CP violation and the matter-antimatter asymmetry
Where and how strongly does nature violate the combined charge-parity (CP) symmetry, and can the observed amount explain why the universe is made of matter rather than antimatter?
History and references
Partly settled. Some of it is understood, some is still argued about.
CP violation was already known in neutral kaons since 1964 (Nobel 1980) when Ginzburg wrote his problem #18. Since 1999, CP violation has also been firmly measured in B mesons (BaBar and Belle, 2001, underpinning the 2008 Nobel Prize to Kobayashi and Maskawa) and, for the first time, in charm mesons (LHCb, 2019). However, the CP violation predicted and measured within the Standard Model is many orders of magnitude too small to explain the observed matter-antimatter (baryon) asymmetry of the universe, so the search for additional sources (e.g. in neutrinos, via leptogenesis) continues.
Matter and antimatter are supposed to be mirror images, but nature keeps a slight, specific bias against the mirror, and that bias may be the reason anything exists at all.
References
- What problems of physics and astrophysics seem now to be especially important and interesting (thirty years later, already on the verge of the XXI century)?, V L Ginzburg, Physics-Uspekhi 42 (4) 353-373, 1999
- Observation of CP Violation in the B0 Meson System, BaBar Collaboration, Physical Review Letters 87, 091801, 2001
- Discovery of CP violation in charm particle decays, LHCb Collaboration, LHCb public results / CERN Courier, 2019
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