Study of the kinematic dependences of $\Lambda_b^0$ production in $pp$ collisions and a measurement of the $\Lambda_b^0 \rightarrow \Lambda_c^+ \pi^-$ branching fraction

TL;DR

This paper measures how the production rates of Lambda_b^0 baryons depend on kinematic variables in proton-proton collisions and provides the most precise measurement to date of its decay branching fraction.

Contribution

It presents the first detailed study of Lambda_b^0 production dependences on kinematic variables and a highly precise measurement of its decay branching fraction.

Findings

Production rates depend on transverse momentum and pseudorapidity.

The branching fraction of Lambda_b^0 to Lambda_c^+ pi^- is measured as (4.30 ± uncertainties) × 10^{-3}.

This is the most precise Lambda_b^0 branching fraction measurement to date.

Abstract

The kinematic dependences of the relative production rates, $f_{\Lambda_b^0}/f_d$, of $\Lambda_b^0$ baryons and $\bar{B}^0$ mesons are measured using $\Lambda_b^0 \rightarrow \Lambda_c^+ \pi^-$ and $\bar{B}^0 \rightarrow D^+ \pi^-$ 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, $\eta$, of the beauty hadron, in the studied kinematic region $1.5 < p_T < 40$ GeV/$c$ and $2 < \eta < 5$. Using a previous LHCb measurement of $f_{\Lambda_b^0}/f_d$ in semileptonic decays, the branching fraction $\mathcal{B}(\Lambda_b^0 \rightarrow \Lambda_c^+ \pi^-) = \Big( 4.30 \pm 0.03 \,\, ^{+0.12}_{-0.11} \pm 0.26 \pm 0.21 \Big) \times 10^{-3}$ is obtained, where the first uncertainty is statistical, the second is systematic, the third is from the previous LHCb measurement of $f_{\Lambda_b^0}/f_d$ and the fourth is due to the $\bar{B}^0 \rightarrow D^+ \pi^-$ branching fraction. This is the most precise measurement of a $\Lambda_b^0$ branching fraction to date.