Paper detail

A Measurement of $\sin 2β$ from $B\to J/ψK^0_S$ with the CDF detector

This paper reports an updated measurement of the Standard Model CP violation parameter $\sin2β$ using the CDF Detector at Fermilab. The entire Run I data sample of 110 pb$^{-1}$ of proton antiproton collisions at $\sqrt{s}=1.8 TeV$ is used to identify a signal sample of $\sim 400$ $B \to J/ψK^0_S$ events, where $J/ψ\to μ^+μ^-$ and $K_S^0 \to π^+π^-$. 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 $\sin2β= 0.79 {+0.41\atop-0.44}$(stat+syst). This value of $\sin 2 β$ is consistent with the Standard Model prediction, based upon existing measurements, of a large positive CP violating asymmetry in this decay mode.