Search for the rare decays $B\ensuremath{\rightarrow}\ensuremath{\pi}{\ensuremath{\ell}}^{+}{\ensuremath{\ell}}^{\ensuremath{-}}$ and ${B}^{0}\ensuremath{\rightarrow}\ensuremath{\eta}{\ensuremath{\ell}}^{+}{\ensuremath{\ell}}^{\ensuremath{-}}$

Search for the rare decays $B \to π ℓ^{+} ℓ^{-}$ and $B^{0} \to η ℓ^{+} ℓ^{-}$

J. P. Lees et al. (BABAR Collaboration)

Phys. Rev. D 88, 032012 – Published 27 August 2013

Abstract

We present the results of a search for the rare flavor-changing neutral-current decays $B \to π ℓ^{+} ℓ^{-}$ ( $π = π^{\pm}$ , $π^{0}$ and $ℓ = e$ , $μ$ ) and $B^{0} \to η ℓ^{+} ℓ^{-}$ using a sample of $e^{+} e^{-} \to Υ (4 S) \to B \bar{B}$ decays corresponding to $428 {fb}^{- 1}$ of integrated luminosity collected by the BABAR detector. No significant signal is observed, and we set an upper limit on the isospin and lepton-flavor averaged branching fraction of $B (B \to π ℓ^{+} ℓ^{-}) < 5.9 \times 10^{- 8}$ and a lepton-flavor averaged upper limit of $B (B^{0} \to η ℓ^{+} ℓ^{-}) < 6.4 \times 10^{- 8}$ , both at the 90% confidence level. We also report 90% confidence level branching fraction upper limits for the individual modes $B^{+} \to π^{+} e^{+} e^{-}$ , $B^{0} \to π^{0} e^{+} e^{-}$ , $B^{+} \to π^{+} μ^{+} μ^{-}$ , $B^{0} \to π^{0} μ^{+} μ^{-}$ , $B^{0} \to η e^{+} e^{-}$ , and $B^{0} \to η μ^{+} μ^{-}$ .

Received 31 March 2013

DOI:https://doi.org/10.1103/PhysRevD.88.032012

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Vol. 88, Iss. 3 — 1 August 2013

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Figure 1
Lowest order Feynman diagrams describing the quark level $b \to d ℓ^{+} ℓ^{-}$ transition in $B$ meson decay: (a) electroweak penguin diagrams and (b) $W^{+} W^{-}$ box diagrams.
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Figure 2
Outputs of (a) the $e^{+} e^{-}$ $B \bar{B}$ neural network for a sample of $B^{+} \to π^{+} e^{+} e^{-}$ signal (solid red) and $B \bar{B}$ background (dashed blue) MC events and (b) the $μ^{+} μ^{-}$ continuum neural network for a sample of $B^{0} \to π^{0} μ^{+} μ^{-}$ signal (solid red) and continuum background (dashed blue) MC events. For both (a) and (b) the signal and background distributions are normalized to equal areas.
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Figure 3
Fit projections of $m_{ES}$ (top) and $Δ E$ (bottom) for the isospin averaged $B \to π e^{+} e^{-}$ fit to the $π^{+} e^{+} e^{-}$ [(a) and (d)], $K^{+} e^{+} e^{-}$ [(b) and (e)], and $π^{0} e^{+} e^{-}$ [(c) and (f)] data sets. Points with error bars represent data. The curves are dotted (magenta) for combinatoric background, dotted-dashed (gray) for $K^{*} / K_{S}^{0} ℓ^{+} ℓ^{-}$ background, dashed (green) for $K^{+} ℓ^{+} ℓ^{-}$ signal and background, and solid (red) for $π ℓ^{+} ℓ^{-}$ signal. The solid blue curve represents the total fit function.
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Figure 4
Fit projections of $m_{ES}$ (top) and $Δ E$ (bottom) for the lepton-flavor averaged fit to the $η_{γ γ} e^{+} e^{-}$ [(a) and (e)], $η_{3 π} e^{+} e^{-}$ [(b) and (f)], $η_{γ γ} μ^{+} μ^{-}$ [(c) and (g)], and $η_{3 π} μ^{+} μ^{-}$ [(d) and (h)] samples. Points with error bars represent data. The curves are dotted (magenta) for combinatoric background, dashed (green) for self-cross-feed, and solid (red) for $η ℓ^{+} ℓ^{-}$ signal. The solid blue curve represents the total fit function.
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Figure 5
Fit projections of $m_{ES}$ and $Δ E$ for the lepton-flavor and isospin averaged $π ℓ^{+} ℓ^{-}$ fit to the $π^{+} e^{+} e^{-}$ [(a) and (d)], $K^{+} e^{+} e^{-}$ [(b) and (e)], $π^{0} e^{+} e^{-}$ [(c) and (f)], $π^{+} μ^{+} μ^{-}$ [(g) and (j)], $K^{+} μ^{+} μ^{-}$ [(h) and (k)], and $π^{0} μ^{+} μ^{-}$ [(i) and (l)] data sets. Points with error bars represent data. The curves are dotted (magenta) for combinatoric background, triple dotted-dashed (cyan) for hadronic peaking background in the $μ^{+} μ^{-}$ modes, dotted-dashed (gray) for $K^{*} / K_{S}^{0} ℓ^{+} ℓ^{-}$ background, dashed (green) for $K^{+} ℓ^{+} ℓ^{-}$ signal and background, and solid (red) for $π ℓ^{+} ℓ^{-}$ signal. The solid blue curve represents the total fit function.
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Figure 6
The negative logarithm of the profile likelihood as a function of branching fraction for (a) $B \to π ℓ^{+} ℓ^{-}$ , (b) $B^{0} \to η ℓ^{+} ℓ^{-}$ , (c) $B^{+} \to π^{+} ℓ^{+} ℓ^{-}$ , (d) $B^{0} \to η e^{+} e^{-}$ , (e) $B^{0} \to π^{0} ℓ^{+} ℓ^{-}$ , and (f) $B^{0} \to η μ^{+} μ^{-}$ The solid black lines are the negative log likelihood curves including only statistical errors, and the dashed green lines correspond to the same curves convolved with a Gaussian distribution whose width is equal to the total systematic error.
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Physical Review D

covering particles, fields, gravitation, and cosmology

Search for the rare decays $B \to π ℓ^{+} ℓ^{-}$ and $B^{0} \to η ℓ^{+} ℓ^{-}$

J. P. Lees et al. (BABAR Collaboration)

Phys. Rev. D 88, 032012 – Published 27 August 2013

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Physical Review D

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Search for the rare decays B→πℓ+ℓ− and B0→ηℓ+ℓ−

J. P. Lees et al. (BABAR Collaboration)

Phys. Rev. D 88, 032012 – Published 27 August 2013

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Search for the rare decays $B \to π ℓ^{+} ℓ^{-}$ and $B^{0} \to η ℓ^{+} ℓ^{-}$