Constraints on the photon polarisation in b → sγ transitions using Bs0→ ϕe⁺e⁻ decays

A bstract An angular analysis of the $$ {B}_s^0 $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>B</mml:mi> <mml:mi>s</mml:mi> <mml:mn>0</mml:mn> </mml:msubsup> </mml:math> → ϕe + e − decay is performed using the proton-proton collision dataset collected between 2011 and 2018 by the LHCb experiment, corresponding to an integrated luminosity of 9 fb − 1 at centre-of-mass energies of 7, 8 and 13 TeV. The analysis is performed in the very low dielectron invariant mass-squared region between 0 . 0009 and 0 . 2615 GeV 2 /c 4 . The longitudinal polarisation fraction of the ϕ meson is measured to be less than 11.5% at 90% confidence level. The $$ {A}_{\textrm{T}}^{\mathcal{R} eCP} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>A</mml:mi> <mml:mi>T</mml:mi> <mml:mrow> <mml:mi>R</mml:mi> <mml:mi>eCP</mml:mi> </mml:mrow> </mml:msubsup> </mml:math> observable, which is related to the lepton forward-backward asymmetry, is measured to be 0 . 116 ± 0 . 155 ± 0 . 006, where the first uncertainty is statistical and the second systematic. The transverse asymmetries, $$ {A}_{\textrm{T}}^{(2)} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>A</mml:mi> <mml:mi>T</mml:mi> <mml:mfenced> <mml:mn>2</mml:mn> </mml:mfenced> </mml:msubsup> </mml:math> and $$ {A}_{\textrm{T}}^{\mathcal{I} mCP} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>A</mml:mi> <mml:mi>T</mml:mi> <mml:mrow> <mml:mi>I</mml:mi> <mml:mi>mCP</mml:mi> </mml:mrow> </mml:msubsup> </mml:math> , which are sensitive to the virtual photon polarisation, are found to be − 0 . 045 ± 0 . 235 ± 0 . 014 and 0 . 002 ± 0 . 247 ± 0 . 016, respectively. The results are consistent with Standard Model predictions.