Hiroshi Yokoya

University of Toyama, Тояма, Toyama, Japan

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Publications (42)94.25 Total impact

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    ABSTRACT: After the discovery of the standard-model-like Higgs boson at the LHC, the structure of the Higgs sector remains unknown. We discuss how it can be determined by the combination of direct and indirect searches for additional Higgs bosons at future collider experiments. First of all, we evaluate expected excluded regions for the mass of additional neutral Higgs bosons from direct searches at the LHC with the 14 TeV collision energy in the two Higgs doublet models with a softly-broken $Z_2$ symmetry. Second, precision measurements of the Higgs boson couplings at future experiments can be used for the indirect search of extended Higgs sectors if measured coupling constant with the gauge boson slightly deviates from the standard model value. In particular, in the two Higgs doublet model with the softly-broken discrete symmetry, there are four types of Yukawa interactions, so that they can be discriminated by measuring the pattern of deviations in Yukawa coupling constants. Furthermore, we can fingerprint various extended Higgs sectors with future precision data by detecting the pattern of deviations in the coupling constants of the standard-model-like Higgs boson. We demonstrate how the pattern of deviations can be different among various Higgs sectors which predict the electroweak rho parameter to be unity; such as models with additional an isospin singlet, a doublet, triplets or a septet. We conclude that as long as the gauge coupling constant of the Higgs boson slightly differs from the standard model prediction but is enough to be detected at the LHC and its high-luminosity run or at the International Linear Collider, we can identify the non-minimal Higgs sector even without direct discovery of additional Higgs bosons at the LHC.
    06/2014;
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    ABSTRACT: We propose a new method to measure a theoretically well-defined top quark mass at the LHC. This method is based on the "weight function method" proposed in ref. [17]. It requires only lepton energy distribution and is basically independent of the production process of the top quark. We perform a simulation analysis of the top quark mass reconstruction with $t\overline{t}$ pair production and lepton+jets decay channel at the leading order. The estimated statistical error of the top quark mass is about 0.4 GeV with an integrated luminosity of 100 fb$^{-1}$ at $\sqrt{s}=14$ TeV. We also estimate some of the major systematic uncertainties and find that they are under good control.
    05/2014;
  • 04/2014;
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    Shinya Kanemura, Hiroshi Yokoya, Ya-Juan Zheng
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    ABSTRACT: We discuss complementarity of discovery reaches of heavier neutral Higgs bosons and charged Higgs bosons at the LHC and the International Linear Collider (ILC) in two Higgs doublet models (2HDMs). We perform a comprehensive analysis on their production and decay processes for all types of Yukawa interaction under the softly-broken discrete symmetry which is introduced to avoid flavour changing neutral currents, and we investigate parameter spaces of discovering additional Higgs bosons at the ILC beyond the LHC reach. We find that the 500 GeV run of the ILC with the integrated luminosity of 500 fb^{-1} shows an advantage for discovering the additional Higgs bosons in the region where the LHC cannot discover them with the integrated luminosity of 300 fb^{-1}. For the 1 TeV run of the ILC with the integrated luminosity of 1 ab^{-1}, production processes of an additional Higgs boson associated with the top quark can be useful as discovery channels in some parameter spaces where the LHC with the integrated luminosity of 3000 fb^{-1} cannot reach. It is emphasized that the complementary study at the LHC and the ILC is useful not only to survey additional Higgs bosons at the TeV scale, but also to discriminate types of Yukawa interaction in the 2HDM.
    04/2014;
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    Shinya Kanemura, Hiroshi Yokoya, Ya-Juan Zheng
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    ABSTRACT: We discuss complementarity of discovery reaches of heavier neutral Higgs bosons and charged Higgs bosons at the LHC and the International Linear Collider (ILC) in two Higgs doublet models (2HDMs). We perform a comprehensive analysis on their production and decay processes for all types of Yukawa interaction under the softly-broken discrete symmetry which is introduced to avoid flavour changing neutral currents, and we investigate parameter spaces of discovering additional Higgs bosons at the ILC beyond the LHC reach. We find that the 500 GeV run of the ILC with the integrated luminosity of 500 fb^{-1} shows an advantage for discovering the additional Higgs bosons in the region where the LHC cannot discover them with the integrated luminosity of 300 fb^{-1}. For the 1 TeV run of the ILC with the integrated luminosity of 1 ab^{-1}, production processes of an additional Higgs boson associated with the top quark can be useful as discovery channels in some parameter spaces where the LHC with the integrated luminosity of 3000 fb^{-1} cannot reach. It is emphasized that the complementary study at the LHC and the ILC is useful not only to survey additional Higgs bosons at the TeV scale, but also to discriminate types of Yukawa interaction in the 2HDM.
    Nuclear Physics B. 03/2014;
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    11/2013;
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    ABSTRACT: This report summarizes the work of the Energy Frontier Higgs Boson working group of the 2013 Community Summer Study (Snowmass). We identify the key elements of a precision Higgs physics program and document the physics potential of future experimental facilities as elucidated during the Snowmass study. We study Higgs couplings to gauge boson and fermion pairs, double Higgs production for the Higgs self-coupling, its quantum numbers and $C\!P$-mixing in Higgs couplings, the Higgs mass and total width, and prospects for direct searches for additional Higgs bosons in extensions of the Standard Model. Our report includes projections of measurement capabilities from detailed studies of the Compact Linear Collider (CLIC), a Gamma-Gamma Collider, the International Linear Collider (ILC), the Large Hadron Collider High-Luminosity Upgrade (HL-LHC), Very Large Hadron Colliders up to 100 TeV (VLHC), a Muon Collider, and a Triple-Large Electron Positron Collider (TLEP).
    10/2013;
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    ABSTRACT: The ILC Higgs White Paper is a review of Higgs Boson theory and experiment at the International Linear Collider (ILC). Theory topics include the Standard Model Higgs, the two-Higgs doublet model, alternative approaches to electroweak symmetry breaking, and precision goals for Higgs boson experiments. Experimental topics include the measurement of the Higgs cross section times branching ratio for various Higgs decay modes at ILC center of mass energies of 250, 500, and 1000 GeV, and the extraction of Higgs couplings and the total Higgs width from these measurements. Luminosity scenarios based on the ILC TDR machine design are used throughout. The gamma-gamma collider option at the ILC is also discussed.
    10/2013;
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    ABSTRACT: We propose a new method to measure various physical parameters, using characteristic weight functions. This method requires only lepton energy distribution and ideally it does not depend on the velocity of the parent particle. We demonstrate an application of this method by simulating a reconstruction of the Higgs boson mass in the H-> WW -> lnu lnu decay mode at the LHC. We show that systematic errors are suppressed compared to statistical errors. In the vector boson fusion channel, the statistical accuracy of the mass determination is estimated to be +12% and -14% at an integrated luminosity of 100fb^{-1}, assuming the Higgs boson mass to be 125GeV and root{s}=14TeV.
    Journal of High Energy Physics 05/2013; · 5.62 Impact Factor
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    Shinya Kanemura, Koji Tsumura, Hiroshi Yokoya
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    ABSTRACT: In the two Higgs doublet model, $\tan\beta$ is an important parameter, which is defined as the ratio of the vacuum expectation values of the doublets. We study how accurately $\tan\beta$ can be determined at linear colliders via the precision measurement of the decay branching fraction of the standard model (SM) like Higgs boson. Since the effective coupling constants of the Higgs boson with the weak gauge bosons are expected to be measured accurately, the branching ratios can be precisely determined. Consequently, $\tan\beta$ can be determined with a certain amount of accuracy. Comparing the method to those using direct production of the additional Higgs bosons, we find that, depending on the type of Yukawa interactions, the precision measurement of the decay of the SM-like Higgs boson can be the best way to determine $\tan\beta$, when the deviations in the coupling constants with the gauge boson from the SM prediction are observed at linear colliders.
    Physical review D: Particles and fields 05/2013; 88(5).
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    Shinya Kanemura, Kei Yagyu, Hiroshi Yokoya
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    ABSTRACT: When the doubly-charged Higgs bosons $H^{\pm\pm}$ mainly decay into the same-sign dilepton, a lower bound on the mass is around 400 GeV by the current LHC data. On the other hand, no such bound has been reported by using the data at LEP and at the LHC for the case where the same-sign diboson decay $H^{\pm\pm}\to W^{\pm(*)} W^{\pm(*)}$ is dominant. We study limits on the mass for such a case by using the current experimental data. From the precise measurement of the total width of the Z boson at the LEP experiment, the mass below 43 GeV is excluded with the 95% C.L. It turns out that the results from four charged lepton searches at LEP do not provide any significant constraint. We show that a new lower bound is obtained in the diboson decay scenario at the LHC with the collision energy to be 7 TeV and the integrated luminosity to be 4.7 fb$^{-1}$. By using the data of the same-sign dilepton events, the lower limit is found to be 60 GeV at the 95% C.L. By the extrapolation of the data to 20 fb$^{-1}$ with the same collision energy, the lower limit is evaluated to be 85 GeV.
    Physics Letters B 05/2013; · 4.57 Impact Factor
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    Mayumi Aoki, Shinya Kanemura, Hiroshi Yokoya
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    ABSTRACT: We study collider signatures for extra scalar bosons in the inert doublet model at the international linear collider (ILC). The inert doublet model is a simple extension of the standard model by introducing an additional isospin-doublet scalar field which is odd under an unbroken Z_2 symmetry. The model predicts four kinds of Z_2-odd scalar bosons, and the lightest of them becomes stable and a candidate of the dark matter as long as it is electrically neutral. Taking into account the constraints from various theoretical and phenomenological conditions, we perform a simulation study for the distinctive signatures of the extra scalars over the standard-model background contributions at the ILC with the center-of-mass energy of sqrt{s} = 250 GeV and 500 GeV. We further discuss observables for determination of the mass of the scalars. We find that the parameter regions which cannot be detected at the large hadron collider can be probed at the ILC.
    Physics Letters B 03/2013; 725(4-5). · 4.57 Impact Factor
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    ABSTRACT: We present search prospects and phenomenology of doubly resonant signals that come from the decay of a neutral weak-singlet color-octet vector state \omega_8 into a lighter weak-triplet color-octet scalar \pi_8, which can arise in several theories beyond the Standard Model. Taking m_{\omega_8}-m_{\pi_8}>m_W, we demonstrate an analysis of the signals pp \to \omega_8 \to \pi^\pm_8 W^\mp (\pi^0_8 Z) \to g W^\pm W^\mp (g Z Z). The present 8 TeV LHC run is found to have the potential to exclude or discover the signal for a range of masses and parameters. The preferred search channel has a boosted W-tagged jet forming a resonance with a second hard jet, in association with a lepton and missing energy.
    Physical review D: Particles and fields 08/2012; 86(7).
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    Hiroaki Sugiyama, Koji Tsumura, Hiroshi Yokoya
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    ABSTRACT: The doubly charged scalar boson (H^{\pm\pm}) is introduced in several models of the new physics beyond the standard model. The H^{\pm\pm} has Yukawa interactions with two left-handed charged leptons or two right-handed charged leptons depending on the models. We study kinematical properties of H^{\pm\pm} decay products through tau leptons in order to discriminate the chiral structures of the new Yukawa interaction. The chirality of tau leptons can be measured by the energy distributions of the tau decay products, and thus the chiral structure of the new Yukawa interaction can be traced in the invariant-mass distributions of the H^{\pm\pm} decay products. We perform simulation studies for the typical decay patterns of the H^{\pm\pm} with simple event selections and tau-tagging procedures, and show that the chiral structure of the Yukawa interactions of H^{\pm\pm} can be distinguished by measuring the invariant-mass distributions.
    Physics Letters B 07/2012; 717(s 1–3). · 4.57 Impact Factor
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    Shinya Kanemura, Koji Tsumura, Hiroshi Yokoya
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    ABSTRACT: We study the feasibility of the Type-X two Higgs doublet model (THDM-X) at collider experiments. In the THDM-X, new Higgs bosons mostly decay into tau leptons in the wide range of the parameter space. Such scalar bosons are less constrained by current experimental data, because of the suppressed quark Yukawa interactions. We discuss a search strategy of the THDM-X with multi-tau lepton final states at International linear collider and Large Hadron Collider. By using the collinear approximation, we show that a four tau lepton signature (e^+e^- -> HA -> 4\tau) can be a clean signal.
    01/2012;
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    Shinya Kanemura, Koji Tsumura, Hiroshi Yokoya
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    ABSTRACT: A detailed simulation study is performed for multi-tau-lepton signatures at the Large Hadron Collider, which can be used to probe additional Higgs bosons with lepton-specific Yukawa interactions. Such an extended Higgs sector is introduced in some of new physics models at the TeV scale. We here consider the two Higgs doublet model with the Type-X Yukawa interaction, where nonstandard Higgs bosons predominantly decay into tau leptons. These extra Higgs bosons can be pair produced via s-channel gauge boson mediation at hadron colliders; q \bar q \to Z \to HA and q \bar q' \to W^\pm \to HH^\pm (AH^\pm), where H, A and H^\pm are CP-even, odd and charged Higgs bosons, respectively. Consequently, multi-tau-lepton originated signals appear in the final state as a promising signature of such a model. We find that the main background can be considerably reduced by requiring the high multiplicity of leptons and tau-jets with appropriate kinematical cuts in the final state. Thus, assuming the integrated luminosity of a hundred of inverse fb, the excess can be seen in various three- and four-lepton channels. With the integrated luminosity of thousands of inverse fb, the determination of the mass as well as ratios of leptonic decay branching ratios of these Higgs bosons would also be possible.
    Physical review D: Particles and fields 11/2011; 85(9).
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    ABSTRACT: Current limits from the LHC on fourth generation quarks are already at the unitarity bound of 500 GeV or so. If they exist, the strong Yukawa couplings are turning nonperturbative, and may form bound states. We study the domain of mb′ and mt′ in the range of 500 to 700 GeV, where we expect binding energies are mainly of Yukawa origin, with QCD subdominant. To be consistent with electroweak precision tests, the t′ and b′ quarks have to be nearly degenerate, exhibiting a new “isospin.” Comparing relativistic expansion with a relativistic bound state approach, we find the most interesting is the production of a color octet, isosinglet vector meson (a “gluon-prime”) via qq̅ →ω8. Leading decay modes are π8±W∓, π80Z0, and constituent quark decay, with qq̅ and tt̅ ′ and bb̅ ′ subdominant. The color octet, isovector pseudoscalar π8 meson decays via constituent quark decay, or to Wg. These decay rates are parameterized by the decay constant, the binding energy and mass differences, and Vtb′. For small Vt′b, one could have a spectacular signal of WWg, where a soft W accompanies a very massive Wg pair. In general, however, one has high multiplicity signals with b, W, and t jet substructures that are not so different from the t′t̅ ′ and b′b̅ ′ search.
    Physical review D: Particles and fields 11/2011; 84(9).
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    Xiao-Gang He, German Valencia, Hiroshi Yokoya
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    ABSTRACT: We consider the phenomenology of CP violation in a color-octet extended scalar sector for t\bar{t} production and decay at the LHC. In particular we study the effect of the two neutral color-octet scalars S_I and S_R that occur in the model. There are two new sources of CP violation: a phase in the couplings of S_{I,R} to top-quarks; and two phases in the quartic couplings of the scalar potential. In resonant production of a single S_{I,R} followed by its decay into t\bar{t} pairs through the parton level process gg to S_{I,R} to t\bar{t}, we find large raw CP asymmetries which can reach 12%. These raw asymmetries are, of course, diluted by standard model (SM) t\bar{t} pairs making observation of CP violation contingent on whether the resonance itself can be extracted from the SM background.
    Journal of High Energy Physics 10/2011; · 5.62 Impact Factor
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    ABSTRACT: We propose a class of observables constructed from lepton energy distribution, which are independent of the velocity of the parent particle if it is scalar or unpolarized. These observables may be used to measure properties of various particles in the LHC experiments. We demonstrate their usage in a determination of the Higgs boson mass.
    Physics Letters B 07/2011; · 4.57 Impact Factor
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    ABSTRACT: The recent data on $W+$dijet excess reported by CDF may be interpreted as the associated production of a $W$ and a new particle of mass about 150 GeV which subsequently decays into two hadron jets. We study the possibility of explaining the $W+$dijet excess by colored scalar bosons. There are several colored scalars which can have tree level renormalizable Yukawa couplings with two quarks, $({\bf 8}, {\bf 2},1/2)$, $(\bar{\bf 6}({\bf 3}), {\bf 3}({\bf 1}), -1/3)$, $(\bar {\bf 6}({\bf 3}), {\bf 1}, -4/3(2/3))$. If one of these scalars has a mass about 150 GeV, being colored it can naturally explain why the excess only shows up in the form of two hadron jets. Although the required production cross section and mass put constraints on model parameters and rule out some possible scenarios when confronted with other existing data, in particular FCNC data, we find that there are strong constraints on the Yukawa couplings of these scalars. Without forcing the couplings to be some special texture forms most of the scalars, except the $({\bf 3}, {\bf 3}, -1/3)$, are in trouble with FCNC data. We also study some features for search of these new particles at the RHIC and the LHC and find that related information can help further to distinguish different models.
    Journal of High Energy Physics 05/2011; · 5.62 Impact Factor

Publication Stats

249 Citations
94.25 Total Impact Points

Institutions

  • 2013–2014
    • University of Toyama
      Тояма, Toyama, Japan
  • 2011–2012
    • National Taiwan University
      • Department of Physics
      T’ai-pei, Taipei, Taiwan
  • 2007–2011
    • CERN
      • Physics Department (PH)
      Genève, Geneva, Switzerland
  • 2006–2007
    • Niigata University
      • Department of Physics
      Niahi-niigata, Niigata, Japan
    • Stony Brook University
      • Institute for Theoretical Physics (C.N. Yang)
      Stony Brook, New York, United States
  • 2003–2005
    • RIKEN
      Вако, Saitama, Japan
  • 2002–2005
    • Hiroshima University
      Hirosima, Hiroshima, Japan