These last three weeks have been very intense and eventful in the home front. In the meanwhile, back at work, and besides the usual research work, I’ve been taking care of what it’s called “run monitoring.”
In a perfect world, once you’re done building a complex detector like IceCube your problems should be over, and you could take data without caring for how the apparatus is doing 1.5 km below the South Pole surface. Unfortunately, that’s not the world we live in.
On a daily basis, we have to make sure that each of the 5160 light sensors (aka DOMs, for Digital Optical Modules) deployed in the deep ice are working and doing fine, and for that we have a very nice monitoring system that can spot most problems automatically.
I’m showing below a screenshot of the monitoring system that shows the frequency with which each DOM saw light. Each little square is a DOM, blue indicating a lower rate of detection, and yellow-ish a higher one. Black DOMs were not taking data at that moment. Depth increases towards the bottom of the image. An interesting feature of this image is the blue horizontal band of DOMs in the middle of the image, which shows that DOMs at that depth record muon events systematically less often than the rest. This is not a detector issue, but a geological feature about 65000 years old that corresponds to a stadial (or cold period) during the last glacial period in the late Pleistocene where a lot of dust seems to have deposited in the then surface of the Antarctic ice. Weaker layers are seen in the upper part of the detector as well. Due to the high dust concentration light can’t propagate too far in the ice without being absorbed, causing the observed decrease in the DOM detection rate.
The detection rate for each DOM in a section of IceCube. Depth increases towards the bottom of the image, with DOMs beginning at 1.5 km deep at the top and ending at 2.5 km in the bottom.
A data-taking period (or “run”) is usually 8 hours long, during which IceCube records about 2000 muons going though the detector per second. It would be great if all these muons were associated with neutrinos of astrophysical origin, but most of them come from well-known cosmic rays hitting the Earth’s atmosphere.
Every second Mother Nature gives IceCube about 2000 more muons to chew on.
Most of the runs that I had to monitor were perfectly fine. With an uptime of 98% IceCube (now running on its final configuration) is doing great, and I’m sure that we’ll have more interesting results in the future with more data coming.
