Measurement ofsin2βfromB→J/ψKS0with the CDF detector

Abstract

This paper reports an updated measurement of the standard model $\mathrm{CP}$ violation parameter $\sin 2\beta$ using the CDF Detector at Fermilab. The entire run I data sample of $110\hspace{0.5em}{\mathrm{pb}}^{-1}$ of proton-antiproton collisions at $\sqrt{s}=1.8\mathrm{}\hspace{0.5em}\mathrm{TeV}$ is used to identify a signal sample of $\sim 400\hspace{0.5em}\overrightarrow{B}J/\psi K_S^0$ events, where $J/\overrightarrow{\psi }{\mu }^{+}{\mu }^{-}$ and $K_S^0\to {\pi }^{+}{\pi }^{-}.$ 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 $\sin 2\beta {=0.79\mathrm{}}_{-0.44}^{+0.41\mathrm{}}(\mathrm{stat}+\mathrm{syst}).\mathrm{}$ This value of $\sin 2\beta$ is consistent with the standard model prediction, based upon existing measurements, of a large positive $\mathrm{CP}$-violating asymmetry in this decay mode.