An impressive start

This has been an excellent week for the LHC, with a succession of fills rapidly increasing the number of proton bunches to 194 per beam. This has allowed the experiments to reach a peak luminosity of 2.5 × 1032 cm-2s-1, thereby surpassing the record for 2010 where we reached 2.0 × 1032 cm-2s-1. At the time of writing, the integrated luminosity delivered by the LHC in 2011 is around 28 inverse picobarns, which is already more than half of the total 2010 dataset.


These are impressive numbers, but what impresses me most is how quickly the LHC operators are now able to turn the machine around between fills, and how well LHC running has been incorporated into the overall operation of CERN’s accelerator complex.

The flexibility of the LHC was illustrated on Thursday when we started a short phase of running at 1.38 TeV per beam, equivalent to the energy-per-nucleon of a lead-ion run. This lower energy data will be used by the experiments, in particular by ALICE, to compare the results of nuclear interactions with ions with those of protons at the same energy per nucleon. Operation at 1.38 TeV per beam with protons will continue until Saturday giving us some more time at 3.5 TeV per beam over the weekend before a scheduled technical stop begins on Monday 28 March.

Another important recent event in the life of CERN was the March Council meeting. It was largely business as usual, but I’d like to highlight the report given to Council on the physics potential of running the LHC through 2011 and 2012, notably in terms of the Standard Model Higgs search. It was gratifying to see a presentation from the joint ATLAS-CMS working group on the subject, since this is a good sign of the healthy nature of the collaborative competition between the two experiments. Two decades ago, it took the LEP experiments a lot longer to reach this point, and it’s important that the LHC experiments have learned to work together so quickly. Taken together, and with good LHC running, the combined results of ATLAS and CMS should allow us to cover the full range for the Higgs, either confirming its existence or demonstrating conclusively that it does not exist. Either outcome would be an important result.

The Council reiterated its resounding endorsement of our plan to run through 2012. The performance of the LHC since the March meeting adjourned gives us every reason to believe that our delegates’ confidence is well placed.


Rolf Heuer