title: Observation of multichannel collisions of cold metastable calcium atoms.
abstract: Recent theoretical work indicates that collisions between metastable alkaline-earth atoms (AEAs) in the presence of external magnetic fields should be largely determined by partial waves with large angular momenta even at very low temperatures. Unusually large inelastic collision cross sections were predicted and doubts have been raised regarding the feasibility of evaporative cooling of metastable AEAs in magnetic traps. Here we present experimental data for 40Ca[4s4p]3 P2 clearly confirming the asserted multichannel character of the collision mechanism. While elastic cross sections are found to be similar to the predicted values, inelastic cross sections exceed the calculations by an order of magnitude. Our results substantiate the expectation of inefficient evaporative cooling.
authors.affiliation: Institut für Laser-Physik, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany. dhansen@physnet.uni-hamburg.de
authors.forename: Dirk
authors.initials: D
authors.lastname: Hansen
authors.forename: Andreas
authors.initials: A
authors.lastname: Hemmerich