Publications (19)50.3 Total impact
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ABSTRACT: The highluminosity e+e− linear collider has been studied as an energy frontier future project in high energy physics, and is expected to be a good place for the precision experiments. The highluminosity e+e− linear collider no longer produces a monochromatic energy spectrum in the center of mass system, but a continuous and rather broad energy spectrum due to beamstrahlung of colliding e+ and e− beams. Without precise knowledge of this energy spectrum alias the luminosity spectrum, the precision experiment in the linear collider should be confronted with a crucial problem. A statistical method based on new developments in information technology is examined with a view of determining the luminosity spectrum. A statistical model is formulated and a likelihood fitting is carried out to determine the luminosity spectrum by using Bhabha events. The e+ and e− beam parameters, describing the luminosity spectrum, can be determined with an uncertainty of several percent by using 10 k Bhabha events under an ideal detector condition. 
Article: GRACE/SUSY: Automatic generation of tree amplitudes in the minimal supersymmetric standard model
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ABSTRACT: GRACE/SUSY is a program package for generating the treelevel amplitude and evaluating the corresponding cross section of processes of the minimal supersymmetric extension of the standard model (MSSM). The Higgs potential adopted in the system, however, is assumed to have a more general form indicated by the twoHiggsdoublet model. This system is an extension of GRACE for the standard model (SM) of the electroweak and strong interactions. For a given MSSM process the Feynman graphs and amplitudes at treelevel are automatically created. The Monte Carlo phase space integration by means of BASES gives the total and differential cross sections. When combined with SPRING, an event generator, the program package provides us with the simulation of the SUSY particle productions.  [Show abstract] [Hide abstract]
ABSTRACT: A new method to construct eventgenerators based on nexttoleading order QCD matrixelements and leadinglogarithmic parton showers is proposed. Matrix elements of loop diagram as well as those of a tree level can be generated using an automatic system. A soft/collinear singularity is treated using a leadinglog subtraction method. Higher order resummation of the soft/collinear correction by the parton shower method is combined with the NLO matrixelement without any doublecounting in this method. An example of the event generator for DrellYan process is given for demonstrating a validity of this method. Comment: 18 pages, 6 figures, version 2: update reference [13]  [Show abstract] [Hide abstract]
ABSTRACT: With an integrated software package {\tt GRACE}, it is possible to generate Feynman diagrams, calculate the total cross section and generate physics events automatically. We outline the hybrid method of parallel computation of the multidimensional integration of {\tt GRACE}. We used {\tt MPI} (Message Passing Interface) as the parallel library and, to improve the performance we embedded the mechanism of the dynamic load balancing. The reduction rate of the practical execution time was studied.  [Show abstract] [Hide abstract]
ABSTRACT: 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.  [Show abstract] [Hide abstract]
ABSTRACT: SUSY23 is a MonteCarlo package for generating supersymmetric (SUSY) processes at e+e− colliders. Twentythree 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.  [Show abstract] [Hide abstract]
ABSTRACT: SUSY23 is a Monte Carlo package for generating supersymmetric (SUSY) processes at e + e  colliders. Twentythree 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. 


Article: e+e> bbud with a tt production
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ABSTRACT: The cross section of e+e>bb¯ud¯μ ν¯μ process with a complete set of tree diagrams, 232 diagrams in the unitary gauge, was calculated at the energy range of sqrt(s)=340500 GeV by using GRACE system. A main contribution to the cross section comes from tt¯ production, where t and t¯ decay into bud¯ and b¯μν¯μ, respectively. It was found that the interference between the diagrams with tt¯ production and those with singlet through WW pair production amounts to 10% at the tt¯ threshold energy region. In the energy region above twice of the top quark mass, more than 95% of the cross section comes from the tt¯ diagrams. 
Article: Event Generators for WW Physics
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ABSTRACT: The report summarizes the results of the activities of the Working Group on Event Generators for WW Physics at CERN during 1995.  [Show abstract] [Hide abstract]
ABSTRACT: The cross section of $e^+e^ \to b \bar{b} u \bar{d} \mu^ \bar{\nu}_\mu$ process with a complete set of tree diagrams, 232 diagrams in the unitary gauge, was calculated at the energy range of $\sqrt{s}$ = 340  500 GeV by using GRACE system. A main contribution to the cross section comes from $t\bar{t}$ production, where $t$ and $\bar{t}$ decay into $bu\bar{d}$ and $\bar{b} \mu^ \bar{\nu}_{\mu}$, respectively. It was found that the interference between the diagrams with $t\bar{t}$ production and those with single$t$ through $ WW $ pair production amounts to 10% at the $t \bar{t}$ threshold energy region. In the energy region above twice of the top quark mass, more than 95% of the cross section comes from the $t\bar{t}$ diagrams. Comment: 17 pages, 8 PostScript figures, LateX; To appear in Phys. Lett. B  [Show abstract] [Hide abstract]
ABSTRACT: grc4f is a Monte Carlo package for generating e+e−→4fermion processes in the standard model. All of the 76 LEP2 allowed fermionic final state processes evaluated at tree level are included in version 1.1 grc4f addresses event simulation requirements at e+e− colliders such as LEP and upcoming 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. 
Article: PVMGRACE
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ABSTRACT: We have implemented PVM in GRACE: an automatic Feynman diagram computation package, to benefit from the available CPU power distributed over a cluster of workstations as well as from a massive parallel machine. It is clearly shown that PVMGRACE gives excellent performance in terms of reduction of elapsed time when the network overhead is kept small as compared to the processing time.  [Show abstract] [Hide abstract]
ABSTRACT: Review of Monte Carlo event generators for signals of new particles at LEP2. The areas covered include SUSY, HIGGS and Leptoquarks. 
Conference Paper: Running PVMGRACE on Workstation Clusters.
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ABSTRACT: We have implemented PVM in GRACE: an automatic Feynman diagram computation package to benefit from the available cpu power distributed over a cluster of workstation. It is clearly shown that PVMGRACE gives excellent results in term of reduction of elapsed time when the network overhead is kept small as compared to the processing time. 
Article: Standard Model Processes at LEP2
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ABSTRACT: We present the results obtained by the Standard Model Process group in the CERN Workshop "Physics at LEP2" (1994/95).  [Show abstract] [Hide abstract]
ABSTRACT: The complete tree level cross section for $e^+e^ \to e^ \bar\nu_e u \bar{d} \gamma$ is computed and discussed in comparison with the cross sections for $e^+e^ \to e^ \bar\nu_e u \bar{d} $ and $e^+e^ \to \bar{u} d u \bar{d}$. Event generators based on the GRACE package for the nonradiative and radiative case are presented. Special interest is brought to the effect of the nonresonant diagrams overlooked so far in other studies. Their contribution to the total cross section is presented for the LEP II energy range and for future linear colliders ($\sqrt s$ =500 GeV). Effects, at the W pair threshold, of order 3\% ($e^ \bar\nu_e u \bar{d}$) and 27\% ($\bar{u} d u \bar{d}$) are reported. Similar behaviour for the radiative case is shown. At $\sqrt s$ = 500 GeV, the relative contribution of the nonresonant diagrams for the radiative channel reaches 42.5\%. Comment: 6 pages, latex, KEKCP015, KEK Preprint 9446, LAPPExp.94.09
Publication Stats
418  Citations  
50.30  Total Impact Points  
Top Journals
Institutions

2007

The Graduate University for Advanced Studies
 School of High Energy Accelerator Science
Миура, Kanagawa, Japan


19972002

High Energy Accelerator Research Organization
 Institute of Particle and Nuclear Studies
Tsukuba, Ibaraki, Japan
