Year: 2026
Type: preprint
Abstract: A light neutrinophilic scalar $ϕ$, which couples predominantly to neutrinos, can be probed through leptonic meson decays for scalar masses $10~\mathrm{MeV}\lesssim m_ϕ\lesssim\mathcal{O}(100)~\mathrm{MeV}$. We study neutrinophilic-scalar emission in $D$-meson decays at BESIII and the future Super Tau-Charm Facility (STCF), focusing on $D_{(s)}^+\to e^+\barν_αϕ$. Accounting for the $m_ϕ$-dependent missing-mass squared ($M_{\rm miss}^2$) distribution within the experimentally selected region, we find the resulting $D^+$ constraint to be substantially weaker than previous estimates based on the integrated three-body decay rate. Extending the $M_{\rm miss}^2$ coverage provides sensitivity to heavier scalars. With the full kinematic range of $M_{\rm miss}^2$ and an integrated luminosity of $1~\mathrm{ab}^{-1}$, the projected STCF sensitivities surpass the existing kaon bound for $m_ϕ\gtrsim 380~\mathrm{MeV}$ in the $D^+$ decay and $m_ϕ\gtrsim 310~\mathrm{MeV}$ in the $D_s^+$ decay. We further discuss direct searches for $D_{(s)}^+\toμ^+\barν_αϕ$ and their potential for probing the neutrinophilic scalar. A complete analytic expression for the three-body decay width is also derived with full dependence on the scalar and charged-lepton masses, including its behavior in the $m_ϕ\to 0$ and $m_\ell\to 0$ limits.
Source: arXiv (Cornell University)
Authors: Cai, Jin-Man, Li, Gang
Institution: Sun Yat-sen University
Language: English
Subfield: Nuclear and High Energy Physics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Awards: G1202647655, G5309767267, G8129826652
OpenAlex ID: W7221019153