Search for pair-produced vector-like leptons in final states with third-generation leptons and at least three b quark jets in proton-proton collisions at $\sqrt{s}$ = 13 TeV

The first search is presented for vector-like leptons (VLLs) in the context of the "4321 model", an ultraviolet-complete model with the potential to explain existing PB physics measurements that are in tension with standard model predictions. The analyzed data, corresponding to an integrated luminosity of $96.5~\textrm{fb}^{-1}$, were recorded in 2017 and 2018 with the CMS detector at the LHC in proton-proton collisions at $\sqrt{s}=13\,\mathrm{TeV}$. Final states with $\geq3$ b-tagged jets and two third-generation leptons ($\tau\tau$, $\tau\nu_{\tau}$, or $\nu_{\tau}\nu_{\tau}$) are considered. Upper limits are derived on the VLL production cross section in the VLL mass range 500-1050 GeV. The maximum likelihood fit prefers the presence of signal at the level of 2.8 standard deviations, for a representative VLL mass point of $600\,\textrm{GeV}$. As a consequence, the observed upper limits are approximately double the expected limits.