Evidence for $CP$ violation in ${B}^{+}\ensuremath{\rightarrow}{K}^{*}(892{)}^{+}{\ensuremath{\pi}}^{0}$ from a Dalitz plot analysis of ${B}^{+}\ensuremath{\rightarrow}{K}_{S}^{0}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{0}$ decays

Evidence for $C P$ violation in $B^{+} \to K^{*} (892)^{+} π^{0}$ from a Dalitz plot analysis of $B^{+} \to K_{S}^{0} π^{+} π^{0}$ decays

J. P. Lees et al. (The BaBar Collaboration)

Phys. Rev. D 96, 072001 – Published 2 October 2017

Abstract

We report a Dalitz plot analysis of charmless hadronic decays of charged $B$ mesons to the final state $K_{S}^{0} π^{+} π^{0}$ using the full BABAR data set of $470.9 \pm 2.8 million$ $B \bar{B}$ events collected at the $Υ (4 S)$ resonance. We measure the overall branching fraction and $C P$ asymmetry to be $B (B^{+} \to K^{0} π^{+} π^{0}) = (31.8 \pm 1.8 \pm 2. 1_{- 0.0}^{+ 6.0}) \times 10^{- 6}$ and $A_{C P} (B^{+} \to K^{0} π^{+} π^{0}) = 0.07 \pm 0.05 \pm 0.0 3_{- 0.03}^{+ 0.02}$ , where the uncertainties are statistical, systematic, and due to the signal model, respectively. This is the first measurement of the branching fraction for $B^{+} \to K^{0} π^{+} π^{0}$ . We find first evidence of a $C P$ asymmetry in $B^{+} \to K^{*} (892)^{+} π^{0}$ decays: $A_{C P} (B^{+} \to K^{*} (892)^{+} π^{0}) = - 0.52 \pm 0.14 \pm 0.0 4_{- 0.02}^{+ 0.04}$ . The significance of this asymmetry, including systematic and model uncertainties, is 3.4 standard deviations. We also measure the branching fractions and $C P$ asymmetries for three other intermediate decay modes.

Received 22 June 2015

DOI:https://doi.org/10.1103/PhysRevD.96.072001

Physics Subject Headings (PhySH)

Hadronic decays

Bottom mesons

CP violation

Particles & Fields

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Vol. 96, Iss. 7 — 1 October 2017

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Figure 1
Schematic representation of the definitions of $\vec{q}$ and $\vec{p}$ used in this analysis for the (left) $K_{S}^{0} π^{+}$ , (center) $K_{S}^{0} π^{0}$ , and (right) $π^{+} π^{0}$ resonances.
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Figure 2
Diagram illustrating the division of the Dalitz plot into different regions for the definition of the PDFs for self cross feed signal events. Each letter indicates whether the dependence is on $m_{π^{+} π^{0}}^{2}$ (A), $m_{K_{S}^{0} π^{+}}^{2}$ (B), or $m_{K_{S}^{0} π^{0}}^{2}$ (C). The remaining region of the Dalitz plot (D1) is where we expect to find fewer SCF events, and where the shapes for $m_{ES}$ and $Δ E$ are less dependent on their position in the Dalitz plot, further described in Table 3.
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Figure 3
Variations of the $Δ E$ distribution as seen in nonresonant signal MC simulation across the $m_{K_{S}^{0} π^{0}}^{2}$ regions (bands starting with label C in Fig. 2). The dotted (black) histogram shows the distribution in region C1, the solid (red) histogram the distribution in region C2, the dashed (green) histogram the distribution in region C3, and the dash-dotted (blue) histogram the distribution in region C4.
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Figure 4
Combined $B^{\pm}$ fit: Measured distributions and fit projections for $B^{\pm} \to K_{S}^{0} π^{\pm} π^{0}$ candidates; (a) $m_{ES}$ , (b) $Δ E$ , (c) ${BDT}_{out}$ , (d) $m_{K_{S}^{0} π^{+}}$ , (e) $m_{K_{S}^{0} π^{0}}$ , and (f) $m_{π^{+} π^{0}}$ . The points with error bars correspond to data, the solid (blue) curves to the total fit result, the dashed (green) curves to the total background contribution, and the dotted (red) curves to the continuum background component. The dash-dotted curves represent the signal contribution. The projected distributions are obtained from statistically precise pseudo experiments generated using the fit results. For all distributions in each panel, the signal-to-background ratio is increased by applying tighter selection requirement on $m_{ES}$ , $Δ E$ , and/or ${BDT}_{out}$ , listed Table 5.
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Figure 5
The $C P$ fit: Measured distributions and fit projections for $B^{+} \to K_{S}^{0} π^{+} π^{0}$ (left column) and $B^{-} \to K_{S}^{0} π^{-} π^{0}$ (right column) candidates; (a) $m_{K_{S}^{0} π^{+}}$ , (b) $m_{K_{S}^{0} π^{-}}$ , (c) $m_{K_{S}^{0} π^{0}}$ (from $B^{+} \to K_{S}^{0} π^{+} π^{0}$ ), (d) $m_{K_{S}^{0} π^{0}}$ (from $B^{-} \to K_{S}^{0} π^{-} π^{0}$ ), (e) $m_{π^{+} π^{0}}$ , and (f) $m_{π^{-} π^{0}}$ . The points with error bars correspond to data, the solid (blue) curves to the total fit result, the dashed (green) curves to the total background contribution, and the dotted (red) curves to the continuum background component. The dash-dotted curves represent the signal contribution. The projected distributions are obtained from statistically precise pseudo experiments generated using the fit results. For all distributions in each panel, the signal-to-background ratio is increased by applying the tighter selection requirements on $m_{ES}$ , $Δ E$ , and/or ${BDT}_{out}$ , listed in Table 5.
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Figure 6
$C P$ parameters $(x \pm Δ x, y \pm Δ y)$ obtained from the fit to data for $B^{\pm} \to K^{* \pm} (892) π^{0}$ resonant decay including the 1 and 2 standard deviation contours (solid and dashed curves). The contours are estimated by calculating the uncertainty and correlation between the two $C P$ parameters. The stars indicate the central values of the $C P$ parameters and the cross sign the origin of the plot.
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Physical Review D

covering particles, fields, gravitation, and cosmology

Evidence for $C P$ violation in $B^{+} \to K^{*} (892)^{+} π^{0}$ from a Dalitz plot analysis of $B^{+} \to K_{S}^{0} π^{+} π^{0}$ decays

J. P. Lees et al. (The BaBar Collaboration)

Phys. Rev. D 96, 072001 – Published 2 October 2017

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Evidence for CP violation in B+→K*(892)+π0 from a Dalitz plot analysis of B+→KS0π+π0 decays

J. P. Lees et al. (The BaBar Collaboration)

Phys. Rev. D 96, 072001 – Published 2 October 2017

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Evidence for $C P$ violation in $B^{+} \to K^{*} (892)^{+} π^{0}$ from a Dalitz plot analysis of $B^{+} \to K_{S}^{0} π^{+} π^{0}$ decays