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Y. Kurihara

Publications and source records attributed to Y. Kurihara.

64 records · Page 4Linked to original sources
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

Polarization asymmetry and the Higgs boson production mechanisms

We calculate the cross section of Higgs boson production in the reaction e+e- -> neutrino anti-neutrino b b-bar for the case of left and right longitudinally polarized electron beam. Complete set of signal and irreducible background diagrams is considered. We propose a new critical test to identify the Higgs boson provided by the ratio of cross sections with left and right beam polarization. This quantity is sensitive to the ratio of Higgs-W and Higgs-Z couplings, since it exhibits the interplay of bremsstrahlung and fusion mechanisms of Higgs boson production inherent to the Standard Model scheme.

hep-ph↗
arXiv1996

Improved QEDPS for Radiative Corrections in e+e- Annihilation

The generator QEDPS, a parton shower model in QED, developed by the present authors has been improved. By a careful study on the shower algorithm it was found that some finite contributions have been missed in the original version. They are small, but cannot be neglected when the contribution of the soft photons is dominant. A method is presented to correct these finite pieces and then a new generator, improved QEDPS, is proposed, which is able to make more precise prediction for the processes observed in e+e- annihilation as far as the initial radiation is concerned.

hep-ph↗
arXiv1996

Test of QEDPS: A Monte Carlo for the hard photon distributions in e+ e- annihilation proecss

The validity of a photon shower generator QEDPS has been examined in detail. This is formulated based on the leading-logarithmic renormalization equation for the electron structure function and it provides a photon shower along the initial e+-. The main interest in the present work is to test the reliability of the generator to describe a process accompanying hard photons which are detected. For this purpose, by taking the HZ production as the basic reaction, the total cross section and some distributions of the hard photons are compared between two cases that these photons come from either those generated by QEDPS or the hard process e+e- -> H Z gamma gamma. The comparison performed for the single and the double hard photon has shown a satisfactory agreement which demonstrated that the model is self-consistent.

hep-ph↗
arXiv1996

WW Cross-sections and Distributions

We present the results obtained by the "WW Cross-sections and Distributions" working group during the CERN Workshop "Physics at LEP2" (1994/1995)

hep-ph↗
arXiv1995

Probing the HHH vertex in e+e-, e-gamma and gamma-gamma collisions for light and intermediate Higgs bosons

We have studied double Higgs production at future linear colliders while paying special attention to the option of high-energy and high-luminosity photon beams. The main purpose was to examine the feasibility of e+e-, e-gamma and gamma-gamma colliders in order to probe the anomalous triple Higgs coupling, which is crucial for understanding the Standard Model. We considered mainly the cases of light and intermediate Higgs bosons. Double Higgs production is almost background free, except in the MH=MZ mass range, which is discussed separately. It is shown that for a light Higgs boson the HHH coupling can be measured even at e+e- collider at 500 GeV. For a intermediate Higgs boson a collider in the TeV region is suitable for such an investigation. We have estimated the bounds on the anomalous HHH coupling, which can be experimentally established using future linear colliders.

hep-ph↗
arXiv1994

Transition radiation of the neutrino magnetic moment

If the neutrino has a finite mass and a magnetic moment it would produce transition radiation when crossing the interface between two media. We found that the probability of transition radiation is larger by an order of magnitude using the quantum theory than that recently reported by one of us using classical electrodynamics, and that the energy spectrum of the radiation is nearly uniform.

hep-ph↗
arXiv1994

$e^+ e^- \to e^- {\bar ν_e} u {\bar d}$ from LEP to linear collider energies

The complete tree level cross section for the process $e^+e^- \to e^- \barν_e u \bar{d}$ is computed using the GRACE system, a program package for automatic amplitude calculation. Special attention is brought to the gauge violation problem induced by the finite width of the $W$-boson. The {\it preserved gauge scheme} is introduced and an event generator which includes double-resonant, single-resonant and non-resonant diagrams with no need for a cut on the electron polar angle is presented. Since no cut needs to be applied to the electron, the generator can be used to estimate background for searches involving jets and missing energy. A monojet event rate estimation based on this process at LEP-I energy is discussed.

hep-ph↗
arXiv1994

Non-resonant diagrams in radiative four-fermion processes

The complete tree level cross section for $e^+e^- \to e^- \barν_e u \bar{d} γ$ is computed and discussed in comparison with the cross sections for $e^+e^- \to e^- \barν_e u \bar{d} $ and $e^+e^- \to \bar{u} d u \bar{d}$. Event generators based on the GRACE package for the non-radiative and radiative case are presented. Special interest is brought to the effect of the non-resonant 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\% ($e^- \barν_e u \bar{d}$) 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 non-resonant diagrams for the radiative channel reaches 42.5\%.

hep-ph↗