Studies of CP violation in $B^0 \to J/\psi K^{*0}$ decays

Abstract

An angular analysis for B decays into two vector mesons gives parameters sensitive to new physics. They are the decay amplitudes of the three helicity states, the asymmetry in triple product, and the CP violating phase. The measurements of these quantities are performed for $B^0 \to J/\psi K^{*0}$ decays in a data sample with 253 fb$^{-1}$ taken by the Belle detector in the KEKB asymmetric $e^+e^-$ collider. With the time-integrated angular analysis, the decay amplitudes' moduli and phase angles are measured to be $|A_0|^2=0.585\pm 0.012 \pm 0.09$, $|A_{\parallel}|^2=0.233\pm 0.013\pm 0.008$, $|A_\perp|^2=0.181\pm 0.012\pm 0.008$, $\arg(A_\parallel)=2.888\pm 0.090\pm 0.008$ radians, and $\arg(A_\perp)=0.239\pm 0.064\pm 0.010$ radians. The difference between $\arg(A_\parallel)$ and $\arg(A_\perp)$ is $2.649\pm0.110$ radians, which is shifted from $\pi$ by more than $4\sigma$; this can be interpreted as evidence for the existence of the final state interaction. The amplitude values are used in triple product correlations to obtainasymmetries of $A_T^{(1)}=0.101\pm 0.033\pm 0.007$ and $A_T^{(2)}=-0.102\pm 0.032\pm 0.003$ for $B^0$ meson decays, and $\bar{A}_T^{(1)}=0.056\pm 0.030\pm 0.006$ and $\bar{A}_T^{(2)} = -0.091\pm 0.028\pm 0.003$ for $\bar{B^0}$ meson decays. The time dependent angular analysis gives the measurements of CP violating parameters $\sin 2\phi_1$ and $\cos 2\phi_1$ to be $0.30 \pm 0.32 \pm 0.02$ and $-0.31 \pm 0.91 \pm 0.10$, respectively. The value of $\cos 2\phi_1$ is $-0.56 \pm 0.86 \pm 0.11$ if $\sin 2\phi_1$ is fixed at the world average value (0.731).