Can the FCC-hh prove the B-L gauge symmetry?

TL;DR

This work assesses the FCC-hh's ability to test the U(1)_{B-L} gauge symmetry via a heavy Z' boson in the dilepton channel. Using full Monte Carlo simulations across a range of (M_{Z'}, g_{B-L}) and backgrounds, the authors optimize kinematic and angular cuts to maximize discovery potential and exclusion reach for an integrated luminosity of 3 ab^{-1}. They find that the FCC-hh can exclude Z' masses up to about 40 TeV for g_{B-L} ~ 1 and achieve a 5σ discovery reach up to ~30 TeV for sizeable couplings, with sensitivity diminishing for smaller couplings. The results highlight the FCC-hh’s capability to probe high-mass resonances beyond current LHC constraints and to substantially advance tests of the B-L gauge sector in new physics scenarios.

Abstract

We present a phenomenological study of the discovery potential at the FCC-hh for a new heavy neutral vector boson, Z', predicted by the $U(1)_{B-L}$ gauge symmetry. Focusing on the parameter space currently not excluded by Large Hadron Collider data, we analyze the dilepton production channel $p p \rightarrow Z^{\prime} \rightarrow l^{+} l^{-}$ ($l^{\pm} = e^{\pm}, μ^{\pm}$) at a center-of-mass energy of $\sqrt{s} = 100$ TeV. Full Monte Carlo simulations was performed for different ($M_{Z'}$, $g_{B-L}$) BSM scenarios and relevant Standard Model backgrounds (including irreducible Drell-Yan, diboson, single top-quark and top-quark pair productions) identifying optimal kinematic and angular selection cuts to guide future searches for this type resonance. We estimate the FCC-hh reach for an integrated luminosity of $\mathcal{L}_{int}$ = 3~$ab^{-1}$. Our results demonstrate that the FCC-hh can exclude Z' masses up to $\sim 40$ TeV with 95\% C.L. for couplings of $g_{B-L} \sim 1$, and up to $\sim 15$ TeV for $g_{B-L} \sim 0.1$. We find the kinematic and angular cuts that optimize the signal over background ratio and achieve a $5σ$ signal up to Z' masses of $\sim 30$ TeV. These findings highlight the FCC-hh potential to uncover new physics signals in the high-mass regime.

Figures (11)

• Figure 1: Different scenarios in the ($M_{Z'}$, $g_{B-L}$) plane considered for the sensitivity analysis at the FCC-hh. The gray region represent the parameter space from the $B-L$ model already excluded by current LHC searches Queiroz:2024ipo.
• Figure 2: Transverse momentum distribution $p_T$ of (a) electrons and (b) positrons at FCC-hh, showing the different background contributions and the (4 TeV, 0.1) scenario.
• Figure 3: Transverse momentum distribution $p_T$ of (a) muons and (b) antimuons at FCC-hh, showing the different background contributions and the (4 TeV, 0.1) scenario.
• Figure 4: Invariant mass distribution of electron-positron pairs at FCC-hh, showing different background contributions and the (4 TeV, 0.1) scenario.
• Figure 5: Invariant mass distribution of muon-antimuon pairs at FCC-hh, showing different background contributions and the (4 TeV, 0.1) scenario.