The Monte Carlo program KoralW version 1.51 and the concurrent Monte Carlo KoralW&YFSWW3 with all background graphs and first-order corrections to W-pair production

Abstract

The version 1.51 of the Monte Carlo (MC) program KoralW for all e + e − → f 1f2 f 3f4 processes is presented. The most important change from the previous version 1.42 is the facility for writing MC events on the mass storage device and reprocessing them later on. In the reprocessing parameters of the Standard Model may be modified in order to fit them to experimental data. Another important new feature is the possibility of including complete O(α) corrections to doubleresonant W -pair component-processes in addition to all background (non-W W ) graphs. The inclusion is done with the help of the YFSWW3 MC event generator for fully exclusive differential distributions (event per event). Technically, it is done in such a way that YFSWW3 runs concurrently with KoralW as a separate slave process, reading momenta of the MC event generated by KoralW and returning the correction weight to KoralW. The latter introduces the O(α) correction using this weight, and finishes processing the event (rejection due to total MC weight, hadronization, etc. Nature of the physical problem:The precise study of W -pair production and decay at LEP2 requires both non-doubleresonant and O(α) corrections. So far each of these corrections is available as a separate Monte Carlo program and there is no Monte Carlo that could simulate in a complete way both effects at the same time. Such a MC event generator would be of importance for example for apparatus simulations or Monte Carlo based fits. The previous version of KoralW [1] included all non-double-resonant corrections to all double-resonant fourfermion processes in e + e − annihilation. The present version 1.51 allows, for the first time ever, the inclusion on an event-per-event basis of the respective O(α) corrections generated at the same time by the independently running Monte Carlo program YFSWW3 [2], as well as a reweighting of any earlier generated events with modified parameter sets. Method of solution:The Monte Carlo method used to simulate the all four-fermion final-state processes in the e + e − collisions in the presence of multiphoton initial-state radiation has not changed since version 1.42 [1]. Adding the O(α) corrections generated by YFSWW3 is done at the level of the UNIX/Linux operating system with the help of the FIFO mechanism ("named pipes"). Typical running time:Approximate times on a PC Pentium III @ 800 MHz for cuts as described in this article: 5 minutes per 1000 constant-weight CCall events (KoralW stand-alone) 50 minutes per 1000 constant-weight CCall events with the O(α) correction (the CMC KoralW&YFSWW3, max. weight for rejection increased by a factor 2).

α-Cluster States in Intermediate Mass Nuclei

“…We will follow the approach of Yennie, Frautschi and Suura in Ref. [35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54]. This choice is made possible by the formulation of Feynman for Einstein's theory, as the entire theory is a local, point particle field theory, albeit with an infinite number of interaction vertices.…”

“…When m = 0 and one wants to use dimensional regularization for the IR regime instead of mg, we normalize the propagator at a Euclidean point k 2 = 2 and use standard factorization arguments [107][108][109][110][111] to take the factorized result for B g from (48) as (49) In physical applications, such mass singularities are absorbed by the definition of the initial state "parton" densities and/or are canceled by the KLN theorem in the final state; we do not exponentiate them in the exactly mass less case.…”

“…[33,34], its extension to Monte Carlo event generators in Refs. [35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54], and the QCD and QED QCD exponentiation in Refs. [55][56][57][58][59][60][61][62][63][64][65], which are extensions of the YFS theory to non-Abelian gauge theories.…”

“…For the record, the results in Refs. [26][27][28][29][30][31][32][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54] have played significant roles in precision tests of SM physics.…”

Measurement of neutral-current four-fermion production at LEP2

“…For comparison to grc4f, EXCALIBUR [7] and KORALW [8] are also used to produce qqµ + µ − signal events.…”