Abstract
We report measurements of $\sin{2\beta}$ and $\cos{2\beta}$ from a time-dependent Dalitz plot analysis of $B^{0} \to D^{(*)} h^{0}$ with $D \to K_{S}^{0} \pi^{+} \pi^{-}$ decays, where the light unflavored and neutral hadron $h^{0}$ is a $\pi^{0}$, $\eta$, or $\omega$ meson. The analysis is performed with a combination of the final data sets of the \babar\ and Belle experiments containing $471 \times 10^{6}$ and $772 \times 10^{6}$ $B\bar{B}$ pairs collected at the $\Upsilon\left(4S\right)$ resonance at the asymmetric-energy B factories PEP-II at SLAC and KEKB at KEK, respectively. We measure $\sin{2\beta} = 0.80 \pm 0.14 \,(\rm{stat.}) \pm 0.06 \,(\rm{syst.}) \pm 0.03 \,(\rm{model})$ and $\cos{2\beta} = 0.91 \pm 0.22 \,(\rm{stat.}) \pm 0.09 \,(\rm{syst.}) \pm 0.07 \,(\rm{model})$. The result for the direct measurement of the angle is $\beta = \left( 22.5 \pm 4.4 \,(\rm{stat.}) \pm 1.2 \,(\rm{syst.}) \pm 0.6 \,(\rm{model}) \right)^{\circ}$. The last quoted uncertainties are due to the composition of the $D^{0} \to K_{S}^{0} \pi^{+} \pi^{-}$ decay amplitude model, which is newly established by a Dalitz plot amplitude analysis of a high-statistics $e^{+}e^{-} \to c\bar{c}$ data sample as part of this analysis. We find the first evidence for $\cos2\beta>0$ at the level of $3.7$ standard deviations. The measurement excludes the trigonometric multifold solution $\pi/2 - \beta = (68.1 \pm 0.7)^{\circ}$ at the level of $7.3$ standard deviations and therefore resolves an ambiguity in the determination of the apex of the CKM Unitarity Triangle. The hypothesis of $\beta = 0^{\circ}$ is ruled out at the level of $5.1$ standard deviations, and thus CP violation is observed in $B^{0} \to D^{(*)} h^{0}$ decays.
Highlights
The breaking of CP symmetry is a physical effect with profound consequences, causing particles and antiparticles to behave differently [1,2,3]
The Belle detector consists of a silicon vertex detector (SVD), a 50-layer central drift chamber (CDC), an array of aerogel threshold Cherenkov counters (ACC), a barrel-like arrangement of time-of-flight scintillation counters (TOF), and an electromagnetic calorimeter comprised of CsI(Tl) crystals (ECL) located inside a superconducting solenoid coil that provides a 1.5 T magnetic field
The model uncertainty accounts for the dependence of the CP violation parameters on the D0 → K 0S π þ π − decay amplitude model determined by the Dalitz plot amplitude analysis using the high-statistics Belle eþ e− → ccdata
Summary
The breaking of CP symmetry is a physical effect with profound consequences, causing particles and antiparticles to behave differently [1,2,3]. In our previous time-dependent CP violation analysis that combined BABAR and Belle data [31], we determined the parameter C that measures direct CP violation in two independent samples of B0 → DðÞ h0 decays. Equation (2) allows the measurement of sin 2β and cos 2β as independent parameters by a time-dependent Dalitz plot analysis of B0 → DðÞ h0 with D → K 0S π þ π − decays. We derive the D0 → K 0S π þ π − decay amplitude model from the data by a Dalitz plot amplitude analysis of a highstatistics eþ e− → ccdata sample This approach ensures full control over the construction and the propagation of uncertainties of the D0 → K 0S π þ π − decay amplitude model, and enables us to further improve the experimental sensitivity and robustness of the measurement. The paper is accompanied by a letter in Physical Review Letters [33]
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