Could Misbehaving Muons Upend the Known Laws of Physics?

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The sphere of particle physics has a brand new and inconceivable star: the muon, which is usually known as a fats electron. For the second time, this unassuming resident of the subatomic world has appeared to flout the recognized legal guidelines of nature. To some consultants, that means it would reveal solely unknown guidelines. 

Muons drew the eye of physicists world wide after an experiment on the Fermi Nationwide Accelerator Laboratory, or Fermilab, in Illinois demonstrated that they’re much more magnetic than anticipated. The outcomes, revealed in April by the Muon g-2 collaboration (pronounced “g minus two”), run counter to the predictions of the highest out there particle physics principle. That leaves three potentialities: the idea itself is fallacious, the experiment was defective, or, most tantalizing, it might additionally imply that we’re near discovering new types of matter and power which can be important to the ordering of the cosmos however have gone undetected.

Many scientists are embracing the latter clarification. In the event that they’re appropriate, this represents the primary credible problem to the Commonplace Mannequin of particle physics, which has dominated for half a century as the most effective description of the universe’s fundamental constructing blocks and the way they work together. Wherever it has made a prediction, it has confirmed true — till now. 

Marcela Carena, head of theoretical physics at Fermilab, believes these outcomes might show extra important than even the landmark 2012 discovery of the Higgs boson, which imbues all the opposite particles with mass. “This may increasingly actually shake the best way we take into consideration all that we all know in the meanwhile about particle physics,” she says. “It’s an enormous discovery, and it’s an enormous discovery that we weren’t anticipating.”

A Magic, Magnetic Second

The potential for unexplained muon phenomena first arose in 2001, when comparable experiments on the Brookhaven Nationwide Laboratory in New York discovered one thing amiss: When shot by way of a magnetic area in a 50-foot-diameter accelerator, the tiny particle didn’t act as anticipated. In technical phrases, its “magnetic second” — a property that basically causes the muons to spin, or wobble, like bar magnets — was surprisingly giant. It wobbled greater than anybody foresaw.

The magnetic second is affected by a menagerie of digital particles that constantly pop out and in of existence. Chris Polly, one other Fermilab physicist, explains in a weblog put up that no particle is ever really alone. Even in a vacuum, it is surrounded by an “entourage” of those digital particles, every of which partially determines its conduct. Calculations of the muon’s magnetic second, known as “g-2” (therefore the collaboration’s title), painstakingly account for these outdoors influences. 

However, a major discrepancy exists between the measured and predicted values. If the recognized digital particles can’t sufficiently clarify that hole — assuming the measurements are correct — researchers deduce that another, unidentified particle(s) should make up the distinction.

Lee Roberts, a physicist at Boston College, labored on each the Brookhaven and Fermilab experiments. “That was an enormous deal,” he says of the revelation twenty years in the past, “as a result of everyone was desperately looking for physics past the Commonplace Mannequin.” After this system misplaced funding, that datapoint stood alone and anomalous for twenty years. Now, Roberts says, “we confirmed the Brookhaven experiment. The 2 outcomes are completely constant.”

Past the Commonplace Mannequin

Thrilling as which may be, the brand new experiment presents a puzzle missing any inkling of an answer. “We all know that one thing new have to be on the market,” Carena says, “however we don’t know what it’s.” Theorists have developed a constellation of explanations, and none notably stand out.

Given the selection, Carena’s most well-liked principle is supersymmetry, a well-liked extension of the Commonplace Mannequin. It posits that each recognized particle possesses an undiscovered companion. These stealthy counterparts could possibly be the digital particles contributing to the muon’s magnetic second, in addition to the elements of the darkish matter thought to account for about 27 p.c of the universe — fixing two mysteries with one eureka.

But she acknowledges that that is wishful pondering: “I believe it will be rather more elegant if we get some clues from this experiment towards different issues within the universe, however nature could not work that manner.” Different hypothetical particles — primarily leptoquarks and Z’ bosons — might fill the hole simply as simply, with out additional broadening our understanding of actuality. If these exist, although, the Giant Hadron Collider ought to finally detect them.

The query is very advanced, partly as a result of scientists do not know the place to hunt the reply. The Fermilab experiment provides solely oblique proof, hinting at new legal guidelines of physics by way of the muon. All in all, it doesn’t clearly determine any explicit suspect. “In an effort to distinguish which of these is correct,” Carena says, “we should look some other place.”

Ready for Clarification

As for why the muons are misbehaving, it’s too quickly to attract any particular conclusions. It’s additionally, maybe, fairly early to confidently say that they’re doing so within the first place. Up to now, the Muon g-2 members have revealed solely about 5 p.c of their knowledge. Given how meticulously they analyzed the primary set, Roberts is optimistic the remaining will reinforce the identical conclusion because it’s launched over the following few years. However for now, the scant proof doesn’t warrant updating the Commonplace Mannequin.

Some physicists have been hesitant to simply accept an overhaul of presumably probably the most profitable scientific principle of all time. In one other examine revealed in Nature on the identical day, Zoltan Fodor of Pennsylvania State College and his colleagues recalculated g-2 to verify for errors within the theoretical work from the previous twenty years. Their math yielded a brand new theoretical worth that differs from the one which physicists have typically agreed on, however matches the experimental outcomes from each Brookhaven and Fermilab.

This means the Commonplace Mannequin could match with the experiments in any case. “Whereas it could have been thrilling to find hints of recent physics,” Fodor writes, “our new principle appears to say that this time, the Commonplace Mannequin is holding up.”

As with all scientific discovery, time and additional analysis will inform. For now, one factor is certain: The Commonplace Mannequin stays incomplete. It says nothing about darkish matter and darkish power, nor why our universe consists of matter quite than antimatter. However physicists could have lately stumbled upon a clue, and to many who in itself warrants celebration. “To seek out one thing outdoors of that Commonplace Mannequin is type of the objective of all particle physics,” Roberts says. “There are all these very deep basic questions, so any perception into that could be very thrilling.”

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