Improved Search for a Higgs Boson Produced in Association with Z -> l+ l- in p anti-p Collisions at s**(1/2)=1.96 TeV

We present a search for the standard model Higgs boson produced with a Z boson in 4.1 fb-1 of data collected with the CDF II detector at the Tevatron. In events consistent with the decay of the Higgs boson to a bottom-quark pair and the Z boson to electrons or muons, we set 95% credibility level upper limits on the ZH production cross section times the H --> bb-bar branching ratio. Improved analysis methods enhance signal sensitivity by 20% relative to previous searches beyond the gain due to the larger data sample. At a Higgs boson mass of 115 GeV/c2 we set a limit of 5.9 times the standard model value.