CDMS is an experiment located underground in the Soudan mine in Minnesota. It consists of two dozens of germanium and silicon ice-hockey pucks cooled down to 40 mK. When a particle hits the detector it produces both phonons and ionization, and certain tell-tale features of these two signals allow the experimenters to sort out electron events (expected to be produced by mundane background processes) from nuclear recoils (expected to be produced by scattering of dark matter particles, as the apparatus is well shielded from ordinary nucleons). The last analysis, published early 2008, was based on a data set collected in the years 2006--2007. After applying blind cuts they saw zero events that look like nuclear recoils, which allowed them to set the best limits so far on the scattering cross section of a garden variety WIMP (for WIMPs lighter than 60 GeV the bounds from another experiment called XENON10 are slightly better).
By now CDMS must have acquired four times more data. The new data set was supposed to be unblinded some time last autumn, and the new improved limits should have been published by now. They were not.
- Fact #1: CDMS submitted a paper to Nature, and they were recently accepted. The paper is embargoed until December 18 (embargo is one of these relics of the last century that somehow persists until today, along with North Korea and Michael Jackson fans) - the collaboration is not allowed to speak publicly about its content. Consequently, CDMS has canceled all seminars scheduled before December 18.
- Fact #2: A film crew that was supposed to make a reportage from unblinding the CDMS data was called off shortly before the scheduled date. They were told to come back in January, when the unblinding will be restaged.
- Theory #1: The common lore is that particle physics papers appearing in Nature (the magazine, not the bitch) are those claiming a discovery. It is not at all impossible that the new data set contains enough events for an evidence or even a discovery. If the zero events in the previous CDMS paper was a downward fluke, several WIMP events could readily occur in the new data. Furthermore, in some fancy theories like inelastic dark matter, a large number of WIMP scattering events is conceivable because the new data were collected in summer when the wind is favorable.
- Theory #2: Data-starved particle theorists once again are freaking out for no reason. There is no discovery; CDMS will just publish their new, improved bounds on the scattering cross section of dark matter. CDMS is acting strangely because they want to draw attention: the experimental community is turning toward noble liquid technologies and funding of solid-state detectors like the one in CDMS is endangered.
Important update: I just received this in an email:
It is still true that the new CDMS data are scheduled to be released on December 18th, and there will be presentations in a number of labs around the world. But if there's no Nature paper then theory #2 becomes far more likely.I was alerted to your blog of yesterday (you certainly don't make contacting you easy). Your "fact" #1, that Nature is about to publish a CDMS paper on dark matter, is completely false. This would be instantly obvious to the most casual observer because the purported date of publication is a Friday, and Nature is published on Thursdays. Your "fact" therefore contains as much truth as the average Fox News story, and I would be grateful if you would correct it immediately. Your comments about the embargo are therefore, within this context, ridiculous. Peer review is a process, the culmination of which is publication. We regard confidentiality of results during the process as a matter of professional ethics, though of course authors are free to post to arxiv at any point during the process (we will not interfere with professional communication of results to peers). Dr Leslie Sage Senior editor, physical sciences Nature