Scientists have never actually seen the Higgs boson. They’ve never seen the inside of a proton, either, and they’ll almost certainly never see dark matter. Many of the fundamental patterns woven into the fabric of nature are completely imperceptible to our clunky human senses.

But scientists don’t need to see particles to learn about their properties and interactions. Physicists can study the subatomic world with particle detectors, which gather information from events that occur much faster and are much smaller than the eye can see.

But what is this information, and how exactly do detectors gather it? At experiments at the Large Hadron Collider, the world's largest and most powerful particle accelerator, it all begins with a near-light-speed race.

Starting with a bang

The LHC is built in a ring 17 miles in circumference. Scientists load bunches of protons into this ring and send them hurtling around in opposite directions, gaining more and more energy with each pass. 

By the time the LHC has boosted the proton beams to their maximum energy, they will have traveled a distance equivalent to a round-trip journey between Earth and the sun. They will be moving so fast that they no longer convert energy into speed but in effect swell with mass instead.

Once the protons are ramped up to their final energy, the LHC’s magnets nudge the two beams into a collision course at four intersections around the ring. 

“When two protons traveling at near light speeds collide head-on, the impact releases a surge of energy unimaginably quickly in an unimaginably small volume of space,” says Dhiman Chakraborty, a professor of Physics at Northern Illinois University working on the ATLAS experiment. “In that miniscule volume, conditions are similar to those that prevailed when the universe was a mere tenth of a nanosecond old.”

This energy is often converted directly into mass according to Einstein’s famous equation, E=mc², resulting in birth of exotic particles not to be found anywhere else on Earth. These particles, which can include Higgs bosons, are extremely short-lived.

“They decay instantaneously and spontaneously into less massive, more stable ‘daughter’ particles,” Chakraborty says. “The large mass of the exotic parent particle, being converted back into energy, sends its much lighter daughters flying off at near light speeds.”

Even though these rare particles are short-lived, they give scientists a peek at the texture of spacetime and the ubiquitous fields woven into it. 

“So much so that the existence of the entire universe we see today—ourselves as observers included—is owed to [the particles and fields we cannot see],” he says.

Enter the detector

All of this happens in less than a millionth of a trillionth of a second. Even though the LHC’s detectors encompass the beampipe and are only a few centimeters away from the collison, it is impossible for them to see the new heavy particles, which often disintegrate before they can move a distance equal to the diameter of an atomic nucleus.

But the detectors can “see” the byproducts of their decay. The Higgs bosons can transform into pairs of photons, for example. When those photons hit the atoms and molecules that make up the detector material, they radiate sparkles of light and jolts of energy like meteorites blazing through the atmosphere. Sensors inhale these dim twinkles and transform them into electrical signals, recording where and when they arrived. 

“Each pulse is a snapshot of space and time,” Chakraborty says. “They tell us exactly where, when and how fast those daughter particles traversed our detector.”

A single proton-proton collision can generate several high-energy daughter particles, some of which produce showers of hundreds more. These streams of particles release detectable energy as they hit the detectors and generate electrical pulses. The time, location, length, shape, height and total energy of each electrical pulse are directly translated into data bits by an electronic readout card.

Much the way biologists chart animal tracks to study the speed, direction and size of a herd, physicists study the shape of these electrical pulses to characterize the passing particles. A long, broad electrical pulse indicates that a large stream of particles grazed across the detector, but a pulse with a sharp peak suggests that a small pack cut straight through.

These electrical pulses create a multifaceted connect-the-dots. Algorithms quickly identify patterns in the cascade of hits and rapidly reconstruct particle energies and tracks.

“We only have a few microseconds to reconstruct what happened before the next batch of collisions arrives,” says Tulika Bose, an associate professor at Boston University working on the CMS experiment. “We can’t keep all the data, so we use automated systems to crudely reconstruct particles like muons and electrons. 

“If the event looks interesting enough based on this limited amount of information, we keep all the data from that snapshot in time and save them for further analysis.”

These interesting events are packaged and dispatched upstairs to a second series of automated gatekeepers that further evaluate the quality and characteristics of these collision snapshots. Preprogrammed algorithms identify more particles in the snapshot. This entire process takes less than a millisecond, faster than the blink of a human eye.

Even then, humans won’t lay eyes on the data until after it undergoes a strenuous suite of processing and preparation for analysis.

Humans can’t see the Higgs boson, but by tracing its byproducts back to a single Higgs-like origin, they were able to gather enough evidence to discover it.

“In the five years since that discovery, we’ve produced hundreds of thousands more Higgs bosons and reconstructed a good number of them,” Chakraborty says. “They’re being studied intensely with the goal of gaining insight into deeper mysteries of nature.”

When describing neutrinos to the public, scientists often share an astounding fact: About 100 trillion of them pass through your body every second. Neutrinos are extremely abundant in the universe, and they only rarely interact with other matter. That’s why they’re constantly streaming through you—and our entire planet.

But every once and a while, a neutrino hits something.

A new result from the IceCube experiment, published today in Nature, provides a unique measurement of how often that happens. Future improvements on the result could lead to discoveries about neutrinos, particle physics or even the Earth’s inaccessible core.

Colliding with matter can cause a neutrino to shed some or all of its energy. When a neutrino loses all of its energy, it is destroyed, converted into a shower of other particles. It’s a small but “very nasty explosion of stuff,” says scientist Sandra Miarecki, who led the recently published study as a student at UC Berkeley and who now works as a professor at the US Air Force Academy in Colorado.

The more energy a neutrino has, and the denser the matter through which it is traveling, the more likely this is to happen. When neutrinos reach energies of millions of billions of electronvolts, they should find it almost impossible to make it all the way through our planet.

That had been the prediction, at least. But until the IceCube experiment, no one had ever actually measured it.

IceCube is an array of 5160 basketball-sized light sensors sunk into a cubic kilometer of Antarctic ice. When a neutrino smacks into a nucleus in the Earth, it converts its energy into another particle, a muon, which creates a flash of blue light as it passes through the ice. IceCube’s sensors record the trail of that light, letting scientists know how much energy the neutrino had and what direction it came from. Measuring the direction tells scientists how much of the Earth the neutrino has traveled through to get there.

For her thesis, Miarecki used data from IceCube’s 2010-2011 year of operation (the year prior to the completion of the detector) to measure what’s called the neutrino cross-section, the likelihood that a neutrino would interact with a nucleus, depending on the neutrino's energy.

“The thing that’s really interesting about this measurement is that we’re using neutrinos with energies tens to hundreds of times higher than what’s available at accelerators like the Large Hadron Collider,” says Spencer Klein of Lawrence Berkeley National Laboratory and UC Berkeley, Miarecki’s thesis advisor. “IceCube is the first experiment that’s big enough to do anything like this.”

This first measurement of the neutrino cross-section at high energies matched scientists’ predictions based on the Standard Model of particle physics. In this dataset, no million-billion-electronvolt neutrinos made it through from the opposite side of the Earth.

The concept of seemingly unstoppable neutrinos finally meeting their match “actually shook me a little,” when he first joined the experiment, says IceCube Spokesperson Darren Grant of the University of Alberta. “I’d been working on neutrinos for, oh goodness, 10 years, but they’d always been at low energies.”

But with more data—and IceCube has collected almost seven more years’ worth since this study began—that measurement will grow more precise. There is still a chance it will reveal a discrepancy, which could point to a new discovery in physics. “It’s just going to take someone to do the work,” Miarecki says.

Knowing the neutrino cross-section with great accuracy could also help out another field: geology.

“It’s one of the few ways I am aware of where you could actually refine the deep interior picture of the Earth to some higher precision than we know it today,” Grant says.

Scientists’ current best measurements of the interior of the Earth come from sensors measuring how vibrations move through the planet during earthquakes. These measurements are highly accurate, and over the last couple of decades, no one has found a way to improve them.

But if scientists can combine their knowledge of neutrinos with their knowledge of the center of the Earth, they should be able to make very accurate predictions about how many neutrinos they will see coming through different sections of the ground. If their measurements disagree with those predictions, it could be a sign that there’s something going on inside the Earth that they don’t yet understand.

In a previous career, Sandra Miarecki flew high above the Earth’s surface. During a 20-year career in the US Air Force that included time as a test pilot, she flew aircraft including the B-52, F-16, MiG-15, helicopters and even the Goodyear Blimp.

She retired from the Air Force in 2007 to pursue a new calling in physics that would set her sights on the depths of the Earth. Now an assistant professor of physics, Miarecki served as the principal researcher in a just-released study that relied on data from a detector encapsulated in ice near the South Pole to determine how high-energy subatomic particles are absorbed as they travel inside the planet.

It was a chance seat assignment on a passenger jet in 2007 that put her next to Robert Stokstad, a Lawrence Berkeley National Laboratory physicist who was then serving as the project director for the lab’s IceCube Neutrino Observatory team. Miarecki was on a scouting trip to find housing in the San Francisco Bay Area in preparation for her pursuit of a PhD at UC Berkeley.

“He was playing with a camera, and I was involved with photography,” she recalls of the meeting on that Southwest Airlines flight, and they struck up a conversation. The subject of science came up, and his description of the IceCube project, then under construction, piqued her interest.

She would later attend a Berkeley Lab IceCube group meeting at Stokstad’s invitation. “I thought I was going to be a cosmology theorist when I first got to Berkeley,” she says, but hands-on experiments were also alluring.

So she worked on a summer project with the collaboration, and enjoyed the experience.

Spencer Klein, a longtime physicist at Berkeley Lab who now leads the lab’s IceCube team, suggested that Miarecki’s dissertation focus on the Earth’s absorption of high-energy neutrinos. Before joining the Air Force, Miarecki had earned a bachelor’s degree in astronomy, and also completed courses in physics and mathematics, at the University of Illinois at Urbana-Champaign.

“I had also toyed with the idea of being a geologist, and when you are using the Earth as an absorption material (for neutrinos), you have to understand the composition and density of the Earth. It was a really nice blend of all my previous experience,” she says. “I was so happy when we came up with this idea.”

Miarecki worked full-time on this research at Berkeley Lab from 2010 to 2015 before taking a job in January 2016 as a physics instructor at the Air Force Academy in Colorado Springs, Colorado. She continued working on her dissertation at the academy, completing that work in December 2016.

When Klein suggested that she submit her dissertation work for publication in Nature, Miarecki balked at first. “I said, ‘Really?’ Then I thought, ‘OK, let’s give it a try,’” she says. “It’s not expected that your graduate dissertation actually gets into Nature.” The study was published today.

She was promoted to assistant professor at the academy in January 2017 and now teaches physics coursework in classical mechanics and electromagnetism as well as the physics of combat aviation.

“When I was going through the military retirement transition course, the attendees had to answer the question, ‘What do you want to be when you grow up,’ which was tongue-in-cheek, of course, because all of us were over 40,” Miarecki recalls. “I realized that I wanted to teach, and I had always been told that I was a great teacher. The military also had selected me to be an instructor pilot at several times during my career.

“I debated whether my 42-year-old brain would be spongy enough to tackle a PhD program, but I decided that I had to try, or I could never live with myself wondering, ‘What could have been?’ Switching from the military to academia was not a big shock because I had spent so much of my military career in a teaching capacity.”

The assistant professor position at the Air Force Academy has brought her career full circle, she notes: “It represents a perfect blend of my previous Air Force career with my love of teaching physics.”

Editor’s note: A version of this article was published by Berkeley Lab.

So, you want to start a physics experiment. Maybe you want to follow hints of an as yet unseen particle. Or maybe you want to learn something new about a mysterious process in the universe. Either way, your next step is to find people who can help you. 

In large science collaborations, such as the ATLAS and CMS experiments at the Large Hadron Collider; the Deep Underground Neutrino Experiment (DUNE); and Fermilab’s NOvA, hundreds to thousands of people spread out across many institutions and countries keep things operating smoothly. Whether they’re senior scientists, engineers, technicians or administrators, each of them has an important role to play.

Think of it like a jigsaw puzzle: This list will give you an idea about how their work fits together to create the big picture.

Dreaming up the experiment

Many particle physics experiments begin with a fundamental question. Why do objects have mass? Or, why is the universe made of matter? 

When scientists encounter these big, seemingly inscrutable questions, part of their job is to identify possible ways to answer them. A large part of this is breaking down the big questions into a program of smaller, answerable questions.

In the case of the LHC, scientists who wondered about things such as undiscovered particles and the origin of mass designed a 27-kilometer particle collider and four giant detectors to learn more. 

Each scientist in a collaboration brings their own unique perspective and skill set to the table, whether it’s providing an understanding of the physics or offering expertise in operations or detector design.

Perfecting the design

Once scientists have an idea about the experiment they want to do and the approach they want to take, it’s the job of the engineers to turn the concepts into pieces of hardware that can be built, function and meet the experiment's requirements.

For example, engineers might have to figure out how the experiment should be supported mechanically or how to connect all the electrical systems and make signals available in a detector.

In the case of NOvA, which investigates neutrino oscillations, scientists needed a detector that was huge and free of dense materials, which made conventional construction techniques unworkable. They had to work with engineers who could understand plastic as a building material so they could be confident about using it to build a gigantic, free-standing structure that fit the requirements.

Keeping things running

Technicians come in when the experimental apparatus and instrumentation are being built and often have complementary knowledge about what they’re working on. They build the hardware and coordinate the integration of components. It’s their work that, in the end, pulls everything together so the experiment functions. 

Once the experiment is built, technicians are responsible for keeping everything humming along at top performance. When physicists notice things going wrong with the detectors, the technicians usually have first eyes on it. It’s a vital task, since every second counts when it comes to collecting data. 

Doing the heavy lifting

When designing and constructing the experiment, the scientists also recruit postdocs and grad students, who do the bulk of the data analysis. 

Grad students, who are still working on their PhDs, have to balance their own coursework with the real-world experiment, learning their way around running simulations, analyzing data and developing algorithms. They also make sure that every part of the detector is working up to par.  In addition, they may work in instrumentation, developing new instruments and electronics.

Postdocs, on the other hand, have already worked on experiments and obtained their PhDs, so they typically assume more of a leadership role in these collaborations. Part of their role is to guide the grad students in a sort of apprenticeship. 

Postdocs are often in charge of certain types of analysis or detector operations. Because they’ve worked on previous experiments, they have a tool kit and experience to draw on to solve problems when they crop up.

Postdocs and grad students often work with technicians and engineers to ensure everything is properly built. 

Making the data accessible

The LHC produces about 25 petabytes of data every year, or 25 billion megabytes. If the average size of an MP3 is about one megabyte per minute, then it would take almost 50,000 years to play 25 petabytes of songs. In physics collaborations, computer scientists and engineers have to organize the computing networks to ensure against bottlenecks or traffic jams when this massive amount of data is shared.

They also maintain the software framework, which takes care of data handling and archiving. Say a scientist wants to know what happened on Feb. 27, 2015, at 3 a.m. Computing experts have to be able to go into the data catalogue and find, among the petabytes of data, where that event is stored.

Sorting out the logistics

One often overlooked group is the administrators. 

It’s up to the administrators to sequence all the different projects so they get the funds they need to make progress. They sort the logistics to make sure the right people are in the right places working on the right things.

Administrators manage a group of people who are constantly coming and going. Is someone traveling to a site from a different institution? The administrators make sure that people get connected, work out itineraries and schedule where visiting scientists will live and work. 

Administrators also organize collaboration meetings, transfer money, and procure and ship equipment. 

Translating discoveries to the public

While every single person involved in an experiment has a responsibility to effectively communicate with others, it can be challenging to communicate about research in a way that’s relatable to people from different backgrounds. That’s where the professional communicators come in. 

Communicators can translate a paper full of jargon and complicated science into a fascinating story that the rest of the world can get excited about.

In addition to doing outreach for the public and writing press releases and pitching stories for the media, communicators offer coaching to people in a scientific collaboration on how to relay the science to a general audience, which is important for generating public interest.

Fitting the pieces

Now that you know many of the pieces that must fall into place for a large physics collaboration to be successful, also know that none of these roles is performed in a vacuum. For an experiment to work, there must be a synergy of tasks: Each relies on the success of the others. Now go start that experiment!

These days the LIGO experiment seems almost unstoppable. In September 2015, LIGO detected gravitational waves directly for the first time in history. Afterward, they spotted them three times more, definitively blowing open the doors on the new field of gravitational-wave astronomy.

On October 3, the Nobel Committee awarded their 2017 prize in physics to some of the main engines behind the experiment. Just two weeks after that, LIGO scientists revealed that they'd seen, for the first time, gravitational waves from the collision of neutron stars, an event confirmed by optical telescopes—yet another first.

These recent achievements weren’t inevitable. It took LIGO scientists decades to get to this point. 

LIGO leader Barry Barish, one of the three recipients of the 2017 Nobel, recently sat down with Symmetry writer Leah Hesla to give a behind-the-scenes look at his 22 years on the experiment.

What has been your role at LIGO?

What steps did LIGO take to be as sensitive as possible?

What did you do to increase sensitivity for Advanced LIGO?

What key steps did you take when you came on board in 1994?

What were the technical changes?

Did you draw on past experience?

Were you concerned the experiment wouldn’t happen? If not, what did concern you?

When did you hear about the first detection of gravitational waves?

What does it feel like to win the Nobel Prize?

Do you have advice for others organizing big science projects?

What are your hopes for the future of LIGO?

Planning to start up a particle physics lab? Better hire an artist.

That was Robert R. Wilson’s thought in the 1960s, when he began forming what would become the Department of Energy’s Fermi National Accelerator Laboratory. He wanted a space to do physics that would inspire all who set foot on the lab. He knew, even then, the importance of mingling art and science. The 11^th person hired was artist Angela Lahs Gonzales, and in her three decades at the lab, she influenced the character and aesthetic of nearly every part of the site.

Gonzales, the daughter of two artists who fled with her from Nazi Germany, had worked with Wilson previously at Cornell University. At Fermilab, she found herself responsible for a multitude of artistic choices. Working closely with Wilson, she created the lab’s logo, a union of dipole and quadrupole magnets used in accelerators to guide and focus the particle beam. She chose a bold color scheme, with vibrant blues, oranges and reds that would coat Fermilab buildings. She designed covers for scientific publications and posters for lab events and lectures.

“There was no project too small or large for Angela,” says Georgia Schwender, the curator of Fermilab’s art gallery. “She seemed to put just as much care and thought into sketches for the Annual Report as she did for a community Easter egg hunt. The whole lab was her canvas and her muse.”

A mix of themes and styles, from history to mythology and op-art to realism, are wrapped around images of accelerators, experiments and the Fermilab site. The images are often bizarre and fantastical, nearly always impressive. In one drawing, Fermilab’s bison dine at an elegant table; in another, winged creatures stare into a bubbling cauldron that contains the Fermilab accelerator complex and main building, Wilson Hall.

Gonzales typically worked in pen, sketching intricate details across paper, but she also branched out into different media, crafting jewelry, flags, vases, tables and even the elevator ceiling tiles. Her reach extended to typography, designs around doorways and drawings of things you might not expect: mundane things like emergency preparedness kits and literal nuts and bolts.

Her word on artistic choices was final. Employees were known to get a talking to if they painted something without consulting Angela. Some colors became tied to the science at hand. One time, an accelerator magnet was painted the wrong shade of blue and thus installed incorrectly, causing some confusion in the control room.

“Gonzales was at the lab from 1967 to 1998, and in that time she was incredibly influential on the style of the lab,” says Valerie Higgins, Fermilab’s archivist. “But you can see how these tendrils of art spiral out to influence the science and the shape of the lab as well.”

More than 100 pieces by Gonzales were featured in a Fermilab art gallery exhibit earlier this year, as the lab celebrated its 50^th anniversary. “A Lasting Mark” ran from June to September before briefly traveling and then being retired. An online catalog of the exhibit is available on the Fermilab site.

At a recent meeting of the Mountain View Handweavers club, five women chatted in their rocking chairs with an unusual newcomer: Engineer Knut Skarpaas of SLAC National Accelerator Laboratory. He was an affable, inquisitive man about the age of their sons and grandsons. 

He explained he was looking for advice on how to build a loom to help particle physicists catch dark matter.

This wasn’t the first time Skarpaas had consulted with experts well outside high-energy physics for a project. Not by a long shot. He has found inspiration for machine designs and fabrication methods in ancient Egyptian jewelry, silversmithing, origami, spider webs and honeycombs. He is currently seeking permission to build a machine primarily from sapphire.

“The mechanical world is his playground,” says colleague Michelle Dolinski of Drexel University.

An insatiable curiosity

Back at his office, Skarpaas’s desk drawers rattle with the gears and tools he played with as a kid when his father, also a SLAC engineer, worked at the same desk. 

“He has many of his father’s gifts, but they are not identical,” says Gordon Bowden, a fellow engineer at SLAC who has worked with father and son. “Curiosity has driven Knut to accumulate much diverse, direct, hands-on experience—a trait becoming more and more rare in engineering.” 

In his briefcase, Knut carries a magnifying glass and a miniature microscope to examine objects he finds. He has picked apart and reassembled thousands of machines since childhood, from his father’s watch to sunken cameras salvaged on scuba expeditions and his grandmother’s Opel Kadett automobile. 

The details, he says, make the difference between something that works and something that doesn’t. But studying things that don’t work can be half the fun. “If the things are actually going to get thrown away anyway, you can take them apart more violently because you’re not going to put them back together,” Skarpaas says.

That might mean hitting them with a sledgehammer, or taking them back to his shop at home where he keeps his 20-ton press. “I can destroy pretty much—well, a lot of things will yield with 20 tons on them,” he says.

Skarpaas says taking things apart and looking at how they break—looking at failures—is important. It shows him the weak points, and then he can make sure those weak points don’t exist in his designs. 

An especially interesting mechanism might earn a place in his filing cabinets among a collection of other components that prove useful when he discusses design problems with his colleagues.

“I’ll just pull one out and say, ‘You mean like this?’ And frequently one of those things can end up being a solution,” Skarpaas says.

Working within extreme constraints

“Knut can see solutions that no one else would see,” says Dolinski. 

She worked with Skarpaas on the construction of a neutrino experiment, the Enriched Xenon Observatory. EXO-200, a 200-kilogram container of liquid xenon, looks for an elusive type of radioactive decay that could help physicists discover fundamental truths about the neutrino, including the nature and origin of its mass.

Engineering for high-energy physics requires a healthy dose of imagination because it often requires working within extreme constraints, Dolinski says. The EXO-200 team, for instance, could not use anything that could be contaminated even slightly with radioactive material, such as most normal materials like steel and ceramics. When measuring to parts-per-quadrillion, almost all things are radioimpure.

So the team made the difficult choice to construct 1000 electrical connections with no solder, no gold plating and no wire bonds. In fact, no wire. Nothing could be bought from a commercial catalog. Every screw, connection, spring and contact was made in-house from a block of raw material. And the connections couldn’t fail. Ever. “Because once you seal this thing up, it’s inaccessible for, you know, a decade,” Skarpaas says. 

Skarpaas recalls a refrain he used to hear from his department head: “Presume you have to make this out of gossamer.”

“And he means, basically, make this out of nothing,” Skarpaas says. Use the fewest materials and the lightest structure—effectively weightless—to have a minimum effect on the physics.

Year after year, Dolinski says, Skarpaas has always found elegant ways to do this. For the LZ dark matter detector, that means using four 1.47-meter-diameter high-voltage grids of hair-thin wires—carefully woven on a Skarpaas-designed loom, informed by the women of the Handweavers’ club.

This year, October 31 was more than just Halloween. It was also the first global celebration of Dark Matter Day. In 25 countries, 11 US states and online, people interacted with scientists, watched demonstrations, viewed films, took in art exhibits and toured laboratories to learn about the ongoing search for dark matter. 

Symmetry has collected a series of photos from participants around the world. Check out how people celebrated Dark Matter Day and download a commemorative dark matter poster (to be printed using visible matter).

Download the poster

Artwork by Ana Kova