The Standard Model of particle physics, which explains the fundamental building blocks of matter and their interactions, is known to be incomplete. Scientists are searching for signs of new physics phenomena to guide them towards a more comprehensive theory. At the recent ICHEP conference, the ATLAS collaboration presented its first results from searches for new physics at record collision energies, focusing on magnetic monopoles and long-lived particles.
Magnetic monopoles are hypothetical single-pole particles that would prove the complete symmetry between electricity and magnetism. They could confirm aspects of grand unified theories beyond the Standard Model. Researchers search for monopoles in high-energy collisions as they would be highly ionizing, leaving significant energy deposits in detectors.
In a new study, ATLAS analyzed heavy-ion (lead–lead) collision data from LHC Run 3, which was collected at an unprecedented energy of 5.36 TeV per pair of nucleons. The researchers looked for ultraperipheral collisions where the ions interact through the weaker but long-ranged electromagnetic force. These collisions can produce the largest magnetic fields in the universe.
No magnetic monopoles were found, setting the world’s best limits on their production rate in ultraperipheral heavy-ion collisions for monopole masses below 120 GeV. The study also introduced a methodology for studying highly ionizing particles in heavy-ion data.
Unlike most new physics searches, this search looked for long-lived particles that do not decay promptly but instead produce decay products away from the interaction point. These particles require dedicated techniques to reconstruct their tracks and might have been missed in previous searches. ATLAS discovered a rare signature of two particle tracks displaced from the interaction point, which could indicate new physics.
The first-of-its-kind search using 13.6 TeV proton–proton collision data from LHC’s Run 3 enabled the detection of these long-lived particles. The event yields in all search regions matched Standard Model expectations. These results set the strictest limits yet on the long-lived supersymmetric partners of electrons, muons, and tau leptons.
Scientists will continue their quest to find long-lived particles, magnetic monopoles, and other hypothetical particles with more data from the LHC and its future upgrade, the High-Luminosity LHC.
Source: https://home.cern/news/news/physics/atlas-probes-uncharted-territory-lhc-run-3-data