ON THE IDENTIFICATION OF THE TRIANGLE MECHANISM WITH PION EXCHANGE

The triangle graph with pion exchange is presently widely used for the description of various processes with large momentum transfer. Here i t is shown that this mechanism can be reliably identified by observing the picture corresponding to so called moving complex triangle singul arities: the position and the width of the peak in the invariant mass distribution of several final particles must distinctly vary with thre e-momentum transfer from initial fast particle to final one. Furthermo re, this procedure gives a simple method to determine the mass of the meson, the exchange of which gives the main contribution to the cross section of the process. These statements are illustrated on an example of the near-threshold eta-meson production in the channel pd --> pd e ta. (C) 1998 Elsevier Science B.V. All rights reserved.