Direct limits on the B_s⁰ oscillation frequency

Abstract

We report results of a study of the B_s⁰ oscillation frequency using a large sample of B_s⁰ semileptonic decays corresponding to approximately 1 fb⁻¹ of integrated luminosity collected by the D0 experiment at the Fermilab Tevatron Collider in 2002-2006. The amplitude method gives a lower limit on the B_s⁰ oscillation frequency at 14.8 ps⁻¹ at the 95% C.L. At Δm_s=19 ps⁻¹, the amplitude deviates from the hypothesis A=0 (1) by 2.5 (1.6) standard deviations, corresponding to a two-sided C.L. of 1% (10%). A likelihood scan over the oscillation frequency, Δm_s, gives a most probable value of 19 ps⁻¹ and a range of 17<Δm_s<21 ps⁻¹ at the 90% C.L., assuming Gaussian uncertainties. This is the first direct two-sided bound measured by a single experiment. If Δm_s lies above 22 ps⁻¹, then the probability that it would produce a likelihood minimum similar to the one observed in the interval 16-22 ps⁻¹ is (5.0±0.3)%.