Performance of Geant4 in simulating semiconductor particle detector response in the energy range below 1 MeV

Geant4 simulations play a crucial role in the analysis and interpretation of experiments providing low energy precision tests of the Standard Model. This paper focuses on the accuracy of the description of the electron processes in the energy range between 100 and 1000 keV. The effect of the different simulation parameters and multiple scattering models on the backscattering coefficients is investigated. Simulations of the response of HPGe and passivated implanted planar Si detectors to \beta{} particles are compared to experimental results. An overall good agreement is found between Geant4 simulations and experimental data

Measurement of the β\beta-asymmetry parameter of 67^{67}Cu in search for tensor type currents in the weak interaction

Precision measurements at low energy search for physics beyond the Standard Model in a way complementary to searches for new particles at colliders. In the weak sector the most general $\beta$ decay Hamiltonian contains, besides vector and axial-vector terms, also scalar, tensor and pseudoscalar terms. Current limits on the scalar and tensor coupling constants from neutron and nuclear $\beta$ decay are on the level of several percent. The goal of this paper is extracting new information on tensor coupling constants by measuring the $\beta$-asymmetry parameter in the pure Gamow-Teller decay of $^{67}$Cu, thereby testing the V-A structure of the weak interaction. An iron sample foil into which the radioactive nuclei were implanted was cooled down to milliKelvin temperatures in a $^3$He-$^4$He dilution refrigerator. An external magnetic field of 0.1 T, in combination with the internal hyperfine magnetic field, oriented the nuclei. The anisotropic $\beta$ radiation was observed with planar high purity germanium detectors operating at a temperature of about 10\,K. An on-line measurement of the $\beta$ asymmetry of $^{68}$Cu was performed as well for normalization purposes. Systematic effects were investigated using Geant4 simulations. The experimental value, $\tilde{A}$ = 0.587(14), is in agreement with the Standard Model value of 0.5991(2) and is interpreted in terms of physics beyond the Standard Model. The limits obtained on possible tensor type charged currents in the weak interaction hamiltonian are -0.045 $< (C_T+C'_T)/C_A <$ 0.159 (90\% C.L.). The obtained limits are comparable to limits from other correlation measurements in nuclear $\beta$ decay and contribute to further constraining tensor coupling constants

Electron shakeoff following the β+ decay of trapped 35Ar+ ions

The electron shakeoff of 35Cl atoms resulting from the β+ decay of 35Ar+ ions has been investigated using a Paul trap coupled to a recoil-ion spectrometer. The charge-state distribution of the recoiling daughter nuclei is compared to theoretical calculations accounting for shakeoff and Auger processes. The calculations are in excellent agreement with the experimental results and enable one to identify the ionization reaction routes leading to the formation of all charge states.D.R. acknowledges support from the Spanish ministry of Economy and Competitiveness under the project FPA2010-14803 and the action AIC10-D000562

Shifting baselines and deciding on the desirable form of multispecies maximum sustainable yield

Multispecies, multigear fisheries occur in most ecosystems in the world, but are typical in tropical ecosystems and especially in emerging economies. However, much of fishery science has been developed from a single-species perspective. Management schemes based on single-species reference points often ignore the trophic link among species and the technical interaction between gears, essentially disconnecting management objectives from the context of an ecosystem—or socioecological system—where fisheries operate. Using the Gulf of Thailand fishery as an example, we demonstrate how aggregate production models can be used to estimate system-level fishery reference points for multispecies fisheries. Our results show that the multispecies maximum sustainable yield changes with ecosystem state—the systemic productivity level due to species composition and ecological (trophic/habitat, etc.) structure—under various development levels of fishing and varies with management objectives such as biodiversity, system resilience, total catch, total value, and employment. Aggregate approaches are a tractable way of estimating sustainable ecosystem-scale extraction for multispecies fisheries, avoiding the dilemma of facing conflicting advice derived from single-species methods and providing a practical, operational step toward ecosystem-based management. However, these methods are sensitive to the ecosystem states over time and decision makers need to make informed decisions on which state they want to maintain (or recover) and thus which system-level reference points to use. Consequently, management of multispecies fisheries must be clear on their system-level fisheries policy objectives

Measurement of the beta-asymmetry parameter of Cu-67 in search for tensor-type currents in the weak interaction

The experimental value, ˜A = 0.587(14), is in agreement with the standard model value of 0.5991(2) and is interpreted in terms of physics beyond the standard model. The limits obtained on possible tensor-type charged currents in the weak interaction Hamiltonian are −0.045 < (C_T + C'_T)/CA < 0.159 (90% C.L.). The obtained limits are comparable to limits from other correlation measurements in nuclear β decay and contribute to further constraining tensor coupling constants.status: publishe

First β-ν correlation measurement from the recoil-energy spectrum of Penning trapped 35Ar ions

We demonstrate a novel method to search for physics beyond the standard model by determining the β-ν angular correlation from the recoil-ion energy distribution after β decay of ions stored in a Penning trap. This recoil-ion energy distribution is measured with a retardation spectrometer. The unique combination of the spectrometer with a Penning trap provides a number of advantages, e.g., a high recoil-ion count rate and low sensitivity to the initial position and velocity distribution of the ions and completely different sources of systematic errors compared to other state-of-the-art experiments. Results of a first measurement with the isotope 35Ar are presented. Although currently at limited precision, we show that a statistical precision of about 0.5% is achievable with this unique method, thereby opening up the possibility of contributing to state-of-the-art searches for exotic currents in weak interactions.status: publishe