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Why is the universe made of matter?: Not up to Standard | The Economist

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THAT the universe is made of matter is obvious enough. What bothers fundamental physicists, though, is why that is. The best current theory of particle physics, called the Standard Model, suggests that basically equal amounts of matter and antimatter should have been produced in the Big Bang. Famously, however, matter and antimatter annihilate on contact and disappear in a puff of pure energy, so a primordial equity between the two would have led to a lifeless, photon-filled universe. One possible reason for the apparent imbalance is a phenomenon called charge conjugation/parity violation (or CP violation for short).

If charge conjugation and parity were conserved, nature would treat particles and their antiversions, which carry the opposite electric charge and opposite value of a property called spin, alike. The Standard Model allows for a whiff of CP violation. But that is nowhere near enough of it to explain matter’s cosmic dominance.

Last November an experiment called LHCb, which feeds off the world’s biggest particle accelerator, the Large Hadron Collider (LHC) near Geneva, saw hints of excess CP violation beyond theorists’ predictions. Now an experiment in America, known as CDF, has spotted something similar. It announced its results at a meeting in La Thuile, in Italy.

Like LHCb, CDF was looking at a subatomic species called mesons. These come in a variety of types, or flavours, each containing a quark and an antiquark. One flavour, known as D0-mesons, is composed of a charm quark and an up antiquark. Its antimatter twin, known as D0-bar, consists of a charm antiquark and an up quark. (A charm quark is a heavier cousin of the up quark which, together with down quarks, makes up the ordinary protons and neutrons found in atomic nuclei; lest things get too straightforward, the down quark is not simply an up antiquark.)

via Why is the universe made of matter?: Not up to Standard | The Economist.


Written by edparnell

March 3, 2012 at 12:02 am

Posted in Science, Space

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