The magnetic second of the muon has posed a scientific puzzle because of the slight distinction between its theoretical and experimental values, suggesting interactions with unknown particles or forces. Analysis involving superior quantum simulations has began to unravel these discrepancies, providing insights into the basic properties of muons and their interactions in particle physics. Credit score: SciTechDaily.com The researchers recognized the origin of discrepancies in latest predictions of the muon’s magnetic second. Their findings may contribute to the investigation of darkish matter and different features of the brand new physics.Magnetic second is an intrinsic property of a particle with spin, arising from interplay between the particle and a magnet or different object with a magnetic discipline. Like mass and electrical cost, magnetic second is without doubt one of the elementary magnitudes of physics. There’s a distinction between the theoretical worth of the magnetic second of a muon, a particle that belongs to the identical class because the electron, and the values obtained in high-energy experiments carried out in particle accelerators.The distinction solely seems on the eighth decimal place, however scientists have been intrigued by it because it was found in 1948. It isn’t a element: it will probably point out whether or not the muon interacts with darkish matter particles or different Higgs bosons, and even whether or not unknown forces are concerned within the course of.Discrepancies in Muon’s Magnetic MomentThe theoretical worth of the muon’s magnetic second, represented by the letter g, is given by the Dirac equation – formulated by English physicist and 1933 Nobel Prize winner Paulo Dirac (1902-1984), one of many founders of quantum mechanics and quantum electrodynamics – as 2. Nonetheless, experiments have proven that g shouldn’t be precisely 2 and there’s an excessive amount of curiosity in understanding “g-2”, i.e. the distinction between the experimental worth and the worth predicted by the Dirac equation. The very best experimental worth presently obtainable, obtained to a powerful diploma of precision on the Fermi Nationwide Accelerator Laboratory (Fermilab) in the US and introduced in August 2023, is 2.00116592059, with an uncertainty vary of plus or minus 0.00000000022.“Exact dedication of the muon’s magnetic second has develop into a key concern in particle physics as a result of investigation of this hole between the experimental knowledge and the theoretical prediction can present data that might result in the invention of some spectacular new impact,” physicist Diogo Boito, a professor on the College of São Paulo’s São Carlos Institute of Physics (IFSC-USP), instructed Agência FAPESP.An article on the topic by Boito and collaborators is printed within the journal Bodily Evaluation Letters.New Insights From Analysis“Our outcomes had been offered at two vital worldwide occasions. First by me throughout a workshop in Madrid, Spain, and later by my colleague Maarten Golterman of San Francisco State College at a gathering in Bern, Switzerland,” Boito mentioned.These outcomes quantify and level to the origin of a discrepancy between the 2 strategies used to make present predictions of muon g-2. “There are presently two strategies for figuring out a elementary element of g-2. The primary relies on experimental knowledge, and the second on laptop simulations of quantum chromodynamics, or QCD, the speculation that research sturdy interactions between quarks. These two strategies produce fairly totally different outcomes, which is a significant drawback. Till it’s solved, we will’t examine the contributions of attainable unique particles corresponding to new Higgs bosons or darkish matter, for instance, to g-2,” he defined.The examine succeeded in explaining the discrepancy, however to grasp it we have to take a number of steps again and begin once more with a considerably extra detailed description of the muon.The muon storage ring at Fermilab. Credit score: Reidar Hahn, FermilabThe muon is a particle that belongs to the category of leptons, as does the electron, however has a a lot bigger mass. For that reason, it’s unstable and survives just for a really brief time in a high-energy context. When muons work together with one another within the presence of a magnetic discipline, they decay and regroup as a cloud of different particles, corresponding to electrons, positrons, W and Z bosons, Higgs bosons, and photons. In experiments, muons are, due to this fact, at all times accompanied by many different digital particles. Their contributions make the precise magnetic second measured in experiments larger than the theoretical magnetic second calculated by the Dirac equation, which is the same as 2.“To acquire the distinction [g-2], it’s crucial to think about all these contributions – each these predicted by QCD [in the Standard Model of particle physics] and others which are smaller however seem in high-precision experimental measurements. We all know a number of of those contributions very nicely – however not all of them,” Boito mentioned.The consequences of QCD sturdy interplay can’t be calculated theoretically alone, as in some vitality regimes they’re impracticable, so there are two potentialities. One has been used for a while and entails resorting to the experimental knowledge obtained from electron-positron collisions, which create different particles made up of quarks. The opposite is lattice QCD, which turned aggressive solely within the present decade and entails simulating the theoretical course of in a supercomputer.“The principle drawback with predicting muon g-2 proper now could be that the end result obtained utilizing knowledge from electron-positron collisions doesn’t agree with the full experimental end result, whereas the outcomes primarily based on lattice QCD do. Nobody was positive why, and our examine clarifies a part of this puzzle,” Boito mentioned.He and his colleagues carried out their analysis precisely to unravel this drawback. “The article stories the findings of quite a lot of research by which we developed a novel technique to match the outcomes of lattice QCD simulations with the outcomes primarily based on experimental knowledge. We present that it’s attainable to extract from the information contributions which are calculated within the lattice with nice precision – the contributions of so-called linked Feynman diagrams,” he mentioned.American theoretical physicist Richard Feynman (1918-1988) received the 1965 Nobel Prize in Physics (with Julian Schwinger and Shin’ichiro Tomonaga) for elementary work in quantum electrodynamics and the physics of elementary particles. Feynman diagrams, created in 1948, are graphical representations of the mathematical expressions that describe the interplay of such particles and are used to simplify the respective calculations.“Within the examine, we obtained the contributions of linked Feynman diagrams within the so-called ‘intermediate vitality window’ with nice precision for the primary time. Right now we’ve got eight outcomes for these contributions, obtained by way of lattice QCD simulations, and all of them conform to a big extent. Furthermore, we present that the outcomes primarily based on electron-positron interplay knowledge don’t agree with these eight outcomes from simulations,” Boito mentioned.This enabled the researchers to find the supply of the issue and take into consideration attainable options. “It turned clear that if the experimental knowledge for the two-pion channel are underestimated for some motive, this may very well be the reason for the discrepancy,” he mentioned. Pions are mesons – particles made up of a quark and an antiquark produced in high-energy collisions.In truth, new knowledge (nonetheless being peer-reviewed) from the CMD-3 Experiment carried out at Novosibirsk State College in Russia seems to point out that the oldest two-pion channel knowledge could have been underestimated for some motive.Reference: “Information-Pushed Dedication of the Gentle-Quark Linked Element of the Intermediate-Window Contribution to the Muon g−2” by Genessa Benton, Diogo Boito, Maarten Golterman, Alexander Keshavarzi, Kim Maltman and Santiago Peris, 21 December 2023, Bodily Evaluation Letters.DOI: 10.1103/PhysRevLett.131.251803Boito’s participation within the examine was a part of his challenge “Testing the usual mannequin: precision QCD and muon g-2,” for which FAPESP awarded him a Section 2 Younger Investigator Grant.