T. Kaneko

Automatic Computation of Cross Sections in HEP Status of GRACE System

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.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.

Numerical calculation of Feynman amplitudes for electroweak theories and an application to e+e−→W+W−γ

The method for the numerical calculation of Feynman amplitudes developed in a previous paper is extended to the standard electroweak theory (Weinberg-Salam model). All possible types of vertices contained in this model are added in the program package. As an application, the tree-level cross section for the process e+e-→W+W-γ is calculated using the presented programs. Comparison of the results with those obtained by other methods is discussed in detail. From the integration of the squared amplitude over the phase space, the radiative correction of O(α) to the differential cross section is calculated.

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.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.

THE GRACE SYSTEM FOR THE MINIMAL SUPERSYMMETRIC STANDARD MODEL

Abstract The algorithm of constructing the Feynman amplitudes for the GRACE system is extended to processes involving supersymmetric particles. New vertex amplitude subroutines needed to compute these processes are now part of the CHANEL library.

Numerical Approach To Two-Loop Three Point Functions With Masses

Extending the method successful for one-loop integrals, the computation of two-loop diagrams with general internal masses is discussed. For the two-loop vertex of nonplanar type, as an example, we show a calculation related to

SUSY23 V2.0 : an event generator for supersymmetric processes at e+e- colliders

Z^0 \to t\bar t

AUTOMATIC CALCULATIONS IN HIGH ENERGY PHYSICS BY GRACE AND COMPHEP

vertex.

Lepton pair productions with double hard photon emission

Abstract S usy23 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. S usy23 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.

A multi-dimensional integration package for a vector processor

Ten three-body processes in e+e− collisions for heavy particle productions such as Higgs, t-quark, W± and Z0 are calculated by two independent computer codes for automatic calculation of Feynman amplitude. The results are in excellent agreement within statistical error of numerical integration (about 0.5%). This demonstrates that these systems are quite powerful for theoretical study for future e+e−, e±γ and γγ colliders. Numerical values of cross sections are summarized in tables and a figure.

SPIN AND SPIN–SPIN CORRELATIONS IN CHARGINO PAIR PRODUCTION AT FUTURE LINEAR e+e- COLLIDERS

Abstract Cross sections for lepton pair productions with double hard photon emission, e + e − → l + l − γγ , have been calculated based on the exact matrix element produced by the automatic amplitude generator GRACE. Differential cross sections versus the invariant mass of double photons are given under the set of generator-level cuts applied by the L3 experiment. Our results are also compared with those obtained by two Monte Carlo generators YFS3 and QEDPS which include multi-photon emission.