Abstract
Polarization observables in photon-induced meson production off nucleons have long been recognized to hold the promise of a detailed understanding of the excited states in the excitation spectrum of the nucleon. Photon beam and proton target polarization are routinely used at the ELSA facility in the Crystal Barrel/TAPS experiment and have yielded a wealth of data on contributing partial waves and nucleon resonances. A detector study on how to complement these ongoing studies by recoil polarization measurements that offer an orthogonal approach with otherwise unmeasurable observables in the field of non-strange meson photoproduction has been performed.Building on experience with silicon detectors operated in the photon beamline environment, first possible layouts of Si detector telescopes for recoil protons were developed. Various geometries, e.g. Archimedean spiral design of annular sensors, sector shapes and rectangular sensors were studied and have been used during test measurements. A prototype for the recoil polarimeter was built and subjected to performance tests in protonproton scattering at the COSY-accelerator in Julich.
Highlights
Polarization observables in photon-induced meson production off nucleons hold the promise of a detailed understanding of the excited states in the nucleon spectrum
Photon beam and proton target polarization are routinely used at the ELSA facility [1] in the Crystal Barrel/TAPS experiment [2] and have yielded a wealth of data on contributing partial waves and nucleon resonances
These studies could be complemented by recoil polarization studies that offer an orthogonal approach with otherwise unmeasurable observables in the field of non-strange meson photoproduction
Summary
Polarization observables in photon-induced meson production off nucleons hold the promise of a detailed understanding of the excited states in the nucleon spectrum. Photon beam and proton target polarization are routinely used at the ELSA facility [1] in the Crystal Barrel/TAPS experiment [2] and have yielded a wealth of data on contributing partial waves and nucleon resonances These studies could be complemented by recoil polarization studies that offer an orthogonal approach with otherwise unmeasurable observables in the field of non-strange meson photoproduction. A first set of studies was aimed at sensor development and validation for measurements of recoil protons under the special conditions of a tagged-photon beam facility To this end, several detector layouts were studied in a variety of experimental conditions. Using large-area double-sided silicon strip sensors, which proved to be sufficiently radiationhard for operation in or very close to the photon beam, an optimized layout was developed and a prototype setup built This was subjected to extensive testing and its suitability was verified in simulations. Parallel to the detector studies, readout and data acquisition for the new addition to the experimental capabilities at ELSA was developed
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