Hadron collider probes of the quartic couplings of gluons to the photon and Z boson

We explore the experimental sensitivities of measuring the gg -> Z gamma process at the LHC to the dimension-8 quartic couplings of gluon pairs to the Z boson and photon, in addition to comparing them with the analogous sensitivities in the gg -> gamma gamma process. These processes can both receive contributions from 4 different CP-conserving dimension-8 operators with distinct Lorentz structures that contain a pair of gluon field strengths, (G) over cap (a)(mu v), and a pair of electroweak SU(2) gauge field strengths, W-mu v(i), as well as 4 similar operators containing a pair of (G) over cap (a)(mu v), and a pair of U(1) gauge field strengths, B-mu v. We calculate the scattering angular distributions for gg -> Z gamma and the Z -> (f) over bar f decay angular distributions for these 4 Lorentz structures, as well as the Standard Model background. We analyze the sensitivity of ATLAS measurements of the Z( -> l(+) l(-), (v) over barv, (q) over barq)gamma final states with integrated luminosities up to 139 fb(-1) at root s = 13 TeV, showing that they exclude values less than or similar to 2 TeV for the dimension-8 operator scales, and compare the Z gamma sensitivity with that of an ATLAS measurement of the gamma gamma final state. We present combined Z gamma and gamma gamma constraints on the scales of dimension-8 SMEFT operators and gamma gamma constraints on the nonlinearity scale of the Born-Infeld extension of the Standard Model. We also estimate the sensitivities to dimension-8 operators of experiments at possible future proton-proton colliders with centre-of-mass energies of 25, 50 and 100 TeV, and discuss possible measurements of the Z spin and angular correlations.

Automated summary

This study explores the experimental sensitivities of measuring the gg -> Z gamma process at the LHC to the dimension-8 quartic couplings of gluon pairs to the Z boson and photon, comparing them with the sensitivities in the gg -> gamma gamma process. Calculations of scattering and decay angular distributions are performed, and the ATLAS measurements are analyzed for sensitivity. Future proton-proton colliders are also considered for potential measurements.