Theorists publish highest-precision prediction of muon magnetic anomaly


TheMuon g-2 storage ring set up and prepared to take information at Fermi National AcceleratorLaboratory Credit:Fermilab

Theoretical physicists at the United States Department of Energy’s (DOE’s) Brookhaven National Laboratory and their partners have actually simply launched the most exact prediction of how subatomic particles called muons– heavy cousins of electrons–“wobble” off their course in an effective magnetic field. The estimations take into consideration how muons connect with all other recognized particles through 3 of nature’s 4 essential forces (the strong nuclear force, the weak nuclear force, and electromagnetism) while decreasing the best source of unpredictability in theprediction The results, released in PhysicalReview Letters as an Editors’ Suggestion, come in the nick of time for the start of a brand-new experiment determining the wobble now underway at DOE’s Fermi National Accelerator Laboratory (Fermilab).

A variation of this experiment, referred to as “Muon g-2,” performed at Brookhaven Lab in the late 1990 s and early 2000 s, producing a series of results showing a disparity in between the measurement and theprediction Though not substantial adequate to state a discovery, those outcomes hinted that brand-new, yet-to-be found particles may be impacting the muons’ habits. The brand-new experiment at Fermilab, integrated with the higher-precision estimations, will offer a more strict test of the Standard Model, the ruling theory of particle physics. If the disparity in between experiment and theory still stands, it might indicate the presence of brand-new particles.

.

“If there’s another particle that pops into existence and interacts with the muon before it interacts with the magnetic field, that could explain the difference between the experimental measurement and our theoretical prediction,” stated Christoph Lehner, one of the Brookhaven Lab theorists associated with the current estimations. “That could be a particle we’ve never seen before, one not included in the Standard Model.”

.

Finding brand-new particles beyond those currently cataloged by the Standard Model has actually long been a mission for particle physicists. Spotting indications of a brand-new particle impacting the habits of muons might assist the style of experiments to look for direct proof of such particles, stated Taku Izubuchi, another leader of Brookhaven’s theoretical physics group.

.

“It would be a strong hint and would give us some information about what this unknown particle might be—something about what the new physics is, how this particle affects the muon, and what to look for,”Izubuchi stated.

.

Themuon anomaly

.

TheMuon g-2 experiment determines exactly what takes place as muons distribute through a 50- foot-diameter electromagnet storage ring. The muons, which have intrinsic magnetism and spin (sort of like spinning toy tops), start with their spins lined up with their instructions of movement. But as the particles go ’round and ’round the magnet racetrack, they connect with the storage ring’s magnetic field as well as with a zoo of virtual particles that appear and out of presence within the vacuum. This all takes place in accordance with the guidelines of the Standard Model, which explains all the recognized particles and their interactions, so the mathematical estimations based upon that theory can exactly forecast how the muons’ positioning need to precess, or “wobble” far from their spin-aligned course. Sensors surrounding the magnet determine the precession with severe accuracy so the physicists can evaluate whether the theory-generated prediction is right.

.

Both the experiments determining this amount and the theoretical forecasts have actually ended up being a growing number of exact, tracing a journey throughout the nation with input from numerous well-known physicists.

.

A race and cooperation for accuracy

.

“There is a race of sorts between experiment and theory,”Lehner stated. “Getting a more precise experimental measurement allows you to test more and more details of the theory. And then you also need to control the theory calculation at higher and higher levels to match the precision of the experiment.”

.

With remaining tips of a brand-new discovery from the Brookhaven experiment– however likewise the possibility that the disparity would vanish with greater accuracy measurements– physicists promoted the chance to continue the search utilizing a higher-intensity muon beam atFermilab In the summer season of 2013, the 2 laboratories collaborated to transportation Brookhaven’s storage ring through a legendary land-and-sea journey from Long Island toIllinois After tuning up the magnet and making a variety of other changes, the group at Fermilab just recently began taking brand-new information.

.

Meanwhile, the theorists have actually been fine-tuning their estimations to match the accuracy of the brand-new experiment.

.

“There have been many heroic physicists who have spent a huge part of their lives on this problem,”Izubuchi stated. “What we are measuring is a tiny deviation from the expected behavior of these particles—like measuring a half a millimeter deviation in the flight distance between New York and Los Angeles! But everything about the fate of the laws of physics depends on that difference. So, it sounds small, but it’s really important. You have to understand everything to explain this deviation,” he stated.

.

The course to lowered unpredictability

.

By”everything” he indicates how all the recognized particles of the Standard Model impact muons through nature’s 4 essential forces– gravity, electromagnetism, the strong nuclear force, and the electroweak force. Fortunately, the electroweak contributions are well comprehended, and gravity is believed to play a presently minimal function in the muon’s wobble. So the current effort– led by the Brookhaven group with contributions from the RBC Collaboration (comprised of physicists from the RIKEN BNL Research Center, Brookhaven Lab, and Columbia University) and the UKQCD cooperation– focuses particularly on the combined results of the strong force (explained by a theory called quantum chromodynamics, or QCD) and electromagnetism.

.

“This has been the least understood part of the theory, and therefore the greatest source of uncertainty in the overall prediction. Our paper is the most successful attempt to reduce those uncertainties, the last piece at the so-called ‘precision frontier’—the one that improves the overall theory calculation,”Lehner stated.

.

The mathematical estimations are incredibly complicated– from setting out all the possible particle interactions and comprehending their private contributions to determining their combined results. To take on the obstacle, the physicists utilized a technique referred to as Lattice QCD, initially established at Brookhaven Lab, and effective supercomputers. The biggest was the Leadership Computing Facility at Argonne National Laboratory, a DOE Office of Science user center, while smaller sized supercomputers hosted by Brookhaven’s Computational Sciences Initiative (CSI)– consisting of one device bought with funds from RIKEN, CSI, and Lehner’s DOE Early Career Research Award financing– were likewise important to the outcome.

.

“One of the reasons for our increased precision was our new methodology, which combined the most precise data from supercomputer simulations with related experimental measurements,”Lehner kept in mind.

.

Other groups have actually likewise been dealing with this issue, he stated, and the whole neighborhood of about 100 theoretical physicists will be talking about all of the lead to a series of workshops over the next numerous months to come to arrangement on the worth they will utilize to compare to the Fermilab measurements.

.

“We’re really looking forward to Fermilab’s results,”Izubuchi stated, echoing the anticipation of all the physicists who have actually come prior to him in this mission to comprehend the tricks of deep space.


Explore even more:
Muons spin tales of undiscovered particles.

.
More info:
T. Blum et al, Calculation of the Hadronic Vacuum Polarization Contribution to the Muon Anomalous Magnetic Moment, PhysicalReview Letters(2018). DOI: 10.1103/ PhysRevLett.121022003

Journal recommendation:
PhysicalReviewLetters

Provided by:
BrookhavenNationalLaboratory

Recommended For You

About the Author: livescience

Leave a Reply

Your email address will not be published. Required fields are marked *