We observe a signal for the doubly charmed baryon Xi(+)(cc) in the charged decay mode Xi(+)(cc)-->Lambda(+)(c)K-pi(+) in data from SELEX, the charm hadroproduction experiment at Fermilab. We observe an excess of 15.9 events over an expected background of 6.1+/-0.5 events, a statistical significance of 6.3sigma. The observed mass of this state is 3519+/-1 MeV/c(2). The Gaussian mass width of this state is 3 MeV/c(2), consistent with resolution; its lifetime is less than 33 fs at 90% confidence.

We observe a signal for the doubly charmed baryon Ξ + cc in the decay mode Ξ + cc → pD + K − to complement the previous reported decay Ξ + cc → Λ + c K − π + in data from SELEX, the charm hadroproduction experiment at Fermilab. In this new decay mode we observe an excess of 5.62 events over a combinatoric background estimated by event mixing to be 1.38 ± 0.13 events. The mixed background has Gaussian statistics, giving a signal significance of 4.8σ. The Poisson probability that a background fluctuation can produce the apparent signal is less than 6.4 × 10 −4. The observed mass of this state is 3518 ± 3 MeV/c 2 , consistent with the published result. Averaging the two results gives a mass of 3518.7 ± 1.7 MeV/c 2. The observation of this new weak decay mode confirms the previous SELEX suggestion that this state is a double charm baryon. The relative branching ratio for these two modes is 0.36 ± 0.21.

The Σ − mean squared charge radius has been measured in the space-like Q 2 range 0.035-0.105 GeV 2 /c 2 by elastic scattering of a Σ − beam off atomic electrons. The measurement was performed with the SELEX (E781) spectrometer using the Fermilab hyperon beam at a mean energy of 610 GeV/c. We obtain r 2 ch Σ − = (0.61 ± 0.12 (stat.) ± 0.09 (syst.)) fm 2 . The proton and π − charge radii were measured as well and are consistent with results of other experiments. Our result agrees with the recently measured strong interaction radius of the Σ − .

A dilute bose gas in a quasi two-dimensional harmonic trap and interacting with a repulsive two-body zero-range potential of fixed coupling constant is considered. Using the Thomas-Fermi method, it is shown to remain in the same uncondensed phase as the temperature is lowered. Its density profile and energy are identical to that of an ideal gas obeying the fractional exclusion statistics of Haldane.

The distorted-wave Born approximation is applied to near-threshold ionization of atomic hydrogen and helium. A model is used which includes the post-collision interaction, electron exchange, electron capture and shake-off. The results of this model are in reasonably good agreement with experimental data. The relative importance of different types of ionization mechanisms is investigated.