Evidence for the strangeness-changing weak decay $Ξ_b^-\toΛ_b^0π^-$

Abstract

Using a $pp$ collision data sample corresponding to an integrated luminosity of 3.0~fb$^{-1}$, collected by the LHCb detector, we present the first search for the strangeness-changing weak decay $Ξ_b^-\toΛ_b^0π^-$. No $b$ hadron decay of this type has been seen before. A signal for this decay, corresponding to a significance of 3.2 standard deviations, is reported. The relative rate is measured to be ${f_{Ξ_b^-}\over{f_{Λ_b^0}}}{\cal{B}}(Ξ_b^-\toΛ_b^0π^-) = (5.7\pm1.8^{+0.8}_{-0.9})\times10^{-4}$, where $f_{Ξ_b^-}$ and $f_{Λ_b^0}$ are the $b\toΞ_b^-$ and $b\toΛ_b^0$ fragmentation fractions, and ${\cal{B}}(Ξ_b^-\toΛ_b^0π^-)$ is the branching fraction. Assuming $f_{Ξ_b^-}/f_{Λ_b^0}$ is bounded between 0.1 and 0.3, the branching fraction ${\cal{B}}(Ξ_b^-\toΛ_b^0π^-)$ would lie in the range from $(0.57\pm0.21)\%$ to $(0.19\pm0.07)\%$.

7 pages, 2 figures, All figures and tables, along with any supplementary material and additional information, are available at https://lhcbproject.web.cern.ch/lhcbproject/Publications/LHCbProjectPublic/LHCb-PAPER-2015-047.html