2018 Impact factor 4.843
Particles and Fields
Eur. Phys. J. C 4, 367-385
DOI 10.1007/s100529800903

Study of $\bf {{\rm B}_{\rm s}^{\rm 0}}$ oscillations and lifetime using fully reconstructed $\bf {{\rm D}_{\rm s}^{\rm -}}$ 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 ${{\rm B}_{\rm s}^{\rm 0}}$ oscillations is performed using approximately 4 million $Z\rightarrow{\rm q}\bar{\rm q}$ events collected by the ALEPH experim ent during 1991-1995. ${{\rm B}_{\rm s}^{\rm 0}}$ candidates are partially reconstructed by combining tracks with fully reconstructed ${{\rm D}_{\rm s}^{\rm -}}$ candidates. The ${{\rm B}_{\rm s}^{\rm 0}}$ 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 ${{\rm B}_{\rm s}^{\rm 0}}$ 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 ${{\rm B}_{\rm s}^{\rm 0}}$ 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 ${{\rm B}_{\rm s}^{\rm 0}}$ decays and is statistically independent of a previous ALEPH analysis selecting ${{\rm B}_{\rm s}^{\rm 0}}\to {{\rm D}_{\rm s}^{\rm (*)-}}\ell^+ \nu$ candidates. Combining these two analyses yields ${\Delta m_{\rm s}}\gt 7.9 $ ps-1at 95%CL and ${\tau_{\rm s}}= 1.51 \pm 0.11$ps.


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