Why scientists are worried about the W Boson: ‘Something Is Missing.’

Scientists Are Concerned About the W Boson
The particle detector inside the collision hall.
Fermilab

You’ve probably heard of protons, which are positive particles that hold atoms together. You’ve probably seen electrons, the negative blips that float around with the protons. You may have even considered photons, the particles emitted by lightbulbs in your room.

But for the time being, we must be concerned about an unusual small particle that normally goes unnoticed: the W boson.

The W boson, together with its accomplice, the Z boson, governs what is known as the “weak force.” I’m going to save you from going down the rabbit hole of how the weak force works since it involves physics that will blow our minds up. Believe me. Just remember that if the sun didn’t have a weak force, it would burn out.

In any case, there’s a saga involving the W boson. A report published Thursday in the journal Science suggests that the particle is more massive than modern physics predicts, based on 10 years of unimaginably accurate data. At first glance, unless you’re a physicist, this may appear trivial. But it’s truly a significant issue for…well, everything.

More specifically, it creates a conundrum for the Standard Model of particle physics, a well-established, evolving theory that explains how all the universe’s particles behave – protons, electrons, photons, and even some we don’t often hear about, like gluons and muons, to name a few. The W boson is also present.

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

But here’s where the Standard Model gets tricky. It’s like living in a symbiotic particle universe. Consider each particle in the model to be a string, carefully structured to connect everything. It doesn’t matter which string is too tight; if one string is too tight, everything goes wacky. As a result, the Standard Model predicts a few parameters for each “string” or particle, one of which is the W boson mass.

Simply put, if this particle does not have the same mass as that particle, the rest of the model will fail. And if that were true, we’d have to revise the model — we’d have to rethink how all the particles in the universe work.

So, do you remember the new paper? We’re about to enter the worst-case scenario.

After a decade of computations, measurements, cross-checking, head-scratching, and heavy breathing by over 400 worldwide researchers, it was determined that the W boson is somewhat heavier than the Standard Model predicts.

“It’s not a large difference, but we can actually tell that it’s different,” said David Toback, a particle physicist at Texas A&M University and research co-author. “There’s something wrong.”

You may be wondering if we’re certain about this. The scientific community had the same reaction, which is why researchers are now focusing on validating that this increased W boson mass is true.

“It’s possible we got it wrong,” Toback explained. “We don’t think so,” he swiftly added.

It’s because the scientists “measured this minuscule difference with such remarkable precision that it sticks out like a sore thumb,” as Toback says. And, interestingly, these measures mirror crime-scene deduction.

Watching for what’s missing

An image of the particles in the Standard Model.
An image of the particles in the Standard Model.
Fermilab

To obtain a W Boson in the first place, two protons must be smashed together. This generates a slew of additional Standard Model particles, and scientists can only hope that one of them is the one they want to investigate. (In this scenario, that would be the W boson.)

The researchers used collision data from a now-decommissioned particle accelerator at the Fermi National Accelerator Laboratory in Illinois for the new observations. Fortunately, it did produce some W bosons and, in fact, contained enough W boson data to obtain around four times the quantity utilized in prior measurements. Jackpot.

However, there is a problem. The W boson is ephemeral. It soon divides into two smaller particles, making direct measurement impossible. One of these is either an electron or a muon, which can be directly detected, while the other is probably stranger than the W boson itself: a neutrino.

Neutrinos are appropriately referred to as “ghost particles” because they do not interact with anything. They’re even zooming through you right now, but you can’t know since they don’t make contact with the atoms that comprise your body. I know, it’s eerie.

Scientists must be inventive in order to overcome this phantom barrier. Here comes the skill of deduction.

When neutrinos vanish, they leave a type of hole behind them. “The neutrino footprint is deficient in energy,” Chiarelli explained. “This informs us where the neutrino went and how much energy it took with it.”

It’s similar to how an X-ray works. “The X-ray travels through, but you can see the contour for the point where you have some bit of metal,” Chiarelli explained. The “missing energy” is represented by the “shape.”

Following the decoding of the neutrino, the scientists employed a series of sophisticated calculations to combine it with the electron or muon data. This resulted in the total W boson mass. This measurement was repeated numerous times to ensure that everything was as precise as possible. Furthermore, all of the data was supported by theoretical calculations that have matured since the last time the W boson was measured.

But there’s one more issue.

As with all scientific endeavors, there is no correct or incorrect solution. There is just one solution. However, prejudice exists in all human reasoning, and the team did not want to be a victim of such personal error. That illustrates the team’s approach, Toback quotes Sherlock Holmes: “One must find ideas to suit facts, not facts to suit theories.”

An aerial view of the collider from 1999.
An aerial view of the collider from 1999.
Fermilab

“Does it make it more stressful?” he wondered. “Yes, but nature is unconcerned with my worries. What we really want to know is the solution.”

As a result, the crew not only double-, triple-, and quadruple-checked their data, but they did it while completely ignorant of the eventual conclusion. Everyone would be looking at the box containing the W boson mass result when it was opened for the first time.

In the year 2020, when tensions are high, the box is ultimately opened, and the W boson mass is clearly in disagreement with the Standard Model’s prediction.

“It wasn’t a eureka moment,” Chiarelli explained. “It was a humbling experience. We were dubious. Skepticism is the organizing principle of science.”

Even that cynicism eroded with time, and here we are.

This all seems very solid. Now what?

This information has, in some ways, been a long time coming. “We’ve understood from the start that the Standard Model cannot be the ultimate theory,” Chiarelli explained.

For example, the Standard Model is notable for being unable to explain gravity, dark matter, and many other enigmatic characteristics of our world.

One possibility is that the new information regarding the W boson mass requires the addition of some particles to the Standard Model to account for the change. This, in turn, could have an impact on what we know about the famed Higgs Boson, or “god particle,” which was finally discovered in 2012 and greeted with thunderous applause.

“But we’re not there,” Toback pointed out. “That would purely guess.”

And, rather than speculating, Toback and Chiarelli believe that we must just follow the facts, even if the data will eventually lead us to a new fundamental theory of particle physics.

“It’s like walking in the dark,” Chiarelli described it. “You know there is a correct path, but you don’t know where it is… Perhaps our measurement will point us in the proper way.”

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