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Measurement of the $B^0 \to K^{*0}e^+e^-$ branching fraction at low dilepton mass

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Abstract

The branching fraction of the rate decay $B^0 \rightarrow K^{*0}e^+e^-$ in the dilepton mass region from 30 to 1000 MeV$/c^2$ has been measured by the LHCb experiment, using $pp$ collision data, corresponding to an integrated luminosity of 1.0 fb$^{-1}$, at a centre-of-mass energy of 7 TeV. The decay mode $B^0 \rightarrow J/\psi(e^+e^-) K^{*0}$ is utilized as a normalization channel. The branching fraction $B^0 \rightarrow K^{*0}e^+e^-$ is measured to be $$ B(B^0 \rightarrow K^{*0}e^+e^-)^{30-1000 MeV/c^2}= (3.1 ^{+0.9 +0.2}_{-0.8 -0.3} \pm 0.2)\times 10^{-7}, $$ where the first error is statistical, the second is systematic, and the third comes from the uncertainties on the B^0 \rightarrow J/\psi K^{*0}$ and $J/\psi \rightarrow e^+e^- $ branching fractions.

Figures and captions

Dominant Standard Model diagrams contributing to the decay ${ B ^0 \rightarrow K ^{*0} e ^+ e ^- }$.

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Output of the BDT for $ B ^0 \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} ( e ^+ e ^- ) K ^{*0} $ data (points) and simulation (red line).

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Invariant mass distributions for the $ B ^0 \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} ( e ^+ e ^- ) K ^{*0} $ decay mode for the (left) HWElectron and (right) HWTIS trigger categories. The dashed line is the signal PDF, the light grey area corresponds to the combinatorial background, the medium grey area is the partially reconstructed hadronic background and the dark grey area is the partially reconstructed $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ background component.

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Invariant mass distributions for the $ B ^0 \rightarrow K ^{*0} e ^+ e ^- $ decay mode for the (left) HWElectron and (right) HWTIS trigger categories. The dashed line is the signal PDF, the light grey area corresponds to the combinatorial background, the medium grey area is the partially reconstructed hadronic background and the black area is the $ B ^0 \rightarrow K ^{*0} \gamma $ component.

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Animated gif made out of all figures.

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Tables and captions

Signal yields with their statistical uncertainties.

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Ratios of efficiencies used for the measurement of the $ B ^0 \rightarrow K ^{*0} e ^+ e ^- $ branching fraction. The ratio $r_{\rm HW}$ for the HWTIS trigger category is assumed to be equal to unity. The uncertainties are the total ones and are discussed in Sec. 6.

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Absolute systematic uncertainties on the $ B ^0 \rightarrow K ^{*0} e ^+ e ^- $ branching ratio (in $10^{-7}$) .

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Created on 27 April 2024.