The Dalitz decays η → e+e-γ and ω → π0e+e- have been measured in the γp → ηp and γp → ωp reactions, respectively, with the A2 tagged-photon facility at the Mainz Microtron. The value obtained for the ...slope parameter of the electromagnetic transition form factor of η, Λ$-2\atop{η}$ = (1.97 ± 0.11tot) GeV-2, is in good agreement with previous measurements of the η → e+e-γ and η → μ+μ-γ decays. The uncertainty obtained in the value of Λ$-2\atop{η}$ is lower than in previous results based on the η → e+e-γ decay. The value obtained for the ω slope parameter, Λ$-2\atop{ωπ^0}$ = (1.99 ± 0.21tot) GeV-2, is somewhat lower than previous measurements based on ω → π0μ+μ-, but the results for the ω transition form factor are in better agreement with theoretical calculations, compared to earlier experiments.
A precise measurement of the differential cross sections dσ/dΩ and the linearly polarized photon beam asymmetry Σ_{3} for Compton scattering on the proton below pion threshold has been performed with ...a tagged photon beam and almost 4π detector at the Mainz Microtron. The incident photons were produced by the recently upgraded Glasgow-Mainz photon tagging facility and impinged on a cryogenic liquid hydrogen target, with the scattered photons detected in the Crystal Ball/TAPS setup. Using the highest statistics Compton scattering data ever measured on the proton along with two effective field theories (both covariant baryon and heavy-baryon) and one fixed-t dispersion relation model, constraining the fits with the Baldin sum rule, we have obtained the proton electric and magnetic polarizabilities with unprecedented precision: α_{E1}=10.99±0.16±0.47±0.17±0.34, β_{M1}=3.14±0.21±0.24±0.20±0.35; in units of 10^{-4} fm^{3} where the errors are statistical, systematic, spin polarizability dependent, and model dependent.
We give an overview of low-energy Compton scattering γ
(∗)
p
→ γ
p
with a real or virtual incoming photon. These processes allow the investigation of one of the fundamental properties of the nucleon, ...i.e. how its internal structure deforms under an applied static electromagnetic field. Our knowledge of nucleon polarisabilities and their generalization to non-zero four-momentum transfer will be reviewed, including the presently ongoing experiments and future perspectives.
For 112 Gb/s polarization-multiplexed quadrature-phase-shift-keying systems, the generalized Gaussian probability density function is used to quantify the impact of carrier phase estimation ...algorithms on the statistical properties of the resultant signal sample values and to obtain an estimate of the system bit error ratio when direct bit error counting is not feasible. The shape parameter in the probability density function is useful for distinguishing the performance of different signal processing algorithms and system configurations.
The Dalitz decay π0 → e+e-γ has been measured in the γp → π0p reaction with the A2 tagged-photon facility at the Mainz Microtron, MAMI. The value obtained for the slope parameter of the π0 ...electromagnetic transition form factor, aπ= 0.030 ± 0.010tot, is in agreement with existing measurements of this decay and with recent theoretical calculations. The uncertainty obtained in the value of aπ is lower than in previous results based on the π0 → e+e-γ decay.
The MUSE experiment at the Paul Scherrer Institute is measuring elastic lepton-proton scattering cross sections in a four-momentum transfer range from
Q
2
of approximately 0.002–0.08 GeV
2
using ...positively and negatively charged electrons and muons. The extraction of the Born cross sections from the experimental data requires radiative corrections. Estimates of the instrumental uncertainties in those corrections have been made using the ESEPP event generator. The results depend in particular on the minimum lepton momentum that contributes to the experimental cross section and the fraction of events with hard initial-state radiation that is detected in the MUSE calorimeter and is excluded from the data. These results show that the angular-dependent instrumental uncertainties in radiative corrections to the electron cross section are less than 0.4% and are negligible for the muon cross section.
The Compton double-polarization observable Σ 2z has been measured for the first time in the Δ (1232) resonance region using a circularly polarized photon beam incident on a longitudinally polarized ...proton target at the Mainz Microtron. This paper reports these results, together with the model-dependent extraction of four proton spin polarizabilities from fits to additional asymmetry data using either a dispersion relation calculation or a baryon chiral perturbation theory calculations with the weighted average of these two fits resulting in γE1E1=–2.87±0.52, γM1M1=2.70±0.43, γE1M2=–0.85±0.72 , and γM1E2=2.04±0.43 , in units of 10–4 fm4 .
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