Measurement of the decay B0s→Øμ+μ- at LHCb

• Main Author: Schaack, Paul Nicholas
• Other Authors: Golutvin, Andrey
• Published: Imperial College London 2012
• Subjects: 539.72
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.560701

The measurements of two branching fraction ratios are reported in this thesis. The first one is a measurement of the ratio of the branching fractions for the decays B0s→ψ'Ø and B0s→J/ψØ. It is based on approximately 36 pb⁻¹ of data collected by the LHCb detector at √s = 7TeV during 2010. The result is 0.68 ± 0.10(stat) ± 0.09(syst) ± 0.07(B), which is compatible with previous measurements from experiments at the Tevatron. The second measurement is the ratio of the branching fractions for the decays B0s→Øμ⁺μ⁻ and B0s→J/ψØ as a function of the dimuon invariant mass. It is based on 1 fb⁻¹ of data collected by the LHCb detector at √s= 7TeV during 2011. The ratio of branching fractions is measured to be (0.558 ± 0.070(stat) ± 0.043(syst) ± 0.006(B)) x 10⁻³. Using the measured branching fraction of the decay J/ψ→μ⁺μ⁻ gives a branching fraction of B(B0s→Øμ⁺μ⁻) = (0.78 ± 0.10(stat) ± 0.06(syst) ± 0.28(B)) x 10⁻⁶. This is the most precise measurement of B(B0s→Øμ⁺μ⁻) and is in agreement with the Standard Model expectation.