## Monday, June 28, 2010 ... //

### LHC: nominal bunches circulated

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Temporary: "Angels, Demons and Black Holes - Experience from communicating the LHC", from 4:30 pm to 5:30 pm Swiss time, by James Gillies, Head of CERN Communications Group

For the first time, the Large Hadron Collider has collided full-fledged bunches of the planned nominal intensity - which is 100 billion protons per bunch.
BBC: LHC smashes beam collision record (click)
The two other key quantities that determine the luminosity are linked to the focusing - and my feeling is that they're pretty good at it - and the number of bunches per beam - which may go up to 2,808 around 2016.

The ATLAS detector has so far collected about 1.55 billion of 2x 3.5 TeV proton-proton collisions - about 30 x 10^{-6} inverse femtobarns (per experiment).

During the weekend, the top luminosity ran at 0.5 x 10^{30} cm^{-2} per second. At that time, CMS was collecting the events at the same rate which makes up 10^{30} cm^{-2} per second in total - which translates to about 10,000 collisions a second in the whole collider. (The other two major detectors are colliding a significant fraction of it as well but you shouldn't simply add their numbers because they can't see "everything" we want to see.)

Note that 1 femtobarn equals 10^{-39} cm^2, so 10^{30} cm^{-2} per second is 10^{-9} inverse femtobarn per second or 1/30 of an inverse femtobarn per year. If they increase the luninosity by a factor of 30, they will reach 1/femtobarn per year - which is enough to fulfill the realistic plan of 1/femtobarn before the end of 2011. (Recall that they will stop the collider at the end of 2011 or when they reach 1/femtobarn, whatever comes first.)

The peak "super" LHC luminosity may reach 10^{34} cm^{-2} per second so we're still at a 10,000 times smaller luminosity than the maximum designed value. Four orders of magnitude away from the goal.

It's expected that they will be playing with these things until August 2010 and at that time, they could start to collide the protons at the highest luminosity they can safely achieve for extended periods of time. The current luminosity is almost certainly not enough to find new physics. However, this may rapidly change after August - and one month of collisions at this expected "serious rate" could be enough to find new physics if Nature turns out to be generous.

Recently, it has become pretty amusing to watch the live LHC control panels, especially the basic one:
LHC1 control panel (click)
It shows the recent history graphs of the proton energy (black) and the intensity of both beams (blue, red) - as well as the general "regime" and "task" that the LHC is working on right now. In the left upper corner, you may choose many other control panels to watch.