7 research outputs found
Measurement of W-pair production in collisions at 189 GeV
The production of W-pairs is analysed in a data samplecollected by ALEPH at a mean centre-of-mass energy of 188.6 GeV,corresponding to an integrated luminosity of 174.2 pb^-1. Crosssections are given for different topologies of W decays intoleptons or hadrons. Combining all final states and assumingStandard Model branching fractions, the total W-pair cross sectionis measured to be 15.71 +- 0.34 (stat) +- 0.18 (syst) pb.Using also the W-pair data samples collected by ALEPH at lowercentre-of-mass energies, the decay branching fraction of the W bosoninto hadrons is measured to be BR (W hadrons) = 66.97+- 0.65 (stat) +- 0.32 (syst) %, allowing a determination of theCKM matrix element |V(cs)|= 0.951 +- 0.030 (stat) +- 0.015 (syst)
A Study of the decay width difference in the B0(s) - anti-B0(s) system using phi phi correlations
In a data sample of about four million hadronic Z decays recorded with the ALEPH detector from 1991 to 1995, the decay is observed, based on tagging the nal state with two mesons in the same hemisphere. The final state is mostly CP even and corresponds to the short-lived mass eigenstate. The branching ratio of this decay is measured to be BR. A measurement of the lifetime of the (short) gives 1.27 0.33 0.07 ps. The lifetime and branching ratio measurements allow two essentially independent estimates to be made of the relative decay width difference in the system, corresponding to an average value $\Delta\Gamma/\Gamma = (25^{+21}_{-14})%
Search for in collisions at LEP2
A search for the pseudoscalar meson eta_b is performed in two-photon interactions at LEP~2 with an integrated luminosity of 699 pb^-1 collected at e+e- centre-of-mass energies from 181 GeV to 209 GeV. One candidate event is found in the six-charged-particle final state and none in the four-charged-particle final state, in agreement with the total expected background of about one event. Upper limits of Gamma_gammagamma(eta_b) * BR(eta_b -> 4 charged particles) 48 eV Gamma_gammagamma(eta_b) * BR(eta_b -> 6 charged particles) 132 eV are obtained at 95\% confidence level, which correspond to 95\% confidence level upper limits of and on these branching ratios
Measurement of the W mass and width in e+ e- collisions at 189-GeV
The mass of the W boson is determined in e + e â collisions at LEP by the direct reconstruction of W decays in WWâqqÂŻqqÂŻ and WWââÎœqqÂŻ events, supplemented by measurements using the kinematic properties of the leptons in the \mathrm{W}\mathrm{W}\rightarrow\mbox{\ell\nu }\mbox{} decay channel. The main sample of W pairs is selected from an integrated luminosity of 174 pb â1 collected with the ALEPH detector in 1998 at a centre-of-mass energy of 188.63 GeV. The combined result from all channels is mW=80.432±0.072(stat.)±0.041(syst.)±0.019(FSI)±0.017(LEP)GeV/c2, where FSI represents the possible effects of final state interactions in the qqÂŻqqÂŻ channel. In a second two-parameter fit to the qqÂŻqqÂŻ , \mathrmeÎœqqÂŻ and ΌΜqqÂŻ channels, where the W mass and width are decoupled, the average W width is found to be { 2.24±0.20(stat.)±0.13(syst.) GeV/ c2 }, consistent with the Standard Model prediction. The combination of the mass measurement presented in this paper together with those derived previously from the W pair cross section at 161 and 172 GeV and direct reconstruction at 172 and 183 GeV gives mW=80.418±0.061(stat.)±0.040(syst.)±0.019(FSI)±0.017(LEP)GeV/c2
Search for the neutral Higgs bosons of the Standard Model and the MSSM in e(+)e(-) collisions at root s=189 GeV
Neutral Higgs bosons of the Standard Model and of the MSSM are searched for in the data collected at a centre-of-mass energy of 188.6GeV by the ALEPH experiment at LEP, with an integrated luminosity of 176 pb(-1). No evidence for a signal is found. A lower limit of 92.9GeV/c(2) at 95% confidence level is set on the mass of the Standard Model Higgs boson, with an expected sensitivity of 95.9 GeV/c(2). In the MSSM, for tan beta greater than or equal to 0.7 and for benchmark parameter choices, observed (expected) lower limits of 82.5 (83.1) GeV/c(2) and 82.6 (83.2) GeV/c(2) are derived for the masses of the neutral Higgs bosons h and A, respectively. An update of the general MSSM parameter scan is also presented