October 1, 2024
5 min learn
A One-in-10-Billion Particle Decay Hints at Hidden Physics
Physicists have detected a long-sought particle course of that will counsel new forces and particles exist within the universe
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As soon as in a really nice whereas, an ephemeral particle referred to as a kaon arises after which rapidly decays away into three different obscure entities. Whether or not or not this occurs in a specific means has little or no bearing on most of us, who will go about our lives with out figuring out both means. However to physicists who’ve been looking for this arcane course of for many years, it issues a lot; discovering out how typically it occurs may reveal hidden points of our universe.
Now, for the primary time, scientists have noticed this uncommon decay, they usually have discovered that it might need barely larger odds of occurring than its predicted probability of about one in 10 billion. If that seems to be true, some unseen actor have to be interfering within the decay—probably a brand new particle or pressure beforehand unidentified in nature.
The discovering, made on the NA62 experiment at CERN, the European laboratory for particle physics close to Geneva, was introduced final week. “This is important,” says Andrzej Buras, a theoretical physicist on the Technical College of Munich. Thirty years in the past Buras, along with his scholar Gerhard Buchalla, made the primary superior theoretical prediction of how typically the decay happens in response to the Normal Mannequin of particle physics. He’s “optimistic” it would show to be extra widespread than anticipated, however he cautions that the experiment’s findings aren’t but robust sufficient to say for positive. “People are excited,” Buras says. “I expect in a few weeks, you will find many new papers [attempting to explain the result], and each one will claim something different.”
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The unlikely course of below scrutiny begins with kaons, that are unusual—actually. They include “strange quarks,” weirder and heavier variations of the quarks inside atoms. First found in 1947, kaons aren’t generally present in nature however could be created inside particle detectors, in addition to by cosmic rays crashing into Earth’s environment. Kaons decay rapidly into plenty of varied different particles. However the specific decay simply noticed merely doesn’t occur within the regular course of issues.
To catch kaons within the act, the experiment sprays a hose of protons at an unmoving goal of beryllium atoms. The collisions produce plenty of kaons, amongst different issues. The kaons then fly down a roughly 150-meter-long vacuum tunnel. Alongside the journey, they decay. On the finish of the tunnel is a detector that goals to measure the id, velocity and power of each single particle that passes via it. Solely by eliminating all the things else can the physicists dwelling in on the uncommon occasion they search: kaons decaying right into a pion (a particle made from an “up” quark and an “anti-down” quark), in addition to a neutrino and an antineutrino. “The point of the experiment is to see everything with 100 percent efficiency—you can’t miss anything,” says NA62 spokesperson Giuseppe Ruggiero of the College of Florence in Italy and the nation’s Nationwide Institute for Nuclear Physics.
This decay is so uncommon as a result of it requires “virtual particles.” The legal guidelines of quantum mechanics, odd as they’re, permit particles to pop into being out of nothing and rapidly disappear once more. Generally these digital particles come up as one particle is reworking into one other—and alter the course of the decay. For example, when kaons decay, they very often bear interference from digital variations of the W and Z bosons (the particles recognized to hold the weak nuclear pressure). This meddling is what permits the kaon to provide a pion and two neutrinos, the method NA62 seeks. The Normal Mannequin—the most effective principle scientists have—predicts this may occur exactly eight instances out of each 100 billion decays.
If it occurs roughly typically, one thing else have to be happening—one thing past what’s described within the Normal Mannequin. “The model works very well, but there are many questions we cannot answer,” Buras says. “The two most important, in my view, are the existence of dark matter and our own existence: Why do we have matter and no antimatter in the universe?”
If measurements of kaon decays don’t match the Normal Mannequin, scientists can conclude that further digital particles of unknown selection have to be muddying these decays. The brand new measurement discovered that the decay occurs about 13 instances in each 100 billion decays—albeit with an estimated uncertainty of about 25 %. “It’s promising—it gives us hope that we may discover a deviation from the Standard Model,” says NA62 group member Cristina Lazzeroni, a physicist on the College of Birmingham in England and former spokesperson for the experiment. “But statistically speaking, it’s not a proof. That’s why we need more data.”
If future measurements verify that the decay contradicts predictions, there are a number of potential digital particles that might determine in.
One chance is a hypothetical particle referred to as a Z′ (pronounced “Z prime”) boson. This may be a a lot heavier model of the recognized Z boson. As an alternative of carrying the weak pressure, because the common Z does, the Z′ would carry one thing else. “It carries a force that probably could shed some light on the open questions [in physics] but has no direct impact on our lives,” Buras says. Another choice is a proposed particle, referred to as a leptoquark, that might remodel quarks into leptons (the class containing electrons and neutrinos), and vice versa.
Although neither of the potential new particles may straight clarify darkish matter or different mysteries of our universe, discovering them may pave the best way towards answering a few of our greatest questions. “It’s like opening a window on a new world,” Lazzeroni says. “Depending on which window you’re opening, the world can be really rich.”
And if these new particles actually exist, they might meddle in different uncommon particle decays being sought at experiments all over the world. In that case, initiatives such because the Giant Hadron Collider magnificence (LHCb) experiment at CERN and the Belle II and Japan Proton Accelerator Analysis Complicated (J-PARC) experiments in Japan also needs to see deviations from the Normal Mannequin of their measurements.
The brand new result’s “very interesting” says André De Gouvea, a theoretical physicist at Northwestern College. “This decay is considered very clean—this means we can compute it with good precision—and is quite sensitive to hypothetical new phenomena.”
The NA62 experiment is because of run for a number of extra years. When it ends, the researchers ought to have about 4 instances extra knowledge than they analyzed for this measurement, which ought to permit them to extend the precision of their detection considerably. Many physicists shall be eagerly awaiting that future evaluation, De Gouvea says. “We may be on our way to having a serious puzzle on our hands in a few years,” he provides.
