Search for the Z Boson Decay to ττμμ in Proton-Proton Collisions at √s=13 TeV

Abstract

The first search for the 𝑍 boson decay to 𝜏⁢𝜏⁢𝜇⁢𝜇 at the CERN LHC is presented, based on data collected by the CMS experiment at the LHC in proton-proton collisions at a center-of-mass energy of 13 TeV and corresponding to an integrated luminosity of 138 fb−1. The data are compatible with the predicted background. For the first time, an upper limit at the 95% confidence level of 6.9 times the standard model expectation is placed on the ratio of the 𝑍 →𝜏⁢𝜏⁢𝜇⁢𝜇 to 𝑍 →4⁢𝜇 branching fractions. Limits are also placed on the six flavor-conserving four-lepton effective-field-theory operators involving two muons and two tau leptons, for the first time testing all such operators.