Abstract
Results are reported for the
$$ {\mathrm{B}}_{\mathrm{s}}^0 $$
B
s
0
→ μ+μ
−
branching fraction and effective lifetime and from a search for the decay B0
→ μ+μ
−
. The analysis uses a data sample of proton-proton collisions accumulated by the CMS experiment in 2011, 2012, and 2016, with center-of-mass energies (integrated luminosities) of 7 TeV (5 fb
−1), 8 TeV (20 fb
−1), and 13 TeV (36 fb
−1). The branching fractions are determined by measuring event yields relative to B+
→ J/ψK+ decays (with J/ψ → μ+μ
−
), which results in the reduction of many of the systematic uncertainties. The decay
$$ {\mathrm{B}}_{\mathrm{s}}^0 $$
B
s
0
→ μ+μ
−
is observed with a significance of 5.6 standard deviations. The branching fraction is measured to be
$$ \mathrm{\mathcal{B}}\left({\mathrm{B}}_{\mathrm{s}}^0\to {\upmu}^{+}{\upmu}^{-}\right)=\left[2.9\pm 0.7\left(\exp \right)\pm 0.2\left(\mathrm{frag}\right)\right]\times {10}^{-9} $$
ℬ
B
s
0
→
μ
+
μ
−
=
2.9
±
0.7
exp
±
0.2
frag
×
10
−
9
, where the first uncertainty combines the experimental statistical and systematic contributions, and the second is due to the uncertainty in the ratio of the
$$ {\mathrm{B}}_{\mathrm{s}}^0 $$
B
s
0
and the B+ fragmentation functions. No significant excess is observed for the decay B0
→ μ+μ
−
, and an upper limit of ℬ(B0 → μ+μ−) < 3.6 × 10−10 is obtained at 95% confidence level. The
$$ {\mathrm{B}}_{\mathrm{s}}^0 $$
B
s
0
→ μ+μ− effective lifetime is measured to be
$$ {\tau}_{\upmu^{+}{\upmu}^{-}}={1.70}_{-0.44}^{+0.61} $$
τ
μ
+
μ
−
=
1.70
−
0.44
+
0.61
ps. These results are consistent with standard model predictions.
