ATLAS experiment records “first physics” at new high-energy frontier

We have proton collisions in the ATLAS experiment† At 4:47 PM CEST, the Large Hadron Collider (LHC) officially kicked off its third operating period (Run 3). The LHC collides with proton beams with a world-record-breaking energy of 13.6 tera electron volts (TeV). The higher beam energy and intensity of Run 3 allows the ATLAS experiment to push the boundaries of its physics research.

Today’s statement of “stable beams” marks the end of the LHC’s recommissioning period, which: started in April 2022† Within a month from today, the LHC will have reached its full Run-3 operating intensity. ATLAS has now enabled all systems to begin recording data used for physics analysis. The LHC will run around the clock for nearly 4 years, with only a few technical stops during the winter months, delivering an unprecedented wealth of proton and heavy ion collisions.

“The ATLAS experiment is poised to capture this new crop of data,” said Andreas Hoecker, spokesperson for ATLAS. “The new run promises to more than triple the currently collected data set at a new energy frontier. We have established a broad scientific program, taking advantage of new upgrades to our experiment.”

The return of LHC rays comes after more than three years of upgrade and maintenance work, with new detector systems and electronic infrastructure installed 100 meters underground in the ATLAS cavern. “We are excited to see the ATLAS control room busy again as we prepare for Run-3 data ingestion,” said Jörg Stelzer, ATLAS Run Coordinator. “Over the past few months, we’ve been re-deploying the experiment and re-establishing the expertise and procedures that led to Run 2’s excellent data processing efficiency. This will be our model for Run 3.”


The higher beam energy and intensity of LHC Run 3 allows the ATLAS experiment to push the boundaries of its physics research.


“Run 3 will increase our sensitivity to new physical processes as we investigate new types of collisions that were previously out of reach,” said Pamela Ferrari, ATLAS Deputy Physics Coordinator. “During the shutdown, we paid special attention to improving our online event filtering system (or “trigger”). By refining our selection upstream with new detector systems, we should be able to identify some of the most difficult-to-recognize signatures left behind by new particles.”

One of the event signatures that would benefit from the new triggers is: dark matter production. “The search for dark matter is a very important part of our physics research program,” says Andreas. “We know from countless observations of gravitational effects that dark matter exists in the universe. If it’s made of particles, as most physicists expect, they can interact with protons or the Higgs boson and be produced in LHC collisions.” Dark matter is invisible and can only be observed if it is produced with other, visible particles. The dark matter then appears as a localized missing energy in a collision event, which physicists can measure.

An important part of ATLAS’s physics program remains, of course, the Higgs boson. The Higgs boson, discovered just a decade ago in 2012 by the ATLAS and CMS experiments, plays a unique role in the universe. Although discovered in Run 1 primarily through its interactions with force-carrying bosons, the larger, higher-energy Run-2 data sample enabled ATLAS to measure Higgs boson interactions with the heaviest, third-generation matter particles (fermions), and to identify all major to observe production methods. In Run 3, these measurements will be further enhanced and the interactions of the Higgs boson with second-generation particles, such as muons, and the interaction with itself will become a focus.

“The Higgs sector is a rich environment for study, as accurate measurements of its properties can yield spectacular results,” Pamela added. phase transition in the early universe that transformed massless elementary particles into massive particles.”

These are just some of the science highlights expected from Run 3. “As we enter this new era of exploration, it is important to champion the competence, dedication and hard work of the hundreds of ATLAS members who will be upgrading and maintaining our experiment during the long shutdown,” said Andreas. “Their work has sown the seeds for the upcoming data harvest.”

The many improvements to the advanced trigger and data acquisition system allow a much wider range of collision events to be investigated, compared to Run 2, while maintaining the same particle acceptance rate. “In addition to the new hardware, ATLAS has upgraded large parts of its software, simulation and computing environment to improve performance, save resources and allow it for use with heterogeneous computing systems,” concludes Andreas.

The launch of the LHC Run 3 was streamed live on CERN’s social media channels, with live commentary in five languages ​​(EnglishFrenchGermanItalianSpanish† Watch the stream below.


about the event display: Run 427394 Evt 3038977 Event representation of a collision event recorded in ATLAS on July 5, 2022, when stable proton beams with an energy of 6.8 TeV per beam were supplied from the LHC to ATLAS for the first time. The lower right image shows a 3D view of the ATLAS detector. Starting from the point where the two beams of protons from the LHC collide, the figure shows the charged particle tracks as they are reconstructed in the inner detector (orange tracks), the energy deposits in the electromagnetic (green boxes) and hadronic (yellow boxes) calorimeters, as well as the reconstructed particle beams (yellow cones). The vessel magnet and muon chambers in the vessel region of the detector (blue boxes) are shown as a semi-transparent cutout. In the center, the image shows the beampipe, where the protons accelerated by the LHC enter the detector. The top left view shows a projection of the same event on the transverse plane, with the charged particle traces reconstructed in the inner detector (orange traces) and the energy deposits in the electromagnetic (green boxes) and hadronic (yellow boxes) calorimeters, as well as the reconstructed particle rays (yellow cones). (Image: ATLAS collaboration/CERN)


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