Wed·Feb 12, 2020Wednesday·February 12, 2020

1. 01*

   Detection prospects for the second-order weak decays of ${}^{124}$Xe in multi-tonne xenon time projection chambers

   Christian Wittweg🇩🇪 · Brian Lenardo🇺🇸 · Alexander Fieguth🇺🇸 · Christian Weinheimer🇩🇪

   We investigate the detection prospects for two-neutrino and neutrinoless second order weak decays of ${}^{124}$Xe -- double electron capture ($0/2\nu \text{ECEC}$), electron capture with positron emission ($0/2\nu \text{EC}{\beta }^{+}$) and double-positron emission ($0/2\nu {\beta }^{+}{\beta }^{+}$) -- in multi-tonne xenon time projection chambers. We simulate the decays in a liquid xenon medium and develop a reconstruction algorithm which uses the multi-particle coincidence in these decays to separate signal from background. This is used to compute the expected detection efficiencies as a function of position resolution and energy threshold for planned experiments. In addition, we consider an exhaustive list of possible background sources and find that they are either negligible in rate or can be greatly reduced using our topological reconstruction criteria. In particular, we draw two conclusions: First, with a half-life of $T_{1/2}^{2\nu \text{EC}{\beta }^{+}}=(1.7\pm 0.6)\cdot 10^{23}\text{yr}$, the $2\nu \text{EC}{\beta }^{+}$ decay of ${}^{124}$Xe will likely be detected in upcoming Dark Matter experiments (e.g. XENONnT or LZ), and their major background will be from gamma rays in the detector construction materials. Second, searches for the $0\nu \text{EC}{\beta }^{+}$ decay mode are likely to be background-free, and new parameter space may be within the reach. To this end we investigate three different scenarios of existing experimental constraints on the effective neutrino mass. The necessary 500 kg-year exposure of ${}^{124}$Xe could be achieved by the baseline design of the DARWIN observatory, or by extracting and using the ${}^{124}$Xe from the tailings of the nEXO experiment. We demonstrate how a combination of ${}^{124}$Xe results with those from $0\nu {\beta }^{-}{\beta }^{-}$ searches in ${}^{136}$Xe could help to identify the neutrinoless decay mechanism.

   nucl-exhep-exnucl-thEPJC(2020)·19 citations
2. 02*

   A method to test the coupling strength of the linear and nonlinear contributions to higher-order flow harmonics via Event Shape Engineering

   Niseem Magdy🇺🇸 · Olga Evdokimov🇺🇸 · Roy A. Lacey🇺🇸

   A Multi-Phase Transport (AMPT) model is used to study the efficacy of shape-engineered events to delineate the degree of coupling between the linear and nonlinear contributions to the higher-order flow harmonics $v_4$ and $v_5$. The study shows that the nonlinear contributions are strongly shape-dependent while the linear contributions are shape-independent, indicating little if any, coupling between the linear and nonlinear flow coefficients. The experimental verification of such patterns could be an invaluable tool for robust extraction of the linear and mode-coupled flow coefficients, especially for beam energies where the charged particle multiplicity and the event statistics precludes the use of current methods to establish the coupling strength.

   nucl-exnucl-thJ.Phys.G(2020)·24 citations
3. 03*

   An Integral Experiment on Polyethylene Using Radiative Capture in Indium Foils in a High Flux D-D Neutron Generator

   Nnaemeka Nnamani · Karl van Bibber🇺🇸 · Lee A Bernstein · Jasmina L Vujic · Jonathan T. Morrell🇺🇸

   The Department of Nuclear Engineering, University of California Berkeley built a D-D neutron generator called the High Flux Neutron Generator (HFNG). It operates in the range of 100-125 keV of accelerating voltage. The generator produces neutron current of about 10^8 per second. These neutrons have energies between 2.2-2.8 MeV. We report here the results of a measurement of the scattered vs unscattered neutron fluence on polyethylene determined via neutron activation of multiple natural indium foils from a D-D neutron generator. Both the angle-integrated spectrum and the angle differential results are consistent with the predictions of the Monte Carlo N-Particle Transport (MCNP) code, using the ENDF/B-VII.1. This supports shielding calculations in the fast energy region with high density polyethylene (HDPE). To the best of our knowledge no integral benchmark experiment has been performed on polyethylene using D(D,n)alpha neutron spectrum.

   nucl-exnucl-th0 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.