Observation of the p-wave shape resonance in atom-molecule collisions

We observe a p-wave resonance in the collisions between metastable neon and rovibrationally ground state HD molecules at a collision energy of kB x 22 mK. This is the first observation of the lowest quasibound angular momentum state in molecular collisions. This measurement was enabled by the reduction of the lowest collision energy achieved without laser cooling, using the phase-space correlation in cold molecular beams. We demonstrate that contrary to higher l-state resonances, the p-wave resonance allows sensitive probing of the leading term of the van der Waals intermolecular interaction. Furthermore, the same sensitivity to the long range part of the interaction potential allows an accurate estimation of p-wave resonance lifetime using only fundamental constants and the dispersion coefficient.