First beam is quickly approaching. For ATLAS. Actually several other experiments have already seen beam (it is hinted that CMS will see something today). But as ATLAS is the last experiment on the ring, it means that we have to wait until the 10th. It is annoying being the last on the ring sometimes.
For the 10th, the beam is only a single beam, so there will be no collisions. But it is still exciting all the same. And what can we expect to see in the detector with single beam? Two things.
One is ‘beam halo’ events. These are muons which have left the beam core and are moving along side the beam. The other is ‘beam gas interactions’ which are when one of the protons in the beam collides with some other particle in the beam pipe (the beam pipe is under vacuum but no vacuum is perfect). Even with these two types of events, we don’t expect to see a lot of hits in the detector. But even a few hits tells us a lot. Single beam is also very useful to help us establish our timing. This means determining when to read-out our electronics relative to when the beam bunch enters the detector. In other words, we won’t be sitting around, bored come Wednesday.
Someone once asked me what ATLAS planned to celebrate with. And the answer is… Champagne, of course. We even have it prepped and ready to go in control room (as seen here). The label reads ‘Break in case of collisions’. Not a problem.