Detective work on dark matter: a revolutionary approach at the Large Hadron Collider –

Researchers at CERN’s ATLAS experiment at the Large Hadron Collider have introduced a new approach to searching for dark matter using semi-visible jets, marking a significant paradigm shift in the field. Their work provides new directions and hard limits in the ongoing quest to understand dark matter.

Researchers are investigating whether dark matter particles are actually produced in a standard model of a particle beam.

The existence of dark matter is a long-standing mystery in our universe. Dark matter makes up about a quarter of our universe but does not interact significantly with ordinary matter. The existence of dark matter has been confirmed by a number of astrophysical and cosmological observations, including recent stunning images from the James Webb Space Telescope. However, no experimental observations of dark matter have been reported to date. The existence of dark matter is a question that high-energy and astrophysicists around the world have been studying for decades.

Advances in dark matter research

“That’s why we conduct basic scientific research and explore the deepest secrets of the universe. “CERN’s Large Hadron Collider is the largest experiment ever built, and particle collisions that create Big Bang-like conditions can be used to search for evidence of dark matter,” explains Professor Deepak Kar from the School of Physics the University of the Witwatersrand in Johannesburg. South Africa. .

A graphical representation of how semi-visible jets appear in the ATLAS detector, if present. Photo credit: CERN

While working on the ATLAS experiment at CERN, Kar and his former PhD student Sukanya Sinha (now a postdoctoral researcher at the University of Manchester) developed a new method for searching for dark matter. Their research was published in the journal Lettres de physique B.

A new approach to deciphering dark matter

“In the last few decades, there has been a plethora of searches for dark matter at colliders, which have so far focused on weakly interacting massive particles called WIMPs,” says Kar. “WIMPS are a class of particles that could explain dark matter because they do not absorb or emit light and do not interact strongly with other particles. However, since no evidence for the existence of WIMPS has been found so far, we realized that the search for dark matter requires a paradigm shift.

Dr. Sukanya Sinha and Professor Deepak Kar. Photo credit: Wits University

“We wondered whether dark matter particles were actually created in a Standard Model particle beam,” Kar said. This led to the exploration of a new detector signature called “semi-visible jets,” which scientists had never studied before.

High-energy proton collisions often result in the creation of a collimated particle beam that is collected in so-called jets from the decay of ordinary quarks or gluons. Semi-visible jets would arise when hypothetical dark quarks decay partly into Standard Model quarks (known particles) and partly into stable dark hadrons (the “invisible fraction”). Because they are created in pairs, usually with additional nozzles from the standard model, an energy imbalance or lack of energy occurs in the detector if all nozzles are not fully balanced. The direction of the missing energy often coincides with one of the semi-visible jets.

This makes the search for semi-visible jets very difficult, as this event signature can also arise from poorly measured jets in the detector. Kars and Sinha’s new way of searching for dark matter opens new avenues in the search for the existence of dark matter.

“Even though my doctoral thesis does not involve the discovery of dark matter, it sets the first, rather strict upper limits of this mode of production and is already inspiring further studies,” explains Sinha.

The ATLAS collaboration at CERN highlighted this as one of the key results presented at the summer conferences.

Experiments at the Large Hadron Collider in Europe, such as the ATLAS calorimeter here, provide more precise measurements of fundamental particles. Photo credit: Maximilien Brice, CERN

The ATLAS experience

The ATLAS experiment is one of the most important scientific initiatives of CERN, the European Organization for Nuclear Research. It is a key component of the Large Hadron Collider (LHC), the world’s largest and most powerful particle accelerator. Located near Geneva, ATLAS stands for “A Toroidal LHC Apparatus” and focuses on exploring fundamental aspects of physics.

ATLAS was developed to investigate a wide range of scientific questions. It is about understanding the fundamental forces that have shaped our universe since the beginning of time and that will determine its fate. One of its main goals is to study the Higgs boson, the particle associated with the Higgs field that gives other particles their mass. The discovery of the Higgs boson in 2012, the result of the joint efforts of ATLAS and the Compact Muon Solenoid (CMS) experiment, was a historic achievement in physics.

The experiment also looks for signs of new physics, including the origins of mass, extra dimensions and particles that might make up dark matter. ATLAS achieves this by analyzing the countless particles created when protons collide at nearly the speed of light in the LHC.

The ATLAS detector itself is a technological marvel. It is huge, about 45 meters long, 25 meters in diameter and weighs about 7,000 tons. The detector consists of different layers, each designed to detect different types of particles created by proton-proton collisions. It includes a range of technologies: trackers to detect the trajectories of particles, calorimeters to measure their energy, and muon spectrometers to identify and measure muons, a type of heavy electron that is essential to much physics research.

The data collected by ATLAS is huge, often expressed in petabytes. This data is analyzed by a global community of scientists, contributing to our understanding of fundamental physics and potentially leading to new discoveries and technologies.