In Practice: What do data analysts do all day?

CMS physicist Nadjieh Jafari switched from theoretical to experimental physics early on in her career. “It was an easy decision," she says. “Once I saw CERN, it became my quest." (Image: Sophia Bennett/ CERN)

Another day, another mountain of data to analyse. In 2016, CERN’s Large Hadron Collider produced more collisions than in all previous years of operation put together. Experimental physicists spend much of their professional lives analysing collision data, working towards a potential discovery or to sharpen our picture of nature. But when the day-to-day findings become predictable, do physicists lose motivation?

What if there’s nothing there? 

CERN has made headlines with its discoveries, but does this mean today’s researchers are just seeking fame and fortune? For most, being front-page news is not what stokes their physics passion, as they stare at their computer screens for hours. Instead, it’s the knowledge and excitement of understanding our universe at the most fundamental level. 

Siegfried Foertsch, run coordinator of the ALICE experiment, is motivated by “the completely new discoveries that lie around the corner. They’ve become ascertainable because of the new energies that the LHC machine is providing.” 

Personalities and History of CERN
Sitting in the ALICE control room, Siegfried explains: “I think what motivates people in these experiments is that you are entering terra incognita, it’s completely new science. It drives most people in these big experiments, it’s about new discoveries.” (Image: Sophia Bennett/CERN)

These headline-worthy discoveries are rare. Instead, researchers make small, incremental findings day-by-day.  “It doesn’t bother me that it’s not going to make front-page news. I know that within the particle physics community the research is important and that’s enough,” says Sneha Malde of the LHCb experiment.

For CMS physicist Anne-Marie Magnan, her colleagues provide the much-needed push.

“We have deadlines, so if you are part of an analysis you have pressure to make progress and you put personal pressure on yourself because you want to see the result. If you’re on a review committee you have deadlines, you need to provide feedback, the same if you’re managing a subgroup, you’re responsible for the group to show results at conferences. So you push people and they push you back to try and make progress," she explains.

Magnan analyses data to search for  Higgs bosons . She describes her daily work as “programming, mostly. A lot of interaction with people, I have students to Skype with and when they say ‘I’m stuck, I don’t know what to do’ we chat and find solutions. At some points I’ve been a subgroup convener. There you encourage people to make progress and provide feedback on their analyses.”

“It’s an exercise of patience because, after time, the incremental findings lead to a result. And even if you’re just working towards a result, you still have to solve technical problems each day,” explains Leticia Cunqueiro Mendez, a senior postdoctoral researcher working with the ALICE detector.

Building bonds: the road to success 

Each one of these incremental, small discoveries are documented by a research paper. At CERN, these papers are often authored by hundreds, even thousands of people, as was the case with the papers announcing the Higgs discovery. And they aren’t just experimental physicists; students, technicians, engineers and computer scientists are all often equally involved.

Having a high level of motivation can only get a physicist so far, working with others is the route to success.

“People need each other here,” says Siegfried Foertsch, “the idea of a physicist without an engineer at CERN is unthinkable, and similarly vice versa. It’s symbiotic.”

“I think the work of the technicians is a major contribution to the applied physics that I’m involved in. They are the unsung heroes in most of what we do to some extent,” says David Francis, Project Leader of the ATLAS Trigger and Data Acquisition System.

For Cunqueiro Mendez, “the main thing is to know the possibilities of your detector and to have an interesting idea of what physics might be observable. For this you need interaction with the theorists so, in principle, you have to be reading papers and attending conferences. Here at CERN, you can meet your theory colleagues for a coffee and discuss your possibilities.”

Eeney meeney miney mo

Working with others can be collaborative, but it can also be competitive. There is a point of pride for one experiment to beat the competition to a discovery.

InPractice,Life at CERN
Sneha Malde standing in the corridor outside of her office (Image: Maximilien Brice/CERN)

While the ATLAS and CMS experiments perform similar searches, the LHCb and ALICE experiments have particular fields of study, and the work that the associated physicists do differs as a result.

Bump searches are what physicists call it when they try to find statistically significant peaks in the data; the presence of a bump could indicate the existence of a new particle. Some of these searches are done at ATLAS and CMS, where new particles are the name of the game. At LHCb and ALICE they try to take precision measurements of phenomenon, more than particles.

“I don’t think I would be very happy just looking at empty plots with nothing in them, which could happen in bump searches if they don’t find anything new,” muses Malde.  “I like the precision measurement aspect of LHCb’s data.”

Studying and searching for different things means the data plots for different experiments look very different.

“I like having obvious things in my plots. I like nice bumps, big ones. We have lots of bumps that don’t disappear, and they are really big peaks. We don’t have bumps, we have mountains!” – Sneha Malde, LHCb data analyst

ATLAS physicist Anatoli Romaniouk, marvels at this range of LHC experiments. They “embrace an incredible field of physics, they search for everything.”

“This is physics; if we know what we are searching for, then we don’t need experiments. If you know what exactly you want to find, it’s already found, or will be found soon. That’s why our experiments are beautiful because these experiments embrace an incredible field of physics, the LHC, it searches for everything,” explains Romaniouk.

The beauty of the unknown

Personalities and History of CERN
ATLAS physicist Anatoli Romaniouk has worked at CERN since 1990. The students he sees in the collaboration “know a bit of electronics, data acquisition and data analysis, very often they do it from second year of university and this is interesting. I find this brilliant, that they practice real physics at an early stage of their education.” (Image: Sophia Bennett/CERN)

The appeal of the unknown, the as yet undiscovered, ignites the curiosity in the physicists and fuels them in their analyses.

“When you have something in theory and think that it could be real – that it could exist – then you start to really think how you can look for it and try to find it,” says CMS physicist Nadjieh Jafari. “You build your experiment based on the theories. The CMS’s muon system was perfectly designed to discover the Higgs boson but at the moment of designing it, it was just an idea that we might find it. For me, that’s the most beautiful part of what we do.”

Read the other articles in the In Practice series here.