The decay of a kaon (K+) into three pions (2 π+, 1 π−) is a process that involves both weak and strong interactions. Weak interactions : The strange antiquark (s) of the kaon transmutes into an up antiquark (u) by the emission of a W+ boson; the W+ boson subsequently decays into a down antiquark (d) and an up quark (u). Strong interactions : An up quark (u) emits a gluon (g) which decays into a down quark (d) and a down antiquark (d).
Scientists devised the first calculation of how the behavior of kaons differs when matter is swapped out for antimatter, known as direct “CP” symmetry violation. Should the calculation not match experimental results, it would be conclusive evidence of new, unknown phenomena that lie outside of the Standard Model-physicists’ present understanding of the fundamental particles and the forces between them.
The target of the present calculation is a phenomenon that is particularly elusive: a one-part-in-a-million difference between the matter and antimatter decay strengths. The calculation determines the size of the symmetry violating effect as predicted by the Standard Model.
Results from the first, less difficult, part of this calculation were reported by the same group in 2012. However, it is only now, with completion of the second part of this calculation-which required more than 200 million core processing hours on supercomputers -that a comparison with the measured size of direct CP violation can be made.
Physicists’ present understanding of the universe requires that particles and their antiparticles behave differently. Only with matter-antimatter asymmetry can they hope to explain why the universe, which was created with equal parts of matter and antimatter, is filled mostly with matter today.
The first experimental evidence for the matter-antimatter asymmetry, known as CP violation, was discovered in 1964 at the Brookhaven National Laboratory in the United States. This was built upon to a more accurate degree in 2000, to uncover direct CP violation – a tiny effect which only affects a few particle decays in a million. Although the Standard Model does successfully relate the matter-antimatter asymmetries, this is insufficient to explain the dominance of matter over antimatter in the universe today.
“This suggests that a new mechanism must be responsible for the preponderance of matter of which we are made,” said Christopher Kelly, RBRC. “This one-part-per-million, direct CP violation may be a good place to first see it. The approximate agreement between this new calculation and the 2000 experimental results suggests that we need to look harder, which is exactly what the team performing this calculation plans to do.” http://www.southampton.ac.uk/news/2015/11/cp-symmetry-calculation.page http://arxiv.org/abs/1505.07863
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