Searching for apparent baryon number violation in $\Lambda_c^+$ decays at the Super Tau-Charm Facility

Abstract

Observation of baryon number violation (BNV) in laboratory experiments would constitute unambiguous evidence for physics beyond the Standard Model. We propose dedicated searches for \textit{apparent} BNV in charm-baryon decays, $\Lambda_c^+\to M^+ +$ missing energy ($M=\pi, K$) where the missing energy stems from a resonance. These channels have not been explored experimentally so far, despite the relatively clean environment potentially provided by near $\Lambda_c^+\overline{\Lambda}_c^-$ threshold production at $e^+e^-$ colliders. Performing state-of-the-art Monte Carlo simulations for the proposed Super Tau-Charm Facility (STCF), we evaluate the signal efficiencies and derive projected model-independent sensitivities under the assumption of negligible background. We further interpret these sensitivities within two theoretical frameworks: a sterile-neutrino-extended low-energy effective field theory ($\nu$LEFT) and R-parity-violating (RPV) supersymmetry. With an integrated luminosity of 1 ab$^{-1}$, STCF can probe new-physics scales of several TeV in the $\nu$LEFT description and constrain the RPV model parameter $\lambda''_{212}/m^2_{\tilde{q}}$ down to about $0.1~\mathrm{TeV}^{-2}$. Our results demonstrate that STCF provides a highly competitive opportunity for probing BNV interactions in rare charm-baryon decays.