Angular analysis of the $B^0 \rightarrow K^{*0} e^+ e^-$ decay in the low-$q^2$ region

Abstract: An angular analysis of the $$B⁰ \rightarrow K^{*0} e⁺ e<sup>-$$ decay is performed using a data sample, corresponding to an integrated luminosity of 3.0 ${\mbox{fb}<sup>{-1}}$, collected by the LHCb experiment in $pp$ collisions at centre-of-mass energies of 7 and 8 TeV during 2011 and 2012. For the first time several observables are measured in the dielectron mass squared ($q<sup>2$) interval between 0.002 and 1.120${\mathrm{\,Ge\kern -0.1em V<sup>2!/}c<sup>4}$. The angular observables $F_{\mathrm{L}}$ and $A_{\mathrm{T}}<sup>{\mathrm{Re}}$ which are related to the $K<sup>{*0}$ polarisation and to the lepton forward-backward asymmetry, are measured to be $F_{\mathrm{L}}= 0.16 \pm 0.06 \pm0.03$ and $$A_{\mathrm{T}}^{{\mathrm{Re}}} = 0.10 \pm 0.18 \pm 0.05$$, where the first uncertainty is statistical and the second systematic. The angular observables $A_{\mathrm{T}}<sup>{(2)}$ and $A_{\mathrm{T}}<sup>{\mathrm{Im}}$ which are sensitive to the photon polarisation in this $q<sup>2$ range, are found to be $$A_{\mathrm{T}}^{(2)} = -0.23 \pm 0.23 \pm 0.05$$ and $$A_{\mathrm{T}}^{{\mathrm{Im}}} =0.14 \pm 0.22 \pm 0.05$$. The results are consistent with Standard Model predictions.