Precise Measurement of Chromoelectric Dipole Moment of the Charm Quark

Abstract

The combined symmetry of charge conjugation and parity ($C\!P$) is tested in the hadronic transition $ψ(3686)\toπ^+π^{-}J/ψ$, using a dataset of $(2712.4\pm14.3)\times10^6$ $ψ(3686)$ events collected by the BESIII detector at the BEPCII collider. The resulting asymmetry observable is $A_{cp} = (0.6\pm1.8\pm0.1)\times10^{-4}$, which is determined by combining the two channels $J/ψ\to e^+e^-$ and $J/ψ\toμ^+μ^-$. Additionally, by considering the relationship between the chromoelectric dipole moment (CEDM) and the $A_{cp}$ observable derived from the quantum chromodynamics multipole expansion theory based on the Chen-Kuang model and the Cornell potential model, we obtain the results of charm quark&#39;s CEDM with $d^{\prime}_{c} = (2.6\pm7.8\pm0.4\pm0.6)\times10^{-16}$ $e$cm, and $d^{\prime}_{c} = (3.5\pm10.5\pm0.6\pm0.5)\times10^{-16}$ $e$cm, respectively. The uncertainties are statistical, systematic, and theoretical, respectively. These results correspond to an upper limit of $|d^{\prime}_{c}|<2.1\times10^{-15}$ $e$ cm at 90\% confidence level, representing an order of magnitude improvement in sensitivity compared to the previous direct bound using the same decay process.