Proposal to Build an Electron-Photon Facility at NAL and to Measure Photon Scattering at High Energies
The National Accelerator Laboratory opens up a new era in our search of what elementary particles are like; the 100-500 GeV era. If we want to look at the structure of hadrons with the resolution provided by the wavelength of such high energy beams, what can be more natural, to paraphrase Bjorken, than looking at them, i.e. shining light at them and watching for scattering or absorption? This is precisely what we propose to do in the experiments suggested here. Photons, real and virtual, have contributed immeasurably to our understanding of hadronic matter through investigations done at lower-energy (1 {le} E {le} 20 GeV) electron accelerators. NAL, albeit a proton machine, will be our only potential source of photons beyond SLAC energies. Proton-nucleus collisions will produce photons, principally in two-step processes involving radiative hadron (notably {pi}{sup 0}) decays. It has been shown that sizeable fluxes can be obtained by the appropriate construction of beam lines. NAL will then be a unique tool for the study of electromagnetic interactions at energies in the 20-300 GeV range. At high energies ({approx}> 200 GeV), available electron fluxes will set the limit on photon intensities for experimentation; at lower energies, fluxes rise strongly, but the electronics logic involved in beam momentum definition and tagging will not permit final yields to be considerably larger than those at 200 GeV. The first generation of photon physics at NAL will therefore restrict itself to processes with relatively large cross-sections. As will be seen, some of the most exciting problems involving photons at presently existing energies will be accessible to conclusive experimentation at NAL. Our group has, from past experience at lower-energy photon laboratories and from recent studies of its members, a keen interest in working on these problems. We have been happily active on earlier feasibility studies of beams and experiments; and we are enthusiastic about the prospect of a photon beam becoming available at NAL at an early date. We propose to participate actively, as we have done in the past, in the design and implementation of the electron-photon facility, and to perform at the earliest possible date an experiment which will yield information on three vitally important processes in photon scattering: (1) measurement of the total hadronic photon cross-section on nucleons and nuclei; (2) elastic photon scattering (proton compton effect); (3) inelastic photon scattering; as a byproduct, we will have data on yields of {pi}{sup 0}, {eta}{sup 0}, X{sup 0}, {omega}{sup 0}, ... through their 2{gamma} or 3{gamma} decay modes. The set of experiments proposed here, together with experiments proposed by other groups, will tell us not only about the structure of the hadrons, but about the behavior of the photon at high energies. It has the virtue of being accessible through one basic, well-integrated set of experimental equipment, as detailed. The facility as well as the detection apparatus is being developed in consultation with the MIT - Canada collaboration. Equipment may be shared, and some of the running may be able to proceed compatibly. The success of this program will depend crucially on the design of appropriate halo-free beam lines; and on the early design and testing of optimal shower detection equipment - for both energy measurement and localization (or trajectory reconstruction). Our group has considerable experience in both these areas. Shower detectors are being built in Santa Cruz and can be conveniently tested at nearby SLAC. Also, a beam designed by our group, which we feel is flexible, economical, and viable, is included in this proposal. The essential feature of our proposal is this: Our shower detection equipment can be tested and calibrated in available SLAC beams before the first turn-on of the NAL photon beam, and will be ready at that time. While information on the longitudinal and lateral shower spread can be extrapolated to NAL energies from existing data up to 15-20 GeV, the validity of such extrapolations must be experimentally tested at an early date. Together with the energy resolution to be expected at NAL energies, such data will vitally affect what can and what cannot be done: resolution of neighboring showers, recognition of radiative meson decays, total energy balance, etc. We feel therefore it is imperative that at the earliest possible date, an electron beam of high purity (if low-intensity) be available for the measurement of such parameters. Our equipment will be present, tested up to SLAC energies, when the first photon beam emerges.
- Research Organization:
- Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC02-07CH11359
- OSTI ID:
- 991306
- Report Number(s):
- FERMILAB-PROPOSAL-0152; TRN: US201021%%273
- Country of Publication:
- United States
- Language:
- English
Similar Records
Topics in Theoretical Physics
Recovery Act - Measurement of Parity Violation in Deep Inelastic Scattering and Studies of the Nucleon Spin Structure at JLab 6 and 11 GeV
Related Subjects
CROSS SECTIONS
DESIGN
DETECTION
ELECTROMAGNETIC INTERACTIONS
ELECTRON BEAMS
ELECTRONS
ELEMENTARY PARTICLES
ENERGY BALANCE
ENERGY RESOLUTION
FEASIBILITY STUDIES
FERMILAB ACCELERATOR
GEV RANGE
PHOTON BEAMS
PHOTONS
RESOLUTION
SCATTERING
STANFORD LINEAR ACCELERATOR CENTER
Accelerators