Strong constraints on the b → sγ photon polarisation from B0 → K*0e+e− decays
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13130_2020_Article_14370.pdf
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Author(s)
Aaij, R.
Abellán Beteta, C.
Ackernley, T.
Adeva, B.
Adinolfi, M.
Afsharnia, H.
Aidala, C. A
Aiola, S.
Ajaltouni, Z.
Akar, S.
Date Issued
December 11, 2020
Publisher
Springer Berlin Heidelberg
Citation
Journal of High Energy Physics. 2020 Dec 11;2020(12):81
Version
Final published version
Abstract
Abstract
An angular analysis of the B0 → K*0e+e− decay is performed using a data sample corresponding to an integrated luminosity of 9 fb−1 of pp collisions collected with the LHCb experiment. The analysis is conducted in the very low dielectron mass squared (q2) interval between 0.0008 and 0.257 GeV2, where the rate is dominated by the B0 → K*0γ transition with a virtual photon. The fraction of longitudinal polarisation of the K*0 meson, FL, is measured to be FL = (4.4 ± 2.6 ± 1.4)%, where the first uncertainty is statistical and the second systematic. The
A
T
Re
$$ {A}_{\mathrm{T}}^{\mathrm{Re}} $$
observable, which is related to the lepton forward-backward asymmetry, is measured to be
A
T
Re
$$ {A}_{\mathrm{T}}^{\mathrm{Re}} $$
= −0.06 ± 0.08 ± 0.02. The
A
T
2
$$ {A}_{\mathrm{T}}^{(2)} $$
and
A
T
Im
$$ {A}_{\mathrm{T}}^{\mathrm{Im}} $$
transverse asymmetries, which are sensitive to the virtual photon polarisation, are found to be
A
T
2
$$ {A}_{\mathrm{T}}^{(2)} $$
= 0.11 ± 0.10 ± 0.02 and
A
T
Im
$$ {A}_{\mathrm{T}}^{\mathrm{Im}} $$
= 0.02 ± 0.10 ± 0.01. The results are consistent with Standard Model predictions and provide the world’s best constraint on the b → sγ photon polarisation.
MIT Department
Massachusetts Institute of Technology. Department of Physics
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DOI of Published Version
https://doi.org/10.1007/JHEP12(2020)081
