This autumn, a global collaboration of scientists released a measurement that had the potential to turn physics’ most important theory on its head. The number they revealed described the behaviour of a subatomic particle known as the muon, and the big question was whether the measurement would fit with the predictions of the Standard Model of particle physics.
If the number didn’t fit, well, that would mean there’s something big that physicists aren’t understanding about how the universe works. Upon the dramatic opening of the envelope containing the measurement, researchers shouted in excitement — the number disagreed with the Standard Model. More investigation is needed to know for certain that it isn’t a statistical fluke, but, still, the mystery of the muon had deepened.
To study something as tiny as a muon requires huge particle accelerators, sensitive detectors, and major computing power. But these collaborations take more than technology: Key to any discovery are the scientists and the culture that they create, including early career scientists who are providing critical work and even shaping the direction of the research overall.
Just ask Jessica Esquivel, scientist at the Muon g-2 Experiment at Fermilab in Illinois. When she was fresh out of graduate school, Esquivel upgraded parts of the machine’s hardware and worked on software that helped fix the data analysis in response to experimental kinks. Now, after just a few years, she leads the experiment’s data-gathering as one of its run coordinators. But the work of her and other early career scientists didn’t just shape scientific results; it also helped change the culture of the project.
“We come in with a very green view of the experiment,” she said. “But a lot of the questions that I asked were very different from those that had been asked before,” including questions about hardware, software, and culture that may be overlooked by someone who’s been working on a project for decades.
The Muon g-2 Experiment is a 15.24 m-diameter magnet that measures the properties of the electron’s heavier cousin, the muon. On April 7, the experiment’s researchers announced that they’d made an extremely precise measurement of the way the particle wobbled in the magnetic field. This measurement differed just slightly from the predictions of particle physics’ underlying framework, the Standard Model. The odds of the measurement being a fluke are around 1 in 40,000, so the team still must take more data in order to officially declare the discrepancy a “discovery.” But if the measurement holds, then it implies that there are unexplained physical phenomena out there, ones that may lead to the discovery or new particles or answer some big outstanding questions, like the true identity of dark matter.
Esquivel joined the experiment back in 2018, shortly after completing her Ph.D, in which she trained a neural network to recognise the results of experiments on the enigmatic neutrino particle. The transition required a steep learning curve — she’d be studying a different particle and a different accompanying set of physical rules, while simultaneously switching from software to hardware. She dove in head first. During the first run, a part of the experiment called the Blumleins — consisting of massive concentric metal tubes filled with castor oil — was sparking.
She had to drain and completely disassemble the component on large tables with support structures for the tubes in order to figure out what was wrong. She and her teammates had to sand down the tubes and replace the insulation, all while she was simultaneously jumping between other labs, upgrading electronics, and developing, testing, and soldering circuit boards for transferring signal between parts of the experiment.
She eventually moved on to research that fit more closely with her graduate school experience — the experiment’s software — tweaking the data analysis package in order to accommodate magnetic effects introduced by faulty components. “There are parts of the software chain that aren’t as glamorous as working on the final analysis itself,” she said. “But if I hadn’t developed the framework to turn on and off the responses for those damaged components, we wouldn’t have been able to calculate the uncertainty around the final value.”
After only two years on the experiment, the team selected Esquivel to serve as one of the run coordinators, a role she holds to this day. During month-long shifts, run coordinators review all the work that the team must complete, assign the tasks, and ensure that those tasks get done — plus, they must communicate with the accelerator division that sends the particle beam used to produce muons in the experiment itself.
The covid-19 pandemic added an extra level of complexity; the Fermilab facility rules minimised the number of people allowed inside the experimental hall at once. It was a trial by fire. “The first day I was a run coordinator, we were trying to turn the experiment on after months of shutdown,” she said, referring to an already-scheduled long closure that was extended due to the ongoing covid-19 pandemic. But she stepped up to the challenge.
As run coordinator, Esquivel has worked to support the wellbeing of postdoctoral researchers and graduate students who do much of the experiments’ day-to-day work. Overworked scientists can lead to unsafe conditions, she explained. “I’m thankful that I can use this position of power, where people are listening to me when I say that we shouldn’t be pushing students to unattainable working limits.” She feels she’s been able to bring a unique perspective in more ways than one — following the police murder of George Floyd, she was able to lead complicated conversations with other Muon g-2 scientists as a Black woman about the fight for racial justice, conversations that the team of scientists previously shied away from speaking about openly in the workplace.
The culture at the experiment didn’t always feel like it valued the input of young or diverse scientists, said Tammy Walton, associate scientist at the Muon g-2 experiment who has worked at the Fermilab since receiving her Ph.D in 2014. She explained that since the g-2 experiment was the continuation of one carried out at Brookhaven National Lab from 1997 to 2001, many of the leadership roles went to highly venerated physicists from the previous iteration, and the newer generation of scientists found it hard to step into leadership roles. Walton said it was even harder for her, both as an early career scientist and the first (and, at the time, only) Black woman on the experiment.
In part thanks to Walton and others, things have started to turn around for the experiment’s early career scientists. Walton said that the experimental leadership increasingly trusts her and others with important decisions about the direction of the experiment — Esquivel attributed this in part to Walton calling out injustice on the experiment when she saw it. This past April, Fermilab associate scientist Sudeshna Ganguly told me in a video interview that younger scientists now take on lots of responsibility across hardware, software, and operations as run coordinators and project leaders — responsibilities that train them for a future in physics research. Esquivel noted that during the April announcement, the collaboration’s senior leadership encouraged younger scientists to take the lead as spokespeople for the results.
Though traditional stereotypes of scientists depict grey-haired, aloof men, the actual history of physics reveals the importance of younger scientists to the field’s progress. Einstein earned his Nobel Prize for work he did at age 26, and Heisenberg for work he did at age 25; Jocelyn Bell Burnell discovered pulsars as a 24-year-old graduate student. Today, graduate students and postdoctoral researchers perform much of the day-to-day work at large physics collaborations. Age doesn’t predict success.
Ultimately, Esquivel hopes that she can implement the machine learning techniques she picked up in graduate school to continue research on the muon — and, in turn, continue to poke holes in particle physics’ most important theory. But she and other early career scientists have already left an impact for the better.