The Hunt for the Higgs

In March 2013, capping a nearly fifty-year search, physicists, including Mark Kruse and others from Duke, reported that they had—without a doubt—found the Higgs boson, a particle that helps explain how everything we see around us got about 1 percent of its mass. One percent may not seem like much, especially in the scale of the universe. But without it, matter and life as we know it wouldn’t exist, Kruse says.

In a way, the announcement provides validation that physicists’ current picture, or mathematical model, of how nature works is correct. The discovery also helps scientists explain what happened in the very early universe—100 trillionth of a second after it exploded into existence—why it evolved the way it did, and even why it evolved at all.

It didn’t just take time to make the discovery; it also involved one of mankind’s most expensive and complex experimental facilities and at least $13 billion in testing.

Yet, while it is a great triumph, the discovery doesn’t solve all the scientific and philosophical challenges physicists run into as they grapple with the consequences of the origins of the universe and its relative infinity. The Higgs particle doesn’t fully complete their model of the way nature works. There are still major holes. And possibly more concerning is that—in this time of financial uncertainty for science—physicists are not quite sure where to look to fill those holes. They wonder how they will compete with genomics, brain science, and other large-scale research projects now captivating the public imagination.

Can the public get excited about the universe when there’s so much going on in the world?

It's not as if physicists haven't been trying to sell the Higgs discovery as an important thing, says Andrew Janiak, a philosopher of science at Duke. "They have. I am just not sure if they have gotten traction, if they have truly captured the public's imagination with it." Getting people interested in such a seemingly esoteric discovery can be hard to do, especially since finding the Higgs “won’t change daily lives, how health is dealt with, how people get around, how we use energy,” Janiak says. “It won’t, at least immediately, so people have a hard time focusing on the research. It is harder to communicate it to a wider public.”

Explaining the Higgs particle and what it means now falls largely to Kruse and his colleagues. It’s a role to which he brings a lot of passion. The idea of existence, of life and death and infinity, used to keep Kruse awake at night. “You can’t wrap your mind around what it all really means, especially as a kid thinking about it for the first time,” he says in a slight Kiwi accent that betrays his New Zealand upbringing. What bothered him most was the disparity between such a short human life and the seemingly infinite span of the universe. He also struggled to understand why anything existed at all.

“Everyone does,” he says. “We live in denial. We put this wall of denial up and don’t think about what it really means that when we are not here, it’s forever. It’s sad. It’s depressing, but it is a fact.”

“At a very philosophical level, part of our human nature is to query why we exist. We ask questions about nature. We ask questions about the universe.”

Kruse now grapples with that fact by exploring nature in search of answers. His tool of choice, as with10,000 other scientists, is the world’s biggest scientific machine, a particle smasher called the Large Hadron Collider, or LHC. The machine’s main mission is to create and study the Higgs boson, a particle thought to explain the existence of all other particles, and therefore matter and life, as we know it.

The LHC is built around a circular tunnel up to 500 feet underground that measures 17 miles across, straddling the Franco-Swiss border near Geneva. Around the machine’s ring sit several apartment-sized instruments, which capture the aftermath of collisions of packets of protons traveling close to the speed of light. From these particle smashes, physicists teased out traces of the Higgs particle, which verified that the Higgs field exists. Kruse is the U.S. outreach and education coordinator for ATLAS, one of the apartment-sized instruments at LHC that snatches signatures of the elusive particle.

The Higgs particle became important to physicists in 1964, when theorists developed it as a way to solve a problem with scientists’ Standard Model of particle physics. The Standard Model is scientists’ simplest explanation of the forces that drive particles to interact deep within the nucleus of an atom. Experiment after experiment has validated aspects of the model.

But there was a problem: For the model to be correct, without alteration, some fundamental particles such as electrons should not have any mass. Experiments already had shown that electrons do have mass. So theorist Peter Higgs and six others calculated a fix. This eventually came to be called the Higgs mechanism, which included the Higgs field and the Higgs particle, and it attempted to explain how fundamental particles could gain mass.

“Scientists sometimes have these highfalutin theories, and they believe they are correct all along,” says Duke physicist Ronen Plesser, who is not a Higgs hunter but works on other theories related to fixing the Standard Model. “In this case, the theory turned out to be right, which is a great validation of the way we understand nature. It suggests that our description of it is correct.”

Higgs particles and the LHC also help scientists understand all the physics that’s happened in the 14 billion years since that singular moment 100 trillionth of a second after the Big Bang. “What’s even more astounding is that humans have been here for just a tiny fraction of the time scale of the universe and yet have built a huge machine to understand most of its history,” Kruse says. “At a very philosophical level, part of our human nature is to query why we exist. We ask questions about nature. We ask questions about the universe.” Physicists, he adds, depend on society’s support to build the machines that might answer these questions. “We really owe it to the rest of society to explain what we are doing and what we found, because our work is answering innate questions about why we are here. These are the questions that make us human and make us unique.”

The Higgs particle he and other scientists have found confirms the existence of the Higgs field, which explains where and how electrons and quarks—fundamental constituents of matter—acquire mass. “This field is truly what generates mass for quarks, which are the building blocks of protons and neutrons, the building blocks of molecules, proteins, cells, plants, animals, planets, stars, galaxies, and all the stuff we see in the universe,” Kruse says.

But the mass of quarks coming from the Higgs mechanism accounts for only 1 percent of the total mass of a proton or neutron.

The other 99 percent of the mass of those particles, and therefore the rest of the observable universe, comes in the form of energy, specifically the forces that bind the quarks that make up protons and neutrons. In other words, the Higgs field explains only 1 percent of the observable mass of everything we see.

Without this 1 percent, “all the atomic structure we are familiar with wouldn’t exist. We wouldn’t exist. There may still be matter, but it wouldn’t be the same. There certainly wouldn’t be life as we know it,” Kruse says.

The world's biggest scientific machine is designed to create and study a particle thought to explain the existence of all other particles.

Plesser adds that, putting life aside, there are two important aspects of finding a Higgs particle. “First is the decades-long experimental search after a deep theoretical prediction and the ultimate discovery. In terms of human drama, that is really cool,” he says. And second, he adds, scientists can say, “Wow, we are awash in the Higgs field, and now we can understand it with theoretical calculations and validate it with experiments.”

Physicists worked nearly fifty years to validate their theories of a Higgs boson. And they finally did. The discovery excites Duke physicist Ashutosh Kotwal, but disappoints him just a bit as well. “It’s good to predict correctly and know a theory is right,” he says, “but we’re always more eager to break theories rather than confirm them.”

Now that scientists have confirmed the Higgs theory, they’re lining another one up in their cross hairs. It’s nicknamed SUSY, short for supersymmetry. And it, too, is an idea that overcomes issues with scientists’ Standard Model of particle physics. The biggest issue is that quantum mechanics—scientists’ description of how particles interact at the atomic scale—can’t quite explain gravity. With SUSY, every particle has a superpartner, a more massive “shadow” particle that carries force. The electron, for example, is matched with the selectron; the photon, with something called the photino. By adding these extra particles, scientists can start to understand how gravity can work on extremely tiny scales.

SUSY, Kotwal says, would also solve the dark-matter problem.

This, too, is a calculated, but so far undetected, particle that would account for the way scientists see stars and galaxies moving. The matter we know about simply doesn't account for what we're seeing. Dark matter would complete that riddle, if we could find what it is.

"Personally, I think SUSY has so much potential to explain a whole bunch of new mysteries about nature," Kotwal says. "If I were a gambler, I'd bet on it. But I am not writing the check. I am convincing other people to do it.”

Kotwal’s role is to crunch the numbers, to look at all the possible ways that scientists could test SUSY with old experiments such as LHC and new ones such as the International Linear Collider, or ILC. This next-generation, multi-billion-dollar machine would be made of two linear accelerators facing each other. They would shoot 10 billion electrons and their antiparticles, positrons, toward each other at nearly the speed of light, collide, and possibly make superparticles that would confirm SUSY and make more Higgs particles. Two other proposals for major particle accelerators are in the works as well.

In negotiating the next generation of particle experiments, Kotwal essentially finds himself wearing two hats—a sombrero and a ball cap. The sombrero represents the broader picture of where high-energy physicists should go next. The ball cap represents the select decisions that need to be made about upgrading ATLAS at LHC and determining what role it can play in high-energy physics fifteen years from now. This puts physicists back at the drawing board, where they are now rigorously calculating which old and new experiments to invest in and what science each one can do to complement the others.

Physicists are doing all of this jockeying between upgrading old experiments and building new ones in large part because they

haven’t yet seen any SUSY particles. Unlike finding the Higgs, where there was a clear target, physicists aren’t exactly sure where the superpartners of electrons and other fundamental particles will turn up. And as a result, they aren’t quite sure what equipment they need to search for them.

Despite the uncertainty, planning for the next big machines starts now. That’s the only way physicists can even think of having a new accelerator experiment come online in 2026, at the earliest. Up until then, a lot of what happens depends on funding and, as a direct consequence, public and policymakers’ reception to building a new particle-colliding machine, Kotwal says. And that’s where captivating the public’s imagination becomes critical, philosopher Janiak adds.

Physicists have been trying to engage the public by linking their discoveries to understanding the origins of the universe. Hyping the Higgs, however, is a big risk. This past June, theorist Peter Higgs, for whom the Higgs boson is named, criticized physicists and the media team at CERN (the European Organization for Nuclear Research), where the LHC is housed, for overselling their results. “The way it’s been plugged by organizations like CERN has worried me. It worried me that once it was discovered they would be caught out, and the perception would be that there was no need for the machine anymore,” he said at the Times Cheltenham Science Festival, according to The Times of London.

Other scientists not in the particle-physics field have said that the media buzz surrounding the discovery of the Higgs particle is a public relations effort to gain traction for rather esoteric research and support the funding of next-generation high-energy physics experiments. But thinking about the discovery in terms of the history of science, Janiak disagrees. He argues that, at the moment, it’s not clear high-energy physicists have such great public relations. “High-energy physics doesn’t appear regularly on the front pages of newspapers and magazines. It’s not as pervasive as research related to medicine and climate change.”

“Knowing about the history of science is really important to understanding what’s going on right now. The Higgs boson and

more generally what’s going on in physics right now poses a major problem,” Janiak adds, explaining that the discoveries in this discipline have become so mathematically technical that it’s difficult for the public to grasp what they mean. People can understand the basic idea of DNA, genetic mutations, and even evolution and quantum mechanics. But Higgs fields and bosons are a little harder to explain concretely, he says.

Kruse says certainly the details are very technical, but that doesn’t mean he and other physicists can’t put the Higgs into a language that is understandable to a lay audience. “Whether we have done that satisfactorily and consistently is another question. I think it can be done and has been done to some extent,” he says. “There are some good explanations out there. Alas, there are also a lot of misleading and poor explanations, which may have created a fog of confusion.”

He adds that physicists don’t think much about their science being eclipsed by other research. “It’s orthogonal to what we do. One field is looking more inward and trying to understand our physical makeup; the other looks outward and tries to understand the universe in which we exist. Both are needed for a full comprehension of why we are here and able to contemplate such questions of our existence.” 

 

Yeager, a former science writer for Duke’s Office of News and Communications, is web producer for Science News.