Probing vector- vs scalar-mediator dark-matter scenarios in $B\to (K,K^*) M_X$ decays

TL;DR

This paper investigates how to distinguish scalar and vector dark-matter mediators in B meson decays by analyzing differential distributions, providing constraints on vector mediator mass and fitting experimental data.

Contribution

It demonstrates that differential decay distributions can discriminate mediator types and constrains the vector mediator mass using current experimental data.

Findings

Scalar and vector mediators can be distinguished via decay distribution measurements.

Current data constrains the vector mediator mass to be less than about 3 GeV.

Both mediator scenarios fit the Belle-II differential distribution data well.

Abstract

Within the hypothesis of the dark-matter origin of the excess in $B\to K M_X$ decays over the standard-model expectation, observed by Belle-II, we show that: (i) Scalar- and vector-medator scenarios may be unambiguously discriminated by measuring the differential distributions in $B\to K M_X$ and $B\to K^* M_X$ decays. (ii) Combining the available data on $\Gamma(B\to K M_X)$ and the upper limit on $\Gamma(B\to K^* M_X)$ provides a tight constraint on the vector mediator mass $M_V\lesssim 3$ GeV. At the same time, no constraints on the scalar-mediator mass are imposed by these data. (iii) Both scalar- and vector-mediator scenarios allow a good description of the differential distributions in $B\to K M_X$ measured by Belle-II and an extraction of dark-model parameters within both scenarios.