Prospects for the $\cal{B}$$(B^0_{(s)} \to \mu^+ \mu^-)$ measurements with the ATLAS detector in the Run 2 and HL-LHC data campaigns

This note estimates the ATLAS detector performance in measuring the branching fractions of the very rare decays $B^0_{s} \to \mu^+ \mu^-$ and $B^0 \to \mu^+ \mu^-$ using data collected during the whole LHC Run 2 campaign and during the whole HL-LHC campaign. The estimation is obtained by means of pseudo-MC experiments based on the measurement of the two processes performed by the ATLAS experiment using the full integrated luminosity collected during the Run 1 data taking campaign.