Measurement of b hadron lifetimes in pp collisions at $\sqrt{s} =$ 8 TeV

Abstract

Measurements are presented of the lifetimes of the B$^0$, B$^0_\mathrm{s}$, $Λ^0_\mathrm{b}$, and B$_\mathrm{c}^+$ hadrons using the decay channels B$^0\to$ J/$ψ$K*(892)$^0$, B$^0\to$J/$ψ$K$^0_\mathrm{S}$, B$^0_\mathrm{s}\to$J/$ψπ^+π^-$, B$^0_\mathrm{s}\to$J/$ψϕ$(1020), $Λ^0_\mathrm{b}\to$J/$ψΛ^0$, and B$_\mathrm{c}\to$J/$ψπ^+$. The data sample, corresponding to an integrated luminosity of 19.7 fb$^{-1}$, was collected by the CMS detector at the LHC in proton-proton collisions at $\sqrt{s}=$ 8 TeV. The B$^0$ lifetime is measured to be 453.0 $\pm$ 1.6 (stat) $\pm$ 1.8 (syst) $μ$m in J/$ψ$K*(892)$^0$ and 457.8 $\pm$ 2.7 (stat) $\pm$ 2.8 (syst) $μ$m in J/$ψ$K$^0_\mathrm{S}$, which results in a combined measurement of $cτ_{\mathrm{B}^0} =$ 454.1 $\pm$ 1.4 (stat) $\pm$ 1.7 (syst) $μ$m. The effective lifetime of the B$^0_\mathrm{s}$ meson is measured in two decay modes, with contributions from different amounts of the heavy and light eigenstates. This results in two different measured lifetimes: $cτ_{\mathrm{B}^0_\mathrm{s} \to \mathrm{J}/ψπ^+π^-} =$ 502.7 $\pm$ 10.2 (stat) $\pm$ 3.4 (syst) $μ$m and $cτ_{\mathrm{B}^0_\mathrm{s} \to \mathrm{J}/ψϕ(1020)} =$ 443.9 $\pm$ 2.0 (stat) $\pm$ 1.5 (syst) $μ$m. The $Λ^0_\mathrm{b}$ lifetime is found to be 443.9 $\pm$ 8.2 (stat) $\pm$ 2.8 (syst) $μ$m. The precision from each of these channels is as good as or better than previous measurements. The B$_\mathrm{c}^+$ lifetime, measured with respect to the B$^+$ to reduce the systematic uncertainty, is 162.3 $\pm$ 7.8 (stat) $\pm$ 4.2 (syst) $\pm$ 0.1 $(τ_{\mathrm{B}^+})$ $μ$m. All results are in agreement with current world-average values.