The cross section of atomic electron Compton scattering γ+e→γ′+e′ was measured in the 4.400–5.475 GeV photon beam energy region by the PrimEx collaboration at Jefferson Lab with an accuracy of 2.6% ...and less. The results are consistent with theoretical predictions that include next-to-leading order radiative corrections. The measurements provide the first high precision test of this elementary QED process at beam energies greater than 0.1 GeV.
Polarization measurements of TEMPO-doped butanol targets Plückthun, M.; Bradtke, Ch; Dutz, H. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
11/1997, Letnik:
400, Številka:
1
Journal Article
Recenzirano
Dynamic nuclear polarization (DNP) measurements have been performed in butanol and deuterated butanol. Both target materials have been chemically prepared for the DNP process with the highly stable ...free nitroxyl radical 2,2,6,6-tetramethyl-piperidine-1-oxyl, also known as TEMPO. Maximum proton polarization values of 89.2% and maximum deuteron polarization values of 38.4% have been obtained in a magnetic field of 2.5 T and at a temperature of about 200 mK. Polarization relaxation times of >200 h (protons) and >100 h (deuterons) have been measured at 0.35 T and 60 mK. The results together with an easy preparation procedure make TEMPO-doped butanol attractive for the frozen spin operation mode of polarized solid-state targets.
High precision measurements of the differential cross sections for $\pi^0$ photoproduction at forward angles for two nuclei, $^{12}$C and $^{208}$Pb, have been performed for incident photon energies ...of 4.9 - 5.5 GeV to extract the ${\pi^0 \to \gamma\gamma}$ decay width. The experiment was done at Jefferson Lab using the Hall~B photon tagger and a high-resolution multichannel calorimeter. The ${\pi^0 \to \gamma\gamma}$ decay width was extracted by fitting the measured cross sections using recently updated theoretical models for the process. The resulting value for the decay width is $\Gamma{(\pi^0 \to \gamma\gamma)} = 7.82 \pm 0.14 ~({\rm stat.}) \pm 0.17 ~({\rm syst.}) ~{\rm eV}$. With the 2.8\% total uncertainty, this result is a factor of 2.5 more precise than the current PDG average of this fundamental quantity and it is consistent with current theoretical predictions.
Spin-transfer observables for p p-->Lambda Lambda have been measured using a transversely polarized frozen-spin target and a beam momentum of 1.637 GeV/c. Current models of the reaction near ...threshold are in good agreement with existing measurements performed with unpolarized particles in the initial state but produce conflicting predictions for the spin-transfer observables Dnn and Knn (the normal-to-normal depolarization and polarization transfer), which are measurable only with polarized target or beam. Measurements of Dnn and Knn presented here are found to be in disagreement with predictions from these models.
The reaction
p
p→
Λ
Λ
was examined by LEAR experiment PS185/3 at 1.525 and 1.640 GeV/c. The proton target was transversely polarized in order to measure the depolarization and spin transfer. ...Theoretical calculations of
D
nn, the component of the depolarization normal to the production plane, differ greatly according to whether quark-gluon or meson-exchange models are employed. The measured
D
nn and spin transfer
K
nn appear to be inconsistent with the specific models cited.
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