Novel $B$-decay signatures of light scalars at high energy facilities

We study the phenomenology of light scalars of masses $m_1$ and $m_2$ coupling to heavy flavour-violating vector bosons of mass $m_V$. For $m_{1,2}lesssim $ few GeV, this scenario triggers the rare $B$ meson decays $B_s^0to 3mu^+ 3mu^-$, $B^0to 3mu^+ 3mu^-$, $B^+to K^+ 3mu^+ 3mu^-$ and $B_s^0to K^{0*} 3mu^+ 3mu^-$; the last two being the most important ones for $m_1sim m_2$. None of these signals has been studied experimentally; therefore we propose analyses to test these channels at the LHCb. We demonstrate that the reach of this facility extends to branching ratios as small as $6.0times 10^{-9}$, $1.6times 10^{-9}$, $5.9times 10^{-9}$ and $1.8times 10^{-8}$ for the aforementioned channels, respectively. For $m_{1,2}gg mathcal{O}(1)$ GeV, we show that slightly modifi