Potential precision of a direct measurement of the Higgs boson total width at a muon colliderr

TL;DR

Direct measurement of the Higgs total width is challenging at hadron colliders; this work evaluates the feasibility of a muon collider performing a direct width measurement via s-channel Higgs production. The authors model the resonance as a Breit-Wigner distribution convolved with a Gaussian beam-energy spread, and perform a scanned fit to observables across two channels, Higgs to bbbar and Higgs to WW*. They report projected precisions of roughly 0.15–0.35 MeV on the width for benchmark beam configurations, with the mass and a product of branching fractions also accurately determined; they also explore a broader resonance with width 42 MeV, showing meaningful constraints under extended scanning. Overall, the results indicate that a muon collider could achieve unprecedented precision in Higgs width measurements, enabling stringent tests of Higgs couplings and potential beyond-Standard-Model scenarios, while beam properties remain the dominant systematic.

Abstract

In the light of the discovery of a 126 GeV Standard-Model-like Higgs boson at the LHC, we evaluate the achievable accuracies for direct measurements of the width, mass, and the s-channel resonant production cross section of the Higgs boson at a proposed muon collider. We find that with a beam energy resolution of R=0.01% (0.003%) and integrated luminosity of 0.5 fb^{-1} (1 fb^{-1}), a muon collider would enable us to determine the Standard-Model-like Higgs width to +/- 0.35 MeV (+/- 0.15 MeV) by combining two complementary channels of the WW^* and b\bar b final states. A non-Standard-Model Higgs with a broader width is also studied. The unparalleled accuracy potentially attainable at a muon collider would test the Higgs interactions to a high precision.

Figures (5)

• Figure 1: Effective cross section for $\mu^+ \mu^- \to h$ versus the collider energy $\sqrt s$ for the SM Higgs boson production with $m_{h}=126~{\,{\rm GeV}}$. A Breit-Wigner line shape with $\Gamma_h=4.21$ MeV is shown (dotted curve). The solid and dashed curves compare the two beam energy resolutions of cases A and B.
• Figure 2: Number of events of the Higgs signal plus backgrounds and statistical errors expected for cases A and B as a function of the collider energy $\sqrt s$ in $b\bar{b}$ and $WW^*$ final states with a SM Higgs $m_{h} =126~{\,{\rm GeV}}$ and $\Gamma_h = 4.21~{\,{\rm MeV}}$.
• Figure 3: Fitted values and errors for the SM Higgs width versus the luminosity per step with the scanning scheme as specified in Eq. (\ref{['eq:scan']}).
• Figure 4: Number of events of the Higgs signal plus backgrounds and statistical errors expected for cases A and B as a function of the collider energy $\sqrt s$ in $b\bar{b}$ and $WW^*$ final states with an exotic Higgs $m_{h} =126~{\,{\rm GeV}}$ and $\Gamma_h = 42~{\,{\rm MeV}}$.
• Figure 5: Fitted values and errors for the Higgs width versus the input values. The step size is set as a rounded half-integer value between $3~{\,{\rm MeV}}-10~{\,{\rm MeV}}$ in accordance with the Higgs width $0.6-10$ times the SM value.