Search Results (5 total)

A new method for the measurement of loss factor for an rf cavity is presented. The method consists of measuring the above quantity by means of the detection of both the rf voltage induced by an electron bunch in the device under test and the bunch charge. The device to be investigated is a copper reentrant T-shaped cavity. The experimental results and their comparison with analytical and numerical results are presented.

An experimental investigation was carried out to measure the response time of GaAs in negative electron affinity conditions as a photoemitter. During the experiment, the photocathode was excited by a short-pulse (38 ps rms) frequency-doubled Nd:YLF laser. Results show that the rms response time of GaAs is shorter than 40 ps.

We report new measurements for the mass, width, and branching ratios for the J / ψ and the ψ^′. These charmonium states are formed exclusively in p̅ p annihilations at the Fermilab Antiproton Accumulator ring, where stochastically cooled antiprotons are brought into collision with the protons of an internal hydrogen gas jet target. The antiproton energy is precisely controlled and measured allowing an accurate measurement of the resonance parameters. From the shape of the excitation curves we find that the widths of J / ψ and ψ^′ are Γ(J / ψ)=99±12±6 keV and Γ(ψ^′)=306±36±16 keV, and that the mass of the J / ψ is 3096.87 ± 0.03 MeV/c². For the J / ψ we obtain B(J / ψ→p̅ p)B(J / ψ→e⁺e^-)=(1.14_-0.12^+0.16±0.10)×10^-4; for the ψ^′ we obtain B(ψ^′→p̅ p)[B(ψ^′→e⁺e^-)+B(ψ^′→J / ψX)B(J / ψ→e⁺e^-)]=(1.17_-0.12^+0.14±0.08)×10^-5.

In order to produce electron beams with the minimum possible energy spread we have investigated the possibility of replacing the usual thermocathodes with a photoemissive source such as GaAs. A comparison carried out between these two sources indicated the latter as the best device to obtain a very-low-energy spread. Beam relaxation after emission also leads to an increase in the energy spread. Therefore an experimental study on the nature of relaxations occurring in electron beams, yielded both by a thermocathode and by a photocathode, has been performed. More specifically, we investigated the possibility of reducing the transverse-longitudinal and the longitudinal-longitudinal relaxations. With this aim, the features of adiabatic acceleration, which damp the pure longitudinal relaxation, have been examined. The experience gained during the measurement cycle demonstrated that an adiabatic structure, accelerating electrons emitted by a GaAs photocathode, leads to the best performances.

Fermilab experiment E-760 studies the resonant formation of charmonium states in proton-antiproton interactions using a hydrogen gas-jet target in the Antiproton Accumulator ring at Fermilab. Precision measurements of the mass and width of the charmonium states χ_c1,χ_c2, a direct measurement of the ψ’ width, and a new precision measurement of the J/ψ mass are presented.