Abstract
The ratio of branching fractions $R_{K/\pi} \equiv \mathcal{B}(B_{c}^{+} \to J/\psi K^{+})/\mathcal{B}(B_{c}^{+} \to J/\psi\pi^{+})$ is measured with $pp$ collision data collected by the LHCb experiment at centre-of-mass energies of 7 TeV and 8 TeV, corresponding to an integrated luminosity of 3${\mbox{fb}^{-1}}$. It is found to be $ R_{K/\pi} = 0.079\pm0.007\pm0.003$, where the first uncertainty is statistical and the second is systematic. This measurement is consistent with the previous LHCb result, while the uncertainties are significantly reduced.
Highlights
The LHCb detector [17, 18] is a single-arm forward spectrometer covering the pseudorapidity range 2 < η < 5, designed for the study of particles containing b or c quarks
The tracking system provides a measurement of charged particle momentum, p, with a relative uncertainty that varies from 0.5% at low momentum to 1.0% at 200 GeV/c
Candidate Bc+ → J/ψ K+ and Bc+ → J/ψ π+ decays are formed from J/ψ h+ combinations that originate from a common vertex
Summary
The LHCb detector [17, 18] is a single-arm forward spectrometer covering the pseudorapidity range 2 < η < 5, designed for the study of particles containing b or c quarks. The subsequent software trigger is composed of two stages, the first of which performs a partial reconstruction and requires either a pair of well-reconstructed, oppositely charged muons having an invariant mass above 2.7 GeV/c2, or a single well-reconstructed muon. The second stage of the software trigger applies a full event reconstruction, and requires at least one of the following two conditions to be fulfilled: either two opposite-sign muons must form a good-quality vertex that is well separated from all of the primary vertices and must have an invariant mass within 120 MeV/c2 of the known J/ψ mass [19], or an algorithm using a boosted decision tree must identify a twoor three-track vertex that is well separated from all of the primary vertices and includes a muon among the constituent tracks. The interaction of the generated particles with the detector, and its response, are implemented using the Geant toolkit [26, 27] as described in ref. [28]
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