Four-fermion Final States Research Articles

Anomalous four-fermion processes in electron-positron collisions

This paper studies the electroweak production of all possible four-fermion collisions with non-standard triple gauge boson couplings. All CP conserving couplings are considered. It is an extension of the methods and strategy, which were recently used for the Standard Model electroweak production of four-fermion final states. Since the fermions are taken to be massless the matrix elements can be evaluated efficiently, but certain phase space cuts have to be imposed to avoid singularities. Experimental cuts are of a similar nature. With the help of the constructed event generator a number of illustrative results is obtained for W-pair production. These show on one hand the distortions of the Standard Model angular distributions caused by either off-shell effects or initial state radiation. On the other hand, also the modifications of distributions due to anomalous couplings are presented, considering either signal diagrams or all diagrams.

On the determination of the trilinear boson couplings in [formula omitted] at LEPII

We present the full tree-order calculation of the process e +e − → ℓ ν ℓ q q′ including the width effects in a way which is consistent with gauge invariance and high-energy unitarity and which has a natural interpretation within standard perturbation theory. We also include C and P preserving deviations from Standard Model trilinear vector boson couplings. An analysis of the sensitivity of these channels on the trilinear couplings, using well measured angular variables of the four-fermion final state, is also presented.

Study of the four-fermion final state at the Z resonance

The process e+e−→, where l is a charged or a neutral lepton and f any charged fermion, is analyzed. The study uses the ALEPH data collected at LEP from 1989 to 1993 at centre-of-mass energies between 88 and 95 GeV, corresponding to almost two million hadronic Z decays and to a total integrated luminosity of 79 pb−1. For all channels, the data agree well with the standard model expectation both in shape and normalization. The indication of an excess in the\(e^ + e^ - \to \tau ^ + \tau ^ - f\bar f\) channel, reported by ALEPH in 1991, is not confirmed.

Semi-analytical approach to four-fermion production in e+e− annihilation

A study of the semi-analytical approach to four-fermion production in e + e − annihilation is presented. We classify all possible four-fermion final states and present results of new calculations for the ‘basic’ processes with the WW, ZZ, and ZH off-shell production together with some examples of ‘background’ processes. The Initial State Radiative corrections are included for the basic processes. Several numerical examples are given in the energy range from LEP 2 up to s = 1 TeV .

All electroweak four-fermion processes in electron-positron collisions

This paper studies the electroweak production of all possible four-fermion states in e + e − collisions. Since the methods employed to evaluate the complete matrix elements and phase space are very general, all four-fermion final states in which the charged particles are detected can be considered. Also all kinds of experimental cuts can be imposed. With the help of the constructed event generator a large number of illustrative results is obtained, which show the relevance of backgrounds to a number of signals. For LEP 200 the W-pair signal and its background are discussed, for higher energies also Z-pair and single W and Z signals and backgrounds are presented.