Measurement of B_d mixing using opposite-side flavor tagging

Abstract

We report on a measurement of the B_d⁰ mixing frequency and the calibration of an opposite-side flavor tagger in the D∅ experiment. Various properties associated with the b quark on the opposite side of the reconstructed B meson are combined using a likelihood-ratio method into a single variable with enhanced tagging power. Its performance is tested with data, using a large sample of reconstructed semileptonic B→μD⁰X and B→μDX decays, corresponding to an integrated luminosity of approximately 1fb-¹. The events are divided into groups depending on the value of the combined tagging variable, and an independent analysis is performed in each group. Combining the results of these analyses, the overall effective tagging power is found to be εD²=(2.48±0.21_-0.06^+0.08)%. The measured B_d⁰ mixing frequency Δm_d=0.506±0.020(stat)±0.016(syst)ps^-1 is in good agreement with the world average value.