That possibility is looking more and more likely, according to the initial results of an international collaboration — hosted by the U.S. Department of Energy’s Fermi National Accelerator Laboratory — that involved key contributions by a Cornell team led by Lawrence Gibbons, professor of physics in the College of Arts and Sciences.

The collaboration, which brought together 200 scientists from 35 institutions in seven countries, set out to confirm the findings of a 1998 experiment that startled physicists by indicating that muons’ magnetic field deviates significantly from the Standard Model, which is used to explain the laws that govern fundamental particles.

Digitizer modules undergo testing in the lab of Lawrence Gibbons, professor of physics, before being shipped to the Fermi National Accelerator Laboratory. Twenty-eight crates of these modules were installed around the muon g-2 ring.

“The question was, what’s going on? Was the experiment wrong? Or is the theory incomplete?” Gibbons said. “And if the theory is incomplete, then confirming what’s going on becomes the first terrestrial evidence of a totally new kind of fundamental particle or force that we don’t know about. It would be the first experiment on Earth that is sort of the equivalent of the discovery of dark matter in space.”

On April 7, the team confirmed that the original findings were correct, which means there must be more to the physics surrounding the muon than previously known.

Muons are like electrons but are more than 200 times more massive. Both are essentially tiny magnets with their own magnetic field. Muons are far more unstable, though, and decay in a few millionths of a second. They are also notoriously difficult to observe at the quantum mechanical level because the vacuum in which they exist is not a big empty cavity, but rather a bubbling, frothing, dynamic environment.

“It’s your cappuccino foam version of the vacuum, where there’s virtual particles winking in and out of existence all the time,” Gibbons said. “And that turns out to affect the strength of the magnetic field of a muon.”

To figure out why, researchers at Brookhaven National Laboratory 20 years ago set out to measure the absolute strength of muon’s magnetic field. They did this by firing a beam of muons into a 14-meter-diameter magnetic ring at nearly the speed of light while a series of detectors captured data. The scientists discovered a major discrepancy in the muon’s magnetic field: It was more than 3.5 standard deviations from the Standard Model predicted by theoretical physicists.

A plan was eventually hatched to repeat the Brookhaven experiment with higher precision. In 2013, the Brookhaven magnetic ring was transported to the Fermilab facility in Batavia, Illinois, where it was coupled with an even stronger particle accelerator that could produce more than 20 times the amount of muons. In 2018, the first of several experiment runs was launched.

This muon g-2 experiment — “g” refers to the value of the magnet’s strength caused by its intrinsic spin, which is slightly larger than two — was successful thanks to a system of detectors developed through a joint partnership between Cornell and the University of Washington.

The University of Washington group built a set of 24 calorimeters out of lead fluoride crystals and silicon photomultipliers that measure a blue light, known as Cherenkov radiation, that results when the positrons from muon decay strike the crystals. By measuring the time and amount of light for each of about 8 billion positrons, the researchers can pinpoint the muon’s precession rate, which is the frequency of its rotational wobble. The rate is directly related to the value of g-2.

The Cornell team built the digitizers that could look at the electronic signal coming out of the detectors and create a digitized version of the waveform that could be analyzed offline. The researchers were supported in the effort by the Laboratory for Elementary-Particle Physics (LEPP), and their digitizers incorporated $200,000 worth of specialized analog-to-digital converter chips donated by Texas Instruments.

Gibbons’ group also built one of the pair of reconstruction packages that helped their collaborators parse and analyze the collected data, and they were assisted in getting the most precise measurements by David Rubin, the Boyce D. McDaniel Emeritus Professor of Physics (A&S), who helped correct for the spread of muon momenta in the stored beam and for the small vertical motion as the beam speeds around the magnetic ring. Two other Cornell faculty, Toichiro “Tom” Kinoshita, professor emeritus of physics, and G. Peter Lepage, the Goldwin Smith Professor of Physics, both in A&S, contributed to the Standard Model prediction of g-2, to which the project compared its results.

As a fitting final touch, Gibbons chose to make the digitizer faceplate Cornell red.

With so much subatomic information to be sifted through, six different groups worked to separately confirm the muon’s precession frequency. Gibbons helped design blinding software that would ensure the groups made their calculations independently.

Then the time came to compare results.

“I have to say, it was nerve-racking. You go into the room, and there’s all these points scattered all over the place from all the offsets, and you have to decide, OK, are we going to compare results now? And will they agree?” Gibbons said. “We were trying to measure something to 500 parts per billion. The range that we had was plus or minus 25 parts per million on the frequencies that we’re trying to measure. There was a huge sigh of relief when we found everything agreed beautifully.”

And when all the international collaborators came together online for the final unblinding of the magnetic field measurement and checked it against the original Brookhaven result?

“Oh man. It was like hats flying in the air,” Gibbons said. “It was a combination of elation and relief.”

The results from this first experimental run represent only 6% of the data the researchers hope to eventually collect. Additional analysis has already begun on a second and third run, which will generate three to four times as much data. It will be 10 years before all the analysis is complete.

“We landed right on top of this result that really could indicate that there’s something totally new going on. We really want to push the uncertainty, the precision, to make the strongest possible statement that we can experimentally,” said Gibbons, who began work on the project in 2011. “We may be onto something really profound, something we don’t understand. And we still have to figure out what it is.”

“Homo erectus is the first hominin that we know about that has a body plan more like our own and seemed to be on its way to being more human-like,” said Ashley Hammond, an assistant curator in the American Museum of Natural History’s Division of Anthropology and the lead author of the new study. “It had longer lower limbs than upper limbs, a torso shaped more like ours, a larger cranial capacity than earlier hominins, and is associated with a tool industry — it’s a faster, smarter hominin than Australopithecus and earliest Homo.”

In 1974, scientists at the East Turkana site in Kenya found one of the oldest pieces of evidence for H. erectus: a small skull fragment that dates to 1.9 million years. The East Turkana specimen is only surpassed in age by a 2-million-year-old skull specimen in South Africa. But there was pushback within the field, with some researchers arguing that the East Turkana specimen could have come from a younger fossil deposit and was possibly moved by water or wind to the spot where it was found. To pinpoint the locality, the researchers relied on archival materials and geological surveys.

“It was 100 percent detective work,” said Dan Palcu, a geoscientist at the University of São Paulo and Utrecht University who coordinated the geological work. “Imagine the reinvestigation of a ‘cold case’ in a detective movie. We had to go through hundreds of pages from old reports and published research, reassessing the initial evidence and searching for new clues. We also had to use satellite data and aerial imagery to find out where the fossils were discovered, recreate the ‘scene,’ and place it in a larger context to find the right clues for determining the age of the fossils.”

Although located in a different East Turkana collection area than initially reported, the skull specimen was found in a location that had no evidence of a younger fossil outcrop that may have washed there. This supports the original age given to the fossil.

Within 50 meters of this reconstructed location, the researchers found two new hominin specimens: a partial pelvis and a foot bone. Although the researchers say they could be from the same individual, there’s no way to prove that after the fossils have been separated for so long. But they might be the earliest postcrania — “below the head” — specimens yet discovered for H. erectus.

The scientists also collected fossilized teeth from other kinds of vertebrates, mostly mammals, from the area. From the enamel, they collected and analyzed isotope data to paint a better picture of the environment in which the H. erectus individual lived.

“Our new carbon isotope data from fossil enamel tell us that the mammals found in association with the Homo fossils in the area were all grazing on grasses,” said Kevin Uno, a paleoecologist at Columbia University’s Lamont-Doherty Earth Observatory. “The enamel oxygen isotope data suggest it was a relatively arid habitat based on comparisons to other enamel data from this area.”

The work suggests that this early H. erectus was found in a paleoenvironment that included primarily grazers that prefer open environments to forest areas and was near a stable body of water, as documented by freshwater sponges preserved in the rocks.

Key to the field work driving this study were the students and staff from the Koobi Fora Field School, which provides undergraduate and graduate students with on-the-ground experience in paleoanthropology. The school is run through a collaboration between The George Washington University and the National Museums of Kenya, and with instructors from institutions from around North America, Europe, and Africa. “This kind of renewed collaboration not only sheds new light on verifing the age and origin of Homo erectus but also promotes the National Museums of Kenya’s heritage stewardship in research and training,” said Emmanuel Ndiema, the head of archaeology at the National Museums of Kenya.

Support for this study was provided in part by the U.S. National Science Foundation, grant no.s REU 1852441, 1358178, and 1624398, Fundac?a?o de Amparo a? Pesquisa do Estado de Sa?o Paulo (FAPESP grant no. 2018/208733-6), and the American Museum of Natural History.

“This case study shows that it is possible to use these neural control technologies, in which devices respond to electrical signals from a patient’s muscles, to help patients using robotic prosthetic ankles move more naturally and intuitively,” says Helen Huang, corresponding author of the study. Huang is the Jackson Family Distinguished Professor in the Joint Department of Biomedical Engineering at NC State and UNC.

“This work demonstrates that these technologies can give patients the ability to do more than we previously thought possible,” says Aaron Fleming, first author of the study and a Ph.D. candidate in the joint biomedical engineering department.

Most of the existing research on robotic prosthetic ankles has focused solely on walking using autonomous control. Autonomous control, in this context, means that while the person wearing the prosthesis decides whether to walk or stand still, the fine movements involved in those movements happen automatically — rather than because of anything the wearer is doing.

Huang, Fleming and their collaborators wanted to know what would happen if an amputee, working with a physical therapist, trained with a neurally controlled powered prosthetic ankle on activities that are challenging with typical prostheses. Would it be possible for amputees to regain a fuller range of control in the many daily motions that people make with their ankles in addition to walking?

The powered prosthesis in this study reads electrical signals from two residual calf muscles. Those calf muscles are responsible for controlling ankle motion. The prosthetic technology uses a control paradigm developed by the researchers to convert electrical signals from those muscles into commands that control the movement of the prosthesis.

The researchers worked with a study participant who had lost one leg about halfway between the knee and the ankle. The participant was fitted with the powered prosthetic ankle and did an initial evaluation. The patient then had five training sessions with a physical therapist, each lasting about two hours, over the course of two-and-a-half weeks. After the training was completed, the participant did a second evaluation.

After training, the study participant was able to do a variety of tasks that had been difficult before, such as going from sitting to standing without any external assistance or squatting to pick something up off the ground without compensating for the movement with other body parts. But one of the most pronounced differences was the study participant’s stability, whether standing or moving. This was reflected in both empirical evaluations — such as testing the patient’s stability when standing on foam — and in the patient’s level of confidence in his own stability.

“The concept of mimicking natural control of the ankle is very straightforward,” Huang says. “But implementation of this concept is more complicated. It requires training people to use residual muscles to drive new prosthetic technologies. The results in this case study were dramatic. This is just one study, but it shows us what is feasible.”

“There is also a profound emotional impact when people use powered prosthetic devices that are controlled by reading the electrical signals that their bodies are making,” Fleming says. “It is much more similar to the way people move intuitively, and that can make a big difference in how people respond to using a prosthesis at all.”

The researchers are already having more people go through the training paradigm and are expanding their testing to assess the results of that training.

Before making this technology more widely available, the researchers also want to engage in real-world beta testing — with people using the robotic prosthesis during their daily routines.

“As with any prosthetic device for lower limbs, you have to make sure the device is consistent and reliable, so that it doesn’t fail when people are using it,” Huang says.

“Powered prostheses that exist now are very expensive and are not covered by insurance,” Fleming says. “So there are issues related to access to these technologies. By attempting to restore normal control of these type of activities, this technology stands to really improve quality of life and community participation for individuals with amputation. This would make these expensive devices more likely to be covered by insurance in the future if it means improving the overall health of the individual.”

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Materials provided by North Carolina State University. Original written by Matt Shipman. Note: Content may be edited for style and length.