LHC Report: Omnium-gatherum

The last couple of weeks have seen a mixed bag of special runs, luminosity production, machine development and down-time.

Van der Meer scans were performed for ATLAS, CMS and ALICE. These scans step the beams transversely across each other and aim at a measurement of the absolute luminosity. A precise determination of the luminosity uncertainty is beneficial for many physics analyses and, indeed, measurements of important physics processes (such as top quark pair production) can be limited by luminosity errors. The scans were ultimately successful but the set-up and execution were affected by a number of technical problems.

One of the main down-times was due to the replacement of an SPS dipole magnet which had developed a vacuum leak. A SPS magnet exchange is a well-practiced intervention. In this case, the whole exercise, including the pump down of the vacuum, took around 24 hours. There were also re-occuring problems with the fast switches of the SPS beam dump system. The LHC, as always, depends on the faultless operation of the rest of the accelerator complex. All of the machines are coming to the end of three long years of sustained operation with only short breaks for preventive maintenance.

A productive weekend delivered around 0.5 fb^-1 and led into a 3-day machine development programme. The programme included a proton-lead test in preparation for the run in the New Year, but mostly concentrated on characterization of the machine in view of post long shutdown operation.

by Mike Lamont for the LHC team