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

TL;DR

This paper presents an angular analysis of B0 decays into J/psi and K*0 mesons, measuring decay amplitudes, CP violation parameters, and triple product asymmetries to search for new physics effects.

Contribution

It provides the first detailed measurement of decay amplitudes, phases, and CP violation parameters in B0 to J/psi K*0 decays using Belle data, revealing evidence for final state interactions.

Findings

Amplitude moduli and phases measured with high precision.

Significant phase difference indicating final state interactions.

CP violation parameters consistent with the Standard Model.

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).