Hadron collider probes of the quartic couplings of gluons to the photon and Z boson
John Ellis, Shao-Feng Ge, Kai Ma
Abstract
A bstract We explore the experimental sensitivities of measuring the gg → Zγ 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 → γγ 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, $$ {\hat{G}}_{\mu v}^a $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mover> <mml:mi>G</mml:mi> <mml:mo>̂</mml:mo> </mml:mover> <mml:mi>μv</mml:mi> <mml:mi>a</mml:mi> </mml:msubsup> </mml:math> , and a pair of electroweak SU(2) gauge field strengths, $$ {W}_{\mu v}^i $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>W</mml:mi> <mml:mi>μv</mml:mi> <mml:mi>i</mml:mi> </mml:msubsup> </mml:math> , as well as 4 similar operators containing a pair of $$ {\hat{G}}_{\mu v}^a $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mover> <mml:mi>G</mml:mi> <mml:mo>̂</mml:mo> </mml:mover> <mml:mi>μv</mml:mi> <mml:mi>a</mml:mi> </mml:msubsup> </mml:math> and a pair of U(1) gauge field strengths, B μν . We calculate the scattering angular distributions for gg → Zγ and the Z → $$ \overline{f}f $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mover> <mml:mi>f</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> <mml:mi>f</mml:mi> </mml:math> 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 − , $$ \overline{\nu}\nu $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mover> <mml:mi>ν</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> <mml:mi>ν</mml:mi> </mml:math> , $$ \overline{q}q $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mover> <mml:mi>q</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> <mml:mi>q</mml:mi> </mml:math> ) γ final states with integrated luminosities up to 139 fb − 1 at $$ \sqrt{s} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msqrt> <mml:mi>s</mml:mi> </mml:msqrt> </mml:math> = 13 TeV, showing that they exclude values ≲ 2 TeV for the dimension-8 operator scales, and compare the Zγ sensitivity with that of an ATLAS measurement of the γγ final state. We present combined Zγ and γγ constraints on the scales of dimension-8 SMEFT operators and γγ 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.