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Why Scientists Are Worried About The W Boson: ‘Something Isn’t Right’

The particle detector inside the collision room.


You’ve probably heard of protons, the positive points anchoring atoms. You have probably encountered electrons, negative points wandering around these protons. You may have even thought about photons, the stuff that comes out of light bulbs in your bedroom.

But right now, we have to worry about a weird little particle that usually escapes the limelight: the W boson.

Along with its partner in crime, the Z boson, the W boson dictates what is called the “weak force”. I’m going to save you from the rabbit hole of weak force functioning because it involves physics that will blow our minds. Believe me. Just know that without the weak force, the sun would cease to burn.

Either way, there’s drama with the W boson. According to a paper published Thursday in the journal Science, 10 years of incredibly precise data suggests the particle is more massive than our physics predicts. Unless you are a physicist, at first glance this may seem trivial. But it’s actually a major problem for…kind of everything.

Specifically, it raises a paradox for the Standard Model of particle physics, a well-established and evolving theory that explains the behavior of all particles in the universe – protons, electrons, photons, and even those we don’t hear about. really talk like gluons. , muons, I could go on. The W boson is there too.

“It’s one of the cornerstones of the Standard Model,” said Giorgio Chiarelli, research director at the Istituto Nazionale di Fisica Nucleare in Italy and co-author of the study.

But here is the crux of the standard model. It’s like a symbiotic particle world. Think of each particle in the model as a string, perfectly organized to tie everything together. If a string is too tight, things start to get wonky – no matter the string. As such, the Standard Model predicts a few parameters for each “string” or particle, and a very important one is the mass of the W boson.

Simply put, if that particle isn’t equal to that mass, the rest of the model wouldn’t quite work. And if that were true, we would have to change the model — we would have to change our understanding of how all particles in the universe to work.

Well, remember the new newspaper? We’re pretty much entering a worst-case scenario.

Why Scientists Are Worried About The W Boson: ‘Something Isn’t Right’

A picture of the particles in the Standard Model.


A decade of calculations, measurements, cross-checking, puzzles and deep breathing by around 400 international researchers have concluded that the W boson is slightly heavier than the Standard Model predicts.

“It’s not a big difference, but we can really clearly see that it’s different,” said David Toback, a Texas A&M University particle physicist and co-author of the study. “Something is wrong.”

You may be wondering if we are sure. The scientific community had the same reaction, so researchers are now focusing on confirming that this larger W boson mass is really the case.

“We may have been wrong,” Toback said. But he quickly added: “We don’t think so.”

That’s because, as Toback explains, the team “measured that tiny difference with such incredible precision that it sticks out like a sore thumb.” And fascinatingly, these measurements are somewhat like a crime scene-type deduction.

See what’s missing

To get a W boson in the first place, you literally have to smash two protons together.

This produces an array of other Standard Model particles, and scientists just have to hope that one of them is the one they want to examine. (In this case, it is the W boson).

For the new measurements, the researchers used collision data from a now decommissioned particle accelerator at the Fermi National Accelerator Laboratory in Illinois. Fortunately, it produced a few W bosons and, in fact, contained enough data on W bosons to obtain about four times the amount used in previous measurements. Jackpot.

But there is a complication. The W boson is fleeting. It quickly splits into two smaller particles, so you can’t measure it directly. One of them is either an electron or a muon, which can be measured directly, but the other is arguably even stranger than the W boson itself: a neutrino.

Neutrinos are aptly called “ghost particles” because they don’t touch anything. They’re even zooming through you right now, but you can’t tell because they’re not touching the atoms that make up your body. Mysterious, I know.

This ghostly obstacle means scientists have to get creative. Enter, the art of deduction.

Once the neutrinos are gone, they leave behind a kind of hole. “The neutrino footprint lacks energy,” Chiarelli said. “It tells us where the neutrino went and how much energy was taken away.”

It’s kind of the same concept as an x-ray. “The x-ray passes, but for the point where you have a piece of metal, you can see the shape,” Chiarelli said. The “form” is the “missing energy”.

Why Scientists Are Worried About The W Boson: ‘Something Isn’t Right’

An aerial view of the 1999 collider.


Then, after decoding the neutrino, the scientists used a bunch of complex equations to add it up with the electron or muon data. This led to the overall mass of the W boson. This measurement was done many times to make sure everything was as accurate as possible. Additionally, all data has been bolstered by theoretical calculations that have matured since the W boson was last measured.

However… there is another complication.

As in all scientific activities, there is no right or wrong answer. There is only the to respond. But as with all human thinking, there is the possibility of bias, and the team didn’t want to fall victim to such personal error. Toback quotes Sherlock Holmes to explain the team’s mentality: “You have to find theories to fit the facts, not facts to fit the theories.

“Is it more stressful?” he remarked. “Yes, but nature doesn’t care about my stress. What we want is to know the answer.”

Therefore, not only did the team check their data two, three or four times, but they did so while being completely blind to the final answer. When the box containing the mass result of the W boson was opened, everyone looked at it for the first time.

Fast forward to 2020, when tensions are high, the box is finally open and the mass of the W boson clearly conflicts with the Standard Model prediction.

“It wasn’t a Eureka moment,” Chiarelli said. “It was a sobering moment. We were skeptical. Science is organized in skepticism.”

But over time, even that skepticism faded and here we are.

It all seems very solid. Now what?

In a sense, this information has been slow to arrive. “We have known from the start that the Standard Model cannot be the ultimate theory,” Chiarelli said.

For example, the Standard Model cannot explain gravity, dark matter, and many other elusive aspects of our universe.

One idea is that this new information about the mass of the W boson could mean that we need to add particles to the Standard Model to account for the change. This, in turn, could impact what we know about the famous Higgs boson, or “god particle”, which was finally detected in 2012 and met with earth-shattering applause.

“But we’re not there yet,” Toback said. “That would be pure speculation.”

And, rather than speculate, Toback and Chiarelli agree that we just have to follow the facts, even though we know that the facts will one day lead us to a fundamental new theory of particle physics.

“It’s like moving in the dark,” Chiarelli said. “You know there’s a path that’s right, but you don’t know where… maybe our measurement can give us the right direction to go.”


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