Publications by authors named "D I Sober"

The explicit breaking of the axial symmetry by quantum fluctuations gives rise to the so-called axial anomaly. This phenomenon is solely responsible for the decay of the neutral pion π into two photons (γγ), leading to its unusually short lifetime. We precisely measured the decay width Γ of the [Formula: see text] process.

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We report on the measurement of the γp→J/ψp cross section from E_{γ}=11.8  GeV down to the threshold at 8.2 GeV using a tagged photon beam with the GlueX experiment.

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We report the first beam-target double-polarization asymmetries in the γ+n(p)→π^{-}+p(p) reaction spanning the nucleon resonance region from invariant mass W=1500 to 2300 MeV. Circularly polarized photons and longitudinally polarized deuterons in solid hydrogen deuteride (HD) have been used with the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab. The exclusive final state has been extracted using three very different analyses that show excellent agreement, and these have been used to deduce the E polarization observable for an effective neutron target.

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There is a significant discrepancy between the values of the proton electric form factor, G(E)(p), extracted using unpolarized and polarized electron scattering. Calculations predict that small two-photon exchange (TPE) contributions can significantly affect the extraction of G(E)(p) from the unpolarized electron-proton cross sections. We determined the TPE contribution by measuring the ratio of positron-proton to electron-proton elastic scattering cross sections using a simultaneous, tertiary electron-positron beam incident on a liquid hydrogen target and detecting the scattered particles in the Jefferson Lab CLAS detector.

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Article Synopsis
  • The study discusses how the size and shape of the neutron skin in lead-208 ((208)Pb) were analyzed using pion photoproduction cross sections measured by the Crystal Ball detector at the MAMI facility.
  • The neutron distribution was characterized with specific measurements: a half-height radius of 6.70 ± 0.03 fm and a diffuseness of 0.55 ± 0.01(stat) (-0.03)(+0.02)(sys) fm, leading to a neutron skin thickness of 0.15 ± 0.03(stat) (-0.03)(+0.01)(sys) fm.
  • This is the first time neutron skin thickness has been effectively measured using an electromagnetic approach, revealing that
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