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Top Comments: A New Observation of Matter-Antimatter Mismatch [1]
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Date: 2025-07-27
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Antimatter was discovered in 1932 when Carl Anderson, studying cosmic radiation, identified a positively charged particle that had exactly the same mass as the negatively charged electron. This discovery confirmed theorist Paul Dirac’s prediction of the existence of antimatter particles—that is particles with reverse charge (if there is one) of the familiar matter particles. This antimatter partner of the electron can be called either a positron (Anderson’s name) or the anti-electron (Dirac’s name).
In Dirac’s theory, the matter/antimatter partners behave exactly alike in all respects except that they have opposite charges. Also, when matter/antimatter partners come in contact, they annihilate each other, producing a pair of very energetic gamma rays (and possibly other particles depending on the particles involved). For cosmology, this creates a problem: The Big Bang would have created equal amounts of matter and antimatter, but the universe today is overwhelmingly made of matter, with only small amounts of antimatter present. If matter and antimatter truly behaved in an identical fashion, then the matter and antimatter would have annihilated each other leaving nothing behind, and we wouldn’t be here. There must be something fundamentally different between the behavior of matter and antimatter for the universe to have evolved the way it has.
In the years since the discovery of antimatter, a few differences have become apparent, specifically in the discovery of differences in the decay rates of unstable particles. It has been known for quite a while that a couple of different mesons show differences in both decay rates and modes of decay (i. e. what particles they produce in decay). [Mesons are transient species made up of a quark-antiquark pair. The specific mesons known to display this phenomenon are the K meson, consisting of an anti-up quark and a strange quark, and the B meson, consisting of a bottom antiquark and a lighter quark, being one among up, down, strange, or charm].
Reported now is confirmation that the matter/antimatter partners of a baryon, a particle consisting of three quarks, have different lifetimes. The most common baryons in the universe are the proton (consisting of two up quarks and one down) and the neutron (one up quark and two downs), which are the particles that make up the nuclei of all atoms. However, the baryon is question is not one of these familiar particles, but a baryon called the lambda-b particle. It consists of an up quark, a down quark, and a bottom quark, while its antiparticle consists of the antimatter counterparts. The particle lifetimes show a 2.5 % difference between matter and antimatter, with a statistical significance greater than 5 sigma (the condition required for calling a phenomenon real).
So can the difference in the decay rates between the matter and antimatter forms of this rare and energetic baryon explain the preponderance of matter in the universe? No, but this discovery bolsters the idea that matter and antimatter really do behave differently, and that there is hope that other as-yet undiscovered phenomena will eventually draw back the curtain on this mystery.
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