Monkeypox is not yet a global public health emergency, the World Health Organization said June 25.

The decision comes as the outbreak of the disease related to smallpox continues to spread, affecting at least 4,100 people in 46 countries as of June 24. That includes at least 201 cases in the United States. Those cases have been found in 25 states and the District of Columbia, according to the U.S. Centers for Disease Control and Prevention.
“Controlling the further spread of outbreak requires intense response efforts,” and the situation should be reevaluated in a few weeks, the WHO committee evaluating the outbreak said in an announcement.

The declaration of a public health emergency would have potentially made it easier to get treatments and vaccines to people infected with or exposed to the virus. Some medications and vaccines that could help fend off monkeypox are approved for use against smallpox, and can be used against monkeypox only with special authorization.

The virus that causes monkeypox, named for its discovery in monkeys in 1958 though it is probably a virus that mainly infects rodents, is not a new threat. Countries in central Africa, where monkeypox is endemic, have had sporadic outbreaks since researchers found the first human case in 1970. Places in western Africa had few cases until 2017. But most cases outside the continent were travel-related, with limited spread to others (SN: 5/26/22).

“Monkeypox has been circulating in a number of African countries for decades and has been neglected in terms of research, attention and funding,” WHO director-general Tedros Ghebreyesus said in a statement announcing the decision. “This must change not just for monkeypox but for other neglected diseases in low-income countries as the world is reminded yet again that health is an interconnected proposition.”

Monkeypox typically kills fewer than 10 percent of people who contract it. At least one person has died in the global outbreak.

As case numbers climb, researchers are working to decipher the genetic blueprint of the virus, in hopes of uncovering whether some viral mutations might explain why the virus has quickly gained a foothold in new places.

Tracing the mutations
The closest known relative of the versions of the virus behind the global outbreak comes from Nigeria, hinting that the outbreak may have got its start there.

In the newest surge in cases, scientists have uncovered more viral changes than anticipated — a sign that the virus may have been circulating undetected among people for a while, perhaps since Nigeria’s 2017–2018 monkeypox outbreak, new research suggests. What’s more, a group of enzymes known for their virus-fighting abilities in the body may be to blame for many of those mutations.

A genetic analysis of monkeypox viruses involved in the global outbreak from 15 people across seven countries shows that these viruses have an average of 50 more genetic tweaks than versions circulating in 2018 and 2019, researchers report June 24 in Nature Medicine. That’s roughly six to 12 times as many mutations as scientists would have expected the virus to develop over that time. Unlike some other types of viruses, poxviruses, which include smallpox and monkeypox viruses, typically mutate fairly slowly.

The changes have a pattern that is a hallmark of an enzyme family called APOBEC3, the researchers say. These enzymes edit DNA’s building blocks — represented by the letters G, C, A and T — in a specific way: Gs change to As and Cs to Ts. The analysis found that particular pattern in the viral sequences, suggesting that APOBEC3s are responsible for the mutations.

Ideally, so many DNA building blocks are swapped for another that a virus is effectively destroyed and can’t infect more cells. But, sometimes, APOBEC3 enzymes don’t make enough changes to knock out the virus. Such mutated, though still functional, viruses can go on to infect additional cells, and possibly another person.

A big question, though, is whether the genetic tweaks seen in the monkeypox virus are helpful, harmful or have no effect at all on the virus.

While it’s still unknown whether the enzymes are directly responsible for the changes in the monkeypox virus, similar mutations are still popping up, the team found. So, APOBEC3s may still be helping the virus change as it continues to spread. One member of the enzyme family is found in skin cells, where people with monkeypox can develop infectious pox lesions.
Different symptoms
Symptoms reported in the global outbreak have been generally milder than those reported in previous outbreaks, perhaps allowing the disease to spread before a person knows they’re infected.

It is not clear whether those differences in symptoms are related to changes in the virus, Inger Damon, director of the CDC’s Division of High-Consequence Pathogens and Pathology, said June 21 in a news briefing hosted by SciLine, a service for journalists and scientists sponsored by the American Association for the Advancement of Science.

Typically, in previous outbreaks, people would develop flu-like symptoms, including fever, headaches, muscle aches and exhaustion about a week or two after exposure to the virus. Then, one to three days after those symptoms start, a rash including large pus-filled lesions pops up generally starting on the face and limbs, particularly the hands, and spreads over the body. Though generally milder, those symptoms are similar to smallpox, but people with monkeypox also tend to develop swollen lymph nodes.

All patients in the U.S. outbreak have gotten rashes, Damon said, “but the lesions have been scattered or localized to a specific body site, rather than diffuse, and have not generally involved the face or the … palms of the hand or the soles of the feet.” Instead, rashes may start in the genital or anal area where they can be mistaken for sexually transmitted diseases, such as syphilis or herpes, she said.

In many cases, the rashes have not spread to other parts of the body. And the classical early symptoms such as fever have been “mild and sometimes nonexistent before a rash appears,” Damon said.

Monkeypox is transmitted from person to person through close skin-to-skin contact or by contact with contaminated towels, clothes or bedding. It may also be spread by droplets of saliva exchanged during kissing or other intimate contact. The CDC is investigating whether the virus might be spread by semen as well as skin-to-skin contact during sex, Agam Rao, a captain in the U.S. Public Health Service, said June 23 at a meeting of the CDC’s Advisory Committee on Immunization Practices.

“We don’t have any reason to suspect it is spread any other way,” such as through the air, Rao said.

In Nigeria, more monkeypox cases have been recorded among women, while the global outbreak has affected mainly men, particularly men who have sex with men. Experts warn that anyone can be infected with monkeypox, and some people face an increased risk of severe disease. Those at increased risk include children, people who are immunocompromised, pregnant people and people with eczema.

The risk of catching monkeypox through casual contact is still low in the United States, Rao said. But data she presented show that while people in the country have contracted monkeypox while traveling abroad, cases have also spread locally.

At the time, Conover was a Ph.D. student in particle physics (she’s now physics senior writer for Science News). She was part of a team building a detector in the cavern to observe elusive particles called neutrinos. It was the Fourth of July 2012. A few hundred kilometers away, scientists were announcing the discovery of another elusive subatomic particle, the Higgs boson, which physicists had been hunting for decades. As hundreds of researchers cheered in the main auditorium at the CERN particle physics lab near Geneva, Conover and the small group of physicists in the chilly French cavern cheered too, as did scientists worldwide. The Higgs boson filled in a missing piece in the standard model of particle physics, which explains just about everything known about the particles that make up atoms and transmit the forces of nature. No Higgs boson, no life as we know it.

In this issue’s cover story, “The Higgs boson at 10,” Conover looks back at the excitement around the discovery of the Higgs boson and looks ahead to the many things that researchers hope to find out with its help. She also reviews a new biography of Peter Higgs, a modest man who made clear that he was just one of many scientists who contributed to the breakthrough.

The discovery is part of Science News history too. Journalists around the world were eagerly awaiting the big announcement, which was being kept under wraps. But when Kate Travis, a Science News editor at the time, uncovered an announcement video accidentally posted early on CERN’s website, we published the big news the day before the official announcement.

“Even though its discovery is 10 years old now, that’s still new in the grand scheme of particle physics, so we’re still learning lots about it,” Conover told me. “It’s very cool that I get the opportunity to write about this particle that is still so new to science.” And it’s very cool that we get to explore it with her.

In the 1920s, laborers and amateur archaeologists at gravel quarry pits in southeastern England uncovered more than 300 ancient, sharp-edged oval tools. Researchers have long suspected that these hand axes were made 500,000 to 700,000 years ago. A new study confirms that suspicion in the first systematic excavation of the site, known as Fordwich.

Dating those tools and more recent finds suggests that humanlike folk inhabited the area between about 560,000 and 620,000 years ago, researchers report in the June Royal Society Open Science. Relatively warm conditions at that time drew hominids to what’s now northern Europe before the evolutionary rise of Neandertals and Homo sapiens.
The results confirm that Fordwich is one of the oldest hominid sites in England. Previous discoveries place hominids in what’s now southeastern England at least 840,000 years ago (SN: 7/7/10) and perhaps as far back as nearly 1 million years ago (SN: 2/11/14). No hominid fossils have been found at Fordwich. It’s unclear which species of the human genus made the tools.

In 2020, archaeologist Alastair Key of the University of Cambridge and colleagues unearthed 238 stone artifacts at Fordwich that display grooves created by striking the surface with another stone. Other finds include three stones with resharpened edges, presumably used to scrape objects like animal hides.

A method for determining when sediment layers were last exposed to sunlight indicated that the newly discovered artifacts date to roughly 542,000 years ago. The previously unearthed hand axes probably came from the same sediment.

Hominids must have fashioned tools at Fordwich a bit earlier than 542,000 years ago because ancient climate data suggest that an ice age at that time made it hard to survive in northern Europe, the team concludes. Warmer conditions between 560,000 and 620,000 years ago would have enabled the hominid toolmakers to live so far north.

Not long before the end of the school year, my husband and I received an e-mail from our fifth-grader’s principal that may now be all-too-familiar to many parents. The subject line included the words, “MULTIPLE COVID CASES.”

Several students in my daughter’s class had tested positive for COVID-19. Her school acted fast. It reinstated a mask mandate for 10 days and required students not up-to-date on their COVID-19 vaccinations to quarantine.

These precautions may have helped — my daughter didn’t end up bringing the virus home. But for kids who do, COVID-19 can hopscotch through households, knocking down relatives one by one. And it’s not clear how long one infection protects you from a second round with the virus.
Recent high-profile cases have put reinfections in the spotlight. Health and Human Services Secretary Xavier Becerra has had two bouts of COVID-19 in less than a month. So has The Late Show host Stephen Colbert. Back at his desk in May, he joked, “You know what they say. ‘Give me COVID once, shame on you. Give me COVID twice, please stop giving me COVID.’”

Just a few months ago, scientists thought reinfections were relatively rare, occurring most often in unvaccinated people (SN: 2/24/22). But there are signs the number may be ticking up.

An ABC News investigation that contacted health departments in every state reported June 8 that more people seem to be getting the virus again. And omicron, the variant that sparked last winter’s surge, is still spawning sneaky subvariants. Some can evade antibodies produced after infection with the original omicron strain, scientists report June 17 in Nature. That means a prior COVID-19 infection might not be as helpful against future infections as it once was (SN:8/19/21). What’s more, reinfection could even add to a person’s risk of hospitalization or other adverse outcomes, a preliminary study suggests.

Scientists are still working to pin down the rate of reinfection. Like most questions involving COVID-19 case numbers, the answer is more than a little murky. “You really need to have a cohort of people who are well followed and tested every time they have symptoms,” says Caroline Quach-Thanh, an infectious diseases specialist at CHU Sainte-Justine, a pediatric hospital at the University of Montreal.

A recent look at hundreds of thousands of COVID-19 cases among people in the province of Quebec found that roughly 4 percent were reinfections, scientists report in a preliminary study posted May 3 at medRxiv.org (SN:5/27/22). Quach-Thanh has seen an even smaller rate in her own study of health care workers first infected between March and September of 2020. Those data are still unpublished, but she points out that most of the people in her study were vaccinated. “A natural infection with three doses of vaccines protects better than just a natural infection,” she says.

As many families, mine included, gear up for summer camps and vacations, I wanted to learn more about our current COVID-19 risks. I chatted with Quach-Thanh and Anna Durbin, an infectious diseases physician at Johns Hopkins Bloomberg School of Public Health who has studied COVID-19 vaccines. Our conversations have been edited for length and clarity.

What’s the latest on reinfections? Is the picture changing?
Durbin: We have to remember that the virus strain that’s circulating now is very different from the earlier strains. Whether you’ve been infected with COVID-19 or vaccinated, your body makes an immune response to fight future infections. It recognizes [the strain] your body originally saw. But as the virus changes, as it did with omicron, it becomes sort of a fuzzier picture for the immune system. It’s not recognizing the virus as well, and that’s why we’re seeing reinfections.

I’ll also say that reinfections — particularly with respiratory viruses — are very common.

How can scientists distinguish a true reinfection from a relapse of an original infection?
Quach-Thanh: There are multiple ways of looking at this. The first is looking at the time elapsed between the first infection and a new positive PCR test. If it has been more than three months, it is unlikely to be just a remnant of a previous infection. We can also look at viral load. A really high viral load usually means it’s a new infection. But the best way to tell is to sequence the virus [to determine its genetic makeup] to see if it is actually a new strain.

What do we know about the health risks of reinfection?
Quach-Thanh: The good thing is that most of the people who got reinfected [in the Quebec study] got a mild disease, and the risk of hospitalization and death was much lower.

When you get reinfected, you might [have symptoms] like a cold, or even sometimes a cough, and a little bit of a fever, but you usually don’t progress to complications as much as you would with your first infection — if you’re vaccinated.

Does reinfection increase your chance of developing long COVID?
Durbin: I think that’s unknown, but it’s being studied.

As we look back at the omicron wave in the U.S. that happened in January and February, now is about the time we would start to see symptoms of long COVID. So far it looks promising. We seem to be seeing a lower incidence of long COVID [after reinfection with omicron] than we did with primary infection, but those data are going to continue to be collected over the next few months.

At this point in the pandemic, how cautious do we need to be?
Quach-Thanh: It depends on your baseline risk of complications. If you’re healthy, if you’re doing most activities outdoors, if you’re vaccinated, life can proceed. But if you’re immune suppressed or elderly, the situation might be different.
If you have symptoms, it would be advisable to not mingle in indoor settings without a mask so that you don’t contaminate other people. There are immunocompromised people who might be at risk of serious infection. We still need to keep them in mind. I think we have to be responsible, and if we’re sick, we should get tested.

Durbin: This is what I tell my friends, family and patients: This virus is here to stay. Any time you’re in a crowded place with poor ventilation and lots of people, there’s a chance there’s going to be transmission. The risk is never going to be zero. It’s a message people don’t want to hear. But as long as there are people to infect, this virus is not going away.

We have to move to acceptance, and we have to be better members of society. If we can, we should stay home when we’re sick. If we can’t stay home, we should wear a mask. We should wash our hands regularly. These are things that work to reduce transmission.

They reduce your risk of getting not just COVID-19, but also a cold or the flu.

A flexible sensor applied to the back of the neck could help researchers detect whiplash-induced concussions in athletes.

The sensor, described June 23 in Scientific Reports, is about the size of a bandage and is sleeker and more accurate than some instruments currently in use, says electrical engineer Nelson Sepúlveda of Michigan State University in East Lansing. “My hope is that it will lead to earlier diagnosis of concussions.”

Bulky accelerometers in helmets are sometimes used to monitor for concussion in football players. But since the devices are not attached directly to athletes’ bodies, the sensors are prone to false readings from sliding helmets.
Sepúlveda and colleagues’ patch adheres to the nape. It is made of two electrodes on an almost paper-thin piece of piezoelectric film, which generates an electric charge when stretched or compressed. When the head and neck move, the patch transmits electrical pulses to a computer. Researchers can analyze those signals to assess sudden movements that can cause concussion.

The team tried out the patch on the neck of a human test dummy, dropping the figure from a height of about 60 centimeters. Researchers also packed the dummy’s head with different sensors to provide a baseline level of neck strain. Data from the patch aligned with data gathered by the internal sensors more than 90 percent of the time, Sepúlveda and colleagues found.

The researchers are now working on incorporating a wireless transmitter into the patch for an even more streamlined design.

There’s a lot more to the story of the Higgs boson than just one man named Higgs.

Despite the appeal of the “lone genius” narrative, it’s rare that a discovery can be attributed solely to the work of one scientist. At first, Elusive, a biography of Peter Higgs written by physicist and author Frank Close, seems to play into that misleading narrative: The book is subtitled “How Peter Higgs solved the mystery of mass.”

But the book quickly — and rightfully — veers from that path as it delves into the theoretical twists and turns that kicked off a decades-long quest for the particle known as the Higgs boson, culminating with its discovery in 2012 (SN: 7/28/12, p. 5). That detection verified the mechanism by which particles gain mass. Higgs, of the University of Edinburgh, played a crucial role in establishing mass’s origins, but he was one of many contributors.

The habitually modest and attention-averse Higgs makes the case against himself as the one whiz behind the discovery, the book notes: According to Higgs, “my actual contribution was only a key insight right at the end of the story.”

The Higgs boson itself doesn’t bestow fundamental particles with mass. Instead, its discovery confirmed the correctness of a theory cooked up by Higgs and others. According to that theory, elementary particles gain mass by interacting with a field, now known as the Higgs field, that pervades all of space.

A paper from Higgs in 1964 was not the first to propose this process. Physicists Robert Brout and François Englert just barely beat him to it. And another team of researchers published the same idea just after Higgs (SN: 11/2/13, p. 4). Crucial groundwork had already been laid by yet other scientists, and still others followed up on Higgs’ work. Higgs, however, was the one to make the pivotal point that the mass mechanism implied the existence of a new, massive particle, which could confirm the theory.
Despite this complicated history, scientists slapped his name on not just the particle, the Higgs boson, but also the process behind it, traditionally called the Higgs mechanism, but more recently and accurately termed the Brout-Englert-Higgs mechanism. (Higgs has reportedly proposed calling it the “ABEGHHK’tH mechanism,” using the first letter of the last names of the parade of physicists who contributed to it, Anderson, Brout, Englert, Guralnik, Hagen, Higgs, Kibble and ’t Hooft.) The postmortem of how Higgs’ name attained outsize importance is one of the most interesting sections of Elusive, revealing much about the scientific sausage-making process and how it sometimes goes awry. Equally fascinating is the account of how the media embraced Higgs as a titan of physics based on his association with the boson, lofting him to a level of fame that, for Higgs, felt unwelcome and unwarranted.

The book admirably tackles the complexities of the Brout-Englert-Higgs mechanism and how particles gain mass, covering details that are usually glossed over in most popular explanations. Close doesn’t shy away from nitty-gritty physics terms like “perturbation theory,” “renormalization” and “gauge invariance.” The thorniest bits are most appropriate for amateur physics aficionados who desire a deeper understanding, and those bits may require a reread before sinking in.

Higgs is famously not a fan of the limelight — he disappeared for several hours on the day he won a Nobel Prize for his work on mass. The physicist sometimes seems to fade into the background of this biography as well, with multiple pages passing with no appearance or contribution from Higgs. Once the scientific community got wind of the possibility of a new particle, the idea took on a life of its own, with experimental physicists leading the charge. Higgs didn’t make many contributions to the subject beyond his initial insight, which he calls “the only really original idea I’ve ever had.”

Thus, the book sometimes feels like a biography of a particle named Higgs, with the person playing a backup role. Higgs is so reserved and so private that you get the sense that Close still hasn’t quite cracked him. While interesting details of Higgs’ life and passions are revealed — for example, his fervent objection to nuclear weapons — deeper insights are missing. In the end, Higgs is, just like the particle named after him, elusive.

Javier Duarte kicked off his scientific career by witnessing the biggest particle physics event in decades. On July 4, 2012, scientists at the laboratory CERN near Geneva announced the discovery of the Higgs boson, the long-sought subatomic particle that reveals the origins of mass. Duarte was an eager graduate student who’d just arrived at CERN.

“I was physically there maybe a week before the announcement,” Duarte says. As buzzing throngs of physicists crowded together to watch the announcement at CERN, Duarte didn’t make it to the main auditorium. That space was for VIPs — and those determined enough to wait in line all night to snag a seat. Instead, he says, he found himself in the basement, in an overflow room of an overflow room.

But the enthusiasm was still palpable. “It was a very exciting time to be getting immersed into that world,” he says. Since then, he and thousands of other physicists from around the world working on CERN experiments have gone all out exploring the particle’s properties.

Scientists predicted the existence of the Higgs boson back in 1964, as a hallmark of the process that gives elementary particles mass. But finding the particle had to wait for CERN’s Large Hadron Collider, or LHC. In 2010, the LHC began smashing protons together at extremely high energies, while two large experiments, ATLAS and CMS, used massive detectors to look through the debris.
The particle’s discovery filled in the missing keystone of the standard model of particle physics. That theory explains the known elementary particles and their interactions. Those particles and interactions are behind just about everything we know. The particles serve as building blocks of atoms and transmit crucial forces of nature, such as electromagnetism. And the mass of those particles is key to their behavior. If electrons were massless, for example, atoms wouldn’t form. Without the Higgs boson, then, one of scientists’ most successful theories would collapse.

The Higgs boson discovery dominated headlines around the globe. About half a million people tuned in to watch the livestreamed announcement, and footage from the event appeared on more than 5,000 news programs. Even oddball minutiae made it into the press, with a few articles analyzing the physicists’ use of the often-scorned font Comic Sans in their presentation. Little more than a year later, the discovery garnered a Nobel Prize for two of the scientists who developed the theory behind the Higgs boson, François Englert and Peter Higgs — for whom the particle is named.
Now, as the discovery turns 10 years old, that initial excitement persists for Duarte and many other particle physicists. As a professor at the University of California, San Diego and member of the CMS experiment, Duarte’s research still revolves around the all-important particle. Progress in understanding the Higgs has been “stunning,” he says. “We’ve come so much farther than we expected to.”

Physicists have been working through a checklist of things they want to know about the Higgs boson. They spent the last decade cataloging its properties, including how it interacts with several other particles. Though measurements have so far been in line with the predictions made by the standard model, if a discrepancy turns up in the future, it may mean there are unknown particles yet to be discovered.

And there’s still more on the agenda. An especially important item is the Higgs boson’s interaction with itself. To help pin down this and other Higgs properties, scientists are looking forward to collecting more data. Scientists turned on an upgraded LHC for a new round of work in April. At the time of the Higgs discovery, collisions at the LHC reached an energy of 8 trillion electron volts. Collisions are expected to roll in at a record 13.6 trillion electron volts starting July 5, and data-taking will continue until 2026. These higher energies offer opportunities to spot heavier particles. And the High-Luminosity LHC, a more powerful iteration of the LHC, is expected to start up in 2029.

“Finding a particle, it sounds like the end of something, but it’s really only the beginning,” says experimental particle physicist María Cepeda of CIEMAT in Madrid, a member of the CMS collaboration.
Coupling up
Studying the Higgs boson is like geocaching, says theoretical particle physicist Gudrun Heinrich of the Karlsruhe Institute of Technology in Germany. Much like hobbyists use a GPS device to uncover a hidden stash of fun trinkets, physicists are using their wits to uncover the treasure trove of the Higgs boson. In 2012, scientists merely located the cache; the next 10 years were devoted to revealing its contents. And that investigation continues. “The hope is that the contents will contain something like a map that is guiding us towards an even bigger treasure,” Heinrich says.

Detailed study of the Higgs boson could help scientists solve mysteries that the standard model fails to explain. “We know that the theory has limitations,” says theoretical particle physicist Laura Reina of Florida State University in Tallahassee. For instance, the standard model has no explanation for dark matter, a shadowy substance that throws its weight around the cosmos, exerting a gravitational pull necessary to explain a variety of astronomical observations. And the theory can’t explain other quandaries, like why the universe is composed mostly of matter rather than its alter ego, antimatter. Many proposed solutions to the standard model’s shortcomings require new particles that would alter how the Higgs interacts with known particles.

The Higgs boson itself isn’t responsible for mass. Instead, that’s the job of the Higgs field. According to quantum physics, all particles are actually blips in invisible fields, like ripples atop a pond. Higgs bosons are swells in the Higgs field, which pervades the entire cosmos. When elementary particles interact with the Higgs field, they gain mass. The more massive the particle, the more strongly it interacts with the Higgs field, and with the Higgs boson. Massless particles, like photons, don’t directly interact with the Higgs field at all.

One of the best ways to hunt for Higgs-related treasure is to measure those interactions, known as “couplings.” The Higgs couplings describe what particles the Higgs boson decays into, what particles can fuse to produce Higgs bosons and how often those processes occur. Scientists gauge these couplings by sifting through and analyzing the showers of particles produced when Higgs bosons pop up in the debris of proton smashups.

Even if unknown particles are too heavy to show up at the LHC, the Higgs couplings could reveal their existence. “Any of these couplings not being what you expect them to be is a very clear sign of incredibly interesting new physics behind it,” says particle physicist Marumi Kado of Sapienza University of Rome and CERN, who is the deputy spokesperson for the ATLAS collaboration.
Physicists have already checked the couplings to several elementary particles. These include both major classes of particles in physics: bosons (particles that carry forces) and fermions (particles that make up matter, such as electrons). Scientists have measured the Higgs’ interactions with a heavy relative of the electron called a tau lepton (a fermion) and with the W and Z bosons, particles that transmit the weak force, which is responsible for some types of radioactive decay. Researchers also pegged the Higgs’ couplings to the top quark and bottom quark. Those are two of the six types of quarks, which glom together into larger particles such as protons and neutrons. (The Higgs is responsible for the mass of elementary particles, but the mass of composite particles, including protons and neutrons, instead comes mostly from the energy of the particles jangling around within.)

The couplings measured so far involve the standard model’s heavier elementary particles. The top quark, for example, is about as heavy as an entire gold atom. Since the Higgs couples more strongly to heavy particles, those interactions tend to be easier to measure. Next up, scientists want to observe the lighter particles’ couplings. ATLAS and CMS have used their giant detectors to see hints of the Higgs decaying to muons, the middleweight sibling in the electron family, lighter than the tau but heavier than the electron. The teams have also begun checking the coupling to charm quarks, which are less massive than top and bottom quarks.

So far, the Higgs has conformed to the standard model. “The big thing we discovered is it looks pretty much like we expected it to. There have been no big surprises,” says theoretical particle physicist Sally Dawson of Brookhaven National Laboratory in Upton, N.Y.

But there might be discrepancies that just haven’t been detected yet. The standard model predictions agree with measured couplings within error bars of around 10 percent or more. But no one knows if they agree to within 5 percent, or 1 percent. The more precisely scientists can measure these couplings, the better they can test for any funny business.
One of a kind
Before the LHC turned on, scientists had a clear favorite for a physics theory that could solve some of the standard model’s woes: supersymmetry, a class of theories in which every known particle has an undiscovered partner particle. Physicists had hoped such particles would turn up at the LHC. But none have been found yet. Though supersymmetry isn’t fully ruled out, the possibilities for the theory are far more limited.

With no consensus candidate among many other theories for what could be beyond the standard model, a lot of focus rests on the Higgs. Physicists hope studies of the Higgs will reveal something that might point in the right direction to untangle some of the standard model’s snarls. “Measuring [the Higgs boson’s] properties is going to tell us much more about what is beyond the standard model … than anything before,” Reina says.

One question that scientists are investigating in LHC smashups is whether the Higgs is truly unique. All the other known elementary particles have a quantum form of angular momentum, known as spin. But the Higgs has a spin of zero, what’s known as a “scalar.” Other types of particles tend to come in families, so it’s not outlandish to imagine that the Higgs boson could have scalar relatives. “It could be there’s a huge scalar sector somewhere hiding and we just saw the first particle of it,” Heinrich says. Supersymmetry predicts multiple Higgs bosons, but there are plenty of other ideas that envision Higgs accomplices.

It’s also possible that the Higgs is not actually elementary. Combinations of particles, such as quarks, are known to make up larger particles with spins of zero. Perhaps the Higgs, like those other scalars, is made up of yet unknown smaller stuff.

While hunting for these answers, physicists will be watching closely for any connection between the Higgs’ behavior and other recent puzzling results. In 2021, the Muon g−2 experiment at Fermilab in Batavia, Ill., reported hints that muons have magnetic properties that don’t agree with predictions of the standard model. And in April, scientists with the CDF experiment — which studied particle collisions at Fermilab until 2011 — found that the W boson’s mass is heavier than the standard model predicts.

The Higgs boson’s relative newness makes it ripe for discoveries that could help sort out these quandaries. “The Higgs boson is the least explored elementary particle, and it could be a door to the other mysteries we still have to uncover or to shed light on,” Heinrich says.
Self-talk
To work out thorny puzzles, physicists sometimes talk to themselves. Fittingly, another puzzle atop scientists’ Higgs to-do list is whether the particle, likewise, talks to itself.

This “self-coupling,” how Higgs bosons interact with one another, has never been measured before. But “it turns out to be really just an incredible barometer of new physics,” says theoretical particle physicist Nathaniel Craig of the University of California, Santa Barbara. For example, measuring the Higgs self-coupling could suss out hidden particles that interact only with the Higgs, oblivious to any of the other standard model particles.

The Higgs self-coupling is closely related to the Higgs potential, an undulating, sombrero-shaped surface that describes the energy of the universe-pervading Higgs field. In the early universe, that potential determined how the fundamental particles gained mass, when the Higgs field first turned on.

How, exactly, that transition from massless to massive happened has some big implications for the cosmos. It could help explain how matter gained the upper hand over antimatter in the early universe. If the Higgs field did play that role in the universe’s beginnings, Craig says, “it’s going to leave some fingerprints on the Higgs potential that we measure today.”

Depending on the full shape of the Higgs potential’s sombrero, at some point in the exceedingly distant future, the Higgs field could shift again, as it did in the early universe. Such a jump would change the masses of fundamental particles, creating a universe in which familiar features, including life, are probably obliterated.

To better understand the Higgs potential, scientists will attempt to measure the self-coupling. They’ll do it by looking for Higgs bosons produced in pairs, a sign of the Higgs interacting with itself. That’s thought to happen at less than a thousandth the rate that individual Higgs bosons are produced in the LHC, making it extremely difficult to measure.

Even with the planned High-Luminosity LHC, which will eventually collect about 10 times as much data as the LHC, scientists predict that the self-coupling will be measured with large error bars of about 50 percent, assuming the standard model is correct. That’s not enough to settle the matter.

If scientists just do what they’re on track to do, “we’re going to fall short,” Duarte says. But new techniques could allow physicists to better identify double-Higgs events. Duarte is studying collisions in which two particularly high-energy Higgs bosons each decay into a bottom quark and a bottom antiquark. Using a specialized machine learning technique, Duarte and colleagues put together one of the most sensitive analyses yet of this type of decay.

By improving this technique, and combining results with those from other researchers looking at different types of decays, “we have a good hope that we’ll be able to observe [the self-coupling] definitively,” Duarte says.
Waiting game
Despite all his passion for the Higgs, Duarte notes that there have been disappointments. After that first rush of the Higgs announcement, “I was hoping for a Higgs-level discovery every year.” That didn’t happen. But he hasn’t lost his optimism. “We expect there to be another twist and turn coming up,” he says. “We’re still hoping it’s around the corner.”

The wait for new physics is no shock to veterans of earlier particle hunts. Meenakshi Narain, a particle physicist at Brown University in Providence, R.I., and a member of the CMS experiment, was an undergraduate student around the time the bottom quark was discovered in the 1970s. After that discovery, Narain joined the search for the top quark. Even though physicists were convinced of the particle’s existence, that hunt still took nearly 20 years, she says. And it took nearly 50 years to uncover the Higgs boson after it was postulated.

The standard model’s flaws make physicists confident that there must be more treasures to unearth. Because of her past experiences with the long-haul process of discovery, Narain says, “I have a lot of faith.”