As 2015 draws to a close, the ATLAS experiment wraps up its first phase of operation at a record-breaking energy frontier.

As final preparations were made for the start of the Large Hadron Collider's (LHC) Run 2, the ATLAS Control Room was the centre of activity. Here are images from the three days that were landmark events...

After a shutdown of more than two years, Run 2 of the Large Hadron Collider (LHC) is restarting at a centre-of-mass energy of 13 TeV for proton–proton collisions and increased luminosity. This new phase will allow the LHC experiments to explore nature and probe the physical laws governing it at scales never reached before.

Today ATLAS and other particle physics experiments at CERN's Large Hadron Collider (LHC) began recording physics data from 13 TeV proton collisions, which allow for precision studies of the Higgs boson and other Standard Model particles, as well as the search for new particles with higher masses. The new data will bring a deeper understanding of nature.

ATLAS is ready for Run 2 of the Large Hadron Collider (LHC) where proton beams will be collided together at a higher centre of mass collision energy of 13 TeV, and reach higher luminosities than ever before.

On 20 May at around 22:24, ATLAS recorded the first 13 TeV test collisions delivered by the Large Hadron Collider. The proton collisions set a new high energy record, marking the beginning of ATLAS' journey into unexplored physics frontiers as we prepare for production data-taking, scheduled to start in early June.

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.