My take: No conclusive discovery of dark matter, but we couldn’t realistically expect that anyway. However, there are two events that, while not definitively dark matter, can’t be ruled out either. The announcement wasn’t earth-shattering, but it was nonetheless exciting. It was cool for me to be in on what may be the early stages of a big and important discovery, both by watching the announcement live and by being at the institution that hosts the experiment.
My semester is over, so I’m at home, sitting on my couch, watching the CDMS talk streaming live. Here’s some of my thoughts as I watch:
4:11 CDT — Talk starts with an overview of dark matter. First detected by strange behavior in galaxies — gravity of stars and other visible matter alone cannot explain the motion. Dark matter is probably made of particles, not a modified form of gravity.
4:13 — Feed is lagging, but doesn’t look like anything is getting cut out, it’s just choppy.
4:15 — Spherical cow model!
4:17 — Discussing the challenges for detection. Need a low background, which is why it’s deep underground in an abandoned mine. Also, neutrons can look like WIMPS (Weakly Interactive Massive Particles, the candidates for dark matter being searched for here).
4:19 — One of my favorite terms — fiducial volume. It basically means the effective volume of the detector, where they can trust data points that seem to originate there.
4:23 — Wonder how many people are trying to watch this stream. It seems like Kavli Institute doesn’t have the infrastructure to handle the size of their audience.
4:26 — FYI The Soudan Mine, in northern Minnesota, is also home to another major particle physics experiment — MINOS, which is measuring neutrino oscillations in the neutrino beam sent from Fermilab, just outside Chicago. The size difference between the detectors is almost comical: CDMS has several small detectors that can be held in the hand. (Each detector is about 300 grams. There are 30 detectors in five towers.) MINOS has a 980-ton detector made of iron.
4:31 — Talking about results now! Background is about .6 events
4:33 — Opening the box….and the feed completely cuts out! Is this all a hoax? (lol, this is a joke.)
4:35 — Looks like the number of events is…. 2! Paper will be on the ArXiv tonight.
4:37 — Discussion of the two events… time of nearly ideal detector performance. Occurred on different detectors on different towers, several months apart. Happened on their inner towers, where they feel their statistics are better. Phonon data looks good, but “charge start time” (not sure what that is) might be a problem on one of the events.
4:40 — Charge start time, I think means when they see the shower of electrons at the detector. For one of the events, this might have been too soon.
4:41 — From what I understand, they estimate a 23% chance that this signal is just due to background events.
4:42 — They cannot call it significant evidence of dark matter, but they can’t reject either event as not being dark matter. In other words, it’s not necessarily dark matter, but they can’t say for sure that it isn’t.
4:44 — Now talking about the next step: SuperCDMS. Installation and commissioning will start summer 2010 in the Soudan site in northern MN. Eventual goal is to get SuperCDMS SNOLab, at the Sudbury Neutrino Observatory (SNO) in western Canada.
4:48 — Summary: cross section limit is less than 3.8 x 10^-44 cm^2 for WIMP mass of 70 GeV at 90% confidence.
4:54 — Q&A session now. Feed cut out again. Probably not worth the aggravation for me to hang around. Thanks for following along!