Beam commissioning at the LHC continues to result in increasing luminosity for the experiments. The end of the first week of August saw data-taking pass another milestone, with integrated luminosity reaching 1 pb–1 – that is, a thousandfold increase since the end of June.
A major factor has been the implementation of multibunch injection from the Super Proton Synchrotron (SPS). This involves sending several bunches to the LHC in one SPS cycle, thus reducing the time needed to fill the collider. In tests on 27 July, using this scheme for the first time, the operators sent four bunches at a time into the LHC to give a total of 25 bunches (including one pilot bunch) in each direction.
Then, from around midnight on 30 July, the machine ran with stable beams of 25 bunches, providing 16 colliding pairs per experiment and delivering a peak instantaneous luminosity of around 2.6 × 1030 cm–2s–1. This corresponds to a total stored beam energy of 1.2 MJ. Further long fills with 25 bunches per beam followed in the first week of August, with peak luminosities of up to
3 × 1030 cm–2s–1 providing up to 120 nb–1 integrated luminosity per fill. By Friday 6 August, with the milestone of 1 pb–1 on the horizon, there was a small and well deserved celebration in the CERN Control Room, for the operations and commissioning teams whose hard work makes this progress possible.
