LHC Update

See here for a new status report on the state of beam commissioning at the LHC. About two weeks ago a peak luminosity of about 2 x 10²⁹cm^-2s^-1 was reached, using beams with 13 bunches, but each bunch relatively low intensity. Since that time, efforts have been directed at increasing the bunch intensity towards nominal values. During this process, there has been little new physics data gathered, although the plan has been to interleave physics runs on weekends with beam commissioning during the week.

On Wednesday, this plan was changed, with the focus now completely devoted to commissioning beams with nominal bunch intensity. The hope is to have collisions of high intensity bunches in two weeks or so and then provide a 4 week period of stable running for physics during August, at luminosities an order of magnitude higher than now available. The limiting factor will be the stored energy in the beam, which is approaching Tevatron levels. To go higher will require much more testing of the beam protection systems.

This week in Hamburg there was a conference people have been waiting a long time for, Physics at the LHC 2010, the first conference devoted to the presentation of LHC experimental results. So far the results are based on very low luminosities, so are only able to check that the machine is working and rediscover various well-known features of the Standard Model. As the luminosity increases, it will start to become possible to observe or rule out various exotic particles at masses not reachable by the Tevatron, as long as the cross-sections are high.

Mostly such things are unmotivated and not expected to turn up, but one story to watch is that of supersymmetry, as the LHC becomes capable of observing strongly-interacting superpartners at masses beyond the Tevatron’s reach. The MSSM includes a huge number of unknown extra parameters, so the masses of these things are unknown. Given one motivation for supersymmetry, that it is supposed to stabilize the electroweak scale, one would expect superpartners to readily show up at the new mass ranges being investigated by the LHC. The problem with this is that it’s hard to understand why they haven’t already been seen at the Tevatron, or indirectly in other experiments through the effects of higher-order processes. Taking current non-observations into account, even if one has faith that superpartners exist at masses the LHC can probe, it doesn’t seem likely that the earliest LHC data will be able to see them (for more specific analysis along these lines, see for instance this talk).

I’m quite dubious that the LHC will ever see superpartners, but many prominent theorists claim that this is likely to happen. It would be interesting to pin them down on what LHC luminosity is needed to see what they are expecting to see.

Update: A particularly noteworthy talk is that of Mike Lamont, where he gives estimates of the progression of integrated luminosity this year. They’re significantly more pessimistic than similar estimates from early this year, with about 50 inverse pb this year instead of 200, but still on track for 1000 inverse pb by late 2011.