Back to the Big Bang

While the Earth has existed for approximately 4.6 billion years, the universe is even older, around 13.8 billion years. We know this thanks to measurements of cosmic background radiation taken by the Planck space telescope. With such colossal numbers involved, it seems impossible to research the beginnings of the universe – or so one might think. But at CERN, it can be done. By conducting collision experiments using the world’s most powerful particle accelerator, researchers can look almost as far back as the Big Bang. And in this case, “almost” means up to just a billionth of a second after it took place.

“For us, the Large Hadron Collider at CERN is a time machine,” says Ben Kilminster, particle physicist at the University of Zurich. “We can use it to reconstruct the conditions in our universe when it was still extremely hot and dense, when all particles could freely transform into one another.” This retrospective analysis allows researchers working on experiments at CERN to measure a wide variety of particle types, including some surprises. The most notable discovery was the Higgs boson in 2012. “It confirmed a key prediction of the Standard Model of particle physics: that elementary particles only acquire mass by interacting with the Higgs boson,” says Kilminster. His research group co-developed the innermost and most precise part of the detector that, among other things, detected the Higgs particle.

Kilminster is now building the next generation of detectors for CERN. The next phase is about to begin, with the Large Hadron Collider  (LHC) being upgraded to create the High-Luminosity LHC, a project which is expected to be completed by 2030. “The energy of the collisions will remain roughly the same, but in the High-Luminosity LHC their total number – known as luminosity – will increase about tenfold,” explains Kilminster. The upgraded collider will generate millions of Higgs bosons annually. “This will allow us to study Higgs bosons in greater detail, potentially generating entirely new particles and opening up new avenues of research.” One possibility is investigating dark matter or physics beyond the Standard Model.

Kilminster’s goal is not to confirm assumptions, but to challenge them. “Only through errors and deviations that don’t fit the current Standard Model can we test and improve our theories,” says the particle physicist. He is certain that our Standard Model is just one of many steps that will allow us to understand the fundamental truths of physics, just as Newton was a stepping stone for Einstein to develop his theories.

In his office, Kilminster shows a single module of the detector currently used at CERN. The rectangle of electronic and optical circuits, measuring about three by six centimeters, is much more inconspicuous than one might expect after seeing images of the giant detectors in use. In simple terms, this kind of detector system forms layers of progressively larger pipes around the point at which the particles collide. And because the particles formed in the collisions spread outwards in a star-shaped pattern, it is the innermost detector pipe that must be able to register them the most quickly and precisely.

Kilminster’s research group developed and built this innermost layer from many thousands of small detector modules in collaboration with Florencia Canelli, a particle physicist at UZH and CERN, who recently became a fellow of the renowned American Physical Society. This layer records the particles generated in the collisions at a rate of 40 million times per second. Such a high rate is necessary because a collision experiment generates around 200 individual collisions, all within just 25 nanoseconds, or billionths of a second.

Kilminster’s team is currently working on the innermost detector layer for the future High-Luminosity LHC. First of all, it must be much faster than previous detectors, which will allow it to register ten times more data per unit of time. Secondly, it needs to be more resilient in order to withstand ten times more radiation.

Kilminster talks about his work with an air of seriousness, yet his office gives a rather different impression. In addition to the usual features, like technical books and pictures of his detectors, there’s also a shelf displaying various robots and figurines – all from nerdy films and series. He has amassed this collection over the years, the particle physicist says rather sheepishly. Then, with a sudden grin, he points to the foremost figure. It’s Sheldon from the cult series The Big Bang Theory, holding a miniature flipchart with a mathematical formula on it. “The formula is from a collision experiment I worked on, and it was featured in the series.”

Particle physics is one of the few fields of research where Europe is the clear world leader, ahead of the both the USA and China. And this is thanks to CERN, the undisputed pioneer in particle accelerators. “Having the most powerful machine means we can ask the most profound research questions,” says Kilminster. When it comes to research, Switzerland has benefited enormously from being one of CERN’s two host countries.

Kilminster and UZH now want to continue to build on this. To do so, they are leading the development of CERN’s next particle accelerator, the Future Circular Collider  (FCC). The High-Luminosity LHC is expected to operate from 2029 until approximately 2040. “But after that, it’s time for a new chapter,” says Kilminster. The FCC is expected to be put into operation starting in 2045 (see box below). “For me, it’s important that Switzerland has a say in how CERN moves forward,” emphasizes the physicist. To this end, Kilminster also represents Switzerland in the European Strategy Group for Particle Physics. Ultimately, he aims to help shape the future of elementary particle research and ensure Europe remains a leader in the field in the long term.

Meanwhile, Kilminster is also involved in other particle physics experiments, for example a project in which a specific type of detector has a single goal: detecting the energy spectrum of collisions with dark matter particles. To achieve this, the detector, which weighs just a few hundred grams, operates deep underground and is additionally encased in ancient lead – such as that from sunken Spanish galleons. “This lead is much less radioactive than materials that have been exposed to cosmic radiation on the surface, as we all are constantly,” Kilminster explains. He and the other researchers involved hope to shield the detector from all radiation – except for dark matter. One such experiment is underway in a mine in Canada, two kilometers below the earth’s surface, while another began recently in France, at the Modane Underground Laboratory, which is found in a twelve-kilometer-long car tunnel.

“Dark matter, in particular, still puzzles us,” says Kilminster. We know it’s there, but what we don’t know is what it’s made of, whether it’s a single particle or dozens of different ones. The new experiments conducted at CERN may also be able to detect dark matter particles. These cannot be measured by detectors; however, the imbalance caused by dark matter, such as energy loss, could be.

These mysteries are what drive Kilminster. He tells the story of physicists at the end of the 19th century. At that time, some believed the answer to every question had been found – thermodynamics, electricity, magnetism and Newton’s laws of motion. Yet there were also gaps, and some things that almost fit, but not quite. “If researchers hadn’t kept digging, today we wouldn’t have quantum mechanics, computers or GPS,” says Kilminster. “All of this was developed because certain people recognized that some puzzles remained to be solved and kept looking for answers.” It’s a quality he quite clearly sees in himself.