Crux of the matter

By | Science & Technology
LHCb Collaboration in front of the LHCb detector. Credit@MaximilienBrice;RachelBarbier

Scientists at the Large Hadron Collider (LHC) near Geneva recently observed two new particles made of exotic types of quarks. Published last week in Physical Review Letters, this is the first time that these types of baryons, called called Xib‘- and Xib*-, have ever been spotted. These Baryons are around five times heavier than protons although fall within the same family. These particles were long predicted to exist from scientific models however specific characteristic such as mass have been uncertain until now.

The primary goal of the Large Hadron Collider beauty (LHCb) experiment is to explore what happened following the Big Bang. This includes studying the baryon number of symmetry in the universe which aims to help explain the asymmetry between matter and antimatter – material made of antiparticles that have the same mass as particles in ordinary matter, however they have opposite charge and other properties such as baryon number. Physics Coordinator of the LHCb experiment, Patrick Koppenburg, told The Positive, “Why when everything cooled down after the Big Bang is there more matter than antimatter? This could be because of the high energy produced during the Big Bang which has previously been inaccessible through experiments, which is why the LHC is so interesting.”

The baryons mentioned in the study are higher-energy configurations meaning they are excited and unstable. Learning about baryons aims to help provide an answer the asymmetry, especially because the total baryon number in the universe is conserved under the Standard Model in physics, which defines all known particles in the universe. The excess of baryons over antibaryons may help explain what researchers see.

Researchers predicted the existence of Xib‘- and Xib*- beforehand using quantum chromodynamics (QCD), which models strong interactions. The theory itself is relatively simple, yet extremely challenging to calculate, which is why experiments such as this are performed. Gathering empirical information through the observation of these predicted particles makes theoretical calculations of strong interactions more precise and accurate.

The strong force is one of the four fundamental forces that direct all matter in the universe (the other three being gravity, electromagnetism and the weak force). Strong interactions bind things together. This ensures the stability of ordinary matter by holding together quarks in hadron particles such as protons and neutrons or on a larger scale, combining together these protons and neutrons in the nucleus of an atom.

Typically, experiments to discover new particles start with known, non-excited and stable particles from previous experiments. These new baryons were created in the collision of stable baryons with light particles in the 27 km-long underground ring of the LHC. This is possible because the strength of the strong force is so great, that the energy of an object bound by it is high enough to produce new particles. Therefore, when hadrons are struck by high-energy particles, such as light particles, they give rise to new hadrons – Xib‘- and Xib*- – instead of simply emitting radiation. Consequently, when an excess of particles is observed above what was introduced to the collider, it is investigated for new particles.

By making measurements of predictions in the Standard Model more precise, scientists may work towards a bigger theory to supersede it. One that might account for dark matter – a hypothetical and unobservable type of matter that accounts for most of the matter in the universe. This spring, the LHC aims to start up again with higher energies than before to enable more massive particles to arise from the high-speed collisions. The aim is to find particles that break the limits of the Standard Model.

What consumer-focussed applications might the LHC provide from its discoveries of new subatomic particles?

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