Home Science Muon G-2 Experiment Reinforces Shock End result, Setting Up “Final Showdown”

Muon G-2 Experiment Reinforces Shock End result, Setting Up “Final Showdown”

Muon G-2 Experiment Reinforces Shock End result, Setting Up “Final Showdown”

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Sub Atomic Particle Quantum Physics Art Illustration

Fermilab’s Muon g-2 experiment has unveiled a brand new precision measurement of the muon’s magnetic property, hinting at undiscovered particles and a possible breakthrough in physics. The outcomes set the stage for a ultimate showdown between the present idea and experiment in 2025.

Findings at Fermilab present discrepancy between idea and experiment, which can result in new physics past the Normal Mannequin.

Physicists now have a brand-new measurement of a property of the muon referred to as the anomalous magnetic second that improves the precision of their earlier outcome by an element of two.

A world collaboration of scientists engaged on the Muon g-2 experiment on the U.S. Division of Power’s Fermi Nationwide Accelerator Laboratory introduced the much-anticipated up to date measurement on August 10. This new worth bolsters the first outcome they introduced in April 2021, and units up a showdown between idea and experiment over 20 years within the making.

“We’re actually probing new territory. We’re figuring out the muon magnetic second at a greater precision than it has ever been seen earlier than,” stated Brendan Casey, a senior scientist at Fermilab who has labored on the Muon g-2 experiment since 2008.

Muon g-2 Experiment

The announcement on August 10, 2023, is the second outcome from the experiment at Fermilab, which is twice as exact as the primary outcome introduced on April 7, 2021. Credit score: Ryan Postel, Fermilab

Past the Normal Mannequin

Physicists describe how the universe works at its most elementary degree with a idea often called the Normal Mannequin. By making predictions primarily based on the Normal Mannequin and evaluating them to experimental outcomes, physicists can discern whether or not the speculation is full — or if there’s physics past the Normal Mannequin.

Muons are elementary particles which are much like electrons however about 200 instances as huge. Like electrons, muons have a tiny inside magnet that, within the presence of a magnetic discipline, precesses or wobbles just like the axis of a spinning prime. The precession velocity in a given magnetic discipline is determined by the muon magnetic second, sometimes represented by the letter g; on the easiest degree, idea predicts that g ought to equal 2.


This seven-minute video gives further details about muons and the brand new outcome by the Muon g-2 collaboration.

The Significance of g-2

The distinction of g from 2 — or g minus 2 — will be attributed to the muon’s interactions with particles in a quantum foam that surrounds it. These particles blink out and in of existence and, like subatomic “dance companions,” seize the muon’s “hand” and alter the way in which the muon interacts with the magnetic discipline. The Normal Mannequin incorporates all recognized “dance companion” particles and predicts how the quantum foam adjustments g. However there may be extra. Physicists are excited in regards to the attainable existence of as-yet-undiscovered particles that contribute to the worth of g-2 — and would open the window to exploring new physics.

Gordan Krnjaic, a theoretical particle physicist at Fermilab and the College of Chicago Kavli Institute for Cosmological Physics, instructed the New York Instances that if the experimental disagreement with idea endured, it could be “the primary smoking-gun laboratory proof of recent physics. And it’d nicely be the primary time that we’ve damaged the Normal Mannequin.”

Uncertainties within the Measurement

The brand new experimental outcome, primarily based on the primary three years of knowledge, introduced by the Muon g-2 collaboration is:
g-2 = 0.00233184110 +/- 0.00000000043 (stat.) +/- 0.00000000019 (syst.)

The measurement of g-2 corresponds to a precision of 0.20 elements per million. The Muon g-2 collaboration describes the end in a paper that they submitted to Bodily Overview Letters.

With this measurement, the collaboration has already reached their purpose of lowering one explicit sort of uncertainty: uncertainty attributable to experimental imperfections, often called systematic uncertainties.

Muon g-2 Results

As a result of great amount of further information that’s going into the 2023 evaluation announcement, the Muon g-2 collaboration’s newest result’s greater than twice as exact as the primary outcome introduced in 2021. Credit score: Muon g-2 collaboration

“This measurement is an unbelievable experimental achievement,” stated Peter Winter, co-spokesperson for the Muon g-2 collaboration. “Getting the systematic uncertainty all the way down to this degree is an enormous deal and is one thing we didn’t count on to realize so quickly.”

Whereas the full systematic uncertainty has already surpassed the design purpose, the bigger side of uncertainty — statistical uncertainty — is pushed by the quantity of knowledge analyzed. The outcome introduced at the moment provides a further two years of knowledge to their first outcome. The Fermilab experiment will attain its final statistical uncertainty as soon as scientists incorporate all six years of knowledge of their evaluation, which the collaboration goals to finish within the subsequent couple of years.

Experiment Particulars

To make the measurement, the Muon g-2 collaboration repeatedly despatched a beam of muons right into a 50-foot-diameter superconducting magnetic storage ring, the place they circulated about 1,000 instances at almost the velocity of sunshine. Detectors lining the ring allowed scientists to find out how quickly the muons have been precessing. Physicists should additionally exactly measure the energy of the magnetic discipline to then decide the worth of g-2.

The Fermilab experiment reused a storage ring initially constructed for the predecessor Muon g-2 experiment at DOE’s Brookhaven Nationwide Laboratory that concluded in 2001. In 2013, the collaboration transported the storage ring 3,200 miles from Lengthy Island, New York, to Batavia, Illinois. Over the following 4 years, the collaboration assembled the experiment with improved methods, instrumentation and simulations. The principle purpose of the Fermilab experiment is to scale back the uncertainty of g-2 by an element of 4 in comparison with the Brookhaven outcome.

Along with the bigger information set, this newest g-2 measurement is enhanced by updates to the Fermilab experiment itself.

“It would nicely be the primary time that we’ve damaged the Normal Mannequin.”

Gordan Krnjaic, Fermilab and UChicago scientist

Conclusion: Way forward for the Experiment

“Our new measurement could be very thrilling as a result of it takes us nicely past Brookhaven’s sensitivity,” stated Graziano Venanzoni, professor on the College of Liverpool affiliated with the Italian Nationwide Institute for Nuclear Physics, Pisa, and co-spokesperson of the Muon g-2 experiment at Fermilab.

Along with the bigger information set, this newest g-2 measurement is enhanced by updates to the Fermilab experiment itself. “We improved quite a lot of issues between our first yr of taking information and our second and third yr,” stated Casey, who lately completed his time period as co-spokesperson with Venanzoni. “We have been always making the experiment higher.”

The experiment was “actually firing on all cylinders” for the ultimate three years of data-taking, which got here to an finish on July 9, 2023. That’s when the collaboration shut off the muon beam, concluding the experiment after six years of knowledge assortment. They reached the purpose of accumulating a knowledge set that’s greater than 21 instances the scale of Brookhaven’s information set.

Physicists can calculate the results of the recognized Normal Mannequin “dance companions” on muon g-2 to unbelievable precision. The calculations contemplate the electromagnetic, weak nuclear and robust nuclear forces, together with photons, electrons, quarks, gluons, neutrinos, W and Z bosons, and the Higgs boson. If the Normal Mannequin is right, this ultra-precise prediction ought to match the experimental measurement.

Calculating the Normal Mannequin prediction for muon g-2 could be very difficult. In 2020, the Muon g-2 Idea Initiative introduced the most effective Normal Mannequin prediction for muon g-2 accessible at the moment. However a brand new experimental measurement of the info that feeds into the prediction and a brand new calculation primarily based on a unique theoretical method — lattice gauge idea — are in rigidity with the 2020 calculation. Scientists of the Muon g-2 Idea Initiative purpose to have a brand new, improved prediction accessible within the subsequent couple of years that considers each theoretical approaches.

The Muon g-2 collaboration contains near 200 scientists from 33 establishments in seven international locations and contains almost 40 college students to this point who’ve acquired their doctorates primarily based on their work on the experiment. Collaborators will now spend the following couple of years analyzing the ultimate three years of knowledge. “We count on one other issue of two in precision once we end,” stated Venanzoni.

The collaboration anticipates releasing their ultimate, most exact measurement of the muon magnetic second in 2025 — organising the last word showdown between Normal Mannequin idea and experiment. Till then, physicists have a brand new and improved measurement of muon g-2 that may be a vital step towards its ultimate physics purpose.

The Muon g-2 collaboration submitted this scientific paper for publication.

Right here is the recording of the scientific seminar held on August 10, 2023.

The Muon g-2 experiment is supported by the Division of Power (US); Nationwide Science Basis (US); Istituto Nazionale di Fisica Nucleare (Italy); Science and Know-how Amenities Council (UK); Royal Society (UK); European Union’s Horizon 2020; Nationwide Pure Science Basis of China; MSIP, NRF and IBS-R017-D1 (Republic of Korea); and German Analysis Basis (DFG).



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