LHC Report: Records are made to be broken

The LHC has spent the last couple of weeks delivering collisions to the four main experiments. At the same time the number of bunches in the beam has been steadily increased.


Since the scrubbing run the LHC has passed through 228, 336, 480 and 624 bunches per beam to reach the latest total of 768 . As can be seen, each step-up is 144 bunches, which represents two extra injections of 72 bunches from the SPS when filling the machine. A few days is spent delivering physics after each step-up to check the performance of the machine and make sure that no intensity-dependent effects are compromising machine protection.

The rewards have been impressive. Each step-up, naturally enough, brings a new in-house record for peak luminosity. In addition, on 21April, with 480 bunches, the LHC set a new world record for luminosity at a hadron collider of around 4.4x1032 cm-2s-1. This exceeded the previous high of 4.024x1032 cm-2s-1 set by Fermilab’s Tevatron collider in 2010. The new record itself lasted only a couple of days and 768 bunches per beam have now given us around 8.4x1032 cm-2s-1.

The integrated luminosity has also increased accordingly and the total for the year for ATLAS and CMS now stands at over 250 pb-1. One 16-hour fill with 624 bunches added nearly 30 pb-1 alone. The stored beam energy at the start of a fill is now over 50 MJ - a soberingly impressive figure.

As of Wednesday 4 May the LHC went into a 5-day machine studies period. This will be followed by a 4-day technical stop, and thereafter 5 more weeks aimed at delivering physics. The push-up in the number of bunches will continue towards a potential maximum for the year of around 1400.

by CERN Bulletin