Simultaneous measurement of the B^0 meson lifetime and mixing frequency with B^0→D*−l+ν_ℓ decays

Abstract

We measure the B^0 lifetime τ_B^0 and the B0−B0[overbar] oscillation frequency Δm_d with a sample of approximately 14000 exclusively reconstructed B^0→D*−ℓ+ν_l signal events, selected from 23 million BB[overbar] pairs recorded at the Υ(4S) resonance with the BABAR detector at the Stanford Linear Accelerator Center. The decay position of the other B is determined with the remaining tracks in the event, and its b-quark flavor at the time of decay is determined with a tagging algorithm that exploits the correlation between the flavor of the b quark and the charges of its decay products. The lifetime and oscillation frequencies are measured simultaneously with an unbinned maximum-likelihood fit that uses, for each event, the measured difference in decay times of the two B mesons (Δt), the calculated uncertainty on Δt, the signal and background probabilities, and b-quark tagging information for the other B. The results are τ_B^0=(1.523^(+0.024)_(−0.023)±0.022)ps and Δm_d=(0.492±0.018±0.013)ps^(−1). The statistical correlation coefficient between τ_B0 and Δm_d is -0.22.