ATLAS quark hunters gather in Amsterdam this week

1 November 2022

Nikhef in Amsterdam is this week hosting the ATLAS Flavor-Tagging workshop 2022. Some seventy experts will discuss the latest techniques for spotting quarks in the proton collisions at the LHC accelerator at CERN.

ATLAS is one of the big experiments at CERN in Geneva. The detector looks at the particles released when protons collide in the LHC accelerator. The accelerator is powerful enough to make Higgs particles and other heavy particles like top quarks.

Two particle jets coming from a decaying Higgs particle in the ATLAS detector. IMAGE ATLAS

Such particles are unstable and decay too quickly to study them directly. Therefore, ATLAS looks for traces of particles that are created during the decay of higgs particles or top quarks. Often these are pairs of bottom or charm quarks.

Flavor-tagging is literally labeling patterns going back to b- or c- quarks in all the tracks in the detector. Over the years, ATLAS physicists at Nikhef and others have developed a variety of techniques to recognize such patterns.

But there is certainly room for improvement, says the workshop organizer, Tristan Du Pree of Nikhef’s ATLAS group. For example, the advent of machine learning and artificial intelligence still have much to offer, he thinks. “That sometimes already works better than we expect, and so actually the question now is why.”

One of the complications in quark hunting is that charm and bottom quarks are also not stable. They disintegrate into a wide range of lighter particles after a short flight. Due to the motion of the protons, these sprays have the shape of a cone, called a jet.

Tristan Du Pree of Nikhef ATLAS.

Different quarks give different jets. Experts at ATLAS are discussing in Amsterdam this week the best techniques for inversely reconstructing the source from observed jets.

During the workshop, which has the logo of a Dutch bicycle with particle sprays in the wheels, experiences and new ideas will be discussed. But at least as important is the physical meeting of experts with similar interests.

Du Pree: “We have not spoken to each other live for almost three years, but only through the screen. For that reason alone, this meeting is very valuable.”