A strong signal for double parton (DP) scattering is observed in a 16 pb(-1) sample of <(p)over bar p> --> gamma/pi(0) + 3 jets + X data from the CDF experiment at the Fermilab Tevatron. In DP events, two separate hard scatterings take place in a single <(p)over bar p> collision. We isolate a large sample of data (similar to 14 000 events) of which 53% are found to be DP. The process-independent parameter of double parton scattering, sigma(eff), is obtained without reference to theoretical calculations by comparing observed DP events to events with hard scatterings in separate <(p)over bar p> collisions. The result sigma(eff) = (14.5 +/- 1.7(-2.3)(+1.7)) mb represents a significant improvement over previous measurements, and is used to constrain simple models of parton spatial density. The Feynman x dependence of sigma(eff) is investigated and none is apparent. Further, no evidence is found for kinematic correlations between the two scatterings in DP events

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We report the observation of a narrow state decaying into J/psipi+pi- and produced in 220 pb(-1) of p p-bar collisions at =1.96 Tesqaure root of sV in the CDF II experiment. We observe 730+/-90 decays. The mass is measured to be 3871.3+/-0.7(stat)+/-0.4(syst) MeV/c2, with an observed width consistent with the detector resolution. This is in agreement with the recent observation by the Belle Collaboration of the X(3872) meson.

The kinematic properties of t t events are studied in the Wϩmultijet channel using data collected with the CDF detector during the 1992-1995 runs at the Fermilab Tevatron collider corresponding to an integrated luminosity of 109 pb Ϫ1 . Distributions of a variety of kinematic variables chosen to be sensitive to different aspects of t t production are compared with those expected from Monte Carlo calculations. A sample of 34 events rich in t t pairs is obtained by requiring at least one jet identified by the silicon vertex detector ͑SVX͒ as having a displaced vertex consistent with the decay of a b hadron. The data are found to be in good agreement with predictions of the leading order t t matrix element with color coherent parton shower evolution. ͓S0556-2821͑99͒04007-2͔

We have observed bottom-charm mesons via the decay mode B-c(+/-) --> J/psi l(+/-)v in 1.8 TeV p (p) over bar collisions using the CDF detector at the Fermilab Tevatron. A fit of background and signal contributions to the J/psi l mass distribution yielded 20.4(-5.5)(+6.2) events from B-c mesons. A fit to the same distribution with background alone was rejected at the level of 4.8 standard deviations. We measured the B-c(+) mass to be 6.40 +/- 0.39(stat) +/- 0.13(syst) GeV/c(2) and the B-c(+) lifetime to be 0.46(-0.16)(+0.18)(stat) +/- 0.03(syst) ps. Our measured yield (production cross section times branching ratio) for B-c(+) --> J/psi l(+)v relative to that for B+ --> J/psi K+ is 0.132(-0.037)(+0.041)(stat) +/- 0.031 (syst)(-0.020)(+0.032)(lifetime)

The Integrable Optics Test Accelerator (IOTA) is a storage ring for advanced beam physics research currently being built and commissioned at Fermilab. It will operate with protons and electrons using injectors with momenta of 70 and 150 MeV/c, respectively. The research program includes the study of nonlinear focusing integrable optical beam lattices based on special magnets and electron lenses, beam dynamics of space-charge effects and their compensation, optical stochastic cooling, and several other experiments. In this article, we present the design and main parameters of the facility, outline progress to date and provide the timeline of the construction, commissioning and research. The physical principles, design, and hardware implementation plans for the major IOTA experiments are also discussed.