Dark sector at BESIII

TL;DR

The paper surveys BESIII searches for GeV-scale dark-sector states coupling to the Standard Model through portals such as light Higgs bosons, axion-like particles, and dark photons. It compiles results from radiative $J/\psi$ decays, rare meson and hyperon decays, and invisible final-state analyses, delivering 90–95% CL upper limits on product branching fractions, couplings, and effective operators across several mass ranges. Key contributions include the most stringent ALP and light Higgs constraints in certain mass windows, first limits on massless dark photons in specific channels, and competitive bounds on dark-baryon and muon-philic scenarios, significantly narrowing the viable parameter space for hidden-sector models. While no definitive dark-sector signals were observed, the obtained exclusions demonstrate BESIII’s power in GeV-scale dark-sector explorations and motivate future analyses with the large, upcoming BESIII data samples, notably the ~20 fb$^{-1}$ of $\psi(3770)$ data.

Abstract

Dark matter (DM) plays a crucial role in explaining the observed astrophysical anomalies, galaxy rotation curves, and other fundamental characteristics of the Universe. Many extensions of the Standard Model (SM), such as the dark hidden-sector model, provide an attractive framework in which DM can couple to SM particles via various portals. These portals give rise to several possible new particles beyond the SM, such as light Higgs bosons, dark photons, and axion-like particles. Furthermore, the origin of DM and the observed asymmetry between visible matter and antimatter may be connected through the introduction of a dark baryon. If the masses of these hypothetical particles lie in the few-GeV range, they can be explored at high-intensity $e^+e^-$ collider experiments, such as the BESIII experiment. This report presents a review of recent BESIII results related to searches for dark-sector particles.

Figures (6)

• Figure 1: $90\%$ CL upper limits on product branching fractions $\mathcal{B}(J/\psi \to \gamma A^0) \times \mathcal{B}(A^0 \to \mu^+\mu^-)$ (left) and mixing angle ($\sin^2 \theta_{A^0}$) (right) as a function of $A^0$ mass.
• Figure 2: The $95\%$ CL upper limits on product branching fractions $\mathcal{B}(J/\psi \to \gamma a)\times \mathcal{B}(a \to \gamma\gamma)$ (left) and axion–photon coupling $g_{a\gamma\gamma}$ (right) as a function of $m_a$. These limits are the most stringent to date in the explored mass region.
• Figure 3: Fits to the missing mass squared $M_{\rm miss}^2$ distributions of the accepted candidates for $D^0 \to \omega \gamma'$ (left) and $D^0 \to \gamma \gamma'$ (middle). The right-hand plot shows the 90% CL upper limits on $|C|^2 + |C_5|^2$ obtained in this work, compared with the result from $\Lambda_c^+ \to p \gamma'$ in Ref. masslessDP.
• Figure 4: Fits to the $E_{\rm extra}$ distributions for (left) $\Sigma^+ \to p + {\rm invisible}$ and (middle) $\bar{\Sigma}^- \to \bar{p} + {\rm invisible}$ DT signal channels. (Right) The 90% C.L. exclusion limit on the $s \to d$ axion–fermion effective coupling obtained from this analysis (hatched region excluded), compared with existing constraints from $K^+ \to \pi^+ a$, $K^+ \to \pi^+ \pi^0 a$, $K$–$\bar{K}$ mixing ($\Delta m_K$), and the CP-violating parameter $\epsilon_K$.
• Figure 5: Fits to the $E_{\rm EMC}$ distributions used to extract signal events for $K_S^0 \to {\rm invisible}$ (left) and the di-pion invariant mass spectrum from visible $\pi^+\pi^-$ decay from the normalization channel (right). Backgrounds from four-pion and non-$\phi$ processes are subtracted from the signal yield shown in the right-hand figure.