A. Liberman

Use of a Low Energy Proton Accelerator for Calibrating a Large NaI(Tl) Array in a High Energy Physics Experiment

We report the use of a 500 keV Van de Graaff proton accelerator to produce ¿-rays in the range 4 - 18 MeV via nuclear reactions for the purpose of calibrating a large NaI(Tl) crystal array. Data analysis indicates an energy calibration to ~ 1% over this range.

Compact Multiwire Proportional Chambers and Electronics for the Crystal Ball Detector

A double gap of cylindrical proportional chambers has been designed and built for use with a large solid angle, modular NaI(Tl) array (The Crystal Ball). The chambers are constructed of three coaxial foam-epoxy shells, covered with an aluminum-mylar laminate. One of the high voltage cathodes in each chamber has been photo-etched to produce a pattern of stripes and precise position measurements of tracks passing transverse to the chamber axis are found by pulse height analyzing the shaped and amplified induced strip signals. Performance of the chamber using both the strip signals and the sense wire readout is presented. The design of both the signal handling electronics and the digital portions of the systems is discussed.

Recent results from the crystal ball detector at SPEAR

Evidence for an ηc candicate with a mass of 2980±15 MeV from the ψ′ inclusive γ spectrum is presented. The corresponding region in the J/ψ inclusive γ spectrum is then studied and shown to be consistent with a broad Breit‐Wigner enhancement superimposed upon a smooth background. Results from a detailed study of the two exclusive decay modes ψ′→γγ ψ→γγ e+e− and ψ′→γγ ψ→γγμ+μ− are also given. These consist of measurements of the cascade branching ratios BR(ψ′→γχ→γγψ) for χ(3.55) and χ(3.51) and upper limits on this branching ratio for χ(3.41), χ(3.45), and χ(3.59). Finally, we give branching ratios for the two decays ψ′→ηψ and ψ′→π °ψ.