Z. Wa̧s

TAUOLA: A Library of Monte Carlo programs to simulate decays of polarized tau leptons

A library of Monte Carlo programs for leptonic and semileptonic decays of the τ lepton is presented. It provides final state with full topology including neutrinos, resonant distributions for intermediate particles and complete spin structure throughout the decay. The program is constructed in such a way that it can be easily attached to any Monte Carlo program simulating the production of τs. It contains subprograms simulating the following decay channels: τ± → vve±, vvμ±, vμ±, vϱ±, va±1, vK±, vK∗±, vnπ±,0, n > 3. The decay products are coded in the Lund format.

PHOTOS: A Universal Monte Carlo for QED radiative corrections in decays

Abstract In this paper we present an algorithm for the Monte Carlo simulation of QED single-photon radiative corrections in decays. The algorithm is implemented in an independent package written in FORTRAN 77. The program is universal, i.e. it allows for easy interfacing with “any” program generating decays of “any” particle. The program can be used to estimate the size of the QED bremsstrahlung in the leading-logarithmic (collinear) approximation. The proper soft-photon behavior is also reproduced. The program is designed such that the inclusion (if necessary) of the exact, process dependent, O (α) matrix element is possible and straightforward. The program provides final states with their full topology, including kinematical effects due to massive particles. For Z decays into pairs of light fermions, an extensive comparison of our algorithm with programs based on exact O (α) matrix elements was performed.

Initial state QED corrections to W-pair production at LEP2/NLC — Monte Carlo versus semi-analytical approach☆

Abstract We present a comparison of the Monte Carlo code KORALW with the SemiANalytical code KORWAN for W-pair production. We focus on the technical precision, total cross section and some differential distributions. We find the technical precision of KORALW in the LEP2 energy range to be of order 10−4 or better. We show that within the 0.1% precision level the O (α2) photonic corrections are not necessary in the YFS framework, at least for the total cross section. A detailed description of the semi-analytical formalism implemented in the KORWAN routine is also given.

Monte Carlo program BHLUMI 2.01 for Bhabha scattering at low angles with Yennie-Frautschi-Suura exponentiation

Abstract A Monte Carlo program for small-angle Bhabha scattering with an overall precision of 0.25% is presented. The QED calculation at this precision level is of vital importance for luminosity measurements at LEP/SLC experiments. BHLUMI is a stand-alone Monte Carlo event generator with three sub-generators: BHLUM2, LUMLOG and OLDBIS. The first of them is based on Yennie-Frautschi-Suura @(α) exponentiation and the two other ones serve, essentially, to cross-check results from the first one. LUMLOG represents pure leading-logarithmic calculation up to @( L 3 α 3 ) and OLDBIS represents ordinary (non-exponentiated) @(α) calculation. The important advantage of LUMLOG and OLDBIS is that they feature a very high technical precision of 0.02%. All three sub-generators form a very powerful tool box of programs for precise calculations of QED corrections to the luminosity measurements in present e ± annihilation experiments.

Upgrade of the Monte Carlo program BHLUMI for Bhabha scattering at low angles to version 4.04

Abstract The new version of the Monte Carlo program for small-angle Bhabha scattering BHLUMI with an overall precision of 0.11% is presented. The main improvements are in the matrix element of the main multi-photon sub-generator based on the Yennie—Frautschi—Suura exponentiation, where the missing second-order terms in the leading-logarithmic (LL) approximation are supplemented and the contribution from the Z resonance is improved. In the LUMLOG sub-generator based on the LL approximation, we implement collinear photon emission in the final state and we also add a down-graded third-order LL matrix element, which has exactly the same incomplete third-order LL contribution as the multi-photon BHLUMI. The new LUMLOG is therefore capable of calculating the missing third-order LL part in the cross sections obtained from the main multi-photon event generator, for arbitrary event selection. The first-order event generator OLDBIS remains unchanged.

The Monte Carlo event generator YFSWW3 version 1.16 for W-pair production and decay at LEP2/LC energies☆☆☆

Abstract We present the Monte Carlo event generator YFSWW3 version 1.16 for the process of W-pair production and decay in electron–positron collisions. It includes O (α) electroweak radiative corrections in the WW production stage together with the O (α 3 ) initial-state-radiation (ISR) corrections in the leading-logarithmic (LL) approximation, implemented within the Yennie–Frautschi–Suura (YFS) exclusive exponentiation framework. The photon radiation in the W decays is generated by the dedicated program PHOTOS up to O (α 2 ) LL, normalized to the W branching ratios. The program is interfaced with the τ decay library TAUOLA and the quark fragmentation/hadronization package JETSET . The semi-analytical code KorWan for the calculations of the differential and total cross-sections at the Born level and in the ISR approximation is included.

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

The version 1.51 of the Monte Carlo (MC) program KoralW for all e + e − ! f1 ¯ f2f3 ¯ f4 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.). The communication between KoralW and YFSWW3 is done with the help of the FIFO facility of the UNIX/Linux operating system. This does not require any modifications of the FORTRAN source codes. From the user’s point of view, the resulting Concurrent MC event generator KoralW&YFSWW3 looks as a regular single MC event generator with all the standard features.

Coherent exclusive exponentiation CEEX: The Case of the resonant e+ e- collision

Abstract We present the first-order coherent exclusive exponentiation (CEEX) scheme, with the full control over spin polarization for all fermions. In particular it is applicable to difficult case of narrow resonances. The resulting spin amplitudes and the differential distributions are given in a form ready for their implementation in the Monte Carlo event generator. The initial-final state interferences are under control. The way is open to the use of the exact amplitudes for two and more hard photons, using Weyl-spinor techniques, without giving up the advantages of the exclusive exponentiation, of the Yennie-Frautschi-Suura type.

Final-state radiative effects for the exactO(α)Yennie-Frautschi-Suura exponentiated (un)stableW+W−production at and beyond CERN LEP2 energies

We present the LL final state radiative effects for the exact O(alpha) YFS exponentiated (un)stable WW pair production at LEP2/NLC energies using Monte Carlo event generator methods. The respective event generator, version 1.12 of the program YFSWW3, wherein both Standard Model and anomalous triple gauge boson couplings are allowed, generates n(\gamma) radiation both from the initial state and from the intermediate W+ W- and generates the LL final state W decay radiative effects. Sample Monte Carlo data are illustrated.

KORALB version 2.1. An upgrade with the TAUOLA library of τ decays

Abstract An upgrade of the Monte Carlo program for τ pair production including τ mass, spin and QED ϕ (α) effects is presented. Its main feature is the interface to the new τ decay Monte Carlo library TAUOLA.