2023-11-28 22:00:45
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 studying whether dark matter particles are actually produced inside a standard model particle jet.
The existence of dark matter is a long-standing enigma in our universe. Dark matter makes up about a quarter of our universe, but it does not interact significantly with ordinary matter. The existence of dark matter has been confirmed by a series of astrophysical and cosmological observations, including recent stunning images from the James Webb Space Telescope. However, to date, no experimental observations of dark matter have been reported. 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 fundamental science research, probing the deepest mysteries of the universe. CERN’s Large Hadron Collider is the largest experiment ever built, and particle collisions creating big bang-like conditions can be exploited to search for evidence of dark matter,” explains Professor Deepak Kar of the School of Physics at the University of the Witwatersrand in Johannesburg, South Africa. .
A graphical representation of how semi-visible jets will appear in the ATLAS detector, if they exist. Credit: CERN
Working at the ATLAS experiment at CERN, Kar and his former doctoral student, Sukanya Sinha (now a postdoctoral researcher at the University of Manchester), developed a new way to search for dark matter. Their research was published in the journal, Physics letters B.
A new approach to unraveling dark matter
“There has been a plethora of dark matter searches at colliders over the past few decades, 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, as no evidence for the existence of WIMPS has been found so far, we realized that the search for dark matter required a paradigm shift.
Dr. Sukanya Sinha and Professor Deepak Kar. Credit: Wits University
“What we were wondering was whether dark matter particles were actually produced inside a Standard Model particle jet,” Kar said. This led to the exploration of a new detector signature known as semi-visible jets, which scientists had never studied before.
High-energy proton collisions often result in the production of a collimated jet of particles, collected in so-called jets, from the decay of ordinary quarks or gluons. Semi-visible jets would appear when hypothetical dark quarks decay partially into Standard Model quarks (known particles) and partially into stable dark hadrons (the “invisible fraction”). Since they are produced in pairs, usually with additional jets from the standard model, energy imbalance or missing energy in the detector occurs when all jets are not completely balanced. The direction of the missing energy is often aligned with one of the semi-visible jets.
This makes searching for semi-visible jets very difficult, as this event signature can also arise due to poorly measured jets in the detector. Kar and Sinha’s new way of searching for dark matter opens new directions in the search for the existence of dark matter.
“Even though my doctoral thesis does not contain a 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 flagship results presented at the summer conferences.
Experiments at the Large Hadron Collider in Europe, such as the ATLAS calorimeter seen here, provide more precise measurements of fundamental particles. 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 the study of fundamental aspects of physics.
ATLAS was designed to explore a wide range of scientific questions. It seeks to understand the fundamental forces that have shaped our universe since the dawn of time and which will determine its destiny. One of its main goals is the study of the Higgs boson, the particle associated with the Higgs field, which gives other particles their mass. The discovery of the Higgs boson in 2012, the result of the joint efforts of ATLAS and the CMS (Compact Muon Solenoid) experiment, was a historic achievement in physics.
The experiment also searches for signs of new physics, including the origins of mass, extra dimensions and particles that could make up dark matter. ATLAS achieves this by analyzing the myriad particles produced when protons collide at near the speed of light within the LHC.
The ATLAS detector itself is a technological marvel. It is enormous, measuring approximately 45 meters long, 25 meters in diameter and weighing approximately 7,000 tonnes. The detector is made up of different layers, each designed to detect different types of particles produced by proton-proton collisions. It includes a range of technologies: trackers to detect particle trajectories, 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 immense, often described in terms of 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.
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