The electromagnetic polarizabilities of the nucleon are fundamental nucleon-structure observables that characterize its response to external electromagnetic fields. The neutron polarizabilities can ...be accessed from Compton-scattering data on light nuclear targets. Recent measurements of the differential cross section for Compton scattering on the deuteron below the pion-production threshold have decreased the uncertainties in the neutron polarizabilities, yet the proton polarizabilities remain known substantially more accurately. Here, as the sensitivity of the cross section to the polarizabilities increases with incident photon energy, measurements above the pion threshold may offer a way for an improved determination of the neutron polarizabilities. In this work, the first measurement of the cross section for Compton scattering on the deuteron above the pion-production threshold is presented.
Rate-dependent effects in the electronics used to instrument the tagger focal plane at the MAX IV Laboratory were recently investigated using the novel approach of Monte Carlo simulation to allow for ...normalization of high-rate experimental data acquired with single-hit time-to-digital converters (TDCs). The instrumentation of the tagger focal plane has now been expanded to include multi-hit TDCs. The agreement between results obtained from data taken using single-hit and multi-hit TDCs demonstrate a thorough understanding of the behavior of the detector system.
The upgraded photon tagging facility at the MAX IV Laboratory Adler, J.-O.; Boland, M.; Brudvik, J. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
07/2013, Letnik:
715
Journal Article
Recenzirano
A description is given of the upgraded photon tagging facility at the MAX IV Laboratory. Two magnetic spectrometers are used to momentum analyze post-bremsstrahlung electrons. The tagged photon range ...extends from 10 to 180MeV with an energy resolution of about 300keV. The system has been operated at rates up to 4×106 photonss-1MeV −1. Different diagnostic tools are described as well as the experimental program.
•Tagged photons in the energy range 10–180MeV with an energy resolution of 300keV are available.•Coherent bremsstrahlung is used to produce linearly polarized photons in the energy range below 70MeV.•Several diagnostic tools are used to monitor the data taking.•The research program includes Compton scattering on deuterium and light nuclei.•Also included are (γ,p), (γ,π), (γ,total) cross-section measurements on nucleons and nuclei.
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Total cross sections, angular distributions, and invariant-mass distributions have been measured for the photoproduction of
pairs off free protons and off nucleons bound in the deuteron. The ...experiments were performed at the MAMI accelerator facility in Mainz using the Glasgow photon tagging spectrometer and the Crystal Ball/TAPS detector. The accelerator delivered electron beams of 1508 and 1557MeV, which produced bremsstrahlung in thin radiator foils. The tagged photon beam covered energies up to 1400MeV. The data from the free proton target are in good agreement with previous measurements and were only used to test the analysis procedures. The results for differential cross sections (angular distributions and invariant-mass distributions) for free and quasi-free protons are almost identical in shape, but differ in absolute magnitude up to 15%. Thus, moderate final-state interaction effects are present. The data for quasi-free neutrons are similar to the proton data in the second resonance region (final-state invariant masses up to
MeV), where both reactions are dominated by the
decay. At higher energies, angular and invariant-mass distributions are different. A simple analysis of the shapes of the invariant-mass distributions in the third resonance region is consistent with strong contributions of an
decay for the proton, while the reaction is dominated by a sequential decay via a
intermediate state for the neutron. The data are compared to predictions from the Two-Pion-MAID model and the Bonn-Gatchina coupled-channel analysis.
The Dalitz decay η→γe+e− has been measured using the combined Crystal Ball and TAPS photon detector setup at the electron accelerator MAMI-C. Compared to the most recent transition form-factor ...measurement in the e+e− channel, statistics have been improved by one order of magnitude. The e+e− invariant mass distribution shows a deviation from the QED prediction for a point-like particle, which can be described by a form-factor. Using the usual monopole transition form-factor parameterization, F(m2)=(1−m2/Λ2)−1, a value of Λ−2=(1.92±0.35(stat)±0.13(syst)) GeV−2 has been determined. This value is in good agreement with a recent measurement of the η Dalitz decay in the μ+μ− channel and with recent form-factor calculations. An improved value of the branching ratio BR(η→γe+e−)=(6.6±0.4(stat)±0.4(syst))⋅10−3 has been determined.
Photoproduction of η -Mesic He 3 Pfeiffer, M.; Ahrens, J.; Annand, J. R. M. ...
Physical review letters,
06/2004, Letnik:
92, Številka:
25
Journal Article
A lead–glass hodoscope calorimeter that was constructed for use in the Jefferson Lab Real Compton Scattering experiment is described. The detector provides a measurement of the coordinates and the ...energy of scattered photons in the GeV energy range with resolutions of 5
mm and 6%/
E
γ
GeV
. Features of both the detector design and its performance in the high luminosity environment during the experiment are presented.
Coincidence and time-of-flight measurement techniques are employed to tag fission neutrons emitted from a 252Cf source sealed on one side with a very thin layer of Au. The source is positioned within ...a gaseous 4He scintillator detector. Together with α particles, both light and heavy fission fragments pass through the thin layer of Au and are detected. The fragments enable the corresponding fission neutrons, which are detected in a NE-213 liquid-scintillator detector, to be tagged. The resulting continuous polychromatic beam of tagged neutrons has an energy dependence that agrees qualitatively with expectations. We anticipate that this technique will provide a cost-effective means for the characterization of neutron-detector efficiency in the energy range 1–6MeV.
•Neutrons emitted from a 252Cf source with a thin window are tagged using the corresponding fission fragments.•The resulting beam of neutrons is continuous and polychromatic.•The energy of each neutron is determined via the time-of-flight technique.•The approach is anticipated to facilitate cost-effective determinations of neutron-detector efficiencies.
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