After the LHC restarted beam operations last week the physicists had at least one pleasant surprise. An unknown source of interference dubbed The Hump that had plagued the collider since December 2009 has vanished over the winter shutdown. The reason for its disappearance is as mysterious as its former existence. Nobody knows where it went or whether it will come back.
This is good news because the Hump had been quite a nuisance for the beam operators. When it was around it could destabilize the beam leading to diminished luminosity, or even an unwanted beam dump. Its failed appearance this year will help with the maximum collection of physics data.
Already the process of setting up the beam parameters for this year is well under way with the machine performing as well as it did last year. This year they want to increase the luminosity and that will require a tighter squeeze of the beams at the intersection points where the protons collide inside the detector experiments. Last year the squeeze was taken down to a beta* of 3.5m but this year they want to get it down to 1.5m. In plane terms that means an improvement by a factor of 3.5/1.5 in the amount of physics data that they can collect. The squeeze is a delicate process performed in a gradual reduction of beta*. The LHC is designed to ultimately reach a squeeze of 0.55m but that will only be possible at the design energy of 7TeV per proton. At the current operating energy of 3.5TeV per proton getting down to 1.5m is quite a challenge. In the first attempts last week the beams were lost at just below 2m. Another go at getting to 1.5m is planned for today.
Update: Rumours of the humps disappearance were premature. It suddenly switched back on. Looks like the time travelers had it switched off during the shutdown to minimise the chances of the source being discovered, but they were just a little slow turning it back on again. Must be a traffic jam in the wormhole.
Update (28 Feb 2011): The squeeze to 1.5m was successfully carried out on Saturday afternoon.