Angular distribution of decay leptons from e(+)e(-) -> W+W- at threshold

The reaction e(+)e(-) --> W+W- produces a W-boson pair with a non-trivial s pin correlation at threshold. This correlation leads to a characteristic an gular correlation between the leptons produced in W+/- --> l(+/-)v (angles relative to the e(-) beam direction): d sigma/dcos theta(+)dcos theta_ simi lar to (1 - cos theta(+))(1 + cos theta_)(1 + cos theta_cos theta(+)). If o nly the l(-) is observed, its angular distribution is d sigma/dcos theta_ s imilar to (1 + cos theta_)(3 - cos theta_), implying a forward-backward asy mmetry of 3/8. An analytic result is also given for the azimuthal correlati on. These results are reproduced by a Monte Carlo program, that also enable s us to study the effects of the W decay width. The threshold behaviour, wh ich stems from the dominance of v-exchange, is contrasted with that due to y- and Z-exchange, which is relevant for annihilation in the helicity state e(R)(-)e(L)(+). (C) 1999 Published by Elsevier Science B.V. All rights res erved.