The beam teams at the Large Hadron Collider are now getting ready to increase peak luminosities up to about 9/μb/s which is 0.28/fb/year. To do this they will switch from their current 25 bunch scheme to a new 49 bunch scheme. Unlike previous filling schemes the bunches will be placed in a pattern that provides less luminosity to the ALICE experiment than the others. ALICE does not need higher luminosity at this time because it is designed for separate experiments using heavy ion collisions that will take place in November.
The new filling scheme is called 1250ns_48b_36_16_36 or 1250ns_49b_36_16_36 if extra diagnostic bunches are included to make up the 49 bunches per beam. 36 is the number of bunch collisions per turn in the experiments ATLAS, CMS and LHCb. This can be compared with the present scheme Multi_25b_16_16_16 which had 16 collisions per turn and delivered peak luminosities of 4/μb/s. if all else is equal we can therefore expect peak luminosities of 4 x 36/26 = 9/μb/s.
Over the last two weeks the total integrated luminosity has increased from 1/pb to about 1.5/pb. The new filling scheme will push the total up faster. In preparation the physicists will do new bunch injection tests today, possibly leading to physics runs with 49 bunches this evening or tomorrow.
In fact the luminosity gathered this month has been a little less than expected but that is because they have been using some of the time to commission better processes. for example they have been testing faster ramping of the energies. That will ultimately improve the recycle time between physics runs. The higher luminosity with 49 bunches should enable them to make up the lost time before the end of the month.
Update: The first 48 bunch physics run was a great success. It delivered 240/nb over 15 hours, before being adjusted for end-of-beam studies. The luminosity started at around 6.6/nb/s and ended at 3.3/nb/s, so the luminosity lifetime was also 15 hours (intensity lifetime was more like 60 to 100 hours). The total integrated luminosity over all runs now stands at about 1.8/pb.