Search for the Rare Decay B → πℓ⁺ℓ^- in the BaBar Experiment

Thesis/Dissertation · Fri Dec 01 00:00:00 EST 2006

DOI:https://doi.org/10.2172/922606· OSTI ID:922606

Ofte, Ingrid ^[1]

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1. Bergen Univ. (Norway)

The rare decay B → πℓℓ^- is the simplest manifestation of a b → dℓ⁺ℓ^- flavor-changing neutral current (FCNC) process. This type of process only proceeds through penguin loop or box diagrams and is sensitive to physics at the electroweak scale. It can be used to constrain parameters of the Standard Model and its extensions. B → πℓ⁺ℓ^- events have not yet been observed; the branching fraction is expected to be an order of magnitude smaller than the measured branching fraction for the similar B → Kℓ⁺ℓ^- decay. Using 230 million B$$\bar{B}$$ meson pairs collected with the BABAR detector, we have done a search for the rare decay B →πℓ⁺ℓ^- . The data was produced in e⁺e^- collision at the Y(4S) resonance in the PEP-II collider between 1999 and 2004. Four exclusive B-meson decay modes have been reconstructed: B⁺ → π⁺ℓ⁺ℓ^- and B⁰ → π⁰ℓ⁺ℓ^- , where ℓ⁺ ℓ^- is either an electron pair (e⁺e^-) or a muon pair (μ⁺μ^-). We find no evidence for a signal, and we obtain upper limits on the branching fractions β. Assuming the isospin relation β(B⁺ → π⁺ℓ⁺ℓ^- ) 2 x ^τB⁺/^τB⁰ β(B⁰ → π⁰ℓ⁺ℓ^-), we obtain an upper limit at 90% confidence level on the lepton-flavor-averaged branching fraction of B → πℓ⁺ℓ^- to be β(B → πeμ) < 9.2 x 10^-8 at 90% C.L. We have also reconstructed two control modes B⁺→ π⁺e^±μ^± and B⁰ → π⁰e^±μ^± and we also obtain an upper limit at 90% confidence level on the lepton-flavor-violating decay B → πeμ of β(B → πeμ) < 9.2 x 10^-8 at 90% C.L. This is the first search for these rare decays at the current B-Factory experiments. This limit is an improvement by four orders of magnitude with respect to the previous experimental limit, and about a factor three above Standard Model predictions.

• Research Organization: SLAC National Accelerator Lab., Menlo Park, CA (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC02-76SF00515
• OSTI ID: 922606
• Report Number(s): SLAC-R-859; TRN: US0801165
• Country of Publication: United States
• Language: English

Related Subjects

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
DECAY
ELECTRON PAIRS
ISOSPIN
MESONS
MUON PAIRS
NEUTRAL CURRENTS
PHYSICS
RESONANCE
STANDARD MODEL
Experiment-HEP
HEPEX