Study of the kinematic dependences of Λ ⁰ _b production in pp collisions and a measurement of the Λ ⁰ _b  → Λ ⁺ _c π ⁻ branching fraction

Abstract

The kinematic dependences of the relative production rates, ${f}_{\varLambda_b^0}/{f}_d$, of Λ ⁰ _b baryons and B ⁰ mesons are measured using Λ ⁰ _b  → Λ ⁺ _c π ⁻ and ${\overline{B}}^0\ \to {D}^{+}{\pi}^{-}$ decays. The measurements use proton-proton collision data, corresponding to an integrated luminosity of 1 fb⁻¹ at a centre-of-mass energy of 7 TeV, recorded in the forward region with the LHCb experiment. The relative production rates are observed to depend on the transverse momentum, p _T, and pseudorapidity, η, of the beauty hadron, in the studied kinematic region 1.5 < p _T < 40 GeV/c and 2 < η < 5. Using a previous LHCb measurement of ${f}_{\varLambda_b^0}/{f}_d$ in semileptonic decays, the branching fraction ℬ(Λ ⁰ _b  → Λ ⁺ _c π ⁻) = (4.30 ± 0.03 ^+ 0.12_− 0.11  ± 0.26 ± 0.21) × 10^− 3 is obtained, where the first uncertainty is statistical, the second is systematic, the third is from the previous LHCb measurement of ${f}_{\varLambda_b^0}/{f}_d$ and the fourth is due to the b ${\overline{B}}^0\ \to {D}^{+}{\pi}^{-}$ branching fraction. This is the most precise measurement of a Λ ⁰ _b branching fraction to date.