Closing in on dark matter

By Matin Durrani

The physics blogosphere has been wild with rumour in recent days that researchers in the Cryogenic Dark Matter Search (CDMS) in the US may have obtained the first direct evidence for dark matter in the form of Weakly Interacting Massive Particles.

The CDMS group gave simultaneous lectures at SLAC and Fermilab late on Thursday evening UK time that would, or would not, announce major new findings, depending on whose blog you read.

My colleague Michael Banks has been listening in to the webcasts and e-mailed me to say that “the outcome is that it is not conclusive evidence of dark matter, but they did have two events on a background of 0.5… so some signal, but not the five events needed for a discovery”.

An arXiv paper on the new results should be there by early morning.

It appears, Michael tells me, that the first event was detected on 27 October 2007, with a recoil energy of roughly 12 keV, and the second was seen earlier that year at roughly 15 keV. A third event lies just outside their box with recoil of 12 keV. Apparently this gives the lower bound on the WIMP mass for these recoil energies as roughly 0.5 GeV.

CDMS has a neat summary here. This is the key sentence: “We estimate that there is about a one in four chance to have seen two backgrounds events, so we can make no claim to have discovered WIMPs.”

We’ll have more on this later in our news channel so stay tuned. In the meantime,
Cosmic Variance has been doing a live blog, which has lots of as-it-happens stuff to get stuck into to.