Search for new phenomena in events with two Z bosons and missing transverse momentum in p(p)over-bar collisions at root s=1.96 TeV

We present a search for new phenomena in events with two reconstructed Z bosons and large missing transverse momentum, sensitive to processes p (p) over bar -> X2X2 -> ZZX(1)X(1), where X-2 is an unstable particle decaying as X-2 -> ZX(1) and X-1 is undetected. The particles X-1 and X-2 may be, among other possibilities, fourth-generation neutrinos or supersymmetric particles. We study the final state in which one Z boson decays to two charged leptons and the second decays hadronically. In data corresponding to an integrated luminosity of 4.2 fb(-1) from proton-antiproton collisions recorded by the CDF II detector at the Tevatron, with center-of-mass energy of 1.96 TeV, we find agreement between data and standard-model backgrounds. We calculate 95% confidence level upper limits on the cross section of the process p (p) over bar -> X2X2 -> ZZX(1)X(1) ranging from 50 fb to 1 pb, depending on the masses of X-1 and X-2.