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Startling discovery threatens to upend Standard Model of particle physics


After a decade-long evaluation, a collaboration of physicists has made essentially the most exact measurement of the mass of a key particle – and it might unravel physics as we all know it. The new measurement differs drastically from predictions based mostly on the Standard Model, hinting at new physics.

Since it was developed within the Nineteen Seventies, the Standard Model of particle physics has been extraordinarily profitable at explaining the interactions of particles and most elementary forces. It doesn’t cowl all the pieces – main lacking items embrace darkish matter and even gravity – however what it does cowl, it covers very nicely, persistently standing as much as experiments that take a look at its predictions.

But now, a well-studied particle could also be threatening to poke a gap in that neat mannequin. The mass of particles may be calculated via their relationships with different particles within the Standard Model, and this predicted mass can then be in comparison with precise measurements made in particle colliders, to check the inner consistency of the Standard Model. This course of has now led to a serious discrepancy, due to an unassuming particle referred to as a W boson.

W bosons are elementary particles that carry the weak drive, mediating nuclear processes like these at work within the Sun. According to the Standard Model, their mass is linked to the lots of the Higgs boson and a subatomic particle referred to as the highest quark. In a brand new examine, nearly 400 scientists on the Collider Detector at Fermilab (CDF) collaboration spent a decade inspecting 4.2 million W boson candidates collected from 26 years of knowledge on the Tevatron collider. From this treasure trove, the group was in a position to calculate the mass of the W boson to inside 0.01 p.c, making it twice as exact because the earlier greatest measurement.

By their calculations, the W boson has a mass of 80,433.5 Mega-electronvolts (MeV), with an uncertainty of simply 9.4 MeV both facet. That’s throughout the vary of some earlier measurements, however nicely outdoors that predicted by the Standard Model, which places it at 80,357 MeV, give or take 6 MeV. That means the brand new worth is off by a whopping seven commonplace deviations.

Further cementing the anomaly, the W boson mass was additionally just lately measured utilizing knowledge from the Large Hadron Collider, in a paper printed in January. That group got here to a price of 80,354 MeV (+/- 32 MeV), which is comfortably near that given by the Standard Model.

So what’s occurring? Some physicists not concerned within the examine are extra comfy siding with the Standard Model, which is comprehensible.

“All these measurements claim to measure the same quantity,” stated experimental physicist Martin Grünewald, in a report by Science. “Somebody must be, I will not say wrong, but maybe made a mistake or pushed the error evaluation too aggressively.”

But the scientists on the brand new CDF evaluation say that the procedures they used to succeed in their determine have been correctly scrutinized over a few years. In truth, the ultimate measured worth was hidden from the analyzers till these high quality checks have been accomplished.

“The number of improvements and extra checking that went into our result is enormous,” stated Ashutosh Kotwal, lead creator of the CDF evaluation. “We took into account our improved understanding of our particle detector as well as advances in the theoretical and experimental understanding of the W boson’s interactions with other particles. When we finally unveiled the result, we found that it differed from the Standard Model prediction.”

If the brand new determine is verified, it might trace at unknown particles or new physics past the Standard Model, that are interfering with the anticipated interactions. After all, we already know that this framework is incomplete, and additional investigations might assist unravel the thriller.

“It’s now up to the theoretical physics community and other experiments to follow up on this and shed light on this mystery,” stated David Toback, CDF co-spokesperson. “If the difference between the experimental and expected value is due to some kind of new particle or subatomic interaction, which is one of the possibilities, there’s a good chance it’s something that could be discovered in future experiments.”

The analysis was printed within the journal Science.

Sources: Fermilab, UK Research and Innovation





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