Welcome back to our new feature: Profiles in Physics @ UMD

We’ll be featuring interviews with people in many roles around the Physics Department and exploring their paths in science. This month, meet Prof. Manuel Franco Sevilla.

 

From Engineering to Particle Physics

Not everyone who becomes a physicist starts out knowing that’s where they’re going. Dr. Franco Sevilla’s path, as for many of us, was a roundabout one; he began his studies in engineering.

 “I didn't know any scientists or anything like that. I come from Spain, so my grandparents’ generation went through a really terrible civil war. Life was very hard then, and they basically had no schooling. Then, among the 10 siblings in my parents’ generation, only one went through four years of college. My generation was the first in which college was kind of expected, so I didn't have many role models in that sense.”

 “I think for me really it started with my brother, who's younger but he's also a bit of a genius. He actually very early on decided that he was going to be a physicist, and he just kept harping on how cool physics was, when I wasn't even sure what that was, and how the two most beautiful theories that the human mind has come up with are general relativity and quantum field theory. So throughout high school I just kept hearing about that, and I was intrigued. But not enough to choose a career like physics.”

“So then, after getting good grades in high school, I was like, ‘okay, people with good grades who like numbers, they do engineering’ so that's why I went into engineering. It was during my freshman year of engineering when I discovered that science was the thing that really made my heart flutter. Physics and math both were really what I wanted to do.”

“When I do something I try to do it well. So even though my heart was not in that [engineering] degree, I still tried to do it as well as I could, and this basically opened the door for me to become a physicist... This allowed me to then come to Stanford to get a PhD in physics, which for me was like nirvana. For the last 15 years I've been the happiest person on Earth”

Dr. Franco Sevilla ultimately chose particle physics as his focus, in part through the influence of his brother. That wasn’t where he started, though.

“When I started my PhD... I actually did not want to do particle physics because I didn't think there was a lot of future in it, but by then I already knew that it was about the most beautiful thing. So I tried rotating with a different group. I didn't like it, so I rotated with particle physics groups and it was just the most fun, as my brother had been repeating, and I just stayed with that.”

Seeking to understand the most fundamental parts of the universe combined with the practical, applied work of building and running experiments was the key.

 Symmetries and Sensors

Today Dr. Franco Sevilla is part of the Flavor Physics Group at UMD, and works on the LHCb Experiment at CERN. This group is studying the fundamentals of how heavy particles decay and how symmetries may be broken at the subatomic level, such as CP symmetry and lepton flavor universality.

“Since particle physics now is the endeavor of very large collaborations, you only build pieces of the full detector. For instance, currently at the University of Maryland my group, together with Professor Jawahery and a number of really talented postdocs and students, we're building the electronics for the readout of one of the subdetectors in the LHCb Experiment.”

 “As experimental particle physicists we have this dual role [hardware and analysis]. We need to build the particle physics detectors, the machines that will give us data that we will then analyze. Often over the course of your career you end up spending 50/50 in experiment building and data analysis.”

 The beauty of research, Dr. Franco Sevilla says, is that “you face challenges and you never quite know if you will be able to find a solution or not.” And sometimes those solutions can come from unexpected places!

He recounts one analytical problem he encountered as a PhD student. “I was trying to update a measurement that had been done by another group before me. I was updating it with much more data, so it needed to be much more precise. Small systematic uncertainties that may not have been a factor for them, they were for me. And so I had this bias in the core fit, and that could not stand. I was using the same approach that this person was using, and I just couldn't get rid of this bias; I was tweaking a lot of things and I just couldn't fix the bias.”

He’d worked for weeks on this seemingly insoluble problem.

“Remember, in science you should daydream and be exposed to diverse ideas. So I was attending some random seminar on statistics and I learned about kernel estimation. Until then I was using what is called parametric probability distribution functions or PDFs. Parametric PDFs are very constrained; but there's this other way of doing PDF estimation in a much less constrained way, called kernel estimation. And so I learned randomly in this seminar about kernel estimation, and I was like, perhaps I can try this? I mean, I've been bumping my head now for more than a month. So I started playing with those kernels and basically that opened up a new world, I could control the bias perfectly with those non-parametric estimators. You can trade bias for statistical uncertainty perfectly and this uncertainty is not a problem because you can estimate it. In this way, a huge problem in my thesis all of a sudden evaporated and I was a happy camper.”

The Love of Teaching

Dr. Franco Sevilla came late to teaching. It initially seemed challenging, but he grew to love it.

Before coming to Maryland, he had given only a few lectures, and didn’t feel they went well. But with work, he found, this could be overcome.

“I came to Maryland and I started teaching and I wasn't sure what to expect. Based on those lectures I was a bit concerned. And then it completely blew my mind! All of a sudden I discovered that I love teaching!”

The biggest challenge, he finds, is to balance the demands of research and teaching, and to maximize the best possible outcome for as many students as possible.

“When I interact with students, I understand there's going to be a distribution in their talents, in the attention that they can pay, and that I am never going to get 100% of the students every time. But you can optimize the percentage. When I was a student, I thought you could only teach at the level of the stronger or the weaker students, but not both. Now I have learned that there are techniques to challenge the more advanced students (for instance, adding a week of General Relativity as extra credit in a Special relativity course), while still bringing in as many students as possible with engaging material, demonstrations, and custom explainers. This is not an easy problem, but the way you teach does affect the dynamical range of the spectrum of students you reach, so I spend a lot of time thinking about this.”

Dr. Franco Sevilla has found that teaching, like everything else about science, can require hard work and careful study. He prepares thoroughly before presenting any lecture or demonstration, making sure to understand how everything works and think through what to say; and analyzes it afterwards to see what to improve for next time.

His policies in class can be strict, particularly on homework deadlines, to allow for more discussion in class. But this has not posed any problems for him.

“For instance, the students – I've been surprised at how reasonable they are. You're so used to the internet where everyone is yelling and nuanced arguments do not fly, and then you speak to these humans and actually you can have a conversation with them. They sometimes convince me, and other times I convince them, it's just really fun, I really enjoy it.”

Student engagement, he finds, is “the million dollar question.” The key is to get students to not just passively listen to a lecture, but actively think and analyze. He builds his lectures carefully, flowing from introductions to examples to problems to work in class.

“And then the whole class stops because they need to think about this. I walk around them, I give them time, I give them a lot of tips, and then we work through that example. And so that kind of keeps them on their toes.”

Dr. Franco Sevilla has given thought to other issues we need to consider as we prepare students for careers in physics. One thing he notes is the danger of survivorship bias. “Something that I think we need to be very careful of in universities is that all professors pretty much have gone through the PhD and the job market in academia and then landed a job. But more and more I think we understand that this straight path is becoming quite unusual.” There is a supply of young physicists that outstrips the demand, and so students need to prepare both for careers in academia and elsewhere.

“To be able to have a career in academia you need three things: a minimum level of talent, that many students have; a minimum level of hard work, that also many students have; and then, in addition, there’s almost always… a significant element of luck.”

“So my advice is that if you feel you really like this, and you think you have the talent, and you're willing to put it in the hours, then see what is your tolerance for risk.”

And this can depend on subfields, too – when planning a career in physics, he emphasizes, it is important to do the research on what kind of physics you want to study, what kind of work you want to do, and what the prospects are for work in that field.

But in the end, he says, it can be worth it.

“Science, I think it's a career like no other. Really, for me it's super fun. I remember when I was a student and I was doing my thesis… and I could just speak to [professors] one on one. I'm saying ‘No I think you're wrong here, because of this, this, and this,’ and if I had a good argument, they would just take it. And so there's a lot of things that are to like.”

“But at the same time you need to understand nothing is ideal. Science is not this high-minded endeavor where we're just all rational, and politics doesn't play a role. Like any human endeavor, science is going to have politics, and it's going to have some humans that are annoying as is the case in everything.”

“So what I would just say is that it's slightly more rational than many other fields, and it's slightly more generous, in the sense that we mostly just want to find the truth. If you have an interesting problem, we often drop everything we're doing, and just help you with the interesting problem.”

“If you read Reddit or the internet about what it's like at grad school or what it's like in the faculty lounges, you're going to read a lot of stories of bad people. And yes, those bad people exist in science like everywhere else. But overall I feel that it's a good place, or at least that it's a better place than many other places. We can still make it better but it's a pretty nice place to be.”

And those kinds of stresses can be present in the wider world, too, in which he sees scientists as playing an important part.

“I feel one of the most important things that we can do as scientists is to be humble,” he says.

“All humans have this bias that when we see a lot of information coming from different sources that kind of looks the same, we start thinking that it must be true. But this completely breaks down in the era in which we live because of strong hidden correlations in the sources of information… Different segments of the population have very strong beliefs on different facts that are often incorrect, and it's just a very insidious problem. Importantly, this affects absolutely everything, so it can also lead scientists to groupthink. I am very aware that I myself may be part of some incorrect groupthink on something or other.

“I don't think humans are generally inclined to just be humble, but if we can, especially scientists, we need to continuously acknowledge the possibility of being wrong, the possibility of other people being right, and how difficult it is to ascertain truth today. I feel that scientists are in a slightly better place than other humans to do this, but of course we're still humans and we are still subject to similar failings as the rest of society. So in general we really need to be careful, try to put our human biases away, and clearly acknowledge the limitations of our knowledge while we help improve the collective wellbeing with our research.”

 Links to read more:

• UMD Flavor Physics http://flavor.physics.umd.edu/
• Prof Franco Sevilla's homepage http://flavor.physics.umd.edu/manuelf/
• LHCb Experiment at CERN https://home.cern/science/experiments/lhcb