One-prong τ\tau decays with kaons

One-prong $\tau$ decays into final states involving kaons are studied with about 161k $\tau^+\tau^-$ events collected by the ALEPH detector from 1991 to 1995. Charged kaons are identified by dE/dx measurement, while $K^0_L$'s are detected through their interaction in calorimeters. Branching ratios are measured for the inclusive mode, $B(\tau^-\rightarrow K^-X\nu_\tau)=(1.52 \pm 0.04\pm0.04)\%$, where $X$ can be any system of neutral particles, and for the exclusive modes \begin{center} \begin{tabular}{rcl} $B(\tau^-\to K^-\nu_\tau)$ &=& $(6.96\pm0.25\pm0.14)\times 10^{-3}$,\\ $B(\tau^-\to K^-\pi^0\nu_\tau)$ &=& $(4.44\pm0.26\pm0.24)\times 10^{-3}$,\\ $B(\tau^-\to K^-\pi^0\pi^0\nu_\tau)$ &=& $(0.56\pm0.20\pm0.15)\times 10^{-3}$,\\ $B(\tau^-\to K^-\pi^0\pi^0\pi^0\nu_\tau)$ &=& $(0.37\pm0.21\pm0.11)\times 10^{-3}$,\\ $B(\tau^-\to K^-K^{0}\nu_\tau)$ &=& $(1.62\pm0.21\pm0.11)\ times 10^{-3}$,\\ $B(\tau^-\to K^{-}K^{0}\pi^0\nu_\tau)$

Study of τ\tau decays involving kaons, spectral functions and determination of the strange quark mass

All ALEPH measurements of branching ratios of tau decays involving kaons are summarized including a combination of results obtained with K^0_S and K^0_L detection. The decay dynamics are studied, leading to the determination of contributions from vector K^*(892) and K^{*}(1410), and axial-vector K_1(1270) and K_1(1400) resonances. Agreement with isospin symmetry is observed among the different final states. Under the hypothesis of the conserved vector current, the spectral function for the K\bar{K}\pi mode is compared with the corresponding cross section for low energy e^+e^- annihilation, yielding an axial-vector fraction of (94^{+6}_{-8})% for this mode. The branching ratio for tau decay into all strange final states is determined to be B(\tau^-\to X^-(S=-1)\nu_\tau)=(28.7\pm1.2)\times 10^{-3}. The measured mass spectra of the strange tau decay modes are exploited to derive the S=-1 spectral function. A combination of strange and nonstrange spectral functions is used to determine the strange quark mass and nonperturbative contributions to the strange hadronic width. A method is developed to avoid the bad convergence of the spin zero hadronic component, with the result m_s(M_\tau^2)=(176^{\,+46}_{\, -57}) MeV/c^2. The evolution down to 1~GeV gives m_s(1~{\rm GeV}^2) = (234^{\,+61}_{\,-76})~{\rm MeV}/c^2

Searches for Charginos and Neutralinos in e+e−e^+ e^- Collisions at s\sqrt{s} = 161 and 172 GeV

The data recorded by the ALEPH detector at centre-of-mass energies of 161, 170, and 172 GeV are analysed for signals of chargino and neutralino production. No evidence of a signal is found, although candidate events consistent with the expectations from Standard Model processes are observed. Limits at 95% C.L. on the production cross sections are derived and bounds on the parameters of the Minimal Supersymmetric Standard Model are set. The lower limit on the mass of the lightest chargino is 85.5 GeV/c^2 for gaugino-like charginos (mu = -500 GeV/c^2), and 85.0 GeV/c^2 for Higgsino-like charginos (M_2 = 500 GeV/c^2), for heavy sneutrinos (M(snu) 200 GeV/c^2) and tanb = sqrt(2). The effect of light sleptons on chargino and neutralino limits is investigated. The assumptions of a universal slepton mass and a universal gaugino mass are relaxed, allowing less model-dependent limits to be obtained

Searches for Charginos and Neutralinos in e+e−e^+ e^- Collisions at s\sqrt{s} = 161 and 172 GeV

The data recorded by the ALEPH detector at centre-of-mass energies of 161, 170, and 172 GeV are analysed for signals of chargino and neutralino production. No evidence of a signal is found, although candidate events consistent with the expectations from Standard Model processes are observed. Limits at 95% C.L. on the production cross sections are derived and bounds on the parameters of the Minimal Supersymmetric Standard Model are set. The lower limit on the mass of the lightest chargino is 85.5 GeV/c^2 for gaugino-like charginos (mu = -500 GeV/c^2), and 85.0 GeV/c^2 for Higgsino-like charginos (M_2 = 500 GeV/c^2), for heavy sneutrinos (M(snu) 200 GeV/c^2) and tanb = sqrt(2). The effect of light sleptons on chargino and neutralino limits is investigated. The assumptions of a universal slepton mass and a universal gaugino mass are relaxed, allowing less model-dependent limits to be obtained