EP Seminar

Combined Time-Dependent CP Violation Measurements by the B factory experiments BaBar and Belle

by Markus Roehrken (CERN)

500-1-001 - Main Auditorium (CERN)

500-1-001 - Main Auditorium


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During the 2000s, the BaBar experiment at SLAC in Stanford/USA and the Belle experiment at KEK in Tsukuba/Japan performed a very successful flavor physics program. In particular, BaBar and Belle discovered CP violation in the neutral and charged B meson system. In this talk, we present the results of two measurements from a novel analysis campaign by the former 'friendly competitors'. The novel approach combines the integrated luminosity of about 1.1 inverse attobarn collected by both experiments in single physics analyses.

The first combined measurement presented is a time-dependent CP violation measurement of $B^{0} \to D^{(*)}_{CP} h^{0}$ decays, where the light neutral hadron $h^{0}$ is a $\pi^{0}$, $\eta$ or $\omega$ meson, and the neutral $D$ meson is reconstructed in decays to the two-body CP eigenstates $K^{+}K^{-}$, $K_{S}^{0}\pi^{0}$ or $K_{S}^{0}\omega$. A first observation of CP violation governed by mixing-induced CP violation according to $\sin{2\beta}$ is reported. The second combined measurement presented is a time-dependent Dalitz plot analysis of $B \to D^{(*)} h^{0}$ with $D \to K_{S}^{0} \pi^{+} \pi^{-}$ decays. These decays provide an experimentally elegant and powerful approach to access $\cos{2\beta}$ in addition to $\sin{2\beta}$, and can therefore resolve an ambiguity in the determination of the apex of the CKM Unitarity Triangle. The second combined measurement is technically demanding and includes a full Dalitz plot amplitude analysis of $D \to K_{S}^{0} \pi^{+} \pi^{-}$ decays that is performed on a high-statistics charm data set. We report the first evidence for $\cos{2\beta}>0$, an observation of CP violation, and the exclusion of the second solution of the CKM Unitarity Triangle of $\beta = (68.1 \pm 0.7)^\circ$ at a significance of 7.3 standard deviations.

During the talk, the speaker will attempt to highlight various unique physics features of the B factory experiments that include diverse interference phenomena, such as variations of Young's double slit experiment, or the Einstein-Podolsky-Rosen correlation that can be exploited in the measurements.


Organized by

M. Pepe-Altarelli, G. Unal.......... Refreshments will be served at 10h30

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