The Multi-Blade is a Boron-10-based gaseous thermal neutron detector developed to face the challenge arising in neutron reflectometry at neutron sources. Neutron reflectometers are challenging ...instruments in terms of instantaneous counting rate and spatial resolution. This detector has been designed according to the requirements given by the reflectometers at the European Spallation Source (ESS) in Sweden. The Multi-Blade has been installed and tested on the CRISP reflectometer at the ISIS neutron and muon source in UK. The results on the detailed detector characterization are discussed in this manuscript.
The polarization observables $T, E, P, H$, and $G$ in photoproduction of
$\eta$ mesons off protons are measured for photon energies from threshold to
$W=2400\,$MeV ($T$), 2280 MeV ($E$), 1620 MeV ...($P, H$), or 1820 MeV ($G$),
covering nearly the full solid angle. The data are compared to predictions from
the SAID, MAID, J\"uBo, and BnGa partial-wave analyses. A refit within the BnGa
approach including further data yields precise branching ratios for the $N\eta$
decay of nucleon resonances. A $N\eta$-branching ratio of $0.33\pm 0.04$ for
$N(1650)1/2^-$ is found, which reduces the large and controversially discussed
$N\eta$-branching ratio difference of the two lowest mass
$J^P=1/2^-$-resonances significantly.
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.
The production of \(\eta^\prime\) mesons in coincidence with forward-going protons has been studied in photon-induced reactions on \(^{12}\)C and on a liquid hydrogen (LH\(_2\)) target for incoming ...photon energies of 1.3-2.6 GeV at the electron accelerator ELSA. The \(\eta^\prime\) mesons have been identified via the \(\eta^\prime\rightarrow \pi^0 \pi^0\eta \rightarrow 6 \gamma\) decay registered with the CBELSA/TAPS detector system. Coincident protons have been identified in the MiniTAPS BaF\(_2\) array at polar angles of \(2^{\circ} \le \theta _{p} \le 11^{\circ}\). Under these kinematic constraints the \(\eta^\prime\) mesons are produced with relatively low kinetic energy (\(\approx\) 150 MeV) since the coincident protons take over most of the momentum of the incident-photon beam. For the C-target this allows the determination of the real part of the \(\eta^\prime\)-carbon potential at low meson momenta by comparing with collision model calculations of the \(\eta^\prime\) kinetic energy distribution and excitation function. Fitting the latter data for \(\eta^\prime\) mesons going backwards in the center-of-mass system yields a potential depth of V = \(-\)(44 \(\pm\) 16(stat)\(\pm\)15(syst)) MeV, consistent with earlier determinations of the potential depth in inclusive measurements for average \(\eta^\prime\) momenta of \(\approx\) 1.1 GeV/\(c\). Within the experimental uncertainties, there is no indication of a momentum dependence of the \(\eta^\prime\)-carbon potential. The LH\(_2\) data, taken as a reference to check the data analysis and the model calculations, provide differential and integral cross sections in good agreement with previous results for \(\eta^\prime\) photoproduction off the free proton.
\(\gamma p \rightarrow K^+ \Lambda\) 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.
Over the last decades, the field of thermal neutron detection has overwhelmingly employed He-3-based technologies. The He-3 crisis together with the forthcoming establishment of the European ...Spallation Source have necessitated the development of new technologies for neutron detection. Today, several promising He-3-free candidates are under detailed study and need to be validated. This validation process is in general long and expensive. The study of detector prototypes using neutron-emitting radioactive sources is a cost-effective solution, especially for preliminary investigations. That said, neutron-emitting sources have the general disadvantage of broad, structured, emitted-neutron energy ranges. Further, the emitted neutrons often compete with unwanted backgrounds of gamma-rays, alpha-particles, and fission-fragments. By blending experimental infrastructure such as shielding to provide particle beams with neutron-detection techniques such as tagging, disadvantages may be converted into advantages. In particular, a technique known as tagging involves exploiting the mixed-field generally associated with a neutron-emitting source to determine neutron time-of-flight and thus energy on an event-by-event basis. This allows for the definition of low-cost, precision neutron beams. The Source-Testing Facility, located at Lund University in Sweden and operated by the SONNIG Group of the Division of Nuclear Physics, was developed for just such low-cost studies. Precision tagged-neutron beams derived from radioactive sources are available around-the-clock for advanced detector diagnostic studies. Neutron measurements performed at the Source Testing Facility are thus cost-effective and have a very low barrier for entry. In this paper, we present an overview of the project.
The reaction \(\gamma p \rightarrow p \pi^0 \eta\) 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 M\(_{N\eta}\) 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 E\(_{\gamma}\) = 1400 - 1500 MeV and the cut M\(_{p\pi^0} \le 1190 \) MeV/\(c^2\) a statistically significant structure in the M\(_{p\eta}\) invariant mass distribution near 1700 MeV/\(c^2\) is observed with a width of \(\Gamma\approx 35\) MeV/\(c^2\) while the mass resolution is \(\sigma_{res}\) = 5 MeV/\(c^2\). Increasing the incident photon energy from 1420 to 1540 MeV this structure shifts in mass from \(\approx\) 1700MeV/c\(^2\) to \(\approx\) 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 \(\approx\) 100 nb around E\(_{\gamma} \approx\) 1490 MeV (W \(\approx \) 1920 MeV), which coincides with the \(p a_0\) threshold. Three scenarios are discussed which might be the origin of this structure in the M\(_{p\eta}\) invariant mass distribution. The most likely interpretation is that it is due to a triangular singularity in the \(\gamma p \rightarrow p a_0 \rightarrow p \pi^0 \eta\) reaction
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.
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