A method for "on-line" determination of beam-jet overlaps; application to cluster fragmentation studies

We present a method for determination of beam-jet overlaps in crossed-beam experiments (particle beam-molecular beam). This quantity, necessary for ex tracting absolute values of collisional cross sections, is difficult to det ermine and most of the experimentalists use normalization procedures or rel y on calculations. In the present method, essentially experimental, there i s no need to know precisely either the beam or local jet characteristics, t he only requirement being to have a beam smaller than the jet's dimensions. It is an "on-line" method, then allowing beam-jet overlaps under the exact conditions of the experiments to be determined; in that respect, it may be a useful tool for all accelerator-based experiments. We have shown, throug h detailed experiments, that the theoretical part entering in the determina tion could be confidently predicted. The method was applied mostly to the d etermination of beam-jet overlaps in cluster-atom collision studies and in the particular conditions of a beam passing very near the jet's capillary e xit. In this special situation, we could prove the applicability of the met hod as well. (C) 2000 American Institute of Physics. [S0034-6748(00)02705-2 ].