We have performed the first direct measurement of the time-integrated flavor untagged charge asymmetry in semileptonic B decays A by comparing the decay rate of Bµ+DX, where D- and K+K-, with the charge-conjugate decay rate. This sample was selected from 1.3 fb-1 of data collected by the D0 experiment in run II of the Fermilab Tevatron collider. We obtain A=[1.23±0.97(stat)±0.17(syst)]×10-2. Assuming that ms/s1, this result can be translated into a measurement of the CP-violating phase in B mixing: s/mstans= [2.45±1.93(stat)±0.35(syst)]×10-2.
Ratoff led the Lancaster group which carried out the complete data analysis and wrote the paper. This is the first direct constraint on the CP violating phase in the B-s system and has had a significant impact on the field, stimulating substantial theoretical developments, as evidenced by 18 citations (SPIRES). RAE_import_type : Journal article RAE_uoa_type : Physics