The European Physical Journal C

ISSN: 1434-6044 (printed version)
ISSN: 1434-6052 (electronic version)

Table of Contents

Abstract Volume 4 Issue 3 (1998) pp 367-385
DOI 10.1007/s100529800903

experimental physics:
Study of ${\rm B_s^0}$ oscillations and lifetime using fully reconstructed ${\rm D_s^-}$ decays

The ALEPH Collaboration , R. Barate et al.

Laboratoire de Physique des Particules (LAPP), IN2P3-CNRS, F-74019 Annecy-le-Vieux Cedex, France

Received: 12 December 1997 / Revised version: 24 February 1998 / Published online: 23 June 1998

Abstract. A search for ${\rm B_s^0}$ oscillations is performed using approximately 4 million ${\rm Z \to q\bar q}$ events collected by the ALEPH experiment during 1991-1995. ${\rm B_s^0}$ candidates are partially reconstructed by combining tracks with fully reconstructed ${\rm D_s^-}$ candidates. The ${\rm B_s^0}$ production flavour is estimated from the sign of the opposite hemisphere charge, a fragmentation kaon in the same hemisphere, or a lepton in the opposite hemisphere. From a total sample of 1620 candidates, with a ${\rm B_s^0}$ purity estimated to be 22%, all values of $\Delta m_{\rm s}$ below 3.9 ps$^{-1}$ and between 6.5 and 8.8 ps$^{-1}$ are excluded at 95% CL. From the same sample, the ${\rm B_s^0}$ lifetime is measured to be $\tau_{\rm s} = 1.47 \pm 0.14{\rm (stat)} \pm 0.08{\rm (syst)}$ ps. This analysis selects mainly hadronic ${\rm B_s^0}$ decays and is statistically independent of a previous ALEPH analysis selecting ${\rm B_s^0} \to {\rm D_s^{(*)-}} \ell^+ \nu$ candidates. Combining these two analyses yields $\Delta m_{\rm s} > 7.9$ ps$^{-1}$ at 95% CL and $\tau_{\rm s} = 1.51 \pm 0.11$ ps.

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Online publication: July 6, 1998
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