Constraining New Physics with the CDF Measurement of CP Violation in $B\to \psi K_S$

Abstract

Recently, the CDF collaboration has reported a measurement of the CP asymmetry in the $B\to \psi K_S$ decay: $a_{\psi K_S}=0.79_{-0.44}^{+0.41}$. We analyze the constraints that follow from this measurement on the size and the phase of contributions from new physics to $B-\text{barB}$ mixing. Defining the relative phase between the full $M_{12}$ amplitude and the Standard Model contribution to be $2{\theta }_d$, we find a new bound: $\sin 2{\theta }_d\text{gsim}-0.6(-0.87)$ at one sigma (95% CL). Further implications for the CP asymmetry in semileptonic B decays are discussed.

Comments: 13 pages, harvmac, 3 figures; v2: a discussion of new physics effects on tree level decays added; references added; accepted for publication in Physical Review Letters