Search for Exclusive Z Boson Production and Observation of High Mass p anti-p --> p gamma gamma p-bar --> p ell+ ell- p-bar Events in p anti-p Collisions at s**(1/2) =1.96 TeV

We present a search for exclusive Z boson production in proton-antiproton collisions at s**(1/2) =1.96 TeV, using the CDF II detector at Fermilab. We observe no exclusive Z --> ell+ ell- candidates and place the first upper limit on the exclusive Z cross section in hadron collisions, sigma_excl(Z) < 0.96 pb at 95% confidence level. In addition, we observe eight candidate exclusive dilepton events from the quantum electrodynamic process p anti-p --> p gamma gamma pbar --> p ell+ ell- pbar, and measure the cross section for M_ell ell > 40 GeV/c2 and |eta_ell| > 40 GeV/c2 and |eta_ell| < 4 to be sigma =0.24+0.13_-0.10 pb, which is the first measurement for this mass range and is consistent with the standard model prediction.