Here’s why the universe has more matter than antimatter
Known asymmetry
The behavior of quarks, which are the fundamental building blocks of matter along with leptons, can shed light on the difference between matter and antimatter. Quarkscome in many different kinds, or “flavors,” known as up, down, charm, strange, bottom, and top plus six corresponding anti-quarks.
The up and down quarks are what make up the protons and neutrons in the nuclei of ordinary matter, and the other quarks can be produced by high-energy processes – for instance by colliding particles in accelerators such as the Large Hadron Collider at CERN.
Particles consisting of a quark and an anti-quark are called mesons, and there are four neutral mesons (B0S, B0, D0,and K0) that exhibit a fascinating behavior. They can spontaneously turn into their antiparticle partner and then back again, a phenomenon that was observed for the first time in 1960. Since they are unstable, they will “decay” – fall apart – into other more stable particles at some point during their oscillation. This decayhappens slightly differently for mesons compared with anti-mesons, which combined with the oscillation means that the rate of the decay varies over time.
The rules for the oscillations and decays are given by a theoretical framework called theCabibbo-Kobayashi-Maskawa (CKM) mechanism. It predicts that there is a difference in the behavior of matter and antimatter, but one that is too small to generate the surplus of matter in the early universe required to explain the abundance we see today.
This indicates that there is something we don’t understand and that studying this topic may challenge some of our most fundamental theories in physics.
New physics?
Our recent result from the LHCb experiment is a study of neutral B0Smesons, looking at their decays into pairs of charged K mesons. The B0Smesons were created by colliding protons with other protons in the Large Hadron Collider where they oscillated into their anti-meson and back three trillion times per second. The collisions also created anti-B0Smesons that oscillate in the same way, giving us samples of mesons and anti-mesons that could be compared.
We counted the number of decays from the two samples and compared the two numbers, to see how this difference varied as the oscillation progressed. There was a slight difference – with more decays happening for one of the B0Smesons. And for the first time for B0Smesons, we observed that the difference in decay, or asymmetry, varied according to the oscillation between the B0Smeson and the anti-meson.
In addition to being a milestone in the study of matter-antimatter differences, we were also able to measure the size of the asymmetries. This can be translated into measurements of several parameters of the underlying theory. Comparing the results with other measurements provides a consistency check, to see if the currently accepted theory is a correct description of nature. Since the small preference of matter over antimatter that we observe on the microscopic scale cannot explain the overwhelming abundance of matter that we observe in the universe, it is likely that our current understanding is an approximation of a more fundamental theory.
Investigating this mechanism that we know can generate matter-antimatter asymmetries, probing it from different angles, may tell us where the problem lies. Studying the world on the smallest scale is our best chance to be able to understand what we see on the largest scale.
This article byLars Eklund, Professor of Particle Physics,University of Glasgowis republished fromThe Conversationunder a Creative Commons license. Read theoriginal article.
Story byThe Conversation
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