The couplings of the Z 0 to charged leptons are studied using measurements of the lepton pair cross sections and forward-backward asymmetries at centre of mass energies near to the mass of the Z 0 . The data are consistent with lepton universality. Using a parametrisation of the lepton pair differential cross section which assumes that the Z 0 has only vector and axial couplings to leptons, the charged leptonic partial decay width of the Z 0 is determined to be Г ol+ol− = 83.1±1.9 MeV and the square of the product of the effective axial vector and vector coupling constants of the Z 0 to charged leptons to be a ̌ 2 ol v ̌ 2 ol = 0.0039± 0.0083 , in agreement with the standard model. A parametrisation in the form of the improved Born approximation gives effective leptonic axial vector and vector coupling constants a ̌ 2 ol = 0.998±0.024 and v ̌ 2 ol = 0.0044±0.0083 . In the framework of the standard model, the values of the parameters ϱ z and sin 2 θ w are found to be 0.998±0.024 and 0.233 +0.045 −0.012 respectively. Using the relationship in the minimal standard model between ϱ z and sin 2 θ w , the results sin 2 θ SM w = 0.233 +0.007 −0.006 is obtained. Our previously published measurement of the ratio of the hadronic to the leptonic partial width of the Z 0 is update: R z = 21.72 +0.71 −0.65 .
Cross sections corrected for the effects of efficiency and kinematic cuts. Errors have systematic effects folded.
Acceptance corrected cross sections. Statistical errors only.
Acceptance corrected cross sections. Statistical errors only.
We present the first measurement of the left-right cross section asymmetry (ALR) for Z boson production by e+e− collisions. The measurement was performed at a center-of-mass energy of 91.55 GeV with the SLD detector at the SLAC Linear Collider which utilized a longitudinally polarized electron beam. The average beam polarization was (22.4±0.6)%. Using a sample of 10 224 Z decays, we measure ALR to be 0.100±0.044(stat)±0.004(syst), which determines the effective weak mixing angle to be sin2θWeff=0.2378 ±0.0056(stat)±0.0005(syst).
R and L refer to Right and Left handed beam polarization.
Effective weak mixing angle.
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 have observed τ pair production at average CM energies of 13.9, 22.3, 34.5 and 43.1 GeV. The cross-sections are consistent with QED, the cut off parameters beingΛ+>161 GeV andΛ−169 GeV (95% CL). The topological branching fraction of the τ to 1 charged particle,B1, is 0.847±0.011 (stat)−0.013+0.016(syst) and no decays to 5 charged particles were observed resulting inB5<0.007 (95% CL). Within the 3 charged track final stateB(τ−→π−π+π−v)/(B(τ−→π−π+π−v)+B(τ−→π−π+π−π0v))=0.37−0.20+0.35
No description provided.
No description provided.
New measurements of the hadronic and leptonic cross sections and of the leptonic forward-backward asymmetries ine+e− collisions are presented. The analysis includes data recorded up to the end of 1991 by the OPAL experiment at LEP, with centre-of-mass energies within ±3 GeV of the Z0 mass. The results are based on a recorded total of 454 000 hadronic and 58 000 leptonic events. A model independent analysis of Z0 parameters based on an extension of the improved Born approximation is presented leading to test of lepton universality and an interpretation of the results within the Standard Model framework. The determination of the mass and width of the Z0 benefit from an improved understanding of the LEP energy calibration.
Statistical and systematic point-to-point errors included. There is an additional 0.2 pct overall systematic uncertainty.
Systematic error of 0.45 pct not included.
Systematic error of 0.25 pct not included.
None
DATA FROM 1989 RUN. The cross section are quoted with their statistical and point-to-point systematic uncertainty of both the multihadron acceptance and the luminosity calculation.
DATA FROM 1990 RUN. The cross section are quoted with their statistical and point-to-point systematic uncertainty of both the multihadron acceptance and the luminosity calculation.
Cross sections corrected for the effects of efficiency and kinematic cuts and background. Data from 1989 run, reanalysed.
This final analysis of hadronic and leptonic cross-sections and of leptonic forward-backward asymmetries in e+e- collisions with the OPAL detector makes use of the full LEP1 data sample comprising 161 pb^-1 of integrated luminosity and 4.5 x 10^6 selected Z decays. An interpretation of the data in terms of contributions from pure Z exchange and from Z-gamma interference allows the parameters of the Z resonance to be determined in a model-independent way. Our results are in good agreement with lepton universality and consistent with the vector and axial-vector couplings predicted in the Standard Model. A fit to the complete dataset yields the fundamental Z resonance parameters: mZ = 91.1852 +- 0.0030 GeV, GZ = 2.4948 +- 0.0041 GeV, s0h = 41.501 +- 0.055 nb, Rl = 20.823 +- 0.044, and Afb0l = 0.0145 +- 0.0017. Transforming these parameters gives a measurement of the ratio between the decay width into invisible particles and the width to a single species of charged lepton, Ginv/Gl = 5.942 +- 0.027. Attributing the entire invisible width to neutrino decays and assuming the Standard Model couplings for neutrinos, this translates into a measurement of the effective number of light neutrino species, N_nu = 2.984 +- 0.013. Interpreting the data within the context of the Standard Model allows the mass of the top quark, mt = 162 +29-16 GeV, to be determined through its influence on radiative corrections. Alternatively, utilising the direct external measurement of mt as an additional constraint leads to a measurement of the strong coupling constant and the mass of the Higgs boson: alfa_s(mZ) = 0.127 +- 0.005 and mH = 390 +750-280 GeV.
The cross section for hadron production corrected to the simple kinematic acceptance region defined by SPRIME/S > 0.01. Statistical errors only are shown. Also given is the cross section value corrected for the beam energy spread to correspond to the physical cross section at the central value of SQRT(S).
The cross section for E+ E- production corrected to the simple kinematic acceptance region defined by ABS(COS(THETA(C=E-))) < 0.7 and THETA(C=ACOL) < 10 degrees. Statistical errors only are shown. Also given is the cross section value corrected for the beam energy spread to correspond to the physical cross sectionat the central value of SQRT(S).
The cross section for mu+ mu- production corrected to the simple kinematic acceptance region defined by N = M(P=3_4)**2/S > 0.01. Statistical errors only are shown. Also given is the cross section value corrected for the beam energy spread to correspond to the physical cross section at the central value of SQRT(S).
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.
Measurements are presented of electroweak boson production using data from $pp$ collisions at a centre-of-mass energy of $\sqrt{s} = 8\mathrm{\,Te\kern -0.1em V}$. The analysis is based on an integrated luminosity of $2.0\mathrm{\,fb}^{-1}$ recorded with the LHCb detector. The bosons are identified in the $W\rightarrow\mu\nu$ and $Z\rightarrow\mu^{+}\mu^{-}$ decay channels. The cross-sections are measured for muons in the pseudorapidity range $2.0 < \eta < 4.5$, with transverse momenta $p_{\rm T} > 20{\mathrm{\,Ge\kern -0.1em V\!/}c}$ and, in the case of the $Z$ boson, a dimuon mass within $60 < M_{\mu^{+}\mu^{-}} < 120{\mathrm{\,Ge\kern -0.1em V\!/}c^{2}}$. The results are \begin{align*} \sigma_{W^{+}\rightarrow\mu^{+}\nu} &= 1093.6 \pm 2.1 \pm 7.2 \pm 10.9 \pm 12.7{\rm \,pb} \, , \sigma_{W^{-}\rightarrow\mu^{-}\bar{\nu}} &= \phantom{0}818.4 \pm 1.9 \pm 5.0 \pm \phantom{0}7.0 \pm \phantom{0}9.5{\rm \,pb} \, , \sigma_{Z\rightarrow\mu^{+}\mu^{-}} &= \phantom{00}95.0 \pm 0.3 \pm 0.7 \pm \phantom{0}1.1 \pm \phantom{0}1.1{\rm \,pb} \, , \end{align*} where the first uncertainties are statistical, the second are systematic, the third are due to the knowledge of the LHC beam energy and the fourth are due to the luminosity determination. The evolution of the $W$ and $Z$ boson cross-sections with centre-of-mass energy is studied using previously reported measurements with $1.0\mathrm{\,fb}^{-1}$ of data at $7\mathrm{\,Te\kern -0.1em V}$. Differential distributions are also presented. Results are in good agreement with theoretical predictions at next-to-next-to-leading order in perturbative quantum chromodynamics.
Inclusive cross-section for $W^+$ and $W^-$ boson production in bins of muon pseudorapidity. The uncertainties are statistical, systematic, beam and luminosity.
Inclusive cross-section for $Z$ boson production in bins of rapidity. The uncertainties are statistical, systematic, beam and luminosity.
Inclusive cross-section for $Z$ boson production in bins of transverse momentum. The uncertainties are statistical, systematic, beam and luminosity.
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