Recent technical advancements have allowed for the production of more sophisticated telescopes and astrophysical instrumentation. This includes the IceCube telescope, which was designed to detect and study high-energy neutrinos in the cosmos.
High-energy neutrino observatories, such as the IceCube telescope, may detect other unusual particles, such as magnetic monopoles, in addition to neutrinos. Magnetic monopoles are hypothetical fundamental particles made up of a single magnetic pole on an isolated magnet.
The IceCube Collaboration has established the most stringent restrictions on relativistic magnetic monopoles to date using their high-energy neutrino observatory. Their findings, which were published in Physical Review Letters, highlight the potential of neutrino telescopes for searching for unusual particles.
“A magnetic monopole traveling near the speed of light (also known as a relativistic monopole) would emit light, known as Cherenkov radiation, as it traversed the ice where IceCube is deployed, leaving a very distinct signature in the detector: a very bright straight track crossing the detector,” Carlos Perez de los Heros, one of the study’s authors, told Phys.org. “Our initial plan was to look for extremely bright tracks in the eight years of data from the IceCube telescope.”
Grand unified theories are a group of hypotheses that explain the development of the early cosmos, implying that all known forces were united into a single force at the time. Similarly, diverse electric and magnetic effects are now thought to be caused by a single force known as the electromagnetic force. Grand unified theories, for example, predict the presence of particles with a single magnetic “pole” (i.e., monopoles).
“There are now signs, but no confirmation, that the strong and nuclear forces were merged with the electromagnetic force in the early cosmos, and that they split as distinct forces as the universe evolved,” de los Heros said. “Magnetic monopoles, along with other stuff, should have been produced shortly after the big bang, according to these hypotheses.”
Because monopoles are theoretically stable, a gas of relic monopoles might still be permeating space today, despite the fact that no observatory has yet observed them. De los Heros and his colleagues were hopeful that the IceCube telescope would finally allow them to be detected.
“The major goal of our analysis was to find a cosmic flow of magnetic monopoles with monopole speeds ranging from 0.75 to 0.995 times the speed of light,” said Alexander Burgman, another researcher participating in the current study, to Phys.org. “Several prior studies have been conducted in search of a cosmic flow of magnetic monopoles, both utilizing IceCube data and observations with other facilities.”
The IceCube project has revealed data gathered by their high-energy neutrino telescope over an eight-year period. This is a far longer observation duration than that considered in earlier monopole searches, which was roughly a year. Finally, the scientists believed that by combining this data with improved data processing and reconstruction capabilities, they would be able to discover monopoles and other strange particles.
“No signal in experimental physics is fully devoid of background noise (signals from other processes that imitate what you’re looking for),” de los Heros stated. “Although it happens seldom, extremely high energy neutrinos from far away may interact near IceCube and generate a muon (a highly penetrating particle that resembles a heavy electron) that would pass the detector. These muons also emit Cherenkov radiation in the detector (which is how IceCube identifies high-energy neutrinos) and may imitate a monopole track, however the light emission pattern of a muon and a monopole differs somewhat.”
The IceCube telescope is capable of recording around 2,700 particle “events” each second. These events might be triggered by muons and neutrinos produced in the environment, astrophysical neutrinos, or a magnetic monopole crossing the detector.
“At first, we discovered several parameters that would identify a magnetic monopole event from the typical ones we saw,” Burgman said. “Among them are the quantity of light measured in the event (magnetic monopoles create a lot of light while propagating through ice) and the unevenness of the light output (monopoles would have a very smooth and even light output throughout their route).”
As a first stage, the researchers were able to exclude the majority of typical events identified by the IceCube telescope based only on their brightness. Following that, scientists trained a machine learning system to categorize the remaining “events” as magnetic monopole- or neutrino-like based on a set of important parameters.
“We trained the IceCube computer cluster to discern between muon tracks and monopole tracks using machine learning and comprehensive computer simulations of the detector response to monopoles and muons,” de los Heros said. “Once the training was finished, the computers were given the eight-year dataset (a total of 630 billion occurrences) with the goal of identifying one or more monopoles in the data.”
In their assessments, de los Heros, Burgman, and his colleagues from the IceCube Collaboration found no occurrences matching the characteristics of a magnetic monopole. Nonetheless, their findings enabled them to establish an upper limit on the cosmic monopole flow.
“Negative outcomes are equally significant in physics because they impose restrictions on ideas,” de los Heros said. “In this situation, our findings indicate that the cosmos has less than a certain number of relativistic monopoles (approximately 2×10-19 per cm2 second and stereoradian, which corresponds to less than 0.1 monopoles in a volume like the Earth at any given time). We would have discovered some if the flux of relativistic monopoles had been larger, since our analysis was sensitive to a higher flux.”
The IceCube collaboration’s new limitations may have significant ramifications for current hypotheses explaining the history of the early cosmos. More particular, their calculations indicate that the flux of relativistic magnetic monopoles cannot be greater than the limit they established.
“Our work adds to the entire panorama of magnetic monopole searches,” Burgman added. “Despite the fact that we did not identify one, the findings of our research will help to direct the future generation of searches. This form of incremental inquiry is essential for studying previously unknown phenomena.”
Surprisingly, the limit on the relic flux of relativistic monopoles given by de los Heros, Burgman, and their colleagues is now the most stringent. In addition to establishing this critical limit, their research reveals the IceCube telescope’s adaptability and broad scientific scope, as well as those of other comparable equipment. The IceCube cooperation is now looking for monopoles with lower speeds than those found in their previous study.
“For monopoles, there is no preferred anticipated speed range,” de los Heros noted. “We looked for monopoles with speeds close to the speed of light (relativistic monopoles), but the quest for slower monopoles continues. However, if IceCube gathers additional years of data, the restriction that we set may be increased more rigorous by include more data in the analysis (if a monopole is not detected).”