There is the Large Hadron Collider and then there are its experiments. When the collider is ready to circulate proton beams, the experiments have to be ready to receive them.

On the morning of 5 May 2015, ATLAS recorded the first scheduled proton beam collisions since the Large Hadron Collider and its experiments started up after two years of maintenance and repairs.

ATLAS uses "beam splash" events to provide simultaneous signals to large parts of the detector, and verify that the readout of different detectors elements are fully synchronized. After the first 2015 Large Hadron Collider beam circulation on Easter Sunday, a run dedicated to taking beam splash events was set up on Tuesday evening, 7 April.

The first long shutdown of the Large Hadron Collider has now ended, after two years of intense but careful activity refurbishing and improving many aspects of ATLAS, mirroring the work to prepare the LHC for collisions at the new energy of 13 TeV.

After completing more than 250 work packages concerning the whole detector and experimental site, the ATLAS and CERN teams involved with Long Shutdown 1 (LS1) operations are now wrapping things up before starting the commissioning phase in preparation for the Large Hadron Collider's restart. The giant detector is now more efficient, safer and even greener than ever thanks to the huge amount of work carried out over the past two years.

Bringing the nine-storey high, many-layered ATLAS detector back to life and preparing it for the Large Hadron Collider's next run is a complex task. Each sub-detector is setup and thoroughly tested before they are joined and the detector as a whole can begin recording data again.

Inspired by Regina Caputo’s excellent post on the CERN accelerator complex, I thought I should give you some fun facts about the LHC (in “human units”).

The LHC 2012 run at a beam energy of 4 TeV has started, corresponding to a collision energy of 8 TeV, compared with the 7 TeV runs in 2010 and 2011. The data target for 2012 is 15 inverse femtobarns for ATLAS (and CMS), three times larger than the total until now. The LHC is scheduled to enter a long technical stop at the end of 2012 to prepare for running at its full design energy of around 7 TeV per beam.

The LHC is designed to collide bunches of protons every 25 ns, i.e., at a 40 MHz rate (40 million/second). In each of these collisions, something happens. Since there is no way we can collect data at this rate, we try to pick only the interesting events, which occur very infrequently; however, this is easier said than done. Experiments like ATLAS employ a very sophisticated filtering system to keep only those events that we are interested in. This is called the trigger system, and it works because the interesting events have unique signatures that can be used to distinguish them from the uninteresting ones.

A very happy new year to the readers of this blog. As we start 2012, hoping to finally find the elusive Higgs boson and other signatures of new physics, an important question needs to be answered first - are we going to have collisions at a center of mass energy of 7 or 8 TeV?