Constraining light dark matter and mediator with $B^+ \rightarrow K^+ \nu \bar \nu$ data

TL;DR

This paper investigates constraints on light dark matter and mediators through $B^+ ightarrow K^+ u ar{ u}$ decays, combining experimental data to limit mediator mass and decay channels.

Contribution

It provides new bounds on light mediator masses and decay modes by integrating multiple experimental constraints and recent Belle II results.

Findings

Mediator mass constrained between 0.35 and 3 GeV if decay to dark matter is kinematically allowed.

If mediator mass is below twice the dark matter mass, it is long-lived and decays mainly into electrons.

The analysis narrows the parameter space for light dark matter models with mediators.

Abstract

We study the decay of $B^+$ meson into $K^+$ plus a light mediator $\phi$, which subsequently decays into a dark matter pair, $\bar \chi \chi$. Integrating constraints from DM relic density, direct detection, collider data and $B$-physics, alongside the recently reported results form Belle II experiment, we analyze the couplings between the mediator, standard model fermions, and the dark matter particles. Our results indicate that if the decay process $\phi \rightarrow \bar \chi \chi$ is kinematically allowed, i.e. $m_\phi > 2m_\chi$, then the mediator mass must be constrained within 0.35 GeV $\lesssim m_\phi \lesssim$ 3 GeV. Conversely, if $m_\phi < 2m_\chi$, the mediator $m_\phi$ is long-lived relative to the detector size, and the only allowed decay channel is $\phi \rightarrow e^+ e^-$.