Search for the charmonium weak decay $\psi(2S)\to D_s^-\pi^+ + c.c.$ and $\psi(2S)\to D_s^-\rho^+ + c.c.$

TL;DR

This study searches for rare weak decays of the $ ext{psi}(2S)$ charmonium state into $D_s$ mesons and light mesons, setting upper limits on their branching fractions due to no observed signal.

Contribution

First experimental search for these specific weak decays of $ ext{psi}(2S)$, providing upper limits that constrain theoretical models and potential new physics.

Findings

No signal observed above background

Upper limits on branching fractions set at 1.4×10⁻⁶ and 7.0×10⁻⁶

Data sample of over 2.7 billion $ ext{psi}(2S)$ events used

Abstract

We search for the weak decays $\psi(2S)\to D_s^-\pi^+ + c.c.$ and $\psi(2S)\to D_s^-\rho^+ + c.c.$ for the first time. The search is based on $(2712.4\pm14.3)\times 10^6$ events containing the charmonium state $\psi(2S)$ collected at the center-of-mass energy $\sqrt{s}=3.686\ \rm{GeV}$ with the BESIII detector. This search offers a unique opportunity to test the Standard Model and search for new physics. Since no signal excess above the background is observed, the upper limits on the branching fractions at the 90\% confidence level are set to be $1.4\times 10^{-6}$ and $7.0\times 10^{-6}$ for $\psi(2S)\to D_s^-\pi^+ + c.c.$ and $\psi(2S)\to D_s^-\rho^+ + c.c.$, respectively.