Publications (70)163.4 Total impact
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ABSTRACT: We derive a full formula for the energy level of a heavy quarkonium state identified by the quantum numbers $n$, $\ell$, $s$ and $j$, up to ${\cal O}(\alpha_s^5 m)$ and ${\cal O}(\alpha_s^5 m \log \alpha_s)$ in perturbative QCD. The QCD Bethe logarithm is given in a oneparameter integral form. The rest of the formula is given as a combination of rational numbers, transcendental numbers ($\pi$, $\zeta(3)$, $\zeta(5)$) and finite sums (besides the 3loop constant $\bar{a}_3$ of the static potential whose full analytic form is still unknown). A derivation of the formula is given.Nuclear Physics B. 08/2014; 
Article: Weight function method for precise determination of top quark mass at Large Hadron Collider
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ABSTRACT: We propose a new method to measure a theoretically welldefined 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; 
Article: Weight function method for precise determination of top quark mass at Large Hadron Collider
04/2014;  [Show abstract] [Hide abstract]
ABSTRACT: We report on a study of top pair production at the International Linear Collider (ILC) around center of mass energy (E$_{\rm CM}$) = 350 GeV using an ILD detector simulator based on the Detailed Baseline Design (DBD) configuration. Here we will report on a result of 6Jet final state, $t\ bar{t} \rightarrow bWbW \rightarrow bqqbqq$. A result for the 4Jet final state, $t\ bar{t} \rightarrow bWbW \rightarrow bqqbl\nu$, which has almost the same statics as that of the 6Jet final state will be included in the future. For an energy scan of 11 center of mass energy points (340  350GeV) and two beam polarization combinations (P($e^+,\ e^$) = ($\pm$0.3, $\mp$0.8)) with 10 fb$^{1}$ each, the statistical errors on the top quark Yukawa coupling, its mass and width are estimated. The results are $\delta y_t$ = 4.2%, $\delta m_t$ = 16 MeV in potential subtracted scheme (PS), and $\delta \Gamma_t$ = 21 MeV.10/2013;  [Show abstract] [Hide abstract]
ABSTRACT: We compute the energy levels of some of the lowerlying heavy quarkonium states perturbatively up to O(alpha_s^5*m) and O(alpha_s^5*m*log[alpha_s]). Stability of the predictions depends crucially on the unknown 4loop poleMSbar mass relation. We discuss the current status of the predictions with respect to the observed bottomonium spectrum.Physics Letters B. 09/2013;  [Show abstract] [Hide abstract]
ABSTRACT: We estimate the presently unknown constant in the 4loop relation between the quark pole mass and the MSbar mass, by requiring stability of the perturbative prediction for E_tot(r)=2m_pole+V_QCD(r) in the intermediatedistance region. The estimate is fairly sharp due to a severe cancellation between 2m_pole and V_QCD(r). This would provide a test, based on general properties of the gauge theory, for the size of ultrasoft contributions to V_QCD(r).Physics Letters B. 09/2013; 728.  [Show abstract] [Hide abstract]
ABSTRACT: Top quark production in the process $e^+e^ \rightarrow t\bar{t}$ at a future linear electron positron collider with polarized beams is a powerful tool to determine the scale of new physics. Studies at the $\ttbar$ threshold will allow for precise determination of the top quark mass in a well defined theoretical framework. At higher energies vector, axial vector and tensorial CP conserving couplings can be separately determined for the photon and the $Z^0$ component in the electroweak production process. The sensitivity to new physics would be dramatically improved w.r.t. to what expected from LHC for electroweak couplings.Nuclear Physics B  Proceedings Supplements 07/2013; · 0.88 Impact Factor  [Show abstract] [Hide abstract]
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  [Show abstract] [Hide abstract]
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  [Show abstract] [Hide abstract]
ABSTRACT: We present algorithms to evaluate two types of multiple sums, which appear in higherorder loop computations. We consider expansions of a generalized hypergeometrictype sums, $\sum_{n_1,...,n_N} [Gamma(a1.n+c1) Gamma(a2.n}+c2) ... Gamma(aM.n+cM)] / [Gamma(b1.n+d1) Gamma(b2.n+d2) ... Gamma(bM.n+dM)] x1^n1...xN^nN $ with $ai.n=\sum_{j=1}^N a_{ij}nj$, etc., in a small parameter epsilon around rational values of ci,di's. Type I sum corresponds to the case where, in the limit epsilon > 0, the summand reduces to a rational function of nj's times x1^n1...xN^nN; ci,di's can depend on an external integer index. Type II sum is a double sum (N=2), where ci,di's are halfintegers or integers as epsilon > 0 and xi=1; we consider some specific cases where at most six Gamma functions remain in the limit epsilon > 0. The algorithms enable evaluations of arbitrary expansion coefficients in epsilon in terms of Zsums and multiple polylogarithms (generalized multiple zeta values). We also present applications of these algorithms. In particular, Type I sums can be used to generate a new class of relations among generalized multiple zeta values. We provide a Mathematica package, in which these algorithms are implemented.Journal of Mathematical Physics 11/2012; 54(3). · 1.30 Impact Factor  [Show abstract] [Hide abstract]
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  [Show abstract] [Hide abstract]
ABSTRACT: 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 centerofmass energy of 500 GeV. The signal and background models incorporate the nonrelativistic QCD corrections which enhance the production cross section near the ttbar threshold. The e+e > t tbar H signal is reconstructed in the 6jet + lepton and the 8jet 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 MonteCarlo 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 ab1, 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%.Physical review D: Particles and fields 04/2011; 84(1).  [Show abstract] [Hide abstract]
ABSTRACT: A golden age for heavy quarkonium physics dawned a decade ago, initiated by the confluence of exciting advances in quantum chromodynamics (QCD) and an explosion of related experimental activity. The early years of this period were chronicled in the Quarkonium Working Group (QWG) CERN Yellow Report (YR) in 2004, which presented a comprehensive review of the status of the field at that time and provided specific recommendations for further progress. However, the broad spectrum of subsequent breakthroughs, surprises, and continuing puzzles could only be partially anticipated. Since the release of the YR, the BESII program concluded only to give birth to BESIII; the $B$factories and CLEOc flourished; quarkonium production and polarization measurements at HERA and the Tevatron matured; and heavyion collisions at RHIC have opened a window on the deconfinement regime. All these experiments leave legacies of quality, precision, and unsolved mysteries for quarkonium physics, and therefore beg for continuing investigations. The plethora of newlyfound quarkoniumlike states unleashed a flood of theoretical investigations into new forms of matter such as quarkgluon hybrids, mesonic molecules, and tetraquarks. Measurements of the spectroscopy, decays, production, and inmedium behavior of c\bar{c}, b\bar{b}, and b\bar{c} bound states have been shown to validate some theoretical approaches to QCD and highlight lack of quantitative success for others. The intriguing details of quarkonium suppression in heavyion collisions that have emerged from RHIC have elevated the importance of separating hot and coldnuclearmatter effects in quarkgluon plasma studies. This review systematically addresses all these matters and concludes by prioritizing directions for ongoing and future efforts.European Physical Journal C 10/2010; 71(2). · 5.25 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Based on a specific model with U(3) family gauge symmetry at $10^3$ TeV scale, we show its experimental signatures to search for. Since the gauge symmetry is introduced with a special purpose, its gauge coupling constant and gauge boson mass spectrum are not free. The current structure in this model leads to family number violations via exchange of extra gauge bosons. We investigate present constraints from flavor changing processes and discuss visible signatures at LHC and lepton colliders.Physics Letters B 07/2010; · 4.57 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: First we present a theoretical framework to compute the fully differential cross sections for the topquark productions and their subsequent decays at hadron colliders, incorporating the boundstate effects which are important in the t\bar{t} threshold region. We include the boundstate effects such that the cross sections are correct in the LO approximation both in the threshold and highenergy regions. Then, based on this framework we compute various kinematical distributions of top quarks as well as of their decay products at the LHC, by means of MonteCarlo eventgeneration. These are compared with the corresponding predictions based on conventional perturbative QCD. In particular, we find a characteristic boundstate effect on the (bW^+)(\bar{b}W^) doubleinvariantmass distribution, which is deformed to the lower invariantmass side in a correlated manner.Journal of High Energy Physics 07/2010; 2010(9). · 5.62 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We compute the full ${\cal O}(\alpha_s^4)$ and ${\cal O}(\alpha_s^4\log\alpha_s)$ corrections to the potential $V_R(r)$ between the static color sources, where $V_R(r)$ is defined from the Wilson loop in a general representation $R$ of a general gauge group $G$. We find a violation of the Casimir scaling of the potential, for the first time, at ${\cal O}(\alpha_s^4)$. The effect of the Casimir scaling violation is predicted to reduce the tangent of $V_R(r)/C_R$ proportionally to specific color factors dependent on $R$. We study the sizes of the Casimir scaling violation for various $R$'s in the case $G=SU(3)$. We find that they are well within the present bounds from lattice calculations, in the distance region where both perturbative and lattice computations of $V_R(r)$ are valid. We also discuss how to test the Casimir scaling violating effect. Comment: 20 pages, 7 figures.Nuclear Physics B 04/2010; · 4.33 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We compute the purely gluonic contribution to the static QCD potential at threeloop order. This completes computation of the static potential at this order.Physical Review Letters 03/2010; 104(11):112003. · 7.73 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Recently we have proposed mechanisms to explain origins of the charged lepton spectrum as well as Koide's mass formula, on the basis of U(3)\times O(3) family gauge symmetry. In this note, we review the basic ideas of these mechanisms. Without technical details, and adding some speculations, we give a sketch of the mechanisms, what the important points are and what assumptions are involved. We adopt a known scenario, in which the charged lepton spectrum is determined by the vacuum expectation value of a scalar field that takes values on 3by3 matrix. Within this scenario, we propose a mechanism, in which the radiative correction induced by U(3) family gauge interaction cancels the QED radiative correction to Koide's mass formula. We consider SU(9)\times U(1) symmetry broken down to U(3)\times O(3) symmetry. This leads to a potential model which predicts Koide's mass formula and the charged lepton spectrum consistent with the experimental values, by largely avoiding fine tuning of parameters. These are discussed within an effective theory, and we argue for its validity and usefulness.Journal of High Energy Physics 04/2009; · 5.62 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Koide's mass formula is an empirical relation among the charged lepton masses which holds with a striking precision. We propose a mechanism for cancelling the QED correction to Koide's formula. This is discussed in an effective theory with U(3) family gauge symmetry and a scenario in which this symmetry is unified with SU(2)_L symmetry at 10^210^3 TeV scale. Comment: 4 pages, no figure; v2: Minor modifications, comment added on anomalies, version to appear in Phys.Lett.BPhysics Letters B 12/2008; · 4.57 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We study boundstate effects on the production cross section in the threshold region at hadron colliders. The boundstate effects are important particularly at the LHC where the gluon fusion is the dominant subprocess. Due to the formation of resonances in the J=0 colorsinglet channel of and the large width of the top quark, the invariantmass distribution peaks at a few GeV below the threshold, and it is significantly enhanced over the naive NLO prediction until several GeV above the threshold. We present predictions of the invariantmass distribution which incorporate both the boundstate effects and initialstate radiations up to NLO. The boundstate effects would lead to a substantial deformation of topquark kinematical distributions in the threshold region.Physics Letters B 01/2008; · 4.57 Impact Factor
Publication Stats
1k  Citations  
163.40  Total Impact Points  
Top Journals
Institutions

1998–2013

Tohoku University
 Department of Physics
Japan 
Universität Heidelberg
 Institute of Theoretical Physics
Heidelberg, BadenWuerttemberg, Germany 
Karlsruhe Institute of Technology
 Institute of Theoretical Particle Physics
Karlsruhe, BadenWuerttemberg, Germany


2008

CERN
 Physics Department (PH)
Genève, GE, Switzerland


1993–1994

The University of Tokyo
 Department of Physics
Tokyo, Tokyoto, Japan
