Search for a low-mass $\tau^-\tau^+$ resonance in association with a bottom quark in proton-proton collisions at $\sqrt{s}=13~\mathrm{TeV}$

A general search is presented for a low-mass $\tau^-\tau^+$ resonance produced in association with a bottom quark. The search is based on proton-proton collision data at a center-of-mass energy of $13~\mathrm{TeV}$ collected by the CMS experiment at the LHC, corresponding to an integrated luminosity of $35.9~\mathrm{fb}^{-1}$. The observed data are consistent with the standard model expectation. Upper limits are determined for two hypothetical signal models: a light pseudoscalar Higgs boson decaying to a pair of $\tau$ leptons produced in association with bottom quarks, and a low-mass boson X decaying in a $\tau$ lepton pair that is produced in the decay of a bottom-like quark B such that $\mathrm{B}\to \mathrm{bX}$. Masses between $25$ and $70~\mathrm{GeV}$ are probed for the light pseudoscalar boson, and $20$ to $70~\mathrm{GeV}$ for the X boson. Through event selections that are optimized for vector-like quarks, the search results extend the reach for new particles to a previously unexplored phase space.