Now that the LHC is running routinely, everyone is wondering when it will produce some new physics. Over at “Not Even Wrong” Peter Woit did a nice comparison of the LHC with the Tevatron based on luminosity. Of course luminosity is not the only thing that counts here. The LHC runs at over three times the energy and this increases the cross-section for most interactions of interest such as Higgs production. In fact it is possible that the LHC could find new physics at higher energies that could not be seen at the Tevatron no matter how long it runs for. It would also be interesting to hear a comparison of the detectors at the LHC and the Tevatron. If any detector experts are listening please tell us about it.
So the important question is not just “when will the LHC increase its luminosity?” , it is “When will it increase its energy further?” The design energy of the LHC is twice the energy it is currently running at. At present they are keeping the energy lower because of the problems that had at the end of 2008 when an overheated joint caused an explosion of helium delaying the start of physics at the LHC for over a year.
The current plan is to run the LHC at 3.5 TeV per beam while concentrating on increasing the luminosity. It will run this way through 2011 until it is shut down for a long repair lasting up to one year. Then they will be ready to increase energy to 7 TeV per beam in 2013.
But if you have been watching the LHC progress you will know that their plans are written on soluble paper and have been known to dissolve very quickly. So what is really likely to happen? At the press conference for the start of physics on 3oth March, Steve Meyer, the technical director at CERN was asked about the prospects of increasing the energy. He explained that the problem in 2008 was caused by a joint with a resistance of 200 nΩ. They have now tested all the joints and the highest resistance left in any of the joints is about 1 nΩ. Most are about 0.3 nΩ which is about what they should be. This was not the only problem, but Meyers says that he is sure the magnets can take the currents required to go to 6.5 TeV.
If this is the case, it is hard to believe that they will shut down the collider for a year without at least trying to go to higher energies. Even if there are problems the quench protection system should ensure that no serious damage is done. There have already been rumours circulating that they will try for 5 TeV per beam later this year. Realistically it depends on how easily they can increase the luminosity and how stable the systems prove to be. It may also depend on the physics. If there are indications that new physics lies at the higher energies they will be inclined to increase it, but if they just need more time at lower energies to turn an uncertain observation into a solid discovery, they will keep running at the current energy.
This video shows Steve Meyers at the press conference, so have a watch and see what you think he would like to do.
Update: From the current plan it can be seen that they want to get stable squeezed beams for the first time this weekend. That will be at 3.5TeV but with beta of 2m and intensity of 35 billion protons per bunch which is a bit higher than current runs. Later they will also try for stable beams with 100 billion but only at 0.9 TeV. If they are successful it will bring them closer to their next operational target which seems to be 3.5TeV/2m/100Billion, They have not indicated how many bunches they will circulate at this intensity but presumeably they will try to step up the number of bunches at these levels. (The design limit is something like 7TeV/0.5m/200Billion/2808 bunches, and they are currently running stable beams with 3.5TeV/11m/10Billion/2 bunches). The plan also shows a long technical stop during next week. Let’s hope they will be ready for the higher luminosities when that is completed.
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