CERN’s new study brings us closer to understanding antimatter and why we exist


Why do we exist? This is arguably the most profound question there is and one that may seem completely outside the scope of particle physics. But our new experiment at CERN’s Large Hadron Collider has taken us a step closer to figuring it out.

To understand why, let’s go back in time some 13.8 billion years to the Big Bang. This event produced equal amounts of the matter you are made of and something called antimatter. It is believed that every particle has an antimatter companion that is virtually identical to itself, but with the opposite charge. When a particle and its antiparticle meet, they annihilate each other – disappearing in a burst of light.

Why the universe we see today is made entirely out of matter is one of the greatest mysteries of modern physics. Had there ever been an equal amount of antimatter, everything in the universe would have been annihilated. Our research has unveiled a new source of this asymmetry between matter and antimatter.

Antimatter was first postulated by Arthur Schuster in 1896, given a theoretical footing by Paul Dirac in 1928, and discovered in the form of anti-electrons, dubbed positrons, by Carl Anderson in 1932. The positrons occur in natural radioactive processes, such as in the decay of Potassium-40. This means your average banana (which contains Potassium) emits a positron every 75 minutes. These then annihilate with matter electrons to produce light. Medical applications like PET scanners produce antimatter in the same process.

The fundamental building blocks of matter that make up atoms are elementary particles called quarks and leptons. There are six kinds of quarks: up, down, strange, charm, bottom and top. Similarly, there are six leptons: the electron, muon, tau and the three neutrinos. There are also antimatter copies of these twelve particles that differ only in their charge.

Antimatter particles should in principle be perfect mirror images of their normal companions. But experiments show this isn’t always the case. Take for instance particles known as mesons, which are made of one quark and one anti-quark. Neutral mesons have a fascinating feature: they can spontaneously turn into their anti-meson and vice versa. In this process, the quark turns into an anti-quark or the anti-quark turns into a quark. But experiments have shown that this can happen more in one direction than the opposite one – creating more matter than antimatter over time.

Third time’s a charm

Among particles containing quarks, only those including strange and bottom quarks have been found to exhibit such asymmetries – and these were hugely important discoveries. The very first observation of asymmetry involving strange particles in 1964 allowed theorists to predict the existence of six quarks – at a time when only three were known to exist. The discovery of asymmetry in bottom particles in 2001 was the final confirmation of the mechanism that led to the six-quark picture. Both discoveries led to Nobel Prizes.