Measurement of sin2β from B→J/ψK S 0 with the CDF detector

This paper reports an updated measurement of the standard model CP violation parameter sin 2β using the CDF Detector at Fermilab. The entire run I data sample of 110 pb -1 of proton-antiproton collisions at √s =1.8 TeV is used to identify a signal sample of ∼400 B→J/ψK S 0 events, where J/ψ→μ + μ - and K S 0 →π + π - . The flavor of the neutral B meson is identified at the time of production by combining information from three tagging algorithms: a same-side tag, a jet-charge tag, and a soft-lepton tag. A maximum likelihood fitting method is used to determine sin2β=0.19 -0.44+0.41 (stat+syst). This value of sin 2β is consistent with the standard model prediction, based upon existing measurements, of a large positive CP-violating asymmetry in this decay mode. ©2000 The American Physical Society.