Search for B0_s - anti-B0_s oscillations in DELPHI using high-p_t leptons

TL;DR

This study searched for B0_s - anti-B0_s oscillations in DELPHI data, improving analysis techniques, but found no oscillation signal, setting new lower limits on the oscillation frequency.

Contribution

The paper presents improved algorithms for vertex reconstruction and flavor tagging, enhancing sensitivity in B0_s oscillation searches using DELPHI data.

Findings

No B0_s oscillation signal observed.

Set lower limit m_s > 8.5 ps^{-1} at 95% C.L.

Combined analysis sensitivity of m_s = 12.0 ps^{-1}.

Abstract

Oscillations in the B0_s - anti-B0_s system were studied in events selected from about 4.3 million hadronic Z^0 decays registered by DELPHI between 1992 and 2000. This paper presents updates of two published analyses ([11,12]). The first analysis, which utilizes leptons emitted with large momentum transverse to a jet, was improved by means of a better algorithm for the vertex reconstuction and a new algorithm for flavour-tagging at production time. The second analysis, which utilizes D_s-lepton events, was improved by optimizing the treatment of proper time resolution. No signal of B0_s oscillations was observed and limits on the mass difference between the physical B0_s states were obtained to be: \Delta m_s > 8.0 ps^{-1} at the 95% C.L. with a sensitivity of \Delta m_s = 9.1 ps^{-1} in the high p_t lepton analysis and \Delta m_s > 4.9 ps^{-1} at the 95% C.L. with a sensitivity of \Delta m_s = 8.6 ps^{-1} in the D_s-lepton analysis. Previously published results on these analyses are superseed. The combination of these results with those obtained in other independent analyses previously performed in DELPHI (D_s-hadron, exclusive B0_s, inclusive vertex) gives: \Delta m_s > 8.5 ps^{-1} at the 95% C.L. with a sensitivity of \Delta m_s = 12.0 ps^{-1}.