4 new particles were found at CERN — and they could crack the secrets of nature’s laws


This month is a time of celebration. CERN has just announced the discovery of four brand new particles at the Large Hadron Collider (LHC) in Geneva. This means that the LHC has now found a total of 59 new particles, in addition to the Nobel Prize-winning Higgs boson, since it started colliding with protons – particles that make up the atomic nucleus with neutrons – in 2009. Exciting, while some of these new particles were expected based on our established theories, some were quite more surprising.

The LHC’s goal is to explore the structure of matter at the shortest distances and highest energies ever tested in the laboratory – testing our best current theory of nature: the Standard Model of particle physics. And the LHC delivered the goods – it allowed scientists to discover the Higgs boson, the last missing piece of the model. That said, the theory is still far from being fully understood.

One of its most troublesome features is its depiction of the strong force that holds the atomic nucleus together. The nucleus is made up of protons and neutrons, which in turn are each made up of three tiny particles called quarks (there are six different types of quarks: high, low, charm, strange, high, and low). If we turned off the mighty force for a second, all matter would immediately disintegrate into a loose quark soup – a state that existed for a fleeting moment at the beginning of the universe.

Make no mistake: the theory of strong interaction, pretentiously called “quantum chromodynamics”, has a very solid foundation. It describes how quarks interact through the strong force by exchanging particles called gluons. You can think of gluons as analogues of the more familiar photon, the particle of light and carrier of electromagnetic force.

However, the way gluons interact with quarks causes the strong force to behave very differently from electromagnetism. While the electromagnetic force weakens when you separate two charged particles, the strong force actually becomes stronger when you separate two quarks. As a result, quarks are forever locked inside particles called hadrons – particles made up of two or more quarks – which include protons and neutrons. Unless, of course, you open them at incredible speeds, like we do at CERN.

To complicate matters further, all particles in the Standard Model have antiparticles that are almost identical to themselves but with the opposite charge (or some other quantum property). If you remove a quark from a proton, the force will eventually be strong enough to create a quark-antiquark pair, with the newly created quark entering the proton. You end up with a proton and a brand new “meson,” a particle made up of a quark and an antiquark. It might sound strange, but according to quantum mechanics, which governs the universe on the smallest of scales, particles can emerge from empty space.

This has been shown repeatedly by experiments – we have never seen a single quark. A nasty feature of the strong force theory is that the calculations of what would be a simple process in electromagnetism can end up being incredibly complicated. We therefore cannot (yet) theoretically prove that quarks cannot exist by themselves. Worse yet, we can’t even calculate which combinations of quarks would be viable in nature and which would not.

Illustration of a tetraquark.