LHC and HL-LHC Bounds on Visible and Invisible Decays in the $B-L$ Model

TL;DR

This paper derives current and projected bounds on the $Z'$ gauge boson in the B-L model using LHC data, showing that LHC constraints surpass previous LEP bounds and will extend further with HL-LHC.

Contribution

It provides updated mass limits on the $Z'$ in the B-L model from LHC data and forecasts future bounds with HL-LHC, considering both visible and invisible decay channels.

Findings

Current LHC bounds: $M_{Z'} > 4$TeV for $g_{BL}=0.1$

Invisible decays weaken the bounds, e.g., $M_{Z'} > 4.8$TeV for $g_{BL}=0.5$ with 90% invisible branching ratio

HL-LHC will probe $Z'$ masses up to 7.5 TeV

Abstract

In this work, we use publicly available data from ATLAS collaboration collected at LHC run 2 at a center-of-mass energy of $\sqrt{s}=13$TeV with an integrated luminosity of $139 fb^{-1}$ to derive lower mass limits on the $Z^\prime$ gauge boson associated with the B-L gauge symmetry. Using dilepton data we find that $M_{Z^\prime} > 4$TeV ($6$TeV) for $g_{BL}=0.1$ ($g_{BL}=0.5$) in the absence of invisible decays. Once invisible decays are turned on these limits are substantially relaxed. Assuming an invisible branching ratio of $BR_{inv}=0.9$, the LHC bound is loosened up to $M_{Z^\prime}> 4.8$TeV for $g_{BL}=0.5$. This analysis confirms that the LHC now imposes stricter constraints than the longstanding bounds established by LEP. We also estimate the projected HL-LHC bounds that will operate with at $\sqrt{s}=14$TeV and a planned integrated luminosity of $\mathcal{L}=3 ab^{-1}$ that will probe $Z^\prime$ masses up to $7.5$TeV.