A way to measure very large Δm for Bs mesons

While present vertex technology cannot measure xs much beyond 20, the Standard Model accommodates significantly larger xs values. This note presents a method to determine very large xs with present technology. The determination is based upon subtle coherence effects between initial Bs mesons and daughter neutral kaons, discovered by one of us several years ago. The method may be useful also for measuring very small width or mass differences in mixed neutral B or D mesons.