The Large Hadron Collider crawled out of a scheduled technical stop two weeks ago and passed through a rocky patch. There was a series of cryogenic failures that slowed the build up back to normal luminosity. They are currently running with the worst hit sectors around point 8 at a temperature of 2.0 Kelvin rather than the normal 1.9 K. This appears to have fixed the problem but as an uninformed outsider I can’t help wondering what extra risks this entails. Another issue was emittance blow-up from the SPS that was limiting peak luminosity to around 4.3/nb/s. This was fixed in the last couple of days and now luminosities have returned to the record levels set before the technical stop of around 5.7/nb/s with bunch intensities up to 138 billion protons per bunch. previous discrepancies between luminosity recorded by CMS and ATLAS have been resolved by data from the Van de Meer scans run just before the technical stop. The two experiments are now in perfect agreement and previous record numbers from CMS have been rescaled downwards. The present luminosity should be close to the maximum they can achieve this year unless they have kept back some tricks for later.
On the plus side, minimum turnaround times are well under two hours which is about half last years waiting time. Recovery from loss of cryogenics also looks much faster than before. This means that if they can avoid problems with cryogenics and RF they should be able to accumulate data at a high rate. As I write they are passing the 2/fb mark for this year’s total with a little under 5 weeks before the next technical stop. It should be a breeze to reach the stated 5/fb target in time for the summer conferences.
There are a few conferences coming up over the next three weeks that could be opportunities for the experiments to present some early results using the 2012 data at 8 TeV. In particular Recontres de Blois opens on 27th May and Physics at LHC begins in Vancouver on the 4th June. However we may need to wait for the big ICHEP conference in Melbourne where they should be able to add about 5/fb from this years data at 8 TeV to last years similar total at 7 TeV. This looks likely to be a watershed moment for the Higgs search with a likelihood of at least an unofficial discovery moment if the combined significance exceeds 5-sigma (it is currently around 4.2 sigma) There is even the possibility that one of the two experiments could pass the discovery threshold with the diphoton decay mode. It depends on how lucky they are with the stats. There is also the possibility that this years data will tell a different story from last year and we will be left waiting for the full year’s dataset to complete the story. Whichever way it goes the ICHEP conference is billed as a historic moment for the Higgs boson, and it is just seven weeks away.