arXiv subjects
Publications and source records attributed to Tomohiko Tanabe.
We summarize the physics case for the International Linear Collider (ILC). We review the key motivations for the ILC presented in the literature, updating the projected measurement uncertainties for the ILC experiments in accord with the expected schedule of operation of the accelerator and the results of the most recent simulation studies.
We present a study of the expected precision for measurement of the top Yukawa coupling, yt, in e+e- collisions at a center-of-mass energy of 1 TeV and assuming a beam polarization of P (e-, e+) = (-0.8,+0.2). Independent analyses of ttH final states containing at least six hadronic jets are performed, based on detailed simulations of SiD and ILD, the two candidate detector concepts for the ILC. We estimate that a statistical precision of yt of 4% can be obtained with an integrated luminosity of 1 $\mathrm{ab}^{-1}$.
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($h \to τ^+ τ^-$) = 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 $Z \to q\overline{q}$ is analyzed. We estimate the measurement accuracy of the branching ratio $Δ(σ\times \mathrm{BR}) / (σ\times \mathrm{BR})$ to be 3.4% with using a multivariate analysis technique.
We evaluate the expected measurement accuracy of the branching ratio of the Standard Model Higgs boson decaying into tau lepton pairs $h \to τ^+ τ^-$ 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 $\mathrm{BR}(h \to τ^+ τ^-) = 6.32 \%$, 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 $e^+ e^- \to ν\overlineν h$ 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 $Δ(σ\cdot \mathrm{BR}) / (σ\cdot \mathrm{BR})$ to be 4.7% and 7.4% for the $q \overline{q} h$ and $ν\overlineν h$ final states, respectively. The results are cross-checked using a cut-based analysis.
We make a systematic and comparative study for the LHC and ILC for the electroweakino searches in the Minimal Supersymmetric Standard Model. We adopt a general bottom-up approach and scan over the parameter regions for all the three cases of the lightest supersymmetric particle being Bino-, Wino-, and Higgsino-like. The electroweakino signal from pair production and subsequent decay to Wh (h to b\bar b) final state may yield a sensitivity of 95% C.L. exclusion (5sigma discovery) to the mass scale M_2, mu ~ 250-400 GeV (200-250 GeV) at the 14 TeV LHC with an luminosity of 300 fb^{-1}. Combining with all the other decay channels, the 95% C.L. exclusion (5sigma discovery) may be extended to M_2, mu ~ 480-700 GeV (320-500 GeV). At the ILC, the electroweakinos could be readily discovered once the kinematical threshold is crossed, and their properties could be thoroughly studied.
We evaluate the measurement accuracy of the branching ratio of $h \to τ^+ τ^-$ 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 $\mathrm{Br}(h \to τ^+ τ^-) = 8.0 \ %$, 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 $Z \to e^+ e^-$, $Z \to μ^+ μ^-$, $Z \to q\bar{q}$ mode are analyzed. The measurement accuracy is calculated to be $Δ(σ\cdot \mathrm{Br}) / (σ\cdot \mathrm{Br}) = 3.5 \ %$. 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 $\mathrm{Br}(h \to τ^+ τ^-) = 6.32 \ %$, 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 $Z \to q\bar{q}$ mode and $WW$-fusion process $e^+ e^- \to ν_e \bar{ν_e} h$ are analyzed. The measurement accuracy is calculated to be $Δ(σ\cdot \mathrm{Br}) / (σ\cdot \mathrm{Br}) = 5.7 \ %$ for Higgs-strahlung with $Z \to q\bar{q}$ and $7.5 \ %$ for $WW$-fusion.
The International Linear Collider (ILC) has recently proven its technical maturity with the publication of a Technical Design Report, and there is a strong interest in Japan to host such a machine. We summarize key aspects of the Beyond the Standard Model physics case for the ILC in this contribution to the US High Energy Physics strategy process. On top of the strong guaranteed physics case in the detailed exploration of the recently discovered Higgs boson, the top quark and electroweak precision measurements, the ILC will offer unique opportunities which are complementary to the LHC program of the next decade. Many of these opportunities have connections to the Cosmic and Intensity Frontiers, which we comment on in detail. We illustrate the general picture with examples of how our world could turn out to be and what the ILC would contribute in these cases, with an emphasis on value-added beyond the LHC. These comprise examples from Supersymmetry including light Higgsinos, a comprehensive bottom-up coverage of NLSP-LSP combinations for slepton, squark, chargino and neutralino NLSP, a stau-coannihilation dark matter scenario and bilinear R-parity violation as explanation for neutrino masses and mixing, as well as generic WIMP searches and Little Higgs models as non-SUSY examples.
In collider physics at the TeV scale, there are many important processes which involve six or more jets. The sensitivity of the physics analysis depends critically on the performance of the jet clustering algorithm. We present a full detector simulation study for the ILC of our new algorithm which makes use of secondary vertices which improves the reconstruction of b jets. This algorithm will have many useful applications, such as in measurements involving a light Higgs which decays predominantly into two b quarks. We focus on the measurement of the Higgs self-coupling, which has so far proven to be challenging but is one of the most important measurements at the ILC.
We report on the feasibility of the direct measurement of the top Yukawa coupling g_t at the International Linear Collider (ILC) during its first phase of operation with a center-of-mass energy of 500 GeV. The signal and background models incorporate the non-relativistic QCD corrections which enhance the production cross section near the t-tbar threshold. The e+e- -> t tbar H signal is reconstructed in the 6-jet + lepton and the 8-jet modes. The results from the two channels are combined. The background processes considered are e+e- -> t bbar W- / tbar b W+ (which includes e+e- -> t tbar), e+e- -> t tbar Z, and e+e- -> t tbar g* -> t tbar b bar. We use a realistic fast Monte-Carlo detector simulation. Signal events are selected using event shape variables, through jet clustering, and by identifying heavy flavor jets. Assuming a Higgs mass of 120 GeV, polarized electron and positron beams with (Pe-,Pe+) = (-0.8,+0.3), and an integrated luminosity of 1 ab-1, we estimate that the e+e- -> t tbar H events can be seen with a statistical significance of 5.2 sigma, corresponding to the relative top Yukawa coupling measurement accuracy of |Delta g_t / g_t| = 10%.
We consider analysis targets at the International Linear Collider in which only a single photon can be observed. For such processes, we have developed a method which uses likelihood distributions using the full event information (photon energy and angle). The method was applied to a search for neutralino pair production with a photon from initial state radiation (ISR) in the case of supergravity in which the neutralino is the lightest supersymmetric particle. We determine the cross section required to observe the neutralino pair production with ISR as a function of the neutralino mass in the range of 100 to 250 GeV.
The ILC physics working group is a mixture of experimentalists and theorists mainly working in Japan. It has its origin in the previous LC physics study group and has been reformed with the initiative of a JSPS Creative Scientific Research project: "Research and Development of a Novel Detector System for the International Linear Collider". The working group is, however, formally independent of the JSPS project and is open to everybody who is interested in ILC physics. The primary task of the working group is to reexamine the ILC physics in the context of the expected LHC outcome and to further strengthen the physics case for the ILC project. The topics covered in the working group activities range from key measurements such as those of the Higgs self-coupling and the top Yukawa coupling to uncover the secrets of the electroweak symmetry breaking to various new physics scenarios like supersymmetry, large extra dimensions, and other models of terascale physics. The working group has held ten General Meetings in the period of May 2007 to June 2009 to discuss the topics mentioned above. This report ummarizes the progress made in this period and sets a milestone for future developments in ILC physics.