Peak Locations and Relative Phase of Different Decay Modes of the a_{1} Axial Vector Resonance in Diffractive Production.
We show that a single I=1 spin-parity J^{PC}=1^{++} a_{1} resonance can manifest itself as two separated mass peaks, one decaying into an S-wave ρπ system and the second decaying into a P-wave f_{0}(980)π system, with a rapid increase of the phase difference between their amplitudes arising mainly from the structure of the diffractive production process. This study clarifies questions related to the mass, width, and decay rates of the a_{1} resonance raised by the recent high statistics data of the COMPASS Collaboration on a_{1} production in πN→πππN at high energies.
Studies of light mesons at COMPASS
To investigate the spectrum of light mesons, the COMPASS experiment has recorded data with a 190 GeV/ c negative pion beam impinging on a liquid hydrogen target. Diffractive dissociation reactions at squared four-momentum transfers to the target between 0.1 and 1.0 (GeV/ c ) 2 are studied. The flagship channel is the π − π + π − final state, for which COMPASS has recorded the at present world’s largest data sample. A new axial-vector signal, the a 1 (1420), has been found with unusual properties, pointing to an exotic nature. The findings are confirmed by the analysis of the π − π 0 π 0 final state.
DESIGN CONSIDERATION TO PPM KLYSTRONS FOR INDUSTRIAL LINAC
Toshiba has been developing the C-band and X-band Periodic Permanent Magnet (PPM) focused klystron in collaboration with KEK and manufactured prototypes for the JLC project. [1] The PPM klystron has an advantage to enhance the total efficiency as a result of eliminating the electric power for the focusing magnet. From experience on the development the PPM focused klystrons for the JLC project, we plan to apply the PPM focused klystron to the medical and industrial linac. The periodic magnet focusing scheme has some technical difficulties such as stop band voltage. To design the PPM klystron for the medical and industrial linac, it is necessary to give heed to electron beam instability; so that the tube parameters of the PPM focused klystrons have some constraints. The size of the accelerator system is substantially reduced if a PPM focused klystron is used. The majority of medical and industrial linacs use frequencies of S-band range. We discuss the availability of the S-band PPM focused klystron in this paper.