Saturday, October 2, 2010

CP violation

The discrete symmetries known as Charge conjugation (C) and parity (P) plays a very important role in Particle physics. C interchanges a particle with its antiparticle whereas P changes the handedness by reversing the space-coordinates x --> -x. The Standard model of particle physics which describes the observed fundamental particles and their interactions very successfully, violates both of these two discrete symmetries maximally. It violates C in the sense that the particle spectra has left handed neutrino but not the left handed anti-neutrino. P is violated in the sense that only left handed fermions have charged weak interactions and not the right handed ones. The combined operation of these two discrete symmetries CP is also violated in the Standard Model due to the presence of a CP violating phase in the quark mixing matrix (CKM matrix). C and CP violations are two of the four necessary criteria (Shakarov's conditions) required to produce the matter-antimatter asymmetry in the Universe. But the amount of CP violation in the quark sector of the Standard Model is too tiny to produce the large matter-antimatter asymmetry. This is one of the motivations to go beyond the Standard Model. This motivation got multiplied many times recently by the observed CP violation in Tevatron, Fermilab. One of it's detectors called DO has claimed to observe like-sign dimuon asymmetry in B meson decay which is 3.2 sigma away from the Standard Model predictions. Although this claim is yet to be confirmed, it has been taken very seriously across the world. I have already seen around ten papers which has explained this asymmetry by incorporating various new physics beyond the standard model. I am not sure whether this amount of CP violation (if confirmed to be correct) will be enough to produce the matter-antimatter asymmetry. If this suffices, then it will basically imply matter-antimatter asymmetry is generated at the TeV scale only. Since Tevatron is supposed to run till 2014 according to a recent proposal, we still have hope that it will verify this claim with much larger precision.

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