The first measurements of the beam-target-helicity-asymmetries E and G in the photoproduction of ω-mesons off protons at the CBELSA/TAPS experiment are reported. E (G) was measured using circularly (linearly) polarised photons and a longitudinally polarised target. E was measured over the photon energy range from close to threshold (E γ = 1108 MeV) to E γ = 2300 MeV and G at a single energy interval of 1108 < E γ < 1300 MeV. Both measurements cover the full solid angle. The observables E and G are highly sensitive to the contribution of baryon resonances, with E acting as a helicity filter in the s-channel. The new results indicate significant s-channel resonance contributions together with contributions from t-channel exchange processes. A partial wave analysis reveals strong contributions from the partial waves with spin-parity J P = 3/2 + , 5/2 + , and 3/2 − .
This paper reports on a measurement of the double-polarization observable G in π 0 photoproduction off the proton using the CBELSA/TAPS experiment at the ELSA accelerator in Bonn. The observable G is determined from reactions of linearly-polarized photons with longitudinally-polarized protons. The polarized photons are produced by bremsstrahlung off a properly oriented diamond radiator. A frozen spin butanol target provides the polarized protons. The data cover the photon energy range from 617 to 1325 MeV and a wide angular range. The experimental results for G are compared to predictions by the Bonn-Gatchina (BnGa), Jülich-Bonn (JüBo), MAID and SAID partial wave analyses. Implications of the new data for the pion photoproduction multipoles are discussed.
The reaction γp → pπ 0 η has been studied with the CBELSA/TAPS detector at the electron stretcher accelerator ELSA in Bonn for incident photon energies from threshold up to 3.1 GeV. This paper has been motivated by the recently claimed observation of a narrow structure in the MNη invariant mass distribution at a mass of 1678 MeV/c 2 . The existence of this structure cannot be confirmed in the present work. Instead, for Eγ = 1400 -1500 MeV and the cut M pπ 0 ≤ 1190 MeV/c 2 a statistically significant structure in the Mpη invariant mass distribution near 1700 MeV/c 2 is observed with a width of Γ ≈ 35 MeV/c 2 while the mass resolution is σres = 5 MeV/c 2 . Increasing the incident photon energy from 1420 to 1540 MeV this structure shifts in mass from ≈ 1700 MeV/c 2 to ≈ 1725 MeV/c 2 ; the width increases to about 50 MeV/c 2 and decreases thereafter. The cross section associated with this structure reaches a maximum of ≈ 100 nb around Eγ ≈ 1490 MeV (W ≈ 1920 MeV), which coincides with the pa0 threshold. Three scenarios are discussed which might be the origin of this structure in the Mpη invariant mass distribution. The most likely interpretation is that it is due to a triangular singularity in the γp → pa0 → pπ 0 η reaction.
Time resolved measurements of the extracted ion currents at the Frankfurt 14 GHz electron cyclotron resonance ion source ͑ECRIS͒ are reported. These measurements were performed to provide more detailed information on the ''biased disk effect'' in an ECRIS. From a first series of measurements with pulsed biased disk voltage it was concluded that the ''biased disk effect'' is mainly due to improvements of the extraction conditions and the enhanced transport of highly charged ions into the extraction area. In this article we present new measurements with an improved setup allowing for a faster pulsing of the biased disk voltage. We also present data for the injection of neutral particles from laser ablated plasmas and Bremsstrahlung spectra for different dc biased disk voltages. All results from these measurements support our previous conclusion.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.