Measurement of the Lambda0(b) decay form-factor

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.

Note:

24 pages, 7 figures Report-no: CERN-EP-2003-056 Journal-ref: Phys. Lett. B585 (2004) 63-84

electron positron: colliding beams
electron positron: annihilation
Z0: electroproduction
Z0: hadronic decay
bottom: pair production
Lambda/b0: semileptonic decay
decay: form factor
form factor: slope
Lambda/c+: hadronic decay
HQET model

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