Observation of the decay $\psip\rar\kstark$

TL;DR

This study measures the decay rates of $ ext{ψ}(2S)$ into specific kaon states, confirming the violation of the 12% rule and observing significant isospin violation with high precision.

Contribution

First precise measurement of $ ext{ψ}(2S)$ decays to $ ext{K}^* ext{K}$ modes, revealing isospin violation and confirming rule violation.

Findings

Branching fraction for $ ext{ψ}(2S) o ext{K}^* ext{K}^ extpm$ is approximately 2.9×10^{-5}.

Branching fraction for $ ext{ψ}(2S) o ext{K}^* ext{K}^0$ is approximately 13.3×10^{-5}.

Results confirm higher-precision violation of the 12% rule.

Abstract

Using 14 million $\psi(2S)$ events collected with the BESII detector, branching fractions of $\psip\rar\kstarkpm$ and $\kstarknn$ are determined to be: $\calB(\psip\rar\kstarkpm)=(2.9^{+1.3}_{-1.7}\pm0.4)\times 10^{-5}$ and $\calB(\psip\rar\kstarknn)=(13.3^{+2.4}_{-2.7}\pm1.9)\times 10^{-5}$. The results confirm the violation of the "12%" rule for these two decay channels with higher precision. A large isospin violation between the charged and neutral modes is observed.