Researchers investigated a new detector signature known as semi-visible jets, which scientists had never looked at before, in order to determine whether Dark Matter particles are produced inside a jet of standard model particles.
The existence of Dark Matter has long been a mystery in our universe. Despite accounting for roughly a quarter of our universe, dark matter has little interaction with ordinary matter. A series of astrophysical and cosmological observations, including the stunning recent images from the James Webb Space Telescope, have confirmed the existence of Dark Matter. However, no experimental observations of dark matter have been reported to date. The existence of Dark Matter has been a question that high energy and astrophysicists around the world have been investigating for decades.
“This is the reason we do research in basic science, probing the deepest mysteries of the universe. The Large Hadron Collider at CERN is the largest experiment ever built, and particle collisions creating big-bang conditions can be exploited to look for hints of dark matter,” says Professor Deepak Kar, from the School of Physics at the University of the Witwatersrand in Johannesburg, South Africa.
There have been a plethora of collider searches for Dark Matter over the past few decades so far have focused on weakly interacting massive particles, termed WIMPs. WIMPS are one class of particles proposed to explain Dark Matter because they do not absorb or emit light and do not interact strongly with other particles.
Professor Deepak Kar
Kar and his former PhD student, Sukanya Sinha (now a postdoctoral researcher at the University of Manchester), pioneered a new method of searching for Dark Matter at CERN’s ATLAS experiment. Their findings were published in the journal Physics Letters B.
“There have been plethora of collider searches for Dark Matter over the past few decades so far have focused on weakly interacting massive particles, termed WIMPs,” according to Kar. “WIMPS are one class of particles proposed to explain Dark Matter because they do not absorb or emit light and do not interact strongly with other particles. However, because no evidence of WIMPS’ has been discovered thus far, we realized that the search for Dark Matter required a paradigm shift.”
“What we were wondering, was whether Dark Matter particles actually are produced inside a jet of standard model particles,” said Kar. This led to the exploration of a new detector signature known as semi-visible jets, which scientists never looked at before.
High energy collisions of protons often result in the production of a collimated spray of particles, collected in what is termed as jets, from the decay of ordinary quarks or gluons. Semi-visible jets would arise when hypothetical dark quarks decay partially to Standard-Model quarks (known particles) and partially to stable dark hadrons (the “invisible fraction”).
Because they are produced in pairs, usually in conjunction with additional Standard-Model jets, an energy imbalance or missing energy in the detector occurs when all of the jets are not fully balanced. The missing energy is frequently aligned with one of the semi-visible jets.
This makes searching for semi-visible jets extremely difficult, as this event signature can also be caused by mis-measured jets in the detector. Kar and Sinha’s new approach to searching for Dark Matter opens up new avenues for investigating the existence of Dark Matter.
“Even though my PhD thesis does not contain a discovery of Dark Matter, it sets the first and rather stringent upper bounds on this production mode and already inspiring further studies,” Sinha said.
