Search for Dark Matter in b -> s Transitions with Missing Energy

TL;DR

The paper addresses the challenge of probing GeV and sub-GeV dark matter by exploiting B meson decays to K(K^*) plus missing energy, within a minimal Higgs-portal singlet scalar model. It derives an effective $b\to s$ transition with missing energy and computes the competing rates for $B^+\to K^+SS$ against the Standard Model $B^+\to K^+\nu\bar{\nu}$, showing that light $m_S$ can yield BRs enhanced by up to two orders of magnitude. By tying the scalar coupling to the observed dark matter relic density, it constrains $\kappa(m_S)$ and translates this into predictions for ${\rm Br}_{B^+\to K^+ + E\!/}$, confronting current BaBar/CLEO limits and projecting sensitivity improvements for future B-factory data up to $m_S\sim 2$ GeV. The work also notes implications for invisible Higgs decays and highlights the viability of collider-based probes for low-mass dark matter in the GeV regime. Overall, it demonstrates that $b\to s$ transitions with missing energy are a powerful complementary channel for light dark matter searches.

Abstract

Dedicated underground experiments searching for dark matter have little sensitivity to GeV and sub-GeV masses of dark matter particles. We show that the decay of B mesons to K(K^*) and missing energy in the final state can be an efficient probe of dark matter models in this mass range. We analyze the minimal scalar dark matter model to show that the width of the decay mode with two dark matter scalars B\to KSS may exceed the decay width in the Standard Model channel, B\to Kν\barν, by up to two orders of magnitude. Existing data from B physics experiments almost entirely exclude dark matter scalars with masses less than 1 GeV. Expected data from B factories will probe the range of dark matter masses up to 2 GeV.

Figures (2)

• Figure 1: Feynman diagrams which contribute to $B$ meson decays with missing energy.
• Figure 2: Predicted branching ratios for the decay $B \to K +$missing energy, with current limits from BaBar (I) Aubert:2003yh, CLEO (III) Browder:2000qr and expected results from BaBar (II). Parameter space above curves I and III is excluded. The horizontal line shows the SM $B\to K\nu\bar{\nu}$ signal. Parameter space to the left of the vertical dashed line is also excluded by $K^+ \to \pi^+E\!\!\!\!/$.