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

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 $B\to K^{\ast }{M}_X$ decays. (ii) Combining the available data on $\Gamma (B\to K{M}_X)$ and the upper limit on $\Gamma (B\to K^{\ast }{M}_X)$ 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.

Comments: 12 pages, Figure with ${\chi }^2$ distributions added