Might Misbehaving Muons Upend the Identified Legal guidelines of Physics?
Muons drew the eye of physicists around the globe after an experiment on the Fermi Nationwide Accelerator Laboratory, or Fermilab, in Illinois demonstrated that they’re way more magnetic than anticipated. The outcomes, printed in April by the Muon g-2 collaboration (pronounced “g minus two”), run counter to the predictions of the highest obtainable particle physics principle. That leaves three potentialities: the idea itself is unsuitable, the experiment was defective, or, most tantalizing, it may additionally imply that we’re near discovering new types of matter and vitality 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 Customary 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 may show extra important than even the landmark 2012 discovery of the Higgs boson, which imbues all the opposite particles with mass. “This may occasionally actually shake the best way we take into consideration all that we all know in the mean time 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 opportunity of 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 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 massive. 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 publish that no particle is ever actually alone. Even in a vacuum, it is surrounded by an “entourage” of those digital particles, every of which partially determines its habits. Calculations of the muon’s magnetic second, known as “g-2” (therefore the collaboration’s identify), painstakingly account for these exterior influences.
Nonetheless, a big 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 a giant deal,” he says of the revelation 20 years in the past, “as a result of everyone was desperately trying to find physics past the Customary Mannequin.” After this system misplaced funding, that datapoint stood alone and anomalous for 20 years. Now, Roberts says, “we confirmed the Brookhaven experiment. The 2 outcomes are completely constant.”
Past the Customary Mannequin
Thrilling as that could be, the brand new experiment presents a puzzle missing any inkling of an answer. “We all know that one thing new should 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 popular principle is supersymmetry, a preferred extension of the Customary Mannequin. It posits that each recognized particle possesses an undiscovered associate. These stealthy counterparts could possibly be the digital particles contributing to the muon’s magnetic second, in addition to the components 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 feel it might be rather more elegant if we get some clues from this experiment towards different issues within the universe, however nature might not work that means.” Different hypothetical particles — primarily leptoquarks and Z’ bosons — may fill the hole simply as simply, with out additional broadening our understanding of actuality. If these exist, although, the Massive Hadron Collider ought to finally detect them.
The query is extremely advanced, partly as a result of scientists do not know the place to hunt the reply. The Fermilab experiment affords solely oblique proof, hinting at new legal guidelines of physics by the muon. All in all, it doesn’t clearly establish any explicit suspect. “In an effort to distinguish which of these is correct,” Carena says, “we must look some place else.”
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. Thus far, the Muon g-2 members have printed solely about 5 p.c of their information. Given how meticulously they analyzed the primary set, Roberts is optimistic the remaining will reinforce the identical conclusion because it’s launched over the subsequent few years. However for now, the scant proof doesn’t warrant updating the Customary Mannequin.
Some physicists have been hesitant to simply accept an overhaul of presumably essentially the most profitable scientific principle of all time. In one other examine printed 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 20 years. Their math yielded a brand new theoretical worth that differs from the one which physicists have usually agreed on, however matches the experimental outcomes from each Brookhaven and Fermilab.
This implies the Customary Mannequin might match with the experiments in any case. “Whereas it could have been thrilling to find hints of latest physics,” Fodor writes, “our new principle appears to say that this time, the Customary Mannequin is holding up.”
As with all scientific discovery, time and additional analysis will inform. For now, one factor is bound: The Customary Mannequin stays incomplete. It says nothing about darkish matter and darkish vitality, nor why our universe consists of matter reasonably than antimatter. However physicists might have just lately stumbled upon a clue, and to many who in itself warrants celebration. “To search out one thing exterior of that Customary Mannequin is type of the objective of all particle physics,” Roberts says. “There are all these very deep elementary questions, so any perception into that could be very thrilling.”