Measurement of CP violation, which describes differences between the properties of matter and antimatter, is a very important goal of LHCb. CP violation is well established in the K0 and B0 meson systems. Recent results from the LHCb collaboration have also provided evidence for CP violation in the decays of D0 mesons. Consequently, there now remains only one neutral heavy meson system, the B0s, where CP violation has not been seen.
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The LHCb collaboration has recently submitted for publication the first evidence for CP violation in the decays of B0s mesons. The paper (available here for experts), submitted to Physical Review Letters, confirms the preliminary results shown at the EPS-HEP meeting in Grenoble, see 22 July 2011 news. The B meson decays into K and π mesons were studied. The decay into a positive K meson red track and a negative π green track is show in the event display above. The four plots on the right hand side show the Kπ invariant mass distribution divided into different components as shown by the legend in the top-right figure. The different charge combination of K and π indicates if the decaying B particle is a matter or an antimatter particle. The two upper plots show that the decay rates of B0d mesons are different, as known from previous experiments. The lower two plots show that the difference is also visible for the B0s mesons. The measured CP asymmetry for the B0d mesons ACP = -0.088 ± 0.011 ± 0.008 constitutes the most precise measurement available to date and the first observation (6σ) at a hadron collider. The measured CP asymmetry for the B0s mesons ACP = 0.27 ± 0.08 ± 0.02 is the first evidence (3.3σ) for CP violation in the decays of these mesons.
LHCb physicists have used 1/3 of data collected in 2011 in this analysis and expect to have ten times more data by the end of this year.