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.

Extra dimensions and Seesaw Neutrinos at the International Linear Collider

We study the capability of the international linear collider (ILC) to probe extra dimensions via the seesaw mechanism. In the scenario we study, heavy Kaluza-Klein neutrinos generate tiny neutrino masses and, at the same time, have sizable couplings to the standard-model particles. Consequently, a Kaluza-Klein tower of heavy neutrinos (N) can be produced and studied at the ILC through the process: e+e- -> vN followed by N -> Wl decay. We show that the single lepton plus two-jets final states with large missing energy from this signal process will provide a good opportunity to measure the masses and cross sections of Kaluza-Klein neutrinos up to the third level. Furthermore, the neutrino oscillation parameters can be extracted from the flavor dependence of the lowest-mode signals, which give us information about the origin of low-energy neutrino masses.

Feasibility study of Higgs pair creation in gamma gamma collider

We studied a feasibility of measuring Higgs boson pair production in a Photon Linear Collider. The optimum energy of gamma gamma collision was estimated with a realistic luminosity distribution. We also discussed simulation study for detecting the signal against W boson pair backgrounds.