Feynman diagrams for the $ B ^0_\mathrm{s} \to\mu^+\mu^-\mu^+\mu^-$ and $ B ^0 \to\mu^+\mu^-\mu^+\mu^-$ decays, via (a) the resonant $ B ^0_\mathrm{s} \to J/\psi\phi $ SM channel, (b) the nonresonant SM channel and (c) the supersymmetric channel. The latter is propagated by scalar $S$ and pseudoscalar $P$ sgoldstino sfermions.

(color online). Invariant mass distribution of $K^+ \pi^- \mu^+ \mu^-$ candidates. The $ B ^0$ and $\overline{ B }{} ^0_\mathrm{s} $ signal distributions are shown by short-dashed black and long-dashed red (gray) lines, respectively. The background shape is denoted by a long-dashed black line. The total fit result is shown as a solid blue (black) line. The inset shows the mass distribution centered around the $\overline{ B }{} ^0_\mathrm{s} $ mass.

Invariant mass distribution of nonresonant $ B^0_{(s)}\to \mu^+ \mu^- \mu^+ \mu^- $ candidates. The solid (dashed) black lines indicate the boundaries of the $ B ^0_\mathrm{s} $ ( $ B ^0$ ) signal window. The blue curve shows the model used to fit the mass sidebands and extract the expected number of combinatorial background events in the $ B ^0_\mathrm{s} $ and $ B ^0$ signal regions. Only events in the region in which the line is solid have been considered in the fit.

Animated gif made out of all figures.

Combined reconstruction and selection efficiencies of all the decay modes considered in the analysis. The uncertainties shown are statistical.

Systematic uncertainties on the branching fractions of $ B^0_{(s)}\to \mu^+ \mu^- \mu^+ \mu^- $ . The combined systematic uncertainties are calculated by adding the individual components in quadrature.