November 30, 2022

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The elementary particle was measured very accurately, and it turned out to be unsuitable

The elementary particle was measured very accurately, and it turned out to be unsuitable

“It’s a big surprise, even for them,” said Freya Blakemann, a particle physicist at the DESY institutes in Hamburg and CERN in Geneva, who is not directly involved in her colleagues’ research at Fermilab near Chicago in the United States. They were published on Thursday in the trade magazine to know Results of 26 years of measurements with the CDF detector, one of the two measurement tools of the Tevatron particle accelerator. The detectors track scattered debris during direct collisions between protons and antiprotons, particles that have been chased by a particle accelerator to nearly the speed of light.

In 4.2 million of those collisions, the W particle formed very briefly, an elementary particle discovered in 1983 at CERN. This W particle quickly disintegrates into other particles, but by following the trajectories of the ejected particles, it is possible to determine the mass of the W particle.

Final conclusion: the mass W of the particle is 80433 MeV, about the mass of the bromine atom, with a measurement uncertainty of 9 MeV. This is not much different from the mass previously published by CDF physicists shortly after the detector closed in 2011.

network of communication

“But this is a new, more accurate measurement,” says Blakeman. “Every screw and wire were included in the detector down to the micrometer, and more accurate calculations were made based on the well-known theory to increase measurement accuracy,” says Blakeman.

As a result, the measurement uncertainty has been reduced from 79 to 9 MeV, and this makes a big difference: now that we know the mass W precisely, it no longer appears to match the rest of particle physics.

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“The measurement took many years, and the reading was hidden throughout until all procedures had been fully examined,” CDF researcher Chris Hayes from the University of Oxford said in a Fermilab press release. “When we revealed the value, it was a surprise.”

“We have the Standard Model, which is a theory about elementary particles that can predict exactly what’s coming from all kinds of measurements. That works great. But if you fill in that measurement, it won’t be consistent,” Blakeman says.

Physicists believe that formulas should be beautiful and simple

Freya Blakeman Particle physicist

The mathematics of the Standard Model predicts relationships between the mass of the W particle and the mass of other particles such as the top quark and the Higgs boson. According to these relationships, the mass of 80357 W should be plus minus 6 MeV: 76 less than the new measurement. Blakeman: “It’s a network of connections, and now all of a sudden one of the particles no longer fits the lines of that network.”

This can mean two things: either a mistake was made, or the theory needs to be expanded. Physicists hope for the latter, because there is something to criticize about the Standard Model despite all its performance.

“There are many different reasons why the Standard Model can’t be the last word,” says Blakeman. A famous example is dark matter, which astronomers see but this is not found in the Standard Model. “Gravity is not in it either, and at high energies the theory stops working. In addition, the Standard Model is ugly and complicated. Many physicists believe that the final formulas should be beautiful and simple.”

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All feathers are possible

With each skewed measurement, they hope it serves as a claw in the search for an extension of the Standard Model: new physics. Blakeman: “There are thousands of different suggestions for this, and most of them lie in adding additional molecules that we haven’t seen yet.”

This seems illogical: why would a one-mile deviation from the expected mass of one particle be indicative of a completely different particle? But in quantum mechanics, a single particle is always affected by a cloud of short-lived particles from all possible plumes – also by undiscovered particles, which probably add one particle per mile.

The Large Hadron Collider, the particle accelerator at CERN, has also published a measurement of the mass W, and another measurement is in the pipeline. “But here we do things a little differently, using different reagents and slightly different methods,” says Blakeman. “I know how difficult this measurement is and how much work it is. But it takes some courage.”