Searcharxiv⌕ Search

arXiv subjects

K. Kato

Publications and source records attributed to K. Kato.

At least 73 records · Page 4Linked to original sources
arXiv2002

The QCD/SM Working Group: Summary Report

This Report documents the results obtained by the Working Group on Quantum ChromoDynamics and the Standard Model for the Workshop ``Physics at TeV Colliders'', Les Houches, France, 21 May - 1 June 2001. The account of uncertainties in Parton Distribution Functions is reviewed. Progresses in the description of multiparton final states at Next-to-Leading Order and the extension of calculations for precision QCD observables beyond this order are summarized. Various issues concerning the relevance of resummation for observables at TeV colliders is examined. Improvements to algorithms of jet reconstruction are discussed and predictions for diphoton and photon pi-zero production at the LHC are made for kinematic variables of interest regarding searches for a Higgs boson decaying into two photons. Finally, several improvements implemented in Monte-Carlo event generators are documented.

hep-ph↗
arXiv2002

The Metal-Insulator Transition in Y1-xCaxTiO3 Caused by Phase Separation

In order to explore the origin of the Metal-Insulator (M-I) transition, the precise crystal structures of the hole-doped Mott insulator system, Y1-XCaXTiO3 (x=0.37, 0.39 and 0.41), are studied for the temperature range between 20K and 300K by the synchrotron radiation (SR) X-ray powder diffraction. For both Y0.63Ca0.37TiO3 and Y0.61Ca0.39TiO3 compositions, the orthorhombic (Pbnm) - monoclinic (P21/n) structural phase transition occurs at around 230K, which is much higher than their own M-I transition temperatures, i.e. 60K and 130K, respectively. For these compositions, the significant phase separation (low-temperature orthorhombic + monoclinic) is also found in the vicinity of the M-I transition temperature. On the other hand, Y0.59Ca0.41TiO3, which dose not exhibit M-I transition and preserve a metallic behavior down to 1.5K, is in two phases state from 20K to 300K. It is concluded that the existence of the phase separation causes the M-I transition in Y1-xCaxTiO3, and the low-temperature orthorhombic phase contributes to the metallic property of this system.

cond-mat.str-el↗
arXiv2001

Spectrum of 10Be in the basis of the leading representation of the SU(3) group

A realization of the approximation of the SU(3) leading representation with the microscopic Hamiltonian and a nucleon-nucleon interaction is presented in detail. An effective Hamiltonian reproducing results of calculations with some known potentials is constructed. It is shown that its structure is quite similar to that of the triaxial rotator, and the wave functions in the Elliott's scheme are linear combinations of Wigner's D-functions although they should be properly normalized.

nucl-th↗
arXiv2001

Generic User Process Interface for Event Generators

Generic Fortran common blocks are presented for use by High Energy Physics event generators for the transfer of event configurations from parton level generators to showering and hadronization event generators.

hep-ph↗
arXiv2000

Fock-Bargmann space and classic trajectories

In recent years, a new approach to the theory of nuclear reactions leading to a break-down of the interacting subsytems into various channels has been developed. This approach was named the Antisymmetrized Molecular Dynamic (AMD), and its main idea lies in the description of the nucleons by wave packets in which the antisymmetrization effects (but not other quantum effects) are accounted for. In the present review, the basic principles of AMD are illustrated on the examples of simplest nuclear systems, and the results are compared with those provided by an exact quantum-mechanical description in the Fock-Bargmann space. The applicability region of AMD is discussed, in particular, in the cases of systems with discrete spectrum, and a relation between the classical AMD trajectories and the quantum distributions is established. At the same time, a new interpretation of Brink orbitals and Slater determinants built on them as eigenfunctions of the coordinate operator defined in the Fock-Bargmann space is proposed. It is shown that these functions form the cluster geometry of nuclear systems.

nucl-th↗
arXiv2000

QED Radiative Correction for the Single-W Production using a Parton Shower Method

A parton shower method for the photonic radiative correction is applied to the single W-boson production processes. The energy scale for the evolution of the parton shower is determined so that the correct soft-photon emission is reproduced. Photon spectra radiated from the partons are compared with those from the exact matrix elements, and show a good agreement. Possible errors due to a inappropriate energy-scale selection or due to the ambiguity of energy scale determination are also discussed, particularly for the measurements on triple gauge-couplings.

hep-ph↗
arXiv2000

Automatic Computation of Cross Sections in HEP

For the study of reactions in High Energy Physics (HEP) automatic computation systems have been developed and are widely used nowadays. GRACE is one of such systems and it has achieved much success in analyzing experimental data. Since we deal with the cross section whose value can be given by calculating hundreds of Feynman diagrams, we manage the large scale calculation, so that effective symbolic manipulation, the treat of singularity in the numerical integration are required. The talk will describe the software design of GRACE system and computational techniques in the GRACE.

hep-ph↗
arXiv2000

QCD

We discuss issues of QCD at the LHC including parton distributions, Monte Carlo event generators, the available next-to-leading order calculations, resummation, photon production, small x physics, double parton scattering, and backgrounds to Higgs production.

hep-ph↗
arXiv1999

QED Radiative Corrections to the Non-annihilation Processes Using the Structure Function and the Parton Shower

Inclusion of the QED higher order radiative corrections in the two-photon process, e+e- -> e+e- mu+mu-, is examined by means of the structure function and the parton shower. Results are compared with the exact $O(α)$ calculations and give a good agreement. These two methods should be universally applicable to any other non-annihilation processes like the single-W productions in the e+e- collisions. In this case, however, the energy scale for the evolution by the renormalization-group equation should be chosen properly depending on the dominant diagrams for the given process. A method to find the most suitable energy scale is proposed.

hep-ph↗
arXiv1999

Implementation of the Non-Linear Gauge into GRACE

A general non-linear gauge condition is implemented into GRACE, an automated system for the calculation of physical processes in high-energy physics. This new gauge-fixing is used as a very efficient means to check the results of large scale evaluation in the standard model computed automatically. We report on some systematic test-runs which have been performed for one-loop two-to-two processes to show the validity of the gauge check.

hep-ph↗
arXiv1999

Quantum Phase Transition of Randomly-Diluted Heisenberg Antiferromagnet on a Square Lattice

Ground-state magnetic properties of the diluted Heisenberg antiferromagnet on a square lattice are investigated by means of the quantum Monte Carlo method with the continuous-time loop algorithm. It is found that the critical concentration of magnetic sites is independent of the spin size S, and equal to the two-dimensional percolation threshold. However, the existence of quantum fluctuations makes the critical exponents deviate from those of the classical percolation transition. Furthermore, we found that the transition is not universal, i.e., the critical exponents significantly depend on S.

cond-mat.dis-nn↗
arXiv1997

susy23 v2.0: an Event Generator for Supersymmetric Processes at $e^+e^-$ Colliders

\susy23 is a Monte-Carlo package for generating supersymmetric (SUSY) processes at $e^+e^-$ colliders. Twenty-three types of SUSY processes with 2 or 3 final state particles at tree level are included in version 2.0. {\susy23} addresses event simulation requirements at $e^+e^-$ colliders such as LEP. Matrix elements are generated by GRACE with the helicity amplitude method for processes involving massive fermions. The phase space integration of the matrix element gives the total and differential cross sections, then unweighted events are generated. Sparticle widths and decay branching ratios are calculated. Each final state particle may then decay according to these probabilities. Spin correlations are taken into account in the decays of sparticles. Corrections of initial state radiation (ISR) are implemented in two ways, one is based on the electron structure function formalism and the second uses the parton shower algorithm called QEDPS. Parton shower and hadronization of the final quarks are performed through an interface to JETSET.

hep-ph↗
arXiv1997

Event Generators for WW Physics

The report summarizes the results of the activities of the Working Group on Event Generators for WW Physics at CERN during 1995.

hep-ph↗
arXiv1997

Automatic Calculation of Complete $O(α)$ Corrections to $e^+e^- \to W^+μ\barν_μ$

Using the automatic system GRACE-LOOP, the full $O(α)$ electroweak corrections has been calculated for the process $e^+e^- \to W^+μ\barν_μ$. The total correction to the cross section is found to be typically -6.4% at $\sqrt{s}=190$ GeV with $10^\circ$ cut on the muon angle from the beam, including the correction from the hard photon emission. It is observed that the correction is rather sensitive to the physical parameters. With the same conditions the correction corresponding to the real W-boson pair is -4.1% and hence the deviation is not negligible.

hep-ph↗
arXiv1996

On the asymptotical equations in the harmonic oscillator representation

In the harmonic oscillator representation, the Schrodinger equation has a form of a set of infinite number of algebraical equations which are labeled by the radial quantum number "n". It is shown that at n>>1 these equations are significantly simplified and become an algebraical analogue of the original differential Schrodinger equation. This result is generalized to the case of multi-channel systems being studied in the framework of the resonating group method.

nucl-th↗
arXiv1996

grc4f v1.0: a Four-fermion Event Generator for e+e- Collisions

grc4f is a Monte-Carlo package for generating e+e- to 4-fermion processes in the standard model. All of the 76 LEP-2 allowed fermionic final state processes evaluated at tree level are included in version 1.0. grc4f addresses event simulation requirements at e+e- colliders such as LEP and up-coming linear colliders. Most of the attractive aspects of grc4f come from its link to the GRACE system: a Feynman diagram automatic computation system. The GRACE system has been used to produce the computational code for all final states, giving a higher level of confidence in the calculation correctness. Based on the helicity amplitude calculation technique, all fermion masses can be kept finite and helicity information can be propagated down to the final state particles. The phase space integration of the matrix element gives the total and differential cross sections, then unweighted events are Generated. Initial state radiation (ISR) corrections are implemented in two ways, one is based on the electron structure function formalism and the second uses the parton shower algorithm called QEDPS. The latter can also be applied for final state radiation (FSR) though the interference with the ISR is not yet taken into account. Parton shower and hadronization of the final quarks are performed through an interface to JETSET. Coulomb correction between two intermediate W's, anomalous coupling as well as gluon contributions in the hadronic processes are also included.

hep-ph↗
arXiv1996

QCD Event Generators

This report is a survey on QCD Event Generator issues of relevance for LEP 2. It contains four main sections: a summary of experience from LEP 1, extrapolations to LEP 2 energies, Monte Carlo descriptions and standardization issues.

hep-ph↗