Beyond Higgs: The Search for New Particles That Could Solve Mysteries of the Universe

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Category: Research News

Published: Wednesday, September 07 2022 00:01

An elusive elementary particle called the Higgs boson is partly to thank for life as we know it. No other elementary particles in the early universe had mass until they interacted with a field associated with the Higgs boson, enabling the emergence of planets, stars and—billions of years later—us.

Despite its cosmic importance, scientists couldn’t prove the Higgs boson even existed until 2012, when they smashed protons together at the most powerful particle accelerator ever built: the Large Hadron Collider (LHC). A decade later, this massive machine, built in a tunnel beneath the France-Switzerland border, is up and running again after a series of upgrades. 

As the search for new particles starts anew, researchers like Assistant Professor of Physics Manuel Franco Sevilla find themselves wondering if they will discover anything beyond Higgs.UMD Assistant Professor of Physics Manuel Franco Sevilla is helping to upgrade the Large Hadron Collider (LHC) at CERN in Switzerland. In the above photo, he is shining a light on silicon sensors to measure whether their dark current increases—a sign that they are properly connected. Photo courtesy of Manuel Franco Sevilla.

“It’s a tough question because particle physics is at a juncture,” said Franco Sevilla, who is working at the LHC this semester. “It’s possible that we are currently in what physicists call a ‘nightmare scenario,’ where we discovered the Higgs, but after that, there’s a big desert. According to this theory, we will not be able to find anything new with our current technology.”

This is the worst-case scenario, but not the only possible outcome. Some scientists say the LHC could make another discovery on par with the Higgs boson, potentially identifying new particles that explain the origin of dark matter or the mysterious lack of antimatter throughout the universe. Others say new colliders—more powerful and precise than their predecessors—must be built to bring the field into a new era.

There are no easy answers, but Franco Sevilla and several other faculty members in UMD’s Department of Physics are rising to the challenge. Some are working directly with the LHC and future collider proposals, while others are developing theories that could solve life’s biggest mysteries. All of them, in their own way, are advancing the ever-changing field of particle physics.

Looking For Beauty

As Franco Sevilla will tell you, there’s beauty all around—if you know where to look. He is one of the researchers who uses the LHC’s high-powered collisions to study a particle called the beauty quark—b quark for short. It’s one of the components of “flavor physics,” which observes the interactions between six “flavors,” or varieties, of elementary particles called quarks and leptons. 

Because these particles sometimes behave in unexpected ways, Franco Sevilla believes that flavor physics might lead to breakthroughs that justify future studies in this field—and possibly even the need for a new particle collider. 

“Some of the most promising things that will break the ‘nightmare scenario’ and allow us to find something are coming from flavor physics,” he said. “We still haven't fully discovered something new, but we have a number of hints, including the famous ‘b anomalies.’”

These anomalies are instances where the b quark decayed differently than predicted by the Standard Model, the prevailing theory of particle physics. This suggests that something might exist beyond this model—which, ever since the 1970s, has helped explain the fundamental particles and forces that shape our world.

Some mysteries remain, though. Physicists still don’t know the origin of dark matter—an enigmatic substance that exerts a gravitational force on visible matter—or why there’s so much matter and so little antimatter in the universe.

Sarah Eno, a UMD physics professor who has conducted research at particle accelerators around the world, including the LHC, said these answers will only come from collider experiments.Sarah Eno, a physics professor at UMD, sits atop a model of a Large Hadron Collider (LHC) dipole magnet at CERN about 10 years ago. At the time, she was participating in LHC experiments and frequently spent her summers at the lab in Switzerland. Credit: Meenakshi Narain.
“What is the nature of dark matter? Nobody has any idea,” Eno said. “We know it interacts via gravity, but we don’t know whether it has any other kinds of interactions. And only an accelerator can tell us that.”

Better, Faster, Stronger

After the third (and current) run of the LHC ends, the collider’s accelerator will be upgraded in 2029 to “crank up the performance,” according to the European Organization for Nuclear Research (CERN), which houses the collider.

With the added benefit of stronger magnets and higher-intensity beams, this final round of experiments could be a game-changer. But once that ends, Eno said the LHC will have reached its limit in terms of energy output, lowering the odds of any new discoveries. The logical next step, she said, would be to construct a new collider capable of propelling the field of particle physics forward.

“The field is now trying to decide what the next machine is,” Eno said.

Around the globe, there are various proposals on the table. There is a significant push for another proton collider in the same vein as the LHC, except bigger and more powerful. Electron-positron colliders—both linear and circular in shape—have also been proposed in China, Japan and Switzerland.

Eno is one of the physicists leading the charge for the construction of an electron-positron collider at CERN. It would be the first stage of the proposed Future Circular Collider (FCC), which would be four times longer than the LHC. By the late 2050s, it would be upgraded to a proton collider, with an energy capacity roughly seven times that of the LHC. Eno, who was appointed one of the U.S. representatives for this project, said the electron-positron collider would allow physicists to study the Higgs boson with significantly higher precision.

“When an electron and positron annihilate, all their energy becomes new states of matter,” Eno said. “This means that when you’re trying to reconstruct the final state, you know the total energy of that final state. This allows you to do much more precise measurements.”

This proposal does come with some challenges. Circular colliders radiate off a lot of energy, making it difficult to accelerate electrons to high energy. Eno said this can be avoided by building a massive collider with a long tunnel (to the tune of 62 miles, in the case of the FCC), preventing electrons from losing steam as they whip around sharp corners.

The radiation problem has pushed some physicists towards another theoretical possibility: a muon collider. Muons are subatomic particles that are like electrons, but 207 times heavier, which keeps them from radiating as much. This would make them ideal candidates for collider research—if only they didn’t decay in 2.2 microseconds.

“If you talk to the muon collider proponents, their faces light up because it’s such a challenge,” Eno said. “And who doesn’t like a challenge?”

Clean Collisions 

One of Eno’s colleagues at UMD—Distinguished University Professor and theoretical physicist Raman Sundrum—endorses the muon collider idea. So much so that he and a team of physicists wrote a paper titled “The muon smasher’s guide,” which appeared in Reports on Progress in Physics in July 2022.

“We build colliders not to confirm what we already know, but to explore what we do not,” the research team wrote in their paper. “In the wake of the Higgs boson’s discovery, the question is not whether to build another collider, but which collider to build.”

They made the case for the world’s first muon smasher, arguing that these collisions would be “far cleaner” than proton collisions, which occur at the LHC. Unlike protons—a composite object made of quarks and gluons—muons are elementary particles with no smaller components. This would let physicists see only what they want to see, without any distractions.

“Muon collisions would make it easier to diagnose what’s going on,” Sundrum said. “When something extraordinary happens, it doesn’t get dwarfed by all of the mundane crashing of many parts.”

Considering that the Higgs boson only appears once in about a billion collisions at the LHC, this level of clarity and precision could make a world of difference. However, the more the field of particle physics advances, the more challenging it is to find something new.

“The Higgs was a needle in the haystack, but discovering newer particles could be even subtler and harder,” Sundrum said.Artistic rendering of the Higgs field. Credit: CERN

Despite these challenges, the LHC could still make a major discovery. Sundrum continues to develop theories that guide and inspire the field, including the idea that the LHC could find a “parent particle” that gave rise to all protons in the universe. If this comes to fruition, it would be worth building new colliders that could validate the LHC’s initial findings and provide a more complete picture of why matter dominates over antimatter in the universe, Sundrum said.

In the coming years and decades, physicists will continue to debate the pros and cons of various collider proposals. The outcome will depend partly on scientific advancements, and partly on political will and funding. Sundrum said it’s not cheap to build a collider—with some projects expected to cost $10 billion—but the discoveries that could come from these experiments are priceless.

“An enormous number of people find it very moving and interesting to know what it’s all about, in terms of where the universe came from, what it means and how the laws work,” Sundrum said. “Individually these experiments are expensive, but as a planet, I think we can easily afford to do it.”

Written by Emily Nunez

From Unexpected Opportunity to Game-changing Discovery

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Category: Department News

Published: Tuesday, September 06 2022 00:01

In the world of startups, opportunity can come knocking in strange ways. Six years ago, Didier Depireux (Ph.D. ’91, physics) was doing research at the University of Maryland when he was approached by Sam Owen, a young scientist who said he’d developed a device to treat motion sickness. Depireux was skeptical but decided to check it out. 

“Since I get very severe motion sickness, I made a deal with him,” Depireux recalled. “I said, ‘I’ll come over with my car and you can drive me around while I use the device. If I haven’t thrown up after 20 minutes while I’m in the back of the car reading, I’ll join the effort.’”

The two made plans to meet in Washington, D.C., on a muggy July afternoon.  Didier Depireux

“So, I go to Georgetown. The windows are down, it’s hot, it’s humid and I’m thinking I will not make it past the first turn,” Depireux explained. “Owen is driving and I’m in the back seat using his device and reading my cellphone. And for the first time in my life—and I’m over 50 years old—I was able to read in the back of a car and not get sick. I thought, ‘I need to join this, this is amazing.’”

Thanks to that strange summer ride-along, Depireux joined Owen in launching a startup called Otolith Labs to address inner ear-related conditions and their often debilitating symptoms. Otolith’s noninvasive vestibular system masking technology—designed for acute treatment of vestibular vertigo—received the FDA’s Breakthrough Device designation and clinical trials are ongoing, with support from investors including AOL founder Jack Davies and billionaire entrepreneur Mark Cuban.

All of this sets the stage for a major test that could lead to the startup’s ultimate goal—FDA approval as early as next year.

“In July we told the FDA we want to do a large-scale pivotal trial with hundreds of participants,” Depireux explained. “If all goes well, we’ll have a meeting next summer where the FDA will approve us and then the device will become available.”

For Depireux, it’s the latest step on a bigger mission that has guided his career.

Didier Depireux“It’s mostly relevance,” he explained. “I would like my life to make a difference, that’s the one thing that keeps me going.”

From philosophy to physics

Depireux was raised in Belgium. A bright, thoughtful boy, he grew up with a strong interest in science and theory, thanks to his father, a physics professor, and his mother, a chemistry teacher.

“I was always very science-y,” Depireux recalled. “Initially, I wanted to become a philosopher and I read this 800-page book—I think it was Kant—and at the end of it I was like, ‘I still don’t know the answer, and I’m not even sure I understand the question anymore.’ That’s when I thought that’s not a good fit for me.”  

Depireux eventually gravitated toward physics. After receiving his B.S. in physics from the University of Liège in Belgium in 1986, he began his graduate work in physics at the University of Maryland, where he focused on string theory and met Distinguished University Professor of Physics Sylvester James Gates Jr., who quickly became a mentor and friend.

“Jim had a huge impact on me. He was a fantastic person to work with and he had so much positive energy,” Depireux said. “I still remember late one night I was working on something, and I was stuck and I wrote to him, and he said, ‘I’ll come over, let’s work this out.’ So we had office hours at 10:30 p.m. just because I couldn’t solve a problem.”

Depireux earned his Ph.D. in 1991 and went on to do postdoctoral work in Quebec, Canada, before returning to College Park in 1994. Inspired by his wife Pamela, who was getting her Ph.D. in neuropharmacology, Depireux took on the challenge of modeling the brain and studying how it processes sound. By 2001, he was also teaching a gross anatomy class at the University of Maryland School of Medicine.

“I think, to this day, I am the only string theorist who has taught gross anatomy,” he reflected.

From his research on the brain and hearing, Depireux shifted his focus to tinnitus—disruptive ringing in the ears. He explored possible treatments and eventually teamed up with former UMD Bioengineering Professor Benjamin Shapiro who was already working on the drug delivery challenges Depireux was trying to solve.

“I wanted to get drug delivery to the ear but I didn’t know how to do it,” Depireux said. “He had this method with nanoparticles to deliver drugs and I had the target so we started working together.”

In 2013, the two launched Otomagnetics, a startup that has made major strides in developing noninvasive methods to treat inner ear diseases and more.

“We’ve gotten very nice results as far as drug delivery goes and Otomagnetics is still an ongoing concern,” Depireux explained, “But raising money for drug delivery is the real challenge, because to get drug delivery to the ear is going to take hundreds of millions of dollars, and that hasn’t happened yet.”

Going all-in on Otolith

Depireux balanced his time between Otomagnetics, his UMD research and teaching at the School of Medicine until 2016, when he experienced Owen’s experimental motion sickness device for the first time. Depireux saw so much potential with the device that he went all-in on Otolith. 

“You have to have pretty strong resilience to join a startup—I went for a year and a half without a salary or anything,” Depireux explained. “It’s not like we didn’t have money, we just needed all of the money to develop the device, get the patents in, all of the things we had to do.”

Though Otolith started with a motion sickness device, its co-founders hoped to make an even bigger impact by developing a device for vertigo, debilitating dizziness often caused by problems in the inner ear.

And they had a plan.

“For tinnitus or ringing in the ears, some patients get relief from a noise masker—they can still perceive their tinnitus, but the noise masker allows them to ignore the tinnitus,” Depireux explained. “So Sam, my cofounder said, ‘Why don’t we come up with a noise masker for the vestibular system?’”

That’s exactly what they did. Their novel device, worn like a headband, treats vertigo by applying localized mechanical stimulation to the vestibular system through calibrated vibrations. 

Depireux says he never would have made it this far without physics.

“My physics training really helped me,” he explained. “In physics, you have this huge problem and you have to break it down. If it’s intractable, you make it tractable, break it into small, simple things we can understand and then we can solve it.”

Promising results and personal stories

Clinical trials of Otolith’s investigational headband have yielded promising results. In the first of a series of ongoing clinical studies, 87.5% of the 40 participants reported a reduction in their vertigo within five minutes of turning on the device. But for Depireux, it’s the personal stories that are most rewarding.

“Somehow my phone number was listed as an emergency contact on clinicaltrials.gov, which I thought would be for emergencies only,” he said. “I’d have patients calling me in tears, telling me, ‘When my grandkids visit, I can finally bend down and pick them up, and it used to be that just bending down would send me into such vertigo that I would have to go to bed for days.’ Or ‘For the first time in years, I’ve been able to walk around the block.’ That’s what really motivates me.”

It's been Depireux’s goal all along—doing relevant research that changes people’s lives.

“We cannot help 100% of vertigo patients, no device does that,” he reflected. “But if we can help even half of those patients, that’s really my hope.”

Looking back on a career path that’s been anything but predictable, Depireux appreciates every challenge and setback that got him to where he is today.

“Something can feel like a failure when things go wrong, but then later you realize you really learned something from it,” he reflected. “I’m so grateful I was given the opportunity to come to the U.S. and study physics and do research in College Park, do this random walk in my career and finally end up doing something that I feel has given me great meaning in my life.”

Written by Leslie Miller

Faculty, Staff, Student and Alumni Awards & Notes

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Category: Department News

Published: Friday, September 02 2022 00:01

We proudly recognize members of our community who recently garnered major honors, began new positions and more.

Recent Physics Grad Sees Many Roads Ahead

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Category: Department News

Published: Friday, September 02 2022 00:01

As Jeffrey Wack (B.S. ’22, physics; B.S. ’22, mathematics) walked across the graduation stage in May 2022, he carried with him a lot of uncertainty about where to go next. His trepidation came from his voracious curiosity for a broad range of things, primarily within physics and math—the subjects of his two degrees—but also from his interests in teaching, outreach and music. The prospect of having to pick just one path forward felt confining to Wack. But that same curiosity served him extremely well during his time at the University of Maryland, and it left him with many opportunities for next steps.Jeffrey Wack (courtesy of same)

Wack collected an impressive resume at UMD. He taught an introductory course on nuclear physics and reactor operations, studied physics in Florence, participated in an optomechanics research project that resulted in a publication, made significant contributions to experimental research with coplanar waveguides, and co-taught a self-designed course on music theory and math. Since graduating, he began working as a fellow at the Museum of Math in New York City, sampling the working world while contemplating graduate school.

“The four years I spent at UMD were the best four years of my life this far,” Wack says. “I’m already having a blast living in New York, but I’m going to miss all the great people I met in College Park.”

Born and raised in Carroll County, Maryland, Wack attributes his broad scientific curiosity to his upbringing and the influence of his father.

“My dad is a pediatrician, but he's very interested in all sorts of science,” Wack says. “I have memories of playing the ‘why’ game with him and just asking him why. You know, you ask why, and then no matter what the answer is, you can always ask why again, and you sort of end up down this rabbit hole.”

Although the younger Wack asked questions about everything, from why fruit grows to what an immune system is, his earliest fascination orbited around astronomy. Then, during high school, his curiosity shifted gears, landing on the curiously strong connection between physics and mathematics.

“There was something about physics and calculus in particular that I really enjoyed,” says Wack. “Those relationships between position and velocity and acceleration, there's something about them that really caught me. Like ‘that's awesome!’”

Following in his older sister’s footsteps, Wack chose to attend UMD, drawn in by the opportunities for learning all things physics and math at a large university. In the fall of 2019, Wack studied abroad in the Maryland-in-Florence program, specifically designed for physics students to continue taking required courses while exposing themselves to a foreign culture and language. He was particularly inspired by the instruction of Luis Orozco, now professor emeritus at UMD and a Fellow at the Joint Quantum Institute (JQI). After the semester abroad ended, Wack reached out to Orozco to see if he could work with him on a research project. Orozco agreed, and during the summer of 2020 invited him to join a nanofiber project. 

Orozco’s research interests include optomechanics, the study of interactions between mechanical systems and electromagnetic waves. The project Wack joined was a multi-national collaboration, with an experimental group at Shanxi University in China and a collaborator at the University of Conception in Chile. The goal was to use light to cool an optical fiber as it travels through it.

Optical fibers are used to confine and direct light, whether it’s for carrying internet signals to homes or aiding in research. The fibers Orozco’s team used are stretched incredibly thin, about a hundred times thinner than human hair. These nano-fibers guide light, but they hardly confine it—some of the light actually travels outside the fiber. This is particularly useful for studying the interaction of light with atoms and ions, which can be brought close to (but remain outside of) the fiber. The downside is that the fiber is quite fragile and prone to tiny vibrations that shake and twist it, disturbing the light as it travels.

To minimize these tiny twists, the team sent in a laser beam of a particular intensity. The interaction of the beam with the material inside the fiber counteracted the fiber’s twisting, minimizing that particular vibration and thus cooling down the fiber overall. To detect this cooling, the team sent a second, probing laser beam and observed how much the fiber’s twists and turns perturbed that beam.

Wack’s role was to analyze the raw photodetector data from the probing laser and use it to extract information about the fiber twists. He analyzed the data and concluded that the method was successful, as detailed in a recent paper published in Photonics Research. But Wack wasn’t satisfied with simply analyzing data. He played the ‘why’ game, trying to understand the deeper physics of what was going on. He made his own, simplified model of the cooling mechanism—not to put in the paper, but enough to model the system to his own satisfaction. “I did that just to entertain myself,” Wack explains.

"Jeffrey contributed crucially in understanding the cooling process, thanks to his analysis of the distribution of the temperature fluctuations,” Orozco says. “The plots he produced made it into figure two of the publication."

By the summer of 2021, COVID-19 restrictions were easing up, and Wack was itching to try hands-on lab work. He joined the group of one of UMD’s most mathematically minded experimentalists, Chesapeake Assistant Professor of Physics and JQI Fellow Alicia Kollár. Kollár’s research concerns coplanar waveguides—little paths printed on a circuit board that microwaves can travel through—to create never before seen geometries and interaction patterns between bits of quantum information known as qubits.

Kollár’s creation of novel geometries relies on a peculiar theoretical property of coplanar waveguides: that stretching or scrunching them up does not change the frequency of microwaves they carry. Wack’s role was to make careful measurements to test how well this property holds in practice.

To investigate this, Wack had to get his hands dirty with several different lab skills. He had to learn to solder and assemble electronics, work with graduate students to create coplanar waveguides of different lengths, analyze data, and model the system using purpose-built software.

“Jeff did really phenomenal work,” Kollár says. “He was really just sort of diving into research, almost like a senior graduate student.”

Wack automated some simulation steps that had previously been done manually and used the new process to quantify a confounding effect—that the frequency change depended on the number of times that the waveguide was bent. If this pattern is confirmed experimentally, Kollár says, it will be used in many future experiments and theoretical studies alike.

On top of his studies and research, Wack also found ways to participate in outreach and teaching throughout his time at UMD. He volunteered to film a slinky demonstration of wave propagation. He taught an introductory course on nuclear physics and reactor theory to undergraduates for the Maryland Undergraduate Training Reactor (MUTR) program, where undergrads can become certified reactor operators. He also has an interest in music, having sung and performed in musicals in high school and having picked up electric bass during his college years. “And also, because I'm such a geek for computers, I do some digital synthesis,” Wack says. He found a way to weave this in with his math interest by creating a co-teaching a course on the math of music for the Student Initiated Courses (STIC) program.

Upon graduating last spring, Wack decided to take a gap year. This summer, he started a fellowship at the Museum of Math, combining his passion for mathematics and outreach. As a docent there, he talks to visitors about the exhibits and thinks a lot about math. As part of the fellowship, he’s also pursuing a personal project: planning a live performance that combines music, physics demos and lectures on math and music theory.

“So many of the paths forward seem appealing to me,” Wack says. “I'm going to go to grad school at some point, but this is part of why I wanted to do a gap year. I'm hoping that over the next two years, it'll come to me like ‘Aha! This is exactly what I want to do.’”

Written by Dina Genkina