Yokoyama, R., Singh, M., Grzywacz, R., Keeler, A., King, T. T., Agramunt, J., et al. (2019). Segmented YSO scintillation detectors as a new beta-implant detection tool for decay spectroscopy in fragmentation facilities. Nucl. Instrum. Methods Phys. Res. A, 937, 93–97.
Abstract: A newly developed segmented YSO scintillator detector was implemented for the first time at the RI-beam Factory at RIKEN Nishina Center as an implantation-decay counter. The results from the experiment demonstrate that the detector is a viable alternative to conventional silicon-strip detectors with its good timing resolution and high detection efficiency for beta particles. A Position-Sensitive Photo-Multiplier Tube (PSPMT) is coupled with a 48 x 48 segmented YSO crystal. To demonstrate its capabilities, a known short-lived isomer in Ni-76 and the beta decay of Co-74 were measured by implanting those ions into the YSO detector. The half-lives and gamma-rays observed in this work are consistent with the known values. The beta-ray detection efficiency is more than 80 % for the decay of Co-74.
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Rasco, B. C., Brewer, N. T., Yokoyama, R., Grzywacz, R., Rykaczewski, K. P., Tolosa-Delgado, A., et al. (2018). The ORNL analysis technique for extracting beta-delayed multi-neutron branching ratios with BRIKEN. Nucl. Instrum. Methods Phys. Res. A, 911, 79–86.
Abstract: Many choices are available in order to evaluate large radioactive decay networks. There are many parameters that influence the calculated beta-decay delayed single and multi-neutron emission branching fractions. We describe assumptions about the decay model, background, and other parameters and their influence on beta-decay delayed multi-neutron emission analysis. An analysis technique, the ORNL BRIKEN analysis procedure, for determining beta-delayed multi-neutron branching ratios in beta-neutron precursors produced by means of heavy-ion fragmentation is presented. The technique is based on estimating the initial activities of zero, one, and two neutrons occurring in coincidence with an ion-implant and beta trigger. The technique allows one to extract beta-delayed multi-neutron decay branching ratios measured with the He-3 BRIKEN neutron counter. As an example, two analyses of the beta-neutron emitter Cu-77 based on different a priori assumptions are presented along with comparisons to literature values.
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Cabrera, M. E., Casas, J. A., Delgado, A., Robles, S., & Ruiz de Austri, R. (2016). Naturalness of MSSM dark matter. J. High Energy Phys., 08(8), 058–30pp.
Abstract: There exists a vast literature examining the electroweak (EW) fine-tuning problem in supersymmetric scenarios, but little concerned with the dark matter (DM) one, which should be combined with the former. In this paper, we study this problem in an, as much as possible, exhaustive and rigorous way. We have considered the MSSM framework, assuming that the LSP is the lightest neutralino, chi(0)(1), and exploring the various possibilities for the mass and composition of chi(0)(1), as well as different mechanisms for annihilation of the DM particles in the early Universe (well-tempered neutralinos, funnels and co-annihilation scenarios). We also present a discussion about the statistical meaning of the fine-tuning and how it should be computed for the DM abundance, and combined with the EW fine-tuning. The results are very robust and model-independent and favour some scenarios (like the h-funnel when M-chi 10 is not too close to m(h)/2) with respect to others (such as the pure wino case). These features should be taken into account when one explores “natural SUSY” scenarios and their possible signatures at the LHC and in DM detection experiments.
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