Strong constraints on the b → sγ photon polarisation from B0 → K*0e+e− decays

LHCb Collaboration

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An angular analysis of the B 0 → 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 (q 2) interval between 0.0008 and 0.257 GeV 2, where the rate is dominated by the B 0 → K *0γ transition with a virtual photon. The fraction of longitudinal polarisation of the K *0 meson, F L, is measured to be F L = (4.4 ± 2.6 ± 1.4)%, where the first uncertainty is statistical and the second systematic. The ATRe observable, which is related to the lepton forward-backward asymmetry, is measured to be ATRe = −0.06 ± 0.08 ± 0.02. The AT(2) and ATIm transverse asymmetries, which are sensitive to the virtual photon polarisation, are found to be AT(2) = 0.11 ± 0.10 ± 0.02 and ATIm = 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. [Figure not available: see fulltext.]

Original languageEnglish
Article number81
JournalJournal of High Energy Physics
Issue number12
Publication statusPublished - 11-Dec-2020


  • Polarization
  • B physics
  • Hadron-Hadron scattering (experiments)
  • Rare decay
  • Flavour Changing Neutral Currents

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