Just after the Big Bang

Heiko Lacker is searching for previously unknown elementary particles

The very substance that makes up the universe still holds many mysteries. Heiko Lacker, professor of experimental particle physics at Humboldt-Universität zu Berlin, explores the microcosm of matter and antimatter with his research group, searching for hitherto unknown elementary particles.

Finding Heiko Lacker’s office at Lise Meitner House is almost as tricky as understanding the subject of his research. The professor for experimental particle physics has been teaching and researching in Adlershof since 2007, focusing on the tiniest building blocks of our world—particles so small that their size is expressed in numbers with 17 zeros after the decimal point. At the same time, his field tackles some of biggest questions in nature: What is matter really made of? Which forces operate at the core of the universe? And why does the universe exist in its current form?

Over decades, particle physics has undergone a remarkable theoretical development, culminating in the so-called Standard Model. It describes all known elementary particles—such as electrons and quarks, which make up neutrons and protons—and three of the four fundamental forces: electromagnetism, the strong and the weak nuclear interactions. “The Standard Model is an excellent theory and explains a great deal,” says Lacker, “but it doesn’t answer all the questions.”

Gravity, for instance, the fourth fundamental force, does not play a role in it. Other phenomena, such as the tiny mass of so-called neutrinos, also remain unexplained. These are the gaps that current research is addressing, which includes Lacker’s work.

One of the most exciting discoveries in recent decades was the Higgs particle. Its existence was confirmed in 2012 at CERN, the European Organisation for Nuclear Research in Geneva. The Higgs particle gives other particles their mass. “In the Standard Model, the particles shouldn’t have any mass at all,” explains Lacker.

“The Higgs field is necessary to keep the Standard Model mathematically consistent.” The fact that this field exists was fascinating, he says, though it has not been fully understood to this day.

Neutrinos remain especially mysterious. They are electrically neutral, extremely light, and notoriously hard to detect. “Most neutrinos pass through the detector completely unnoticed,” explains Lacker. “They are about a million times lighter than an electron.” This enormous discrepancy is difficult to explain within the Standard Model.

One possible explanation: Neutrinos might be their own antiparticles—so-called Majorana neutrinos. If that were the case, it could help answer a fundamental question: Why is there more matter than antimatter in the universe? Because one thing is clear: “If the Big Bang had produced equal amounts of matter and antimatter, our universe would be empty—except for photons and neutrinos.”

To investigate such questions, colossal experiments are required—experiments that can only be conducted at CERN. Located there is the Large Hadron Collider (LHC), a particle accelerator with a circumference of 27 kilometres. Proton bunches collide there at a rate of 40 million times per second.

“Most collision events are completely uninteresting, and the truly interesting ones have to be filtered out in fractions of a second,” says Lacker.

After that, huge amounts of data are left to be analysed. One of the four experiments at the LHC is the ATLAS experiment. It’s aim is to explore the fundamental building blocks of matter and the forces of nature. Experiments like those conducted with the ATLAS detector rely on the collaboration of thousands of scientists worldwide.

Lacker himself is involved both in the ATLAS experiment and the planned SHiP project. SHiP—short for Search for Hidden Particles—was first conceived in 2013, though it only received the green light from CERN in 2024. “We decided not to build a dedicated hall at CERN ourselves, but now CERN is providing the infrastructure,” says Lacker. “The funding for the detector must be covered by the participating countries.” His goal: “We want parts of the detector installed in the hall by 2032.”

What fascinates him most about particle physics is that it offers a window into the earliest moments of the universe. “We understand physics up to 10⁻¹² seconds after the Big Bang,” says Heiko Lacker. “We now want to explore everything that came before.” The SHiP experiment could help provide new answers to the biggest unsolved questions—or raise even more.

Heike Gläser for Adlershof Journal

Experimental High Energy Physics (HEP) Group — Humboldt-Universität zu Berlin