Search for pair-produced vector-like leptons in $\geq3\mathrm{b} + \mathrm{N}{\tau}$ final states

A search for vector-like leptons (VLLs) is presented in the context of the 4321 model, a UV-complete model with the potential to explain existing B-physics measurements that are in tension with standard model predictions. The analyzed data correspond to an integrated luminosity of $97~\textrm{fb}^{-1}$, and were recorded by the CMS detector at the LHC in proton-proton collisions at $\sqrt{s}=13~\textrm{TeV}$ at the LHC. Final states with $\geq3$ b jets and two third-generation leptons ($\tau\tau$, $\tau\nu_{\tau}$, or $\nu_{\tau}\nu_{\tau}$) are targeted. Expected upper limits are derived on the VLL production cross section in the VLL mass range $500-1050~\textrm{GeV}$, assuming only electroweak production. At the low end of this mass range, the expected limits are below the expected production cross section, whereas at the high end of the mass range the expected upper limits on the production cross section are several times higher than the expected cross section for electroweak production. A mild excess, consistent with a possible signal, is observed in the data, such that the observed upper limits are approximately double the expected limits. The maximum likelihood fit prefers the presence of signal at the level of $2.8~\sigma$, for a representative VLL mass point of $600~\textrm{GeV}$.