQ) pairs in 110±8pb−1of p¯p collisions at s=1.8TeV recorded by the Collider Detector at Fermilab. We assume third generation leptoquarks decay to a τ lepton and a b quark with branching ratio β. We observe one candidate event, consistent with standard model background expectations. We place upper limits on σ(p¯p→LQLQ¯)̇β2 as a function of the leptoquark mass MLQ. We exclude at 95% confidence level scalar leptoquarks with MLQ<99GeV/c2, gauge vector leptoquarks with MLQ<225GeV/c2, and nongauge vector leptoquarks with MLQ<170GeV/c2 for β=1.
The cross sections times branching ratio. KAPPA is an 'anomalous magnetic moment' (theoretical parameter). See text for details.
Cross-sections for hadronic and leptonic two-fermion events, and leptonic forward-backward asymmetries, have been measured in e + e − collisions at a centre-of-mass energy of 161 GeV, using the OPAL detector at LEP. Results are presented both including and excluding the dominant production of radiative γZ 0 events. We have measured R b , the ratio of the number of b b to all multihadronic events at 161 GeV, and compared it to the result obtained at 130–136 GeV. All results agree well with the Standard Model expectations. In a model-independent fit to the Z 0 lineshape, the data presented here give an improved precision on the γZ 0 -interference term. The data have also been used to obtain new limits on extensions of the Standard Model described by effective four-fermion contact interactions.
No description provided.
No description provided.
THETA(P=4 5) is an acollinearity angle between electron and positron.
We have searched for excited states of charged and neutral leptons, e ∗ , μ ∗ , τ ∗ and ν ∗ , in e + e − collisions at s =161 GeV using the OPAL detector at LEP. No evidence for their existence was found. With the most common coupling assumptions, the topologies from excited lepton pair production include ℓ + ℓ − γγ and ℓ + ℓ − W + W − , with the subsequent decay of the virtual W bosons. From the analysis of these topologies, 95% confidence level lower mass limits of 79.9 GeV for e ∗ , 80.0 GeV for μ ∗ , 79.1 GeV for τ ∗ , 78.3 GeV for ν e ∗ , 78.9 GeV for ν μ ∗ and 76.2 GeV for ν τ ∗ are inferred. From the analysis of W + W − and γγ topologies with missing energy and using alternative coupling assingments which favour charged ℓ ∗± and photonic ν ∗ decays, 95% confidence level lower mass limits of 77.1 GeV for each ℓ ∗± flavour and 77.8 GeV for each ν ∗ flavour are inferred. From the analysis of the ℓ + ℓ − γ , ℓ ± W ∓ and single γ final states expected from excited lepton single production, upper limits on the ratio of the coupling to the compositeness scale, f Λ , are determined for excited lepton masses up to the kinematic limit.
95 pct upper limits for pair production of the excited leptons.
The differential cross-sections for e + e − → e + e − , e + e − → μ + μ − and e + e − → τ + τ − , and the total cross-section for e + e − → qq̄ at centre-of-mass energies of 130–140 GeV were studied using about 5 pb −1 of data collected with the OPAL detector at LEP in October and November 1995. The results are in agreement with the Standard Model predictions. Four-fermion contact interaction models were fitted to the data and lower limits were obtained on the energy scale Λ at the 95% confidence level.
No description provided.
No description provided.
No description provided.
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