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World's largest particle accelerator restarts

The CERN research facility houses the Large Hadron Collider (LHC), the world's largest particle accelerator. The accelerator has been undergoing further development for three years, and operations were restarted in April. Sara Strandberg is a professor at Fysikum and works at CERN, the European Organization for Nuclear Research in Switzerland. Here she tells us more about how she became interested in physics and her research at the ATLAS experiment.

Sara often discussed astronomy and physics with her parents while growing up. Her interest grew over time and eventually she started studying in the Project Program  at Fysikum.

– Half of the time was coursework and the other half consisted of projects. It was a good way to get in touch with the particle physics research group and the training was collaborative.

Sara did her graduate work on D0 (D-zero), an experiment at a particle accelerator at Fermilab in Chicago, and she also did her PhD there.

Sara Strandberg, professor and researcher, Department of Physics, Stockholm University

In conjunction with a postdoctoral position at Berkeley, she began research on the ATLAS experiment at CERN. She then received a research grant from the Swedish Research Council and returned to Fysikum with a lectureship in 2011. Since then, Sara has been employed on a permanent basis.

My focus is on searching for extensions of the Standard Model that can explain the dark matter of the Universe and the Higgs mass fine-tuning problem. In particular, I search for the supersymmetric partner of the top quark. Since 2018, I lead the SHIFT project, a five-year project funded by the Knut and Alice Wallenberg Foundation, where we develop and search for models that include partner particles to the top quark in order to solve the Higgs mass fine-tuning problem.

In the ATLAS project, the data is used to search for new unknown particles, but also for measurements of particles that are already known. The plan up to 2040 is to increase the amount of data, which will make it possible, among other things, to investigate the pair production of the Higgs particle.

More than 10 000 scientists are associated with CERN and 3000 of them are working on the ATLAS experiment.
– We have two tracks for our research - looking for supersymmetric particles and trying to find evidence for pair production of the Higgs boson. Although the Standard Model is a very successful theory, there are things it can't explain, such as dark matter and the asymmetry between matter and antimatter. The need for physics beyond the Standard Model is what motivates our research.  All of us involved in the ATLAS experiment are helping to build and operate the detector. We take turns  doing shifts to oversee the data acquisition, we calibrate, maintain and upgrade all the hardware, and we write all the software needed to reconstruct the vast amounts of data the detector generates.  So most of the time is spent not analysing the data but collecting it.

After the Big Bang, particles were massless. Then there was a phase transition and the particles gained mass by interacting with the Higgs field. It is possible that the same phase transition also generated the asymmetry between matter and antimatter that we see in the Universe today. By observing the pair production of Higgs particles, we can learn more about the properties of the Higgs field and the phase transition that took place in the early Universe. And CERN is the only place where this research is possible.  Through CERN, PhD students and postdocs have a unique opportunity to be part of the international scientific community.

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