Exotic New Particles Seen in Hadron Collider Unearth New Secrets of Physics

Physicists at the European Organization for Nuclear Research (CERN) announced on 5 July that they had observed three exotic new types of particles that had never been seen before—shining a light into a subatomic world we don't fully understand.

The observation was made using the Large Hadron Collider (LHC), the world's biggest particle accelerator. It works by accelerating two beams of hadrons—protons or ions specifically—around and around in a 27-kilometer circle before smashing them into each other at nearly the speed of light.

Afterwards, extremely sensitive detectors are used to look at what happened in the fractions of a second following that collision. The idea is that high-energy collisions of particles can temporarily produce rare, exotic particles we don't ordinarily see, and these rare particles can tell us about some of the most fundamental characteristics of our universe: Where mass comes from, for example, and what dark matter and dark energy are.

The LHC first started up on September 10, 2008. Since then it has undergone various alterations, and until this spring it had been offline for more than three years for maintenance and upgrade work.

Scientist at the LHC
A scientist looks at a section of the Large Hadron Collider at the European Organization for Nuclear Research near Geneva, Switzerland. The machine smashes particles together to investigate the mysteries of the subatomic world. Fabrice Coffrini/AFP/Getty

Last week, scientists switched the accelerator on again, launching beams of particles at higher energy levels than ever before. The collisions produced three never-before-seen particles: a new kind of pentaquark, a new kind of tetraquark and the first ever pair of tetraquarks.

Quarks are tiny particles that combine to form hadrons—a class of particle that includes the common atomic building blocks known as protons and neutrons—and they come in six types known as flavors. These flavors are up, down, charm, strange top, and bottom.

Quarks themselves are joined together via gluons, which is what enables them to make larger particles. Quarks are bound together by the strong nuclear force—one of the four fundamental forces of the universe alongside the weak nuclear force, electromagnetism, and gravity.

Typically, quarks combine in groups of twos and threes. Protons, for instance, are made of three quarks. However, in rare cases quarks can combine in groups of four or five—tetraquarks and pentaquarks respectively.

While these have been observed before, the most recent discovery marked the first time they had been found in certain combinations.

"These discoveries are quite significant since they confirm the existence of 'exotic' pentaquark and tetraquark states with different quark combinations, also including the strange quark this time," Nicola Neri, senior member of the LHCb experiment in which the particles were discovered, told Newsweek.

"The quark and gluon composition of hadrons can be very complex due to our limited capability to calculate the effects of strong interactions. However, the strong force is similar for light quarks: up, down, and strange quarks. This is a symmetry of their nature that has to be reflected in exotic pentaquark and tetraquark states and in their properties when substituting a strange quark with an up or down quark.

"We can predict relations between those states and verify by measuring their properties as mass, intrinsic width, and quantum numbers, if the experimental results agree with the theory. These measurement will help in understanding the nature of the 'exotic' hadrons and the binding mechanism forming such states.

"It is important to identify patterns among different 'exotic' hadrons to be able to verify theoretical predictions and improve our understanding of strong interactions. In particular we do not know how to predict masses, widths and quantum numbers of exotic states, since we are still unable to make precise calculations starting from first principles."

Neri added that LHC experiments involving large data samples and highly advanced sensors will help in developing models for predictions.

The recent LHC run is one of many that are expected to be carried out in unprecedented numbers in the coming four years, enabled by the collider's recent upgrade and maintenance work. The upcoming series of experiments is called Run 3.

The LHCb section in particular, where the new quark combinations were discovered, has undergone a complete revamp. That section of the LHC is now expected to see its collision count increase by a factor of three, according to CERN.

LHCb is designed to probe the slight differences between matter and antimatter by studying a specific type of quark known as a beauty quark. It uses a 5,600-tonne detector and is operated by about 1,565 scientists from 20 countries.