Jonas Strandberg wants to know how the universe and its tiniest particles work. He was on the team that found the Higgs particle, and is now looking for more, and heavier, Higgs particles that may contribute to theories of particle physics. This would in turn shed light on mysteries of the cosmos such as dark matter and dark energy.
Associate Professor of Particle Physics
Wallenberg Academy Fellow 2015
KTH Royal Institute of Technology
Studying the Higgs particle and potential supersymmetrical partners using data from the CERN LHC particle accelerator.
In summer 1998 France hosted and won the World Cup. Strandberg will never forget that summer. He was a physics student at Stockholm University and had been invited to take part in a summer program at CERN, the world’s most advanced laboratory for particle physics, near Geneva, on the border between Switzerland and France.
“I loved being at CERN. It’s a fantastic environment. There were 250 students from all over the world on the program, and the atmosphere was great. Before then I had been unsure about my career choice, but at CERN I realized that experimental particles physics was for me.”
Only a year later Strandberg was back at CERN to work on his thesis. Since then he has returned several times, and has been part of an historic research breakthrough. On July 4, 2012 the news broke that researchers at CERN had found a new elementary particle – the long-sought-after Higgs particle.
“We worked incredibly hard and under enormous pressure to make the discovery. So when it was over it was actually a bit of an anticlimax,” Strandberg laughs, adding “It did feel fantastic to have been part of one of the most important breakthroughs in physics.”
Then the fun starts
Particle physics is about understanding how the universe works. The Higgs particle is an important jigsaw piece in the Standard Model of physics, which describes the interaction between elementary particles, the smallest constituent parts of all the matter around us. The theory behind the Higgs particle was formulated in the 1960s by François Englert and Peter W. Higgs, who were awarded the Nobel Prize in Physics in 2013 following the success at CERN.
“Simply put, the Higgs particle imparts mass to all particles in the universe. Without mass, all particles would travel at the speed of light, and no atoms could be formed, hence no stars or planets either,” Strandberg explains.
“This grant means a great deal for my research. Most of all, it provides long-term security, which will enable me to complete a research program I really believe in. It is also confirmation that I have a good research plan.”
He grew up on the Swedish island of Gotland, and knew he wanted to be a researcher as early as elementary school. The opportunity to travel appealed to him. And he has spent many years abroad. Strandberg studied for his doctorate at the world’s second-largest particle physics laboratory – Fermilab near Chicago. He was a postdoc at the University of Michigan and then joined CERN, where he worked on the analyses that resulted in discovery of the Higgs particle.
Now he is back at CERN once more after a number of years in Sweden. He has a two-year position as coordinator in the Atlas experiment. The aim is to refine knowledge of the properties of the Higgs particle, and to look for new elementary particles. We catch up with him during a flying visit to KTH Royal Institute of Technology’s particle physics and astroparticle physics department at AlbaNova, where he has worked since 2011.
“We researchers actually enjoy our work even more since the discovery itself. I usually liken it to an explorer who finds a new country that is then explored. So now we have gone ashore and are looking to see whether the particle is exactly the one we had predicted, or whether we find something that differs from the theory. We measure more thoroughly and obtain more data about the properties of the Higgs particle.”
Proton collisions provide clues
CERN has the world’s most powerful particle accelerator – the Large Hadron Collider (LHC). By allowing protons to collide with each other in a 27-kilometer-long tunnel, 100 meters underground, the researchers can recreate the conditions existing a mere fraction of a second after Big Bang.
“Most elementary particles are short-lived. When the universe was created there was a kind of soup made up of all these particles. Then the universe expanded and cooled down, and when it was cold enough the particles decayed. In the LHC we can see these particles pop up and disappear again.”
The Atlas detector registers signals from the decay products; the particles are then reconstructed on powerful computers using mathematical algorithms.
“Only one Higgs particle is created every ten billion proton collisions, so it takes a long time to fish up the evidence.”
Important to society
The universe is 95 percent dark matter and dark energy, phenomena that the Standard Model as yet cannot explain. Strandberg is therefore studying whether there are more and heavier Higgs particles, according to a complementary theory that all elementary particles have a supersymmetrical partner.
This kind of basic research that Strandberg is carrying out with funding from the Knut and Alice Wallenberg Foundation is important for long-term societal development. He explains:
“A hundred years ago, when relativity theory and quantum mechanics were born, it was not believed that they would have any practical utility. But nowadays we use relativity theory to build GPS technology, and quantum mechanics is an essential basis for making nanoelectronics. So in a hundred years there will surely be a need to calculate something so precisely that we will have to use Higgs particles.”
Text Susanne Rosén
Translation Maxwell Arding
Photo Magnus Bergström