Measurement of the Lambda_b^0 Decay Form Factor

TL;DR

This paper measures the Lambda_b^0 baryon decay form factor using data from the DELPHI experiment, providing insights into its semileptonic decay properties and form factor slope within the framework of HQET.

Contribution

It presents the first measurement of the Lambda_b^0 decay form factor slope using a large dataset and a combined likelihood fit, applying Heavy Quark Effective Theory.

Findings

Form factor slope rho-hat^2 = 2.03 +/- 0.46 (stat) +0.72/-1.00 (syst)

Branching fraction Br(Lambda_b^0 -> Lambda_c^+ l^- anti-nu_l) = (5.0^{+1.1}_{-0.8} (stat) +1.6/-1.2 (syst))%

Limits on other branching fractions obtained

Abstract

The form factor of Lambda_b^0 baryons is estimated using 3.46 10^6 hadronic Z decays collected by the DELPHI experiment between 1992 and 1995. Charmed Lambda_c^+ baryons fully reconstructed in the pK-pi+, pK0_S, and Lambda pi+pi+pi- modes, are associated to a lepton with opposite charge in order to select Lambda_b^0 -> Lambda_c^+ l^- anti-nu_l decays. From a combined likelihood and event rate fit to the distribution of the Isgur-Wise variable w, and using the Heavy Quark Effective Theory (HQET), the slope of the b-baryon form factor is measured to be: rho-hat^2 = 2.03 +/- 0.46 (stat) ^{+0.72}_{-1.00} (syst). The exclusive semileptonic branching fraction Br(Lambda_b^0 -> Lambda_c^+ l^- anti-nu_l) can be derived from rho-hat^2 and is found to be (5.0^{+1.1}_{-0.8} (stat) ^{+1.6}_{-1.2} (syst))%. Limits on other branching fractions are also obtained.