LHC Report: A new luminosity record
After about one month of operation, the LHC has already accumulated an integrated luminosity of 28 pb-1, which corresponds to over 50% of the total delivered to the experiments in 2010. This impressive start to the LHC run in 2011 bodes well for the rest of year.
Following careful collimator set-up and validation, the first phase of beam commissioning 2011 has come to an end. The first stable beams were declared on Sunday 13 March with a moderate 3 bunches per beam and an initial luminosity of 1.6 × 1030 cm-2s-1. Machine protection tests continued during the following week as the commissioning team made absolutely sure that all critical systems (beam dumps, beam interlock system, etc.) were functioning properly.
When these tests had finished, the way was opened to increased intensity and the LHC quickly moved through the first part of its planned, staged intensity increase. Fills with increasing numbers of bunches were delivered to the experiments, culminating in a fill with 200 bunches per beam on the evening of Tuesday 22 March. With the reduced beam size at the interaction points in ATLAS and CMS this gave a peak luminosity of 2.5 × 1032 cm-2s-1, comfortably beating last year's record made with 368 bunches.
On Thursday 24 March, the LHC switched to an energy of 1.38 TeV/beam to provide the experiments with some proton-proton collisions at the equivalent nucleon-nucleon centre of mass energy seen during the heavy ion run at the end of last year. These collisions are required to compare the behaviour of nucleon-nucleon collisions in the heavy ion environment with collisions free of the effects of the heavy ion medium. The data required should be delivered by the start of the weekend when the LHC will switch back to 3.5 TeV for some more physics running before the start of the 4 day technical stop planned for the end of March.
