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

Abstract

An angular analysis of the $B^0\to K^{\ast 0}{e}^{+}{e}^{-}$ decay is performed using a data sample, corresponding to an integrated luminosity of 3.0 ${\mbox{fb}^{-1}}$, 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 ($q^2$) interval between 0.002 and 1.120$\mathrm{Ge}{\mathrm{V}}^2/c^4$. The angular observables $F_{\mathrm{L}}$ and $A_{\mathrm{T}}^{\mathrm{Re}}$ which are related to the $K^{\ast 0}$ polarisation and to the lepton forward-backward asymmetry, are measured to be $F_{\mathrm{L}}=0.16\pm 0.06\pm 0.03$ 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 $A_{\mathrm{T}}^{(2)}$ and $A_{\mathrm{T}}^{\mathrm{Im}}$ which are sensitive to the photon polarisation in this $q^2$ 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.

18 pages, 5 figures