BABAR time-dependent CP violation experiment 2026-10-18
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BABAR used asymmetric Electron-Positron collisions near the Upsilon meson resonance to prepare neutral B meson pairs. It reconstructed one decay into charmonium plus a kaon, and used flavour tagging on the other B meson with charged leptons or kaons. Silicon tracking reconstructed decay vertices for the decay-time difference. Self-tagging decays calibrated mistags and time resolution; charged decays provided a control. The tagged time distributions established CP violation, limited by backgrounds, mistags and vertex alignment.[ref]
The Lorentz boost converts vertex separation to at leading order. Unequal beam energies thus make a time difference measurable as a distance.[ref]
Figure 1.
From flavour tag and decay vertices to a toy CP asymmetry
. Functional B meson readout above, an original illustrative time-dependent neutral-B CP asymmetry below. The curves are a teaching model, not measured events or a detector drawing. Details.
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