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 − .

Total cross sections for Σ − and π − on beryllium, carbon, polyethylene and copper as well as total cross sections for protons on beryllium and carbon have been measured in a broad momentum range around 600 GeV/c. These measurements were performed with a transmission technique adapted to the SELEX hyperon-beam experiment at Fermilab. We report on results obtained for hadron-nucleus cross sections and on results for σ tot (Σ − N) and σ tot (π − N), which were deduced from nuclear cross sections.

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We report on a high-statistics search for the Θ(1540) + resonance in Σ − -nucleus collisions at 340 GeV/c . No evidence for this resonance was found in our data sample which contains 13 millions K 0 s → π + π − decays above background. For the decay channel Θ + → K 0 s p and the kinematic range xF > 0.05 we find the production cross section to be BR(Θ + → K 0 s p) • σ0 < 1.8 µb per nucleon at 99% CL.