The Large Hadron Collider is quickly making its way back to normal physics runs after the technical stop and a power cut that knocked out the cryogenics for an extra couple of days. For a while we will be more interested in new results presented at the EPS conference in just six days time, but first the beams operation groups need to decide how they are going to run the collider for the rest of 2011. A one day “mini-Chamonix” has been organised for today to consider whether and how and by how much luminosity can be further increased. The presentation slides are available here.
There are 107 days remaining for proton physics this year. The most likely means for increasing peak luminosity further now is to increase bunch intensity and decrease emittance (i.e. the transverse spread of the beam over position and momentum space.) This plot shows the statistics so far.
Everybody now believes that 4/fb can be delivered to ATLAS and CMS this year and 1/fb to LHCb. This is just by running with present parameters and assuming a reasonable run efficiency, but more is possible.
Present peak luminosity is 1.28/nb/s. CMS and ATLAS would be happy to see that go up to 3/nb/s. Any more would provide more pile-up than they want at this time, but they would still want to go higher near the end of the run to test for ways to deal with high pile-up.
From the injection chain the best bunch intensity with multiple bunches this year is around 1.6E+11 protons per bunch with emittance of 2um. This would double the peak luminosity. Ways to go higher are being studied during MD time, but for next year.
As far as I can tell from all the other slides there are no barriers to these numbers from beam stability or machine protection considerations.
Other ways to increase luminosity such as 25ns bunch spacing and ATS squeeze are still under study. We may see more tests during MD but no real physics runs (with these new features) until at least next year (actually some more squeeze is still a possibility according to the conclusion)
We now just have to wait to see what they decide by the end of today.
The final conclusions are in and it looks promising. This is the table of possibilities they have to discuss.
So increasing intensity and decreasing emittance poses no risk and can be done gradually. A factor of 2.7 is then available. The experiments wont want much more than that so any further increases may result in luminosity leveling.