Analysis of Neutral B-Meson Decays into Two Muons

Branching fraction and effective lifetime measurements of the rare decay B 0 s -and searches for the decays B 0 -and B 0 s - are reported using proton-proton collision data collected with the LHCb detector at center-of-mass energies of 7, 8, and 13 TeV, corresponding to a luminosity of 9 fb -1 . The branching fraction BB 0 s - 3.09 0.460.15 -0.43-0.11 10 -9 and the effective lifetime B 0 s - 2.07 AE 0.29 AE 0.03 ps are measured, where the first uncertainty is statistical and the second systematic. No significant signal for B 0 -and B 0 s - decays is found and upper limits BB 0 - < 2.6 10 -10 and BB 0 s - < 2.0 10 -9 at the 95% C.L. are determined, where the latter is limited to the range m > 4.9 GeV=c 2 . The results are in agreement with the standard model expectations.