The ratio between the branching fractions of the $B^0\rightarrow \rho(770)^{ 0}\gamma$ and $B^{ 0}\rightarrow K^{ *}(892)^{ 0}\gamma$ decays is measured with proton-proton collision data collected by the LHCb experiment at centre-of-mass energies of 7, 8, and 13 TeV, corresponding to an integrated luminosity of 9 fb${ }^{ -1}$. The measured value is \begin{ equation*} \frac{ { { \cal B}}(B^0\rightarrow \rho(770)^{ 0}\gamma)}{ { { \cal B}}(B^0\rightarrow K^{ *}(892)^{ 0}\gamma)}=0.0189\pm 0.0007\pm 0.0005, \end{ equation*} where the first uncertainty is statistical and the second systematic. The branching fraction for $B^0\rightarrow \rho(770)^{ 0}\gamma$ decays is hence obtained as \begin{ equation*} { \cal{ B}}(B^0\rightarrow \rho(770)^{ 0}\gamma) =(7.9\pm 0.3\pm 0.2\pm 0.2) \times 10^{ -7}, \end{ equation*} where the last uncertainty is due to the branching fraction of the normalisation mode. This result assumes that both the $\rho(770)^0$ and $K^{ *}(892)^0$ decays saturate the dihadron mass spectra considered in the analysis. It is consistent with the current world-average value and by far the most precise measurement to date.
Categories: hep-ex