Showing papers by "J. J. Veillet published in 2003"

Search for anomalous weak dipole moments of the tau lepton

Abstract: The anomalous weak dipole moments of the $\tau$ lepton are measured in a data sample collected by ALEPH from 1990 to 1995 corresponding to an integrated luminosity of 155~pb$^{-1}$. Tau leptons produced in the reaction $e^+ e^- \rightarrow \tau^+ \tau^-$ at energies close to the ${\rm Z}$ mass are studied using their semileptonic decays to $\pi$, $\rho$, $a_1 \rightarrow \pi 2\pi^0$ or $a_1 \rightarrow 3 \pi$. The real and imaginary components of both the anomalous weak magnetic dipole moment and the CP-violating anomalous weak electric dipole moment, $ {\rm Re}\,\mu_{\tau}$, ${\rm Im}\,\mu_{\tau}$, ${\rm Re}\,d_{\tau}$ and ${\rm Im}\,d_{\tau}$, are measured simultaneously by means of a likelihood fit built from the full differential cross section. No evidence of new physics is found. The following bounds are obtained (95\% CL): $|{\rm Re}\, \mu_{\tau} | 1.14 \times 10^{-3}$, $|{\rm Im}\, \mu_{\tau} | 2.65 \times 10^{-3}$, $|{\rm Re}\, d_{\tau} | 0.91 \times 10^{-3}$, and $|{\rm Im}\, d_{\tau} | 2.01 \times 10^{-3}$.

Improved search for $B_{s}^{0} - \overline{B}_{s}^{0}$ oscillations

Abstract: An improved search for B s 0 oscillations is performed in the ALEPH data sample collected during the first phase of LEP, and reprocessed in 1998. Three analyses based on complementary event selections are presented. First, decays of B s 0 mesons into hadronic flavour eigenstates are fully reconstructed. This selection yields a small sample of candidates with excellent decay length and momentum resolution and hi gh average B s 0 purity. Semileptonic decays with a reconstructed D s - meson provide a second sample with larger statistics, high average B s 0 purity, but a poorer momentum and decay length resolution due to the partial decay reconstruction. Finally, semileptonic b-hadron decays are inclusively selected and yield the data sample with the highest sensitivity to B s 0 oscillations, as the much higher statistics compensate for the low average B s 0 purity and poorer time resolution. A lower limit is set at $\Delta m_{s} > 10.9$ ps-1 at 95% C.L., significantly lower than the expected limit of 15.2 ps-1.