From CERN (CH) ATLAS via Symmetry: “ATLAS releases ‘full orchestra’ of analysis instruments”

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Symmetry Mag

Stephanie Melchor

Courtesy of CERN.

The ATLAS collaboration has begun to publish likelihood functions, information that will allow researchers to better understand and use their experiment’s data in future analyses.

Meyrin, Switzerland, sits serenely near the Swiss-French border, surrounded by green fields and the beautiful Rhône river. But a hundred meters beneath the surface, protons traveling at nearly the speed of light collide and create spectacular displays of subatomic fireworks inside the experimental detectors of the Large Hadron Collider at CERN, the European particle physics laboratory.

One detector, called ATLAS [images above], is five stories tall and has the largest volume of any particle detector in the world. It captures the trajectory of particles from collisions that happen a billion times a second and measures their energy and momentum. Those collisions produce incredible amounts of data for researchers to scour, searching for evidence of new physics. For decades, scientists at ATLAS have been optimizing ways to archive their analysis of that data so these rich datasets can be reused and reinterpreted.

Twenty years ago, during a panel discussion at CERN’s First Workshop on Confidence Limits, participants unanimously agreed to start publishing likelihood functions with their experimental results. These functions are essential to particle physics research because they encode all the information physicists need to statistically analyze their data through the lens of a particular hypothesis. This includes allowing them to distinguish signal (interesting events that may be clues to new physics) from background (everything else) and to quantify the significance of a result.

As it turns out, though, getting a room full of particle physicists to agree to publish this information was the easiest part.

In fact, it was not until 2020 that ATLAS researchers actually started publishing likelihood functions along with their experimental results. These “open likelihoods” are freely available on the open-access site HEPData as part of a push to make LHC results more transparent and available to the wider community.

“One of my goals in physics is to try and make it more accessible,” says Giordon Stark, a postdoctoral researcher at the University of California, Santa Cruz, who is on the development team for the open-source software used to publish the likelihood functions.

The US Department of Energy’s Office of Science and the National Science Foundation support US involvement in the ATLAS experiment.

Stark says releasing the full likelihoods is a good step toward his goal.

See the full article here .


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