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# Measurement of ${\cal B}r(H \to Z\gamma)$ at the 250 GeV ILC

Dec 2022

The $e^+e^- \to HZ$ process with the subsequent decay of the Higgs boson $H\to Z\gamma$ is studied, where both $Z$ bosons are reconstructed in the finalstates with two jets. The analysis is performed using Monte Carlo data samplesobtained with detailed ILD (The International Large Detector) detectorsimulation assuming an integrated luminosity of 2~ab$^{-1}$, beam polarizationsof ${\cal{P}}_{e^-e^+} = (-0.8, +0.3)$, and center-of-mass energy of\mbox{$\sqrt{s}$ = 250~GeV}. The analysis is repeated for the case of two0.9~ab$^{-1}$ data samples with polarizations ${\cal{P}}_{e^-e^+} = (\mp0.8,\pm0.3)$. Contributions of the potential background processes are studied usingall available ILD MC event samples. The largest background comes from the$e^+e^- \to W^+W^-$ process supplemented by an energetic photon produced byinitial state radiation. To suppress this background we require that at leastone of the $Z$ bosons decays to $b$-jets. To reduce the jet reconstructionuncertainties the $M_{\Delta} = M(jj\gamma) - M(jj) + M(Z_{\rm nom})$ variableis used, where $M(Z_{\rm nom})$ = 91.2~GeV. The $M_{\Delta}$ distributions areobtained for the studied signal and backgrounds to estimate the expectedaccuracy of the ${\cal B}r(H \to Z\gamma)$ measurement. The accuracy is 22$\%$for the option of the single polarization sample described above anddeteriorate to 24$\%$ in case of the sample with two polarizations. Theproposed method can be applied at any future $e^+e^-$ collider.

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