Giovanna Cottin, an academic at the Universidad Adolfo Ibáñez and a young researcher at the Saphir Millennium Institute, will lead a group with two other theoretical physics researchers to build bridges between experiments at the Large Hadron Collider and long-lived particles, which are theorised but as yet undiscovered elementary particles. This is in line with Cottin's research, who has specialised in the development and implementation of strategies to detect these particles predicted by robust theoretical models. If discovered, these new particles would open the door to new physics.

By Jorge Román

Since it became operational in 2009, the Large Hadron Collider (LHC) has revolutionised physics. In addition to confirming the existence of the Higgs boson in July 2012, the LHC has found almost 60 hadrons (non-elementary particles), among many other discoveries. However, it has not yet found clear signs of the existence of new elementary particles or of physics that goes beyond the standard model (the current theory that explains subatomic phenomena).

One of the possible reasons why new particles have not been detected may be that the right signals are not being searched for. This is what Giovanna Cottin argues in her recently awarded Fondecyt project "Searching for New Physics at the Lifetime Frontier". ("Searching for New Physics at the Lifetime Frontier"). There are theories that go beyond the standard model and predict the existence of long half-life particles that have not yet been detected. Cottin's work is precisely to characterise the possible exotic signals that these particles would generate and, in doing so, to give clues to the experimental physics community as to what to look for. It is the stage before data analysis: it would be like telling a detective whether to look for fingerprints, hairs, skin remnants or specific stains at a "crime scene" and how to collect these signals in order to analyse them properly.

Francisca Garay, an academic at the Institute of Physics of the Pontificia Universidad Católica de Chile and Alternate Director of our institute, explains that "in the experiments, for example, in Atlas, [...] we are looking for particles that decay immediately, so there is a lot of physics that we could be losing by looking "wrong", that is, not thinking that there could be particles that travel a lot".

The 11th workshop of the long-lived particle community took place today. Giovanna Cottin presented on long-lived neutral lepton signals and moderated a session on the long-lived particle working group at the LHC.

The 11th workshop of the long-lived particle community took place today. Giovanna Cottin presented on long-lived neutral lepton signals and moderated a session on the long-lived particle working group at the LHC.

"I've always liked to have a good understanding of where the area [of particle physics] is going," explains Cottin. For her, working as one of the people coordinating the theoretical group "aligns super well" with her research and that is one of the reasons she decided to accept the role. She says she feels a lot of "responsibility to the scientific community" in taking on this task, which she sees as an opportunity to "squeeze in" the questions she has been asking in her research.

An initiative open to the global physics community

The LLP Working Group - the Long-Lived Particle Working Group at the LHC, which is part of CERN's LPCC centre - brings together experimental and theoretical physicists to generate discussion and discoveries in the area of long-lived particles at the LHC. This centre was created in 2020 because they are of great importance in theoretical predictions.

"This initiative is not closed to CERN," explains Cottin. "The idea that this exists at CERN is to open up these studies to the world community. Because, in fact, there is a large, informal global community called the Long-Lived Particle Community made up of long-lived particle researchers from all over the world. Creating this theoretical working group at CERN is a way of synthesising the work that this community does and channelling their research through support and coordination from CERN.

Cottin's leadership is shared with Nishita Desai (an academic at the Tata Institute for Fundamental Research, who works with dark matter models) and José Francisco Zurita (an academic at the Institute of Corpuscular Physics at the University of Valencia and CSIC, who specialises in models predicting new Higgs bosons), together with nine other researchers representing the LHC experiments. "They needed another person and that's why they called me," says Cottin, whose role as coordinator was approved by all. She sees it not only as recognition of her work, but also as a sign of how the search for long-lived particles has grown in the global physics community.

"Giovanna's appointment [...] is not only important for her as a scientist - because of the recognition of her contribution and expertise in this area - but it is also very important for our theoretical group within Saphir," says Juan Carlos Helo, an academic at the University of La Serena and research associate at the Saphir Millennium Institute. According to Helo, Cottin's new position will give greater visibility to the activities of Saphir's theoretical physics group within the long-lived particle community.

"If we can, thanks to the input from the LLP theoretical group, get the experiments to change their search types, assuming that there could be particles that live longer, there is potential to discover new physics," says Garay. And that Giovanna Cottin is on the team leading the theoretical area of this search "is super important. [She has a lot of passion, especially for this topic, [...] so she's going to leave everything on the track.

Giovanna Cottin, an academic at the Universidad Adolfo Ibáñez and young researcher at the Saphir Millennium Institute, talks in this video about the importance of particle physics and how enriching diversity is in the scientific community.

Giovanna Cottin, an academic at the Universidad Adolfo Ibáñez and young researcher at the Saphir Millennium Institute, talks in this video about the importance of particle physics and how enriching diversity is in the scientific community.

New opportunities

Cottin sees this opportunity as a way to harvest projects for the future: to determine what is needed, to define interesting research topics and to ask for support from the theoretical and experimental community at the international level. "We want to get the most out of the LHC results," says Cottin, "we need to know what those results look like when you choose a different model [from the usual ones].

As Cottin explains, determining which theoretical model to apply in experimental physics research is complex "because there are far more theoretical models than experimental results". This means that there are human limitations to this work, as the experimental analysis is very complex and does not necessarily fit two or more models. There are models that predict the presence of dark matter, others that predict the presence of neutral heavy leptons, and others that explain some anomalies, but there are many, many more. So which model to choose depends very much on the direction the theoretical group wants to take, on the questions they consider essential. This is also a risk, because the chosen model may not produce any results at all.

However, Cottin is clear that if the course taken does not bear fruit, there is a great openness to amend the path: "Science is always dynamic. And when things warrant a change of course, it will be changed, but always with the objectives of a mandate imposed by CERN [...] that has to do with helping these CERN experiments and the potential that these experiments have in [discovering] new physics," says Cottin.

Cottin's work with the long-lived particle theory group also opens up several opportunities: new topics to explore and a deepening of the Saphir Millennium Institute's theory group's links with CERN and the international long-lived particle community. "New projects with scientists from this international scientific community could also be articulated," says Juan Carlos Helo.

"I feel it's going to be super fruitful and positive for Saphir," says Cottin. She believes this is an opportunity to "strengthen the connections with CERN in the theoretical area". Her dream is that "with some recommendation from this group, a new fundamental particle will be discovered," she says. "That would be the ultimate: to help in that search in an assertive and accurate way.