A Way to Measure Very Large Delta m for B_s Mesons

While present vertex technology cannot measure x_s much beyond 20, the Standard Model accomodates significantly larger x_s values. This note presents a method to determine very large x_s with present technology. The determination is based upon subtle coherence effects between initial B_s 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.