Measurement of properties of $$ {\mathrm{B}}_{\mathrm{s}}^0 $$→ μ+μ− decays and search for B0→ μ+μ− with the CMS experiment

Abstract

Results are reported for the B 0 s → µ + µ − branching fraction and effective lifetime and from a search for the decay B 0 → 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 B 0 s → µ + µ − is observed with a significance of 5.6 standard deviations. The branching fraction is measured to be B(B 0 s → 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 B 0 s and the B + fragmentation functions. No significant excess is observed for the decay B 0 → µ + µ − , and an upper limit of B(B 0 → µ + µ −) < 3.6 × 10 −10 is obtained at 95% confidence level. The B 0 s → µ + µ − effective lifetime is measured to be τ µ + µ − = 1.70 +0.61 −0.44 ps. These results are consistent with standard model predictions.

The flavor of UV physics

“…Flavor observables. The likelihood for the B s → µ + µ − branching ratio comprises measurements by the ATLAS [88], CMS [89] and LHCb collaborations [90]. Each of the three measurements arises from a combined analyses of the branching fractions of B s → µ + µ − and B d → µ + µ − decays, the latter being irrelevant to our analysis.…”

Low-energy phenomenology of scalar leptoquarks at one-loop accuracy

“…The relevant observables for these operators are the LFU ratios R K [12,14,129] and R K * [13,15], the branching ratio of B s → µ + µ − [19,20,130], the angular observable P 5 in B → K * µ + µ − [21], and branching ratios in other b → sµµ transitions [18,[131][132][133]. In our analysis, we use the results from the global fit of b → s observables done in [66].…”

Probing New Physics in b → d transitions

“…3 Impact on the B 0 → µ + µ − decay There are several experimental analyses of the B 0 → µ + µ − decay performed by the ATLAS, CMS and LHCb collaborations [50][51][52][53][54][55]. No significant evidence of B 0 → µ + µ − decay was found so far, and only upper limits are set up.…”