Observation is reported for a structure near the J/[psi][phi] threshold in B+ → J/[psi][phi]K+ decays produced in {bar p}p collisions at √s = 1.96 TeV with a statistical significance of beyond 5 standard deviations. There are 19 ± 6 events observed for this structure at a mass of 4143.4{sub -3.0}{sup +2.9}(stat) ± 0.6(syst) MeV/c2 and a width of 15.3{sub -6.1}{sup +10.4}(stat) ± 2.5(syst) MeV/c2, which are consistent with the previous measurements reported as evidence of the Y(4140).

Evidence is reported for a narrow structure near the J/[psi][phi] threshold in exclusive B+ → J/[psi][phi]K+ decays produced in {bar p}p collisions at √s = 1.96 TeV. A signal of 14 ± 5 events, with statistical significance in excess of 3.8 standard deviations, is observed in a data sample corresponding to an integrated luminosity of 2.7 fb−1, collected by the CDF II detector. The mass and natural width of the structure are measured to be 4143.0 ± 2.9(stat) ± 1.2(syst) MeV/c2 and 11.7{sub -5.0}{sup +8.3}(stat) ± 3.7(syst) MeV/c2.

We observe a narrow enhancement near 2m[sub p] in the invariant mass spectrum of p[bar p] pairs from radiative J/[psi][yields][gamma]p[bar p] decays. No similar structure is seen in J/[psi][yields][pi][sup 0] p[bar p] decays. The results are based on an analysis of a 58 million event sample of J/[psi] decays accumulated with the BESII detector at the Beijing electron-positron collider. The enhancement can be fit with either an S- or P-wave Breit Wigner resonance function. In the case of the S-wave fit, the peak mass is below 2m[sup p] at M= 1859[sub -10][sup+3] (stat)[sub -25][sup+5] (sys) MeV/c[sup 2] and the total width is[Lambda]

This thesis reports on the final measurement of the flavor-mixing phase in decays of strange-bottom mesons (B_s) into J/psi and phi mesons performed in high-energy proton-antiproton collisions recorded by the Collider Experiment at Fermilab. Interference occurs between direct decays and decays following virtual particle-antiparticle transitions (B_s-antiB_s). The phase difference between transition amplitudes (“mixing phase”) is observable and extremely sensitive to contributions from non-standard-model particles or interactions that may be very hard to detect otherwise – a fact that makes the precise measurement of the B_s mixing phase one of the most important goals of particle physics. The results presented include a precise determination of the mixing phase and a suite of other important supplementary results. All measurements are among the most precise available from a single experiment and provide significantly improved constraints on the phenomenology of new particles and interactions.

The near-threshold enhancement in the p p-bar invariant mass spectrum of the reaction J/Psi --> gamma p p-bar, observed in an experiment by the BES Collaboration, is analysed. It is shown, within the Watson-Migdal approach to final state interactions, that the mass dependence of the p p-bar spectrum close to the threshold can be reproduced by the S-wave p p-bar interaction of the Jülich N N-bar model in the isospin I=1 state. Difficulties in the consistent interpretation of the p invariant mass spectrum of the reaction J/Psi --> pi^0 p p-bar, where there are no obvious signs for a final state interaction, are discussed.

The authors measure the dipion mass spectrum in X(3872) → J/???− decays using 360 pb−1 of {bar p}p collisions at √s = 1.96 TeV collected with the CDF II detector. The spectrum is fit with predictions for odd C-parity (3S1, 1P1, and 3D{sub J}) charmonia decaying to J/??+?−, as well as event C-parity states in which the pions are from?° decay. The latter case also encompasses exotic interpretations, such as a D°{bar D}*° molecule. Only the 3S1 and J/?? hypotheses are compatible with the data. Since 3S1 is untenable on other grounds, decay via J/?? is favored, which implies C = +1 for the X(3872). Models for different J/?-? angular momenta L are considered. Flexibility in the models, especially the introduction of?-? interference, enable good descriptions of the data for both L = 0 and 1.

We present an update of the study of the Y(4260) resonance, produced in the process ee− →?{sub ISR}?+?− J/? using initial-state radiation events at the PEP-II e+e− storage rings. This study is based on 454 fb−1 of data recorded with the BABAR detector at a center-of-mass energy in the?(4S) resonance region. From a fit with a single non-relativistic Breit-Wigner shape we obtain updated parameters for the Y(4260) resonance which are m{sub Y} = 4252 ± 6−3{sup +2} MeV/c2 and?{sub Y} = 105 ± 18−6{sup +4} MeV/c2; we also measure?(?+?− J/?)?{sub e{sup +}e−} = (7.5 ± 0.9 ± 0.8) eV. We cannot confirm the recent BELLE observation of a broad structure around 4.05GeV/c2 in this decay mode.