First collisions at the LHC with unprecedented Energy! (Ask a particle physisicist)

[Alex K]

Not a whole lot from my perspective - data flows more slowly than hoped because the luminosity (more or less the rate of collisions) was somewhat below expectations. There was a slight excess in.the old data which could have pointed to a new very heavy particle, but the significance does not so far increase with the new data...

Why have there been fewer collisions?

I don't wholly understand all those technical reasons as I'm not a collider physicist, but here is one important factor: The collider lets pairs of little clouds of protons (bunches with 100 billion protons each) cross 20 million times per second. Let this be a fixed number. Now, maybe you can imagine that the frequency with which the protons in those bunches actually hit each other frontally, depends crucially on how focused those bunches are, how narrow. If you imagine two sets of marbles collide, you immediately see that if the they are very dilute in the sideways directions, there will hardly be any collisions.

This means that if anything interferes with the beam of proton bunches which causes it to lose focus, this will reduce the number of proton - proton collisions achieved.