Beams in the Large Hadron Collider came to a stop today, closing out four years of record-breaking operation for the ATLAS experiment. Run 2 saw the extraordinary exploration of the high-energy frontier, as the ATLAS experiment brought new understanding of particle physics.

Geneva, 23 May 2017. A new season of record-breaking kicked off today, as the ATLAS experiment began recording first data for physics of 2017. This will be the LHC’s third year colliding beams at an energy of 13 tera electron volts (TeV), allowing the ATLAS Experiment to continue to push the limits of physics.

With the year’s first proton beams now circulating in the Large Hadron Collider, physicists have today recorded “beam splashes” in the ATLAS experiment

Friday morning, 29 April 2016: what was expected to be a productive shift turned out to be very different.

This morning the Large Hadron Collider (LHC) circulated the first proton-proton beams of 2016 around its 27 kilometre circumference. The beams were met with great enthusiasm in the ATLAS Control Centre as they passed through the ATLAS experiment.

Faster and Faster! This is how it gets as soon as LS1 ends and the first collisions of LHC Run 2 approaches. As you might have noticed, at particle physics experiments we LOVE acronyms! LS1 stands for the first Long Shutdown of the Large Hadron Collider.

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.

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.

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?

Beneath our feet on this warm November night, we have realized the ancient dream of turning lead into gold.

Another milestone has been passed in the long run of ATLAS toward new physics. On Monday August 9, 2010 ATLAS has recorded the first inverse picobarn (pb^-1) of 7 TeV collisions. The trend is good and we recently reached the 0.1 pb^-1 per day of integrated luminosity (meaning that we can now collect in ~10 days the amount of data we have collected over the last 4 months).

In the evening of Saturday May 15, we have reached a new peak luminosity record of 6 10²⁸ cm^-2s^-1

It took a little bit of time, but the wait was worth it. The LHC has successfully achieved its first physics run with "squeezed beams"!

Now that the LHC has established colliding stable beams at a center of mass energy of 7 TeV, the next step to maximize its physics reach is to provide the most luminosity possible. As Leo posted, we need to increase the number of proton - proton collisions to make sure we have a chance of seeing the physics that we are looking for. The reason for that is because different p.hysics processes have different probabilities. These probabilities are referred to as cross-sections (in a vague reference to the particle's size). If one multiplies a cross section by a luminosity than what you get is a number of events.

I was home sick today, probably from the stress of getting ready for "M-Day" (aka Media Day), more likely though I finally succumbed to the cold that had been spreading through the Control Room. As it so happened, my laptop had been in the shop because it experience an "incident" (actually I just dropped it) last Monday (the week before Media Day), and I just picked it up yesterday.

Many collisions will be needed to unveil the secrets eventually hidden at the 7 TeV energy regime.

After decades of planning. After years of delays and immeasureable amounts of patience and hard work. The physics operations of the LHC has begun!

After ramping of the beams to 3.5 TeV and tuning, final checks, and some emotions due to an unforeseen beam dump, the 7 TeV collisions finally appeared on the on-line monitors of the ATLAS Control Room.

During this morning LHC has been working to give us the beam conditions for collisions.

So how will this whole "First 7 TeV Collisions" event happen? Well, here is my (somewhat naive) understanding of what will happen.

This Tuesday, if all goes according to plan, will mark the end of a very long journey for many High Energy Physicists. The first 7 TeV Collisions will signal the end of the the commissioning period of the LHC and its experiments.

Last night a new very important milestone has been reached by the LHC: two counter-circulating proton beams have been accelerated for the first time to 3.5 TeV, the energy that they should routinely reach in the 2010-2011 running period.

It has been a BUSY weekend! The LHC has been working around the clock get the machine commissioned, and ATLAS has been enjoying the many Firsts that have resulted.

High Energy Physicists have been waiting for many years to see the LHC turn on. Now that it has been turned on, the network of physicists around the world have quickly been harnessed. It can be considered a phase transition in particle physics.

At 21:32 pm on December 8th, the LHC did something that no other accelerator has ever done before.

On Sunday December 6, 2009 at 8.00 the ATLAS Pixel Detector has measured, for the first time, tracks emerging from LHC collisions. It has been a very smooth start.

The most recent schedule envisions beam reaching ATLAS in late November with low-energy collisions shortly thereafter.