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XENON Collaboration(Aprile, E. et al), & Orrigo, S. E. A. (2015). Lowering the radioactivity of the photomultiplier tubes for the XENON1T dark matter experiment. Eur. Phys. J. C, 75(11), 546–10pp.
Abstract: The low-background, VUV-sensitive 3-inch diameter photomultiplier tube R11410 has been developed by Hamamatsu for dark matter direct detection experiments using liquid xenon as the target material. We present the results from the joint effort between the XENON collaboration and the Hamamatsu company to produce a highly radio-pure photosensor (version R11410-21) for the XENON1T dark matter experiment. After introducing the photosensor and its components, we show the methods and results of the radioactive contamination measurements of the individual materials employed in the photomultiplier production. We then discuss the adopted strategies to reduce the radioactivity of the various PMT versions. Finally, we detail the results from screening 286 tubes with ultra-low background germanium detectors, as well as their implications for the expected electronic and nuclear recoil background of the XENON1T experiment.
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XENON Collaboration(Aprile, E. et al), & Orrigo, S. E. A. (2015). Search for Event Rate Modulation in XENON100 Electronic Recoil Data. Phys. Rev. Lett., 115(9), 091302–6pp.
Abstract: We have searched for periodic variations of the electronic recoil event rate in the (2-6) keVenergy range recorded between February 2011 and March 2012 with the XENON100 detector, adding up to 224.6 live days in total. Following a detailed study to establish the stability of the detector and its background contributions during this run, we performed an unbinned profile likelihood analysis to identify any periodicity up to 500 days. We find a global significance of less than 1 sigma for all periods, suggesting no statistically significant modulation in the data. While the local significance for an annual modulation is 2.8 sigma, the analysis of a multiple-scatter control sample and the phase of the modulation disfavor a dark matter interpretation. The DAMA/LIBRA annual modulation interpreted as a dark matter signature with axial-vector coupling of weakly interacting massive particles to electrons is excluded at 4.8 sigma.
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Orrigo, S. E. A. et al, Rubio, B., Agramunt, J., Algora, A., & Molina, F. (2015). β-delayed γ-proton decay in 56Zn: analysis of the charged-particle spectrum. Acta Phys. Pol. B, 46(3), 709–712.
Abstract: A study of the beta decay of the proton-rich T-z = 2 nucleus Zn-56 has been reported in a recent publication. A rare and exotic decay mode, beta-delayed gamma-proton decay, has been observed there for the first time in the fp shell. Here, we expand on some of the details of the data analysis, focussing on the charged particle spectrum.
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Fujita, Y., Rubio, B., Adachi, T., Blank, B., Fujita, H., Gelletly, W., et al. (2015). Gamow-Teller excitations studied by weak and strong interactions. Acta Phys. Pol. B, 46(3), 657–668.
Abstract: Studying weak nuclear responses, especially the Gamow-Teller (GT) transitions starting from stable as well as unstable nuclei, provide crucial and critical information on nuclear structure. Therefore, the study of GT transitions is a key issue in nuclear physics and also nuclear-astrophysics. Under the assumption of isospin symmetry, it is expected that the structure of mirror nuclei and the GT transitions starting from their ground states are identical. We have studied the corresponding GT transitions starting from T-z = +/- 1 and +/- 2 p f -shell nuclei, respectively, by means of hadronic (He-3,t) charge-exchange reactions and mirror beta decays. The results on GT strength distributions measured in beta decays and (He-3,t) reactions performed at an intermediate incident energy of 140 MeV/nucleon and 0 degrees are compared. The combined results help provide an understanding of nuclear structure of nuclei far-from-stability.
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XENON100 Collaboration(Aprile, E. et al), & Orrigo, S. E. A. (2014). First axion results from the XENON100 experiment. Phys. Rev. D, 90(6), 062009–7pp.
Abstract: We present the first results of searches for axions and axionlike particles with the XENON100 experiment. The axion-electron coupling constant, g(Ae), has been probed by exploiting the axioelectric effect in liquid xenon. A profile likelihood analysis of 224.6 live days x 34-kg exposure has shown no evidence for a signal. By rejecting g(Ae) larger than 7.7 x 10(-12) (90% C. L.) in the solar axion search, we set the best limit to date on this coupling. In the frame of the DFSZ and KSVZ models, we exclude QCD axions heavier than 0.3 and 80 eV/c(2), respectively. For axionlike particles, under the assumption that they constitute the whole abundance of dark matter in our galaxy, we constrain gAe to be lower than 1 x 10(-12) (90% C.L.) for masses between 5 and 10 keV/c(2).
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