Probing anomalous $Z\gamma \gamma \gamma$ couplings at a future muon collider

Abstract

The sensitivity to anomalous quartic gauge couplings (AQGCs) of the $\gamma \gamma \gamma Z$ interaction is studied in the ${\mu }^{+}{\mu }^{-}\to {\mu }^{+}\gamma \gamma {\mu }^{-}$ scattering at a future muon collider with unpolarized beams. The anomalous $\gamma \gamma \gamma Z$ vertex is described by two couplings, ${\zeta }_1$ and ${\zeta }_2$. The differential and total cross sections are calculated for the center-of-mass energies of 3 TeV, 14 TeV, and 100 TeV. For these values of the collision energy the $95\%$ C.L. exclusion regions for AQGCs are obtained depending on the systematic error. In particular, for the 14 TeV muon collider with the integrated luminosity $L=20$ ab${}^{-1}$ the best sensitivities are derived to be ${\zeta }_1=3.1\times 10^{-5}$ TeV${}^{-4}$ and ${\zeta }_2=6.5\times 10^{-5}$ TeV${}^{-4}$. These constraints are three orders of magnitude stronger than the bounds obtained for the 27 TeV HE-LHC with $L=15$ ab${}^{-1}$. At the 100 TeV muon collider with $L=1000$ ab${}^{-1}$ AQGCs can be probed up to $(1.64÷3.4)\times 10^{-8}$ TeV${}^{-4}$. The partial-wave unitarity constraints on couplings ${\zeta }_1$, ${\zeta }_2$ are evaluated. It is shown that the unitarity is not violated in the region of the AQGCs examined in the present paper.

Comments: 23 pages, 6 figures