Probing axion-like particle couplings to leptons via the $\gamma\gamma jj$ signal at the FCC-ee

Abstract

We study the sensitivity of the Future Circular Collider in electron-positron mode (FCC-ee) to the axion-like particle (ALP) couplings with leptons via the process $e^{+}e^{-} \rightarrow \gamma\gamma jj$ at the center-of-mass energy $\sqrt{s}=91$ GeV with the integrated luminosity $\mathcal{L}=150~\text{ab}^{-1}$. We analyze three scenarios, $\mathbf{c}_R=0$, $\mathbf{c}_L=0$ and $\mathbf{c}_R=\mathbf{c}_L$, for both unpolarized and polarized beams with $(P_{e^-}, P_{e^+}) = (+80\%, -80\%)$, and derive projected lower limits on the effective coupling strengths. The polarized case provides higher sensitivity than the unpolarized case. Specifically, for the $\mathbf{c}_R=0$ scenario (probing the ALP-neutrino coupling $\text{Tr}(g_{a\nu\nu})/f_a$), the projected sensitivity in the polarized case reaches approximately $0.0105~\text{GeV}^{-1}$ for the ALP mass in the range $10$--$24$ GeV; for $\mathbf{c}_L=0$ (probing the ALP-charged lepton coupling $\text{Tr}(g_{a\ell\ell})/f_a$), it reaches $0.0174~\text{GeV}^{-1}$ in the $10$--$27$ GeV range; and for $\mathbf{c}_R=\mathbf{c}_L$ (probing the ALP-neutrino coupling $\text{Tr}(g_{a\nu\nu})/f_a$), it reaches $0.00394~\text{GeV}^{-1}$ in the $45$--$80$ GeV range. In these ALP mass ranges, our projected sensitivities are complementary to the projected sensitivities from other search channels at future colliders.