Search for ZH to llbb production in 4.2 fb^-1 of ppbar collisions at sqrt(s) = 1.96 TeV

We present a search for the standard model Higgs boson produced in association with a Z boson in 4.2 fb^-1 of p-pbar collisions, collected with the D0 detector at the Fermilab Tevatron at sqrt(s) = 1.96 TeV. Selected events contain one reconstructed Z to llbb candidate and at least two jets, including at least one b-tagged jet. In the absence of an excess over the background expected from other standard model processes, limits on the ZH cross section multiplied by the branching ratios are set. The limit at M_H = 115 GeV is a factor of 5.9 larger than the standard model prediction.