Measurement of the mass of Higgs boson through HZ production at FCC-ee

The associated production of a Higgs boson with a $Z$ boson in the collisions of electron and positron beams at Future Circular Collider (FCC-ee) have been studied. Here, the $Z$ boson decays into dileptons, while the Higgs boson decays to all possible channels, mostly to the $b\bar{b}$. The collisions provide a clean and powerful channel to probe the ($HZZ$) coupling at future lepton colliders. Following the event generation, the analysis is performed using the recoil mass method, which allows model-independent reconstruction of the Higgs boson depending on the kinematics of the final-state leptons. This method enables precise identification of the Higgs signal peak independent of its decay mode and significantly reduces systematic uncertainties. The recoil mass distributions from the signal process ($e^+e^- \to HZ$, $Z \to l^+l^-$) and the main backgrounds ($ZZ$, $WW$, $t\bar{t}$ and other standard model processes) have been analyzed using a dedicated analysis code. Monte Carlo simulations corresponding to an integrated luminosity of $5$ ab$^{-1}$ have been used for the analysis, assuming the high performance of the IDEA detector concept. The results are presented for center-of-mass energies of $\sqrt{s} = 240$ GeV and $\sqrt{s} = 365$ GeV to compare the sensitivities and highlight the potential of future $e^+e^-$ colliders in probing the $HZZ$ interaction with high precision.

💡 Research Summary

This paper presents a sophisticated investigation into the precision measurement of the Higgs boson mass through the $HZ$ production process at the proposed Future Circular Collider (FCC-ee). The core of the research lies in leveraging the exceptionally clean environment of electron-positron ($e^+e^-$) collisions to probe the fundamental properties of the Higgs sector with unprecedented accuracy.

The study focuses on the associated production of a Higgs boson with a $Z$ boson ($e^+e^- \to HZ$), specifically analyzing the channel where the $Z$ boson decays into lepton pairs ($l^+l^-$). The methodological centerpiece of this work is the “recoil mass method.” This technique is highly significant because it allows for the reconstruction of the Higgs boson’s mass based solely on the kinematics of the $Z$ boson’s decay products. Consequently, the measurement becomes “model-independent,” meaning the identification of the Higgs signal peak is decoupled from the specific decay mode of the Higgs boson itself (such as $H \to b\bar{b}$ or $H \to \tau\tau$). This independence is crucial for minimizing systematic uncertainties and ensuring that any potential physics beyond the Standard Model (BSM) does not bias the mass measurement.

To evaluate the experimental potential, the researchers utilized Monte Carlo simulations based on an integrated luminosity of $5 \text{ ab}^{-1}$, assuming the high-performance capabilities of the IDEA detector concept. The analysis rigorously accounts for major background processes, including $ZZ, WW, t\bar{t}$, and other Standard Model interactions, which could potentially mimic the Higgs signal. By employing a dedicated analysis code, the study demonstrates the effectiveness of distinguishing the Higgs signal from these backgrounds.

Furthermore, the research compares the sensitivities at two distinct center-of-mass energies: $\sqrt{s} = 240$ GeV and $\sqrt{s} = 365$ GeV. This comparison highlights the strategic importance of different running energies in maximizing the precision of the $HZZ$ coupling measurement. The findings underscore the immense potential of the FCC-ee to serve as a “Higgs factory,” providing the high-precision data necessary to test the Standard Model to its limits and potentially uncover new physical phenomena through subtle deviations in Higgs boson interactions.