Measuring BR($h to tau ^+ tau ^-$) at the ILC: a full simulation study

We evaluate the expected measurement accuracy of the branching ratio of the Standard Model Higgs boson decaying into tau pairs at the ILC with a full simulation of the ILD detector concept. We assume a Higgs mass of 125 GeV, a branching ratio of BR($h to tau ^+ tau ^-$) = 6.32%, a beam polarization of electron (positron) of -0.8(+0.3), and an integrated luminosity of 250 fb$^{-1}$. The Higgs-strahlung process $e^+ e^- to Zh$ with $Z to qoverline{q}$ is analyzed. We estimate the measurement accuracy of the branching ratio $Delta (sigma times mathrm{BR}) / (sigma times mathrm{BR})$ to be 3.4% with using a multivariate analysis technique.

Full Simulation Study of the Higgs Branching Ratio into Tau Lepton Pairs at the ILC with $sqrt{s} = 500$ GeV

We evaluate the expected measurement accuracy of the branching ratio of the Standard Model Higgs boson decaying into tau lepton pairs $h to tau ^+ tau ^-$ at the ILC with a center-of-mass energy of $sqrt{s} = 500$ GeV with a full simulation of the ILD detector. We assume a Higgs mass of $M_h = 125$ GeV, a branching ratio of $mathrm{BR}(h to tau ^+ tau ^-) = 6.32 %$, beam polarizations of $P(e^+, e^-) = (-0.8,+0.3)$, and an integrated luminosity of $int L dt = 500 mathrm{fb^{-1}}$. The Higgs-strahlung process $e^+ e^- to Zh$ with $Z to q overline{q}$ and the $WW$-fusion process $e^+ e^- to u overline{ u} h$ are expected to be the most sensitive channels at $sqrt{s} = 500$ GeV. Using a multivariate analysis technique, we estimate the expected relative measurement accuracy of the branching ratio $Delta(sigma cdot mathrm{BR}) / (sigma cdot mathrm{BR})$ to be 4.7% and 7.4% for the $q overline{q} h$ and $ u overline{ u} h$ final states, respectively. The results are cross-checked using a cut-based analysis.

Evaluation of measurement accuracy of $h to tau ^+ tau ^-$ branching ratio at the ILC with $sqrt{s} = 250$ GeV and 500 GeV

We evaluate the measurement accuracy of the branching ratio of $h to tau ^+ tau ^-$ at $sqrt{s} = 250$ GeV and 500 GeV at the ILC with the ILD detector simulation. For the $sqrt{s} = 250$ GeV, we assume the Higgs mass of $M_h = 120$ GeV, branching ratio of $mathrm{Br}(h to tau ^+ tau ^-) = 8.0 %$, beam polarization of $P(e^-, e^+) = (-0.8, +0.3)$, and integrated luminosity of $int L dt = 250 mathrm{fb ^{-1}}$. The Higgs-strahlung process $e^+ e^- to Zh$ with $Z to e^+ e^-$, $Z to mu ^+ mu ^-$, $Z to qbar{q}$ mode are analyzed. The measurement accuracy is calculated to be $Delta (sigma cdot mathrm{Br}) / (sigma cdot mathrm{Br}) = 3.5 %$. The scaled result to $M_h = 125$ GeV is estimated to be $4.2 %$. For the $sqrt{s} = 500$ GeV, we assume the Higgs mass of $M_h = 125$ GeV, branching ratio of $mathrm{Br}(h to tau ^+ tau ^-) = 6.32 %$, beam polarization of $P(e^-, e^+) = (-0.8, +0.3)$, and integrated luminosity of $int L dt = 500 mathrm{fb ^{-1}}$. The Higgs-strahlung process $e^+ e^- to Zh$ with $Z to qbar{q}$ mode and $WW$-fusion process $e^+ e^- to u_e bar{ u_e} h$ are analyzed. The measurement accuracy is calculated to be $Delta (sigma cdot mathrm{Br}) / (sigma cdot mathrm{Br}) = 5.7 %$ for Higgs-strahlung with $Z to qbar{q}$ and $7.5 %$ for $WW$-fusion.

A feasibility study of the measurement of Higgs pair creation at a Photon Linear Collider

We studied the feasibility of the measurement of Higgs pair creation at a Photon Linear Collider (PLC). From the sensitivity to the anomalous self-coupling of the Higgs boson, the optimum $gamma gamma$ collision energy was found to be around 270 GeV for a Higgs mass of 120 GeV/$c^2$. We found that large backgrounds such as $gamma gamma rightarrow W^+W^-, ZZ,$ and $bbar{b}bbar{b}$, can be suppressed if correct assignment of tracks to parent partons is achieved and Higgs pair events can be observed with a statistical significance of $sim 5 sigma$ by operating the PLC for 5 years.