Listening for Dark Matter


The COUPP program puts a new twist on an old technology, bubble chambers, to search for dark matter. Recently, COUPP has been able to discriminate between potential dark matter signals and one of the most troublesome backgrounds, alpha decays, by listening to the sound of bubble formation – alphas are louder. Results showing this effect and setting new limits on dark matter interactions were published in January (PRL, 106, 021303). The COUPP-4 chamber is now operating in an underground lab called SNOLAB with better than 98% rejection of alpha backgrounds. The figure above shows this discrimination – the Acoustic Parameter is a measure of the loudness of a bubble, with the red population representing what a dark matter particle would sound like and the blue population representing largely alpha events. When the current run finishes, the COUPP program will have taken another big step forward in sensitivity to dark matter.

– Hugh Lippincott