“Anytime there is progress it opens up possibilities”

Chiara Amendola is a 25-year-old PhD student at the Laboratoire Leprince-Ringuet (LLR) in Paris. Originally from the south of Italy, she did her pre-doctoral studies in Rome, and began her association with CMS while working on her master’s thesis.

“I spent nine months with CMS during my master’s studies. My thesis was on a search for dark matter produced at colliders, in the mono-Higgs channel. What this means is that we were targetting a signal with one Higgs boson produced in association with a lot of missing energy — so we looked for collision events where there was a Higgs boson surrounded by something that we couldn’t see with the detector, which could be the signal for dark matter.”

It was back then that Chiara had her first encounter with the CMS detector, in its underground cavern.

“I was at CERN during Long Shutdown 1, and saw it when it was opened up. It was a nice moment to realise how huge it is even though we use it to study such small things. I was also lucky to see it open and be able to see the distinction between the different detectors.”

During the first year of her PhD studies, Chiara worked on writing algorithms for the CMS Level-1 Trigger. The Trigger is the decision-making system of CMS that determines which few hundred of the 40 million collision events taking place each second inside the detector are stored for further analysis.

“What is needed is a system that makes the first selection to understand which collision events are useful and which are not. This system needs to be efficient and has to provide a huge reduction of the rate of the events that we record: from millions to hundreds per second. The reason we need a huge reduction is because we don’t have enough storage available for all the collisions. And this selection needs to be efficient because if an event doesn’t pass the trigger it is lost forever. So we need a clever way to select the events we are interested in. And it works in two levels: the first [the Level-1 Trigger] relies mostly on the hardware because it has to make really fast decisions, and the second [the High-Level Trigger] is software-based, and can take more time and use the whole detector information. I work on the former.”

Now on her second year, Chiara will soon start analysing data from CMS to study the Higgs boson.

“We keep studying the Higgs boson because there are many things that we don’t know yet. We don’t know if there is one Higgs boson or if there is a complete set of Higgs bosons. We don’t know why the interaction with the Higgs boson brings different masses to different particles. So, lots of questions need to be addressed.”

Specifically, she will be working on what are known as “di-Higgs” searches.

“One of the most interesting things now in Higgs searches is looking for the production of two Higgs bosons in the same collision event. What you want to see is how the Higgs boson couples interacts with itself with other Higgs bosons. And we’re also trying to see if two bosons can be produced starting from a bigger Higgs boson, as is foreseen in some physics models beyond the Standard Model, or from another new particle.”

But it’s not just studying the Higgs boson that excites Chiara. She was drawn to particle physics because of the potential for scientific exploration.

“The charming aspect about particle physics is the search for answers to the big questions of the universe as we know it. We want to know a bit more about the origin of the universe, a bit more about how nature works. You can never acquire full expertise in this field, because there is always something new going on. Anytime there is progress it opens up a lot of possibilities. Right now there isn’t a solid path to follow, and maybe it’s more exciting than probing a theory that is already solid.”

Although based in Paris, Chiara makes the occasional trip to CERN. This summer, she spent a month and a half at CERN, mainly to attend meetings in person. These meetings provide occasions for fruitful interactions in a multicultural and international environment.

“I think one of the most attractive parts of being in a large collaboration is having a lot of people from all over the world. CMS also encourages you to meet people. When you are at CERN, you want to meet your collaborators in person [instead of only via video-conferencing] after the formal meeting and exchange ideas. Even though CMS is a large collaboration, you also work closely with some small groups and you end up with a lot of people supporting you and sharing their expertise.”

In addition to meetings, another reason why CMS members travel to CERN is to be on shift in the CMS Control Room, where the detector is controlled from.

“Being on shift is a great experience because you actually see what is happening in your detector. When you analyse the data, sometimes you lose the feeling that there is something real to see. So even though shifts are really busy and a bit stressful, it is something that puts you in a different perspective. And it’s kind of fun!”

Chiara also has some pearls of wisdom for aspiring scientists.

“I would advise not to get lost in your work. For how exciting it can be, you are not your analysis. If your analysis fails, you are not necessarily failing, so don’t tie yourself with your results. And be ready to work a lot and have a lot of patience!”

As young as CMS…

A handful of CMS members were born around the time the CMS itself came into being. They are as old (or as young!) as the collaboration they are now a part of. To give you a unique point of view of what it means to scientists in the early stages of their careers to be involved in such a long-standing enterprise, we interviewed a few of them. Find out more about what brought them to particle physics, what they work on in CMS and what they look forward to in the years to come.

About

In October 1992, a ‘Letter of Intent’ was submitted to the LHC Experiments Committee (LHCC), offically marking the formation of the CMS Collaboration. This website commemorates the 25th anniversary of CMS, celebrated in 2017.