Abstract : A search is performed for heavy metastable particles that decay into jet pairs with a macroscopic lifetime (cτ˜1cm) in pp¯ collisions at s=1.96TeV using data from the CDF II detector at Fermilab corresponding to an integrated luminosity of 3.2fb-1. To estimate the standard model background, a data-driven approach is used. Probability-density functions are constructed to model secondary vertices from known processes. No statistically significant excess is observed above the background. Limits on the production cross section in a hidden valley benchmark phenomenology are set for various Higgs boson masses as well as metastable particle masses and lifetimes.