LHC constraints on a (B-L)3 gauge boson

Abstract

In this paper, we explore the constraints that the LHC can place on a massive gauge boson X that predominantly couples to the third generation of fermions. Such a gauge boson arises in scenarios where the B-L of the third generation is gauged. We focus on the mass range 10≤mX≲2mW, where current constraints are lacking, and develop a dedicated search strategy. For this mass range, we show that (semi)-leptonic b+b-τ+τ- is the optimal channel to look for the X at the LHC. The QCD production of b quarks, combined with the cleanliness of the leptons coming from the decay of the τ, allows us to detect the X gauge boson with couplings of gX∼(0.005-0.01), for mX<50 GeV, and a coupling of O(0.1) for a heavier X gauge boson with 100 fb-1 of integrated luminosity. This is about a factor of 2-10 improvement over previous constraints coming from the decay of ϒ→τ+τ-. Extrapolating to the full HL-LHC luminosity of 3000 fb-1, the bounds on gX can be enhanced by another factor of 2 for mX<50 GeV.