S. Jadach

The τ decay library TAUOLA, version 2.4

The τ decay library TAUOLA has been enriched. The present version of the program includes more than twenty decay channels, including: (a) leptonic modes τ- → nνe- → nνμ-(γ), (b) one-meson modes: νπ-, νK-, (c) t wo-meson modes: νπ- π0(ϱ-), νK0π- (K∗-), νK- π0(K∗-), (d) three-meson modes: νπ-2ν 0(a-1), ν2π-π+ (a-1), νK+ K- π-, ν K0K0π-, νK- K0π0, νK- π0π0, νK- π-π+, νK0π0π-, νηπ-π 0, (e) four-pion modes: νπ-3π0, ν2π-π+π0 (including the ωπ- contribution), (f) multi-pion modes: νnπ±,0 with n > 4, and finally the decay τ- → νπ- π0γ from the ω → πγ. Complete O(α) QED corrections are included in the leptonic decay channels, and for other decay channels an interface is provided to the PHOTOS Monte Carlo generator for approximate simulation of the QED corrections. An interface to the τ pair production generators KORALB and KORALZ is also included. Final-state MC events are coded in the common block proposed by the Particle Data Group.

The precision Monte Carlo event generator KK for two-fermion final states in e+e− collisions

We present the Monte Carlo event generatorKK version 4.13 for precision predictions of the Electroweak Standard Model for the process e C e !f N fCn , fD;;d;u;s;c;b, at centre-of-mass energies from lepton threshold to 1 TeV, that is for LEP, SLC, future Linear Colliders, b;c; -factories, etc. Effects due to photon emission from initial beams and outgoing fermions are calculated in QED up to second order, including all interference effects, within Coherent Exclusive Exponentiation (CEEX), which is based on Yennie‐Frautschi‐Suura exponentiation. Electroweak corrections are included in first order, with higher-order extensions, using the DIZET 6.21 library. Final-state quarks hadronize according to the parton shower model using JETSET. Beams can be polarized longitudinally and transversely. Decay of the leptons is simulated using the TAUOLA library, taking into account spin polarization effects as well. In particular the complete spin correlations density matrix of the initial-state beams and final state ’s is incorporated in an exact manner. Effects due to beamstrahlung are simulated in a realistic way. The main improvements with respect to KORALZ are: (a) inclusion of the initial‐final state QED interference, (b) inclusion of the exact matrix element for two photons, and (c) inclusion of the transverse spin correlations in decays (as in KORALB).

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.

BHWIDE 1.00: O(α) YFS exponentiated Monte Carlo for Bhabha scattering at wide angles for LEP1/SLC and LEP2☆

Abstract We present O (α) YFS exponentiated results for wide angle Bhabha scattering at LEP/SLC energies using a new Monte Carlo event generator BHWIDE 1.xx. Our calculations include two options for the pure weak corrections, as presented in Beenakker et al. and in Bohm et al. From comparison with the results of Beenakker et al., Montagna et al. and Cacciari et al., we conclude that the total precision of our BHWIDE results is 0.3% (0.5%) in the LEP1/SLC regime within ±100 MeV ( +2.75 −2.5 GeV ) of the Z peak. For LEP2, the corresponding precision is currently estimated at 1.5%; the latter could be improved if the data in LEP2 so require. Both precision tags represent clear improvements over what is currently available in the literature.

Toward a model independent analysis of electroweak data

Abstract We set the framework for a model-independent analysis of the data on electroweak precision tests. Starting from three basic observables, the mass ratio m w / m z , the Z partial width and the forward-backward asymmetry for changed leptons, we define three dimensionless parameters ϵ 1 , ϵ 2 and ϵ 3 which contain the snall radiative correction effects one is interested in, with large m t -effects only appearing in ϵ 1 . The results on the epsilons implied by the present experimental data are discussed as well as the predictions of the Standard Model, as functions of m t and m H , with special attention to evaluating the theoretical errors. We formulate a hierarchy of simple and general assumptions, valid in large classes of models, which are needed in order to relate the epsilons to an increasingly larger set of observables including the τ-polarisation asymmetry, the forward-backward asymmetry for the b-quark, deep inelastic neutrino scattering and atomic parity violation. Correspondingly the analysis of present data is performed in stages and the conclusions are examined at each stage. Finally the case of the Standard Model is recovered as a very relevant particular example.

Monte Carlo program KORALW 1.02 for W-pair production at LEP2NLC energies with Yennie-Frautschi-Suura exponentiation

Abstract The Monte Carlo program KORALW version 1.02 for W-pair production is presented. Its main features are: multiple initial state photonic radiation with finite transverse photon momenta generated according to the Yennie-Frautschi-Suura Monte Carlo technique and massive kinematics for all final particles. Matrix element features second-order leading-logarithmic initial-state QED corrections. The dedicated semi-analytical program KORWAN, with structure-function based leading-logarithmic initial-state photonic radiation up to third order, is also included in the distribution package.

Radiative corrections to muon pair and quark pair production in electron-positron collisions in the Z0 region

Abstract A calculation of first-order radiative corrections to the process e + e − → μ + μ − is presented, which is in particular applicable to the Z 0 region. The emphasis is on a detailed treatment of hard photon effects, which affect the size of the corrections in the Z 0 region considerably. The technique used is that of a Monte Carlo simulation of μ + μ − and μ + μ − γ events. In an appendix the generalization to quark pair production is presented.

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.

Monte Carlo program KoralW 1.42 for all four-fermion final states in e+e− collisions*

Abstract The Monte Carlo program KoralW version 1.42 is presented. It generates all four-fermion final states with multibranch dedicated Monte Carlo presamplers and complete, massive, Born matrix elements. The presamplers cover the entire phase space. Multiphoton bremsstrahlung is implemented in the ISR approximation within the YFS formulation with the O (α 3 ) leading-log matrix element. The anomalous WWV couplings are implemented in CC03 approximation. The standard decay libraries (JETSET, PHOTOS, TAUOLA) are interfaced. The semi-analytical CC03-type code KorWan for differential and total cross sections is included.