Jan 14, 2024 08:40 AM
https://physics.aps.org/articles/v17/6
EXCERPTS: The magnetic moment of the muon, which describes how this electron-like particle wobbles in a magnetic field, has been a stubborn nut for particle physicists to crack. The experimentally determined values of this parameter have long disagreed with those from theoretical predictions, a trend that continued with a recent result from the Muon g-2 experiment at Fermi National Accelerator Laboratory in Illinois (see Research News: Mismatch with Standard-Model Predictions Reaches 5 Sigma).
Such a discrepancy is exciting, as it could provide a hint of new physics that might resolve some of the outstanding problems in particle physics. However, the size of the discrepancy depends on which group of theorists you talk to. Resolving that theoretical discrepancy is currently the top goal for researchers in the muon-moment community.
[...] If the muon were a classical object, its moment would equal 2 (in dimensionless units). But it is not. The measured value is about 0.1% more than 2. That tiny extra bit—the muon’s so-called anomalous magnetic moment (aµ)—arises from interactions of the muon with particles that briefly pop in and out of existence. These “virtual” particles form a haze around the muon, influencing how it responds to a magnetic field.
Virtual particles come in all varieties: electrons, neutrinos, vector bosons, and everything in between. But the ones that give theorists the biggest headache are the hadrons, which are quark-containing particles such as pions and protons. “This is the source of all the difficulties,” El-Khadra says.
[...] So what does the future hold for new physics? For now, no one wants to speculate. But both Blum and El-Khadra note that if the final theoretical prediction ends up being close to the current lattice estimates, there would still be a discrepancy with experimental values. And no matter what happens, theorists will have to explain why their two main calculation methods gave such different answers. “I’m by no means pessimistic,” Blum says. “There’s going to be something very interesting to discover.” (MORE - missing details)
EXCERPTS: The magnetic moment of the muon, which describes how this electron-like particle wobbles in a magnetic field, has been a stubborn nut for particle physicists to crack. The experimentally determined values of this parameter have long disagreed with those from theoretical predictions, a trend that continued with a recent result from the Muon g-2 experiment at Fermi National Accelerator Laboratory in Illinois (see Research News: Mismatch with Standard-Model Predictions Reaches 5 Sigma).
Such a discrepancy is exciting, as it could provide a hint of new physics that might resolve some of the outstanding problems in particle physics. However, the size of the discrepancy depends on which group of theorists you talk to. Resolving that theoretical discrepancy is currently the top goal for researchers in the muon-moment community.
[...] If the muon were a classical object, its moment would equal 2 (in dimensionless units). But it is not. The measured value is about 0.1% more than 2. That tiny extra bit—the muon’s so-called anomalous magnetic moment (aµ)—arises from interactions of the muon with particles that briefly pop in and out of existence. These “virtual” particles form a haze around the muon, influencing how it responds to a magnetic field.
Virtual particles come in all varieties: electrons, neutrinos, vector bosons, and everything in between. But the ones that give theorists the biggest headache are the hadrons, which are quark-containing particles such as pions and protons. “This is the source of all the difficulties,” El-Khadra says.
[...] So what does the future hold for new physics? For now, no one wants to speculate. But both Blum and El-Khadra note that if the final theoretical prediction ends up being close to the current lattice estimates, there would still be a discrepancy with experimental values. And no matter what happens, theorists will have to explain why their two main calculation methods gave such different answers. “I’m by no means pessimistic,” Blum says. “There’s going to be something very interesting to discover.” (MORE - missing details)