A bstract Results are reported for the $$ {\mathrm{B}}_{\mathrm{s}}^0 $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>B</mml:mi> <mml:mi>s</mml:mi> <mml:mn>0</mml:mn> </mml:msubsup> </mml:math> → 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 $$ {\mathrm{B}}_{\mathrm{s}}^0 $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>B</mml:mi> <mml:mi>s</mml:mi> <mml:mn>0</mml:mn> </mml:msubsup> </mml:math> → μ + μ − is observed with a significance of 5.6 standard deviations. The branching fraction is measured to be $$ \mathrm{\mathcal{B}}\left({\mathrm{B}}_{\mathrm{s}}^0\to {\upmu}^{+}{\upmu}^{-}\right)=\left[2.9\pm 0.7\left(\exp \right)\pm 0.2\left(\mathrm{frag}\right)\right]\times {10}^{-9} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>ℬ</mml:mi> <mml:mfenced> <mml:mrow> <mml:msubsup> <mml:mi>B</mml:mi> <mml:mi>s</mml:mi> <mml:mn>0</mml:mn> </mml:msubsup> <mml:mo>→</mml:mo> <mml:msup> <mml:mi>μ</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:msup> <mml:mi>μ</mml:mi> <mml:mo>−</mml:mo> </mml:msup> </mml:mrow> </mml:mfenced> <mml:mo>=</mml:mo> <mml:mfenced> <mml:mrow> <mml:mn>2.9</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.7</mml:mn> <mml:mfenced> <mml:mo>exp</mml:mo> </mml:mfenced> <mml:mo>±</mml:mo> <mml:mn>0.2</mml:mn> <mml:mfenced> <mml:mtext>frag</mml:mtext> </mml:mfenced> </mml:mrow> </mml:mfenced> <mml:mo>×</mml:mo> <mml:msup> <mml:mn>10</mml:mn> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>9</mml:mn> </mml:mrow> </mml:msup> </mml:math> , where the first uncertainty combines the experimental statistical and systematic contributions, and the second is due to the uncertainty in the ratio of the $$ {\mathrm{B}}_{\mathrm{s}}^0 $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>B</mml:mi> <mml:mi>s</mml:mi> <mml:mn>0</mml:mn> </mml:msubsup> </mml:math> 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 $$ {\mathrm{B}}_{\mathrm{s}}^0 $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>B</mml:mi> <mml:mi>s</mml:mi> <mml:mn>0</mml:mn> </mml:msubsup> </mml:math> → μ+μ − effective lifetime is measured to be $$ {\tau}_{\upmu^{+}{\upmu}^{-}}={1.70}_{-0.44}^{+0.61} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>τ</mml:mi> <mml:mrow> <mml:msup> <mml:mi>μ</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:msup> <mml:mi>μ</mml:mi> <mml:mo>−</mml:mo> </mml:msup> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mn>1.70</mml:mn> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.44</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.61</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> ps. These results are consistent with standard model predictions.
Tópico:
Particle physics theoretical and experimental studies
