Constraints on the photon polarisation in $b\to s\gamma$ transitions using $B_s^0\to \varphi e^{+}{e}^{-}$ decays

Abstract

An angular analysis of the $B_s^0\to \varphi e^{+}{e}^{-}$ decay is performed using the proton-proton collision dataset collected between 2011 and 2018 by the LHCb experiment, corresponding to an integrated luminosity of $9{\mathrm{fb}}^{-1}$ at centre-of-mass energies of 7, 8 and $13\mathrm{TeV}$. The analysis is performed in the very low dielectron invariant mass-squared region between $0.0009$ and $0.2615{\mathrm{GeV}}^2/c^4$. The longitudinal polarisation fraction of the $\varphi$ meson is measured to be less than $11.5\%$ at $90\%$ confidence level. The $A_{\mathrm{T}}^{\mathcal{R}eCP}$ observable, which is related to the lepton forward-backward asymmetry, is measured to be $0.116\pm 0.155\pm 0.006$, where the first uncertainty is statistical and the second systematic. The transverse asymmetries, $A_{\mathrm{T}}^{(2)}$ and $A_{\mathrm{T}}^{\mathcal{I}mCP}$, which are sensitive to the virtual photon polarisation, are found to be $-0.045\pm 0.235\pm 0.014$ and $0.002\pm 0.247\pm 0.016$, respectively. The results are consistent with Standard Model predictions.

arXiv comment22 pages, 5 figures. All figures and tables, along with any supplementary material and additional information, are available at https://lbfence.cern.ch/alcm/public/analysis/full-details/3433/ (LHCb public pages)

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