\(K^+\Lambda(1405)\) photoproduction has been studied at the BGOOD experiment via the all neutral decay, \(\Lambda(1405)\rightarrow\Sigma^0\pi^0\). The unique BGOOD experimental setup allows both the ...cross section and \(\Lambda(1405)\) invariant mass distribution (line shape) to be measured over a broad \(K^+\) polar angle range, extending to extreme forward \(K^+\) angles unattainable at previous experiments. Evidence is provided for the role of a triangle singularity driven by the \(N^*(2030)\) resonance, which appears to contribute significantly to \(K^+\Lambda(1405)\) photoproduction. This is observed in both the angular distributions and the integrated cross section which was determined with unprecedented energy resolution. The measured line shape is also in agreement with the previous results of CLAS and ANKE, and is consistent with two poles derived in \(\chi\)PT based models.
Photoproduction of \(\eta\) mesons from neutrons} \abstract{Results from measurements of the photoproduction of \(\eta\) mesons from quasifree protons and neutrons are summarized. The experiments ...were performed with the CBELSA/TAPS detector at the electron accelerator ELSA in Bonn using the \(\eta\to3\pi^{0}\to6\gamma\) decay. A liquid deuterium target was used for the measurement of total cross sections and angular distributions. The results confirm earlier measurements from Bonn and the MAMI facility in Mainz about the existence of a narrow structure in the excitation function of \(\gamma n\rightarrow n\eta\). The current angular distributions show a forward-backward asymmetry, which was previously not seen, but was predicted by model calculations including an additional narrow \(P_{11}\) state. Furthermore, data obtained with a longitudinally polarized, deuterated butanol target and a circularly polarized photon beam were analyzed to determine the double polarization observable \(E\). Both data sets together were also used to extract the helicity dependent cross sections \(\sigma_{1/2}\) and \(\sigma_{3/2}\). The narrow structure in the excitation function of \(\gamma n\rightarrow n\eta\) appears associated with the helicity-1/2 component of the reaction.
This paper reports on a measurement of the double-polarization observable G in \(\pi^0\) 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), J\"ulich-Bonn (J\"uBo), MAID and SAID partial wave analyses. Implications of the new data for the pion photoproduction multipoles are discussed.
The \(\gamma p \rightarrow K^+\Sigma^0\) differential cross section at extremely forward angles was measured at the BGOOD experiment. A three-quarter drop in strength over a narrow range in energy ...and a strong dependence on the polar angle of the \(K^+\) in the centre-of-mass of the reaction is observed at a centre-of-mass energy of 1900\,MeV. Residing close to multiple open and hidden strangeness thresholds, the structure appears consistent with meson-baryon threshold effects which may contribute to the reaction mechanism.
\(\gamma p \rightarrow K^+ \Lambda\) differential cross sections and recoil polarisation data from threshold for extremely forward angles are presented. The measurements were performed at the BGOOD ...experiment at ELSA, utilising the high angular and momentum resolution forward spectrometer for charged particle identification. The data discriminates between conflicting results in the world data set and enable extraction of the cross section as the minimum momentum transfer to the recoiling hyperon is approached.
In a search for $\omega$ mesic states, the production of $\omega$-mesons in
coincidence with forward going protons has been studied in photon induced
reactions on $^{12}$C for incident photon ...energies of 1250 - 3100 MeV. The
$\pi^0 \gamma$ pairs from decays of bound or quasi-free $\omega$-mesons have
been measured with the CBELSA/TAPS detector system in coincidence with protons
registered in the MiniTAPS forward array. Structures in the total energy
distribution of the $\pi^0 \gamma$ pairs, which would indicate the population
and decay of bound $\omega~^{11}$B states, are not observed. The $\pi^0 \gamma$
cross section of 0.3 nb/MeV/sr observed in the bound state energy regime
between -100 and 0 MeV may be accounted for by yield leaking into the bound
state regime because of the large in-medium width of the $\omega$-meson. A
comparison of the measured total energy distribution with calculations suggests
the real part $V_0$ of the $\omega~^{11}$B potential to be small and only
weakly attractive with $V_0(\rho=\rho_0) = -15\pm$ 35(stat) $\pm$20(syst) MeV
in contrast to some theoretical predictions of attractive potentials with a
depth of 100 - 150 MeV.
BGO-OD is a newly commissioned experiment to investigate the internal structure of the nucleon, using an energy tagged bremsstrahlung photon beam at the ELSA electron facility. The setup consists of ...a highly segmented BGO calorimeter surrounding the target, with a particle tracking magnetic spectrometer at forward angles. BGO-OD is ideal for investigating meson photoproduction. The extensive physics programme for open strangeness photoproduction is introduced, and preliminary analysis presented.
PDF