Observation of diffractive J/psi production at the Fermilab Tevatron

We report the first observation of diffractive J/psi(→ mu (+)mu (-)) production in [(p)power bar] collisions at roots = 1.8 TeV. Diffractive events are identified by their rapidity gap signature. In a sample of events with two muons of transverse momentum p(T)(mu) gt 2 GeV/c within the pseudorapidity region \ eta \ lt 1.0, the ratio of diffractive to total J/[psi] production rates is found to be R-J/psi = [1.45 +/- 0.25]%. ne ratio R-J/psi(X) is presented as a function of x-Bjorken. By combining it with our previously measured corresponding ratio R-jj(x) for diffractive dijet production, we extract a value of 0.59 +/- 0.15 for the gluon fraction of the diffractive structure function of the proton

Searches for new physics in events with a photon and b-quark jet at CDF

We have searched for evidence of physics beyond the standard model in events that include an energetic photon and an energetic b-quark jet, produced in 85 pb(-1) of (p) over barp collisions at 1.8 TeV at the Tevatron Collider at Fermilab. This signature, containing at least one gauge boson and a third-generation quark, could arise in the production and decay of a pair of new particles, such as those predicted by supersymmetry, leading to a production rate exceeding standard model predictions. We also search these events for anomalous production of missing transverse energy, additional jets and leptons (e, mu and tau), and additional b quarks. We find no evidence for any anomalous production of gammab or gammab + X events, We present limits on two supersymmetric models: a model where the photon is produced in the decay (χ) over tilde (0)(2)→gamma(χ) over tilde (0)(1), and a model where the photon is produced in the neutralino decay into the gravitino LSP, (χ) over tilde (0)(1)→gamma(G) over tilde. We also present our limits in a model-independent form and test methods of applying model-independent limits

Search for the supersymmetric partner of the top quark in pp\u304 collisions at 1as=1.8 TeV

We report on a search for the supersymmetric partner of the top quark (top squark) produced in tt\u304 events using 110 pb-1 of pp\u304 collisions at 1as = 1.8 TeV recorded with the Collider Detector at Fermilab. In the case of a light top squark, the decay of the top quark into a top squark plus the lightest supersymmetric particle (LSP) could have a significant branching ratio. The observed events are consistent with standard model tt\u304 production and decay. Hence, we set limits on the branching ratio of the top quark decaying into a top squark plus LSP, excluding branching ratios above 45% for a LSP mass up to 40 GeV/c2