Electroweak Couplings of the Higgs Boson at a Multi-TeV Muon Collider

TL;DR

This work projects the precision reach for Higgs–gauge couplings and self-couplings at a multi-TeV muon collider, using vector-boson fusion as the main production mechanism and a κ-framework augmented by a minimal EFT operator set. It introduces inclusive and exclusive (1$\mu$) strategies to disentangle $WWH$ and $ZZH$ effects, and performs both one- and two-parameter fits for $\kappa_W$, $\kappa_Z$, and, in the HH sector, $\kappa_3$ and $\kappa_{W2}$. Key results show exceptional potential: at $\sqrt{s}=30$ TeV with $\mathcal{L}\sim 90~\mathrm{ab}^{-1}$, projected 95% CL sensitivities reach $\Delta\kappa_W \sim 0.023\%$, $\Delta\kappa_Z \sim 0.21\%$, $\Delta\kappa_{W2} \sim 0.20\%$, and $\Delta\kappa_3 \sim 2.0\%$, with $HHH$ sensitivity around a few percent. These measurements translate into probes of new-physics scales $\Lambda$ in the TeV range, demonstrating the muon collider’s unique ability to test the Higgs sector and potential beyond-SM dynamics at the highest energy frontier.

Abstract

We estimate the expected precision at a multi-TeV muon collider for measuring the Higgs boson couplings with electroweak gauge bosons, $HVV$ and $HHVV\ (V=W^\pm,Z)$, as well as the trilinear Higgs self-coupling $HHH$. At very high energies both single and double Higgs productions rely on the vector-boson fusion (VBF) topology. The outgoing remnant particles have a strong tendency to stay in the very forward region, leading to the configuration of the "inclusive process" and making it difficult to isolate $ZZ$ fusion events from the $WW$ fusion. In the single Higgs channel, we perform a maximum likelihood analysis on $HWW$ and $HZZ$ couplings using two categories: the inclusive Higgs production and the 1-muon exclusive signal. In the double Higgs channel, we consider the inclusive production and study the interplay of the trilinear $HHH$ and the quartic $VVHH$ couplings, by utilizing kinematic information in the invariant mass spectrum. We find that at a centre-of-mass energy of 10 TeV (30 TeV) with an integrated luminosity of 10 ab$^{-1}$ (90 ab$^{-1}$), one may reach a 95\% confidence level sensitivity of 0.073\% (0.023\%) for $WWH$ coupling, 0.61\% (0.21\%) for $ZZH$ coupling, 0.62\% (0.20\%) for $WWHH$ coupling, and 5.6\% (2.0\%) for $HHH$ coupling. For dim-6 operators contributing to the processes, these sensitivities could probe the new physics scale $Λ$ in the order of $1-10$ ($2-20$) TeV at a 10 TeV (30 TeV) muon collider.

Figures (8)

• Figure 1: VBF production of a single Higgs boson at a high energy muon collider via $WW$ fusion. For $ZZ$ fusion, replace the $W$ propagator by the $Z$ propagator and the outgoing neutrinos by muons.
• Figure 2: Double Higgs production at a high energy muon collider via $WW$ fusion. The production goes through the VBF topology, as in Fig. \ref{['fig:VBF']}.
• Figure 3: $\mu^+\mu^- \to \mu^+\mu^- H$ via $ZZ$ fusion with $\sqrt s = 3, 10$ and 30 TeV for (a) angular distribution $\theta_{\mu^-}$, and (b) total cross section versus an angular cut $\theta_{\mu^-}^{\rm cut}$.
• Figure 4: (a) Invariant mass distribution for the Higgs boson and $Z$ boson at $\sqrt s=10$ TeV with an energy resolution $10\%$, and (b) the $b$-quark angular distribution $\theta_b$ in the lab frame for $\sqrt s = 3, 10, 30$ TeV.
• Figure 5: (a) $p_T^{H}$ distribution of the Higgs boson in $1\mu$ channel (b) Separation of the $b$ jets from $H\to b\bar{b}$.