The Large Hadron Collider has today surpassed 2000/μb/s in peak luminosity for both ATLAS and CMS. This was achieved during the Adjust phase of fill number 1992 using 1380 bunches per beam, just before stable beams were declared this morning.
Luminosity has been gradually increased above the 1280/μb/s limit reached before the technical stop at the end of last month. So far only emittance has been used to enhance the luminosity. This does not increase the overall intensity of the beams so there is no increased risk or extra demand on the cryogenics. At the recent mini-chamonix meeting it was predicted that emittance could provide an extra 35% luminosity but now they are 55% above where they were before. This extra is probably just due to the fact that the final runs before the technical stop suffered from some emittance blowup or injection losses that meant they were not as good as they could have been.
It was intended that further luminosity improvements would be attempted by increasing bunch intensity. This has the potential to double the peak luminosity again. This plan has been held back because of the technical difficulties of running at the high intensities they are now using. This can effect the vacuum and cryogenics leading to premature dumping of the beams and increasing times for returning to stable beams. Indeed the current rate of luminosity delivery is around 35/pb per day, just slightly better than the 30/pb per day when they ran with 1092 bunches during June. The proportion of time in stable beams recently has only been about 30% but there are signs that this is getting better.
There are just 24 days left before they break for the next Machine Development slot and the beam operation groups will be keen to make further progress with both stability and luminosity during that time. With 1.75/fb now delivered they are already on target to reach 2.6/fb at the next technical stop. After that there will be a final run lasting eight weeks before they switch from proton physics to heavy ions for they last part of the year. It is not yet clear at what point the experiment collaborations will decide to update their analysis but clearly this level of data is guaranteed to have enormous impact, especially on the Higgs searches.