A Study of B Meson Oscillations Using Hadronic Z^0 Decays Containing Leptons

TL;DR

This paper measures B meson oscillation parameters using hadronic Z^0 decays with leptons, providing new limits on mass differences, CP violation, and CPT violation in B meson systems.

Contribution

It presents the first measurement of B^0_d and B^0_s oscillation parameters using a large hadronic Z^0 decay sample with leptons, including limits on Delta(m_s) and CP/CPT violation parameters.

Findings

Measured Delta(m_d) = 0.444 +/- 0.029 + 0.020 - 0.017 ps^-1

Set a lower limit Delta(m_s) > 3.1 ps^-1 at 95% CL

Constrained CP and CPT violation parameters in B meson mixing

Abstract

An event sample enriched in semileptonic decays of b hadrons is selected using an inclusive lepton selection from approximately 3.0 million hadronic Z^0 decays collected with the OPAL detector. This sample is used to investigate B meson oscillations by reconstructing a proper decay time for the parent of each lepton, using a jet charge method to estimate the production flavour of this parent, and using the lepton charge to tag the decay flavour. We measure the mass difference between the two B^0_d mass eigenstates Delta(m_d) = 0.444 +/- 0.029 + 0.020 - 0.017 ps^-1. For the B^0_s system, we find Delta(m_s) > 3.1 ps^-1 at the 95% confidence level. This limit varies only a little if alternative limit setting approaches are adopted. Regions at higher Delta(m_s) are also excluded with some methods for setting the limit. By studying the charge symmetry of the B^0_d mixing structure, we are able to constrain possible CP and CPT violating effects. We measure the CP violation parameter Re(epsilon_B) = -0.006 +/- 0.010 +/- 0.006 and the indirect CPT violating parameter Im(delta_B) = -0.020 +/- 0.016 +/- 0.006. If we invoke CPT symmetry, then we obtain Re(epsilon_B) = 0.002 +/- 0.007 +/- 0.003.