As you can see in the picture I took this morning, it is foggy here at CERN today as we await the first circulating beam of protons in the LHC since last year. When this will happen exactly is a little foggy as well. There will probably be protons put into the LHC sometime this evening, so perhaps overnight we will have a circulating beam.
At the ATLAS detector, we are excited for the first beam to ATLAS this year, which will happen first (the way the LHC is configured, the beam has to go almost all the way around the LHC’s ring from where it is injected to get to the ATLAS detector).
The beam will first be made to stop before ATLAS by moving the beam collimator in its way. This will cause a huge cascade of particles to hit the ATLAS detector (similar to what was done recently at the CMS detector ), and it will be quite useful for us at ATLAS to detect all these particles and check our timing.
After that the collimator is removed and beam will pass through the ATLAS detector, at which point is has just about made one revolution around the LHC. This will be repeated for the beam going in the other direction around the LHC. Then in the coming days or weeks we will have two beams of protons in the LHC at the same time…and finally collisions!