Science

Strange boson measurement may have been a fluke, Large Hadron Collider data shows

A team of researchers from CERN’s Large Hadron Collider has measured the mass of the W boson and found that it matches the Standard Model of Particle Physicsall theory that describes the four fundamental forces and the characteristics smallest units of matter.

THE the discovery of the team against a precise measure taken last year by a collaboration of hundreds of scientists To the CDF collaboration, who had the pleasant surprise to discover that the W boson, an elementary particle responsible for the weak nuclear forcewas much more massive than previously believed – a finding that violated standard model expectations.

The ~73 megaelectronvolt gap between the two measurements is the difference between the actual mass of the boson being nearly in agreement with the Standard Model and significantly at odds with it.

The CERN team announcement their result during the Rencontres de Moriond conference last month. Their number comes from A reanalysis of some 14 million candidate W bosons produced in collisions between protons in the Large Hadron Collider as part of the ATLAS experiment in 2011.

They found a boson mass of 80,360 ±16 MeV, 10 MeV lower and 16% more accurate than the previous ATLAS estimate, according to a Press release from CERN.

“This updated result from ATLAS provides a rigorous test and confirms the consistency of our theoretical understanding of electroweak interactions,” said Andreas Hoecker, spokesperson for the ATLAS experiment. release.

But things are not so simple. Last year, the CDF Collaboration measured the mass of the boson at 80,433 ± 9 MeV, based on collisions performed at the Tevatron accelerator at Fermilab in Illinois, also in 2011. (Tevatron shut down shortly after the experimental test of 2011.)

The difference between the two measurements taken at CERN and at Fermilab seems small, but it isis massive on the subatomic scale and has important implications for the Standard Model. For perspective, the estimated boson mass of the CDF collaboration is about 80 times the mass of a proton.

“Since the ATLAS experiment paper describes a ‘reanalysis’ of the same data that ATLAS already published in 2017, ATLAS getting a similar value to before is to be expected,” Ashutosh said. Kotwal, physicist at Duke University and member. of the CDF collaboration, in an email to Gizmodo. “The reanalysis essentially uses the same technique as the previous post. It is interesting that a press release was issued announcing a modified analysis of the old data.

“The CDF measurement continues to be the world’s most accurate measurement of the mass of the W boson,” Kotwal added.

Jthese separate experiences, which together involve thousands of scientists, proposed very different numbers for the mass of this fundamental particle. Neither team has identified anything wrong with their approaches.

“We’ve spent the last year showing the results all over the world, and there have been no substantive concerns about the methods or the cross-checks,” said David Toback, a physicist at Texas A&M University and gatekeeper. -word of the CDF collaboration. , in an email to Gizmodo. “A combination of collaborations from around the world were called in to see if they could figure out the differences, and they couldn’t find an explanation for the differences either.”

So what’s going on? The Standard Model has been the guiding framework for our understanding of particle physics since the early 1970s. It’s not perfect, a fact physicists are well aware of: TThe model ignores dark matter, the catch-all term for enigmatic something we cannot observe directly, the dark energy, which constitutes 68% of the universe And is apparently responsible for accelerating the expansion of the universe, or gravity, a fundamental force in all our lives, but which does not seem to exist on subatomic scales.

Obtaining exact measurements for fundamental particles like the W boson helps physicists understand the limits of the Standard Model; once these limits have been identified, scientists are better prepared to discover new things.

In other words, known unknowns run rampant in the subatomic world, and sometimes getting really wacky results is a good thing. Determine what is a genuine discovery and what is a fluke in the data is the challenge.

Toback said that some people might be tempted conclude that the measurement with the smallest or least error bars differs from the Standard Model estimate, i.e. the ATLAS figure– is the correct one.

“I’m not interested in simplicity. CDF is not interested in simplicity. Science does not offer “truth”; it offers our best understanding of the moment,” Toback said. “We eagerly await the ATLAS publication of their conference proceedings with all the gory details, so that we can understand them at the same level that we understand our own.

In addition to the CDF work and the recent ATLAS analysis, further W boson measurements are expected from ATLAS, the Compact Muon Solenoid and LHCb, all experiences along the Grand Hadrons Collider.

It is possible that the Large Hadron Collider is merely too little energy to produce particles that might help clarify what the Standard Model overlooks. If so, we will have to wait a modernized LHC or one much more massive collider induce new reactions between the particles.

Plus: 10 years after the Higgs boson, what’s the next big thing for physics?

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