Search for new physics with baryons at BESIII

TL;DR

The paper investigates potential new-physics connections between baryons and dark sectors and probes baryon-number-violating processes in the strange-baryon sector. It leverages BESIII’s extensive $J/cpsi$ data and employs recoil- and double-tag techniques to search for invisible final states in $ ext{Sigma}^{+}$ decays, dark baryons in $ ext{Xi}^{-}$ decays, and $ar{ extLambda}$–$ extLambda$ oscillations. No evidence of new physics is found, but the study sets the most stringent 90% C.L. limits to date on invisible baryon decays and $ riangle B=2$ transitions in strange baryons, e.g., $ ext{B}( ext{Sigma}^{+} o p+ ext{inv})<3.2 imes10^{-5}$, $ ext{B}( ext{Xi}^{-} o ext{pi}^{-}+ ext{inv})<10^{-5}$, and $P( ext{Lambda})<1.4 imes10^{-6}$ with $ ext{delta}m_{ extLambdaar{ extLambda}}<2.1 imes10^{-18}$ GeV. These results tighten constraints on light dark-sector particles, baryonic dark matter, axion-like particles, and $ riangle B=2$ interactions, highlighting the impact of precision, intensity-frontier baryon studies and informing future analyses with larger data samples.

Abstract

The BESIII experiment at BEPCII provides a clean environment to test baryon-dark sector connections and baryon-number violation. Using $10^{10}$ $J/ψ$ events, searches were performed for $Σ^{+}\to p+\text{inv}$, $Ξ^{-}\toπ^{-}+\text{inv}$, and $\barΛ-Λ$ oscillations. No excess was observed, yielding $\mathcal{B}(Σ^{+}\to p+\text{inv})<3.2\times10^{-5}$, $\mathcal{B}(Ξ^{-}\toπ^{-}+\text{inv})<(4-7)\times10^{-5}$, and $P(Λ)<4.4\times10^{-6}$ (90\% C.L.). These are the most stringent limits on invisible baryon decays and $ΔB=2$ transitions in strange baryons, probing new physics beyond the Standard Model.

Figures (3)

• Figure 1: Upper: Fit to the extra EMC energy distribution used to extract the $\Sigma^{+}\to p + \mathrm{invisible}$ signal. Below: Constraints on effective FCNC couplings derived from the measured upper limit.
• Figure 2: Upper: Diagram of the decay $\Xi^{-}\to\pi^{-}+\chi$, where $\chi$ is a dark baryon. Below: Upper limits on the branching fraction as a function of the assumed dark-baryon mass.
• Figure 3: Upper: Illustration of $\bar{\Lambda}$--$\Lambda$ oscillation. Below: Invariant mass distribution of $M_{p\pi^{-}}$ for (a) WS events in the signal region and (insert) over the full span, where the filled circle with error bar is from data, the pink filled histogram, normalized arbitrarily, stems from simulated WS signal events, and the arrows in the inset figure show the edges of the signal region; (b) RS events from data, where the filled circles with error bars are from data, the blue solid line represents the result of the fit and the dashed line shows the background contribution.