Measurement of the Λb 0 decay form factor

2004 
The form factor of Λb 0 baryons is estimated using 3.46×106 hadronic Z decays collected by the DELPHI experiment between 1992 and 1995. Charmed Λc + baryons fully reconstructed in the pK-π+, pK S 0, and Λπ+π+π - modes, are associated to a lepton with opposite charge in order to select Λb 0→Λc +l-νl 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 ρ2=2.03±0.46(stat) -1.00 +0.72(syst). The exclusive semileptonic branching fraction Br(Λb 0→Λc +l-νl) can be derived from ρ2 and is found to be (5.0-0.8 +1.1(stat)-1.2 +1.6(syst))%. Limits on other branching fractions are also obtained. © 2004 Published by Elsevier B.V.
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