Tests of the standard model and constraints on new physics from measurements of fermion-pair production at 130-172GeV at LEP

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 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 gaugino pair production with subsequent decay of the gaugino into a light gluino and a quark pair

Search for anomalous production of di-lepton events with missing transverse momentum in e(+)e(-) collisions at root s = 161 and 172 GeV

Events containing a pair of charged leptons and significant missing transverse momentum are selected from a data sample corresponding to a total integrated luminosity of 20.6 pb^-1 at centre-of-mass energies of 161 GeV and 172 GeV. The observed number of events, four at 161 GeV and nine at 172 GeV, is consistent with the number expected from Standard Model processes, predominantly arising from W+W- production with each W decaying leptonically. This topology is also an experimental signature for the pair production of new particles that decay to a charged lepton accompanied by one or more invisible particles. Further event selection criteria are described that optimise the sensitivity to particular new physics channels. No evidence for new phenomena is observed and limits on the production of scalar charged lepton pairs and other new particles are presented

Measurement of triple gauge boson couplings from W+W− production at √s=172 GeV

We present measurements of triple gauge boson coupling parameters using data recorded by the OPAL detector at LEP2, at a centre-of-mass energy of 172 GeV. A total of 120 W-pair candidates has been selected in the qq¯qq¯qq¯qq¯ , qq¯ℓν¯ℓqq¯ℓν¯ℓ and ℓν¯ℓℓ¯′νℓ′ℓν¯ℓℓ¯′νℓ′ decay channels, for an integrated luminosity of 10.4 pb −1−1 . We use these data to determine several different anomalous coupling parameters using the measured cross-section and the distributions of kinematic variables. We measure αBϕ=0.35+1.29−1.07±0.38αBϕ=0.35−1.07+1.29±0.38 , αWϕ=0.00+0.30−0.28±0.11αWϕ=0.00−0.28+0.30±0.11 , αW=0.18+0.49−0.47±0.23αW=0.18−0.47+0.49±0.23 , Δgz1=−0.03+0.40−0.37±0.14Δg1z=−0.03−0.37+0.40±0.14 , Δκ(HISZ)γ=0.03+0.55−0.51±0.20Δκγ(HISZ)=0.03−0.51+0.55±0.20 , and Δκ=0.33+0.49−0.46±0.21Δκ=0.33−0.46+0.49±0.21 . Combining the αWϕαWϕ result with our previous result obtained from the 161 GeV data sample we measure αWϕ=−0.08+0.28−0.25±0.10αWϕ=−0.08−0.25+0.28±0.10 . All of these measurements are consistent with the Standard Model

Measurements of the B-S(0) and Lambda(0)(b) lifetimes

This paper presents updated measurements of the lifetimes of the Bs0 meson and the Λb0 baryon using 4.4 million hadronic Z0 decays recorded by the OPAL detector at LEP from 1990 to 1995. A sample of Bs0 decays is obtained using Ds−ℓ+ combinations, where the Ds− is fully reconstructed in the φπ−, Full-size image (<1 K) and K−K0S decay channels and partially reconstructed in the Full-size image (<1 K) decay mode. A sample of Λb0 decays is obtained using Λc+ℓ− combinations, where the Λc+ is fully reconstructed in its decay to a pK−π+ final state and partially reconstructed in the Λℓ+νX decay channel. From 172±28 Ds−ℓ+ combinations attributed to Bs0 decays, the measured lifetime is Full-size image (<1 K), where the errors are statistical and systematic, respectively. From the 129±25 Λc+ℓ− combinations attributed to Λb0 decays, the measured lifetime is Full-size image (<1 K), where the errors are statistical and systematic, respectively

Spin alignment of leading K*(892)degrees mesons in hadronic Z degrees decays

Helicity density matrix elements for inclusive K*(892)(0) mesons from hadronic Z(0) decays have been measured over the full range of K*(0) momentum using data taken with the OPAL experiment at LEP. A preference for occupation of the helicity zero state is observed at all scaled momentum x(p) values above 0.3, with the matrix element rho(00) rising to 0.66+/-0.11 for x(p)>0.7. The values of the real part of the off-diagonal element rho(1-1) are negative at large x(p), with a weighted average value of -0.09+/-0.03 for x(p)>0.3, in agreement with new theoretical predictions based on Standard Model parameters and coherent fragmentation of the q (q) over bar system from the Z(0) decay. All other helicity density matrix elements measured are consistent with zero over the entire x(p) range. The K*(0) fragmentation function has also been measured and the total rate determined to be 0.74+/-0.02+/-0.02 K*(892)(0) mesons per hadronic Z(0) decay. (C) 1997 Published by Elsevier Science B.V

Search for CP violation in Z0 ---> tau+ tau- and an upper limit on the weak dipole moment of the tau lepton

Contains fulltext : 124918.pdf (preprint version ) (Open Access

Search for unstable heavy and excited leptons in e(+)e(-) collisions at root s=170-172 GeV

We have searched for unstable neutral and charged heavy leptons, N and L+/-, and for excited states of neutral and charged leptons, v*, e*, mu* and tau*, in e(+)e(-) collisions at centre-of-mass energies of 170 and 172 GeV using the OPAL detector at LEP. No evidence for their existence was found. Front the analysis of charged-current decays of pair-produced unstable heavy leptons, and of charged-current and photonic decays of pair-produced excited leptons, lower limits on their masses are derived. From the analysis of charged-current and photonic decays of singly-produced excited leptons, upper Limits on the ratio of the coupling to the compositeness scale, f/A, are determined for masses up to the kinematic limit