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lhcb-public releaseThe LHCb collaboration has just presented at the Rencontres de Moriond EW and in a special CERN Seminar the first observation of CP violation in charm particle decays. Quarks can be split into two sectors: those with the same electrical charge as the up quark (up-type quarks, charge +2/3), and those with the same as the down quark (down-type quarks, charge -1/3). Differences in the properties of matter and antimatter, arising from the so-called phenomenon of CP violation, had been observed in the past using the decays of K and B mesons, i.e. of particles that contain strange or beauty quarks, which are both down-type quarks. By contrast, despite decades of experimental searches, CP violation in the decays of charmed particles, i.e. containing the charm quark, which is an up-type quark, escaped detection so far. The result announced today constitutes the first observation of CP violation in decays of a charmed particle.
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The final result, which uses essentially the full data sample collected by LHCb so far, is given by the quantity ΔACP=(-0.154±0.029)%, whose difference from zero quantifies the amount of CP violation observed. In particular, this turns out to differ from zero by 5.3σ (5.3 standard deviations), thus surpassing the threshold of 5σ adopted by particle physicists to assert without reservation that a discovery is made. This represents the first observation of CP violation in charm particle decays, opening up a new field in particle physics: the study of CP-violating effects in the sector of up-type quarks, and searches for new physics effects using charm CP asymmetry measurements.
I am, somehow, less interested in the weight and convolutions of Einstein’s brain than in the near certainty that people of equal talent have lived and died in cotton fields and sweatshops. - Stephen J. Gould