LHC Report: 2 inverse femtobarns!

The LHC is enjoying a confluence of twos. This morning (Friday 5 August) we passed 2 inverse femtobarns delivered in 2011; the peak luminosity is now just over 2 x10³³ cm^-2s^-1; and recently fill 2000 was in for nearly 22 hours and delivered around 90 inverse picobarns, almost twice 2010's total.

In order to increase the luminosity we can increase of number of bunches, increase the number of particles per bunch, or decrease the transverse beam size at the interaction point. The beam size can be tackled in two ways: either reduce the size of the injected bunches or squeeze harder with the quadrupole magnets situated on either side of the experiments. Having increased the number of bunches to 1380, the maximum possible with a 50 ns bunch spacing, a one day meeting in Crozet decided to explore the other possibilities.

The size of the beams coming from the injectors has been reduced to the minimum possible. This has brought an increase in the peak luminosity of about 50% and the 2 x 10³³ cm^-2s^-1 level has now been passed. The next stage is to adiabatically increase the bunch intensity with the all out maximum being around 1.6 x 10¹¹ protons per bunch. The mechanics of squeezing further are reasonably complicated and this possibility has been shelved until after the next technical stop.

The higher peak luminosity has given some impressive production rates and we are seeing over 6 inverse picobarn an hour at the start of a fill. However, recently operational efficiency has been hit and fills have been lost. These difficulties have been caused by electrical network glitches, the effects of radiation on electronics, vacuum spikes, and UFOs, among other things. Some of these are clearly related to high intensity and high luminosity; it might be said that we are victims of our own success. Nevertheless on 2 August the LHC managed 90 inverse picobarns in one day.

by Mike Lamont for the LHC Team