Fri·Nov 17, 2017Friday·November 17, 2017

1. 01*

   Comparison of heavy-ion transport simulations: Collision integral in a box

   Ying-Xun Zhang🇨🇳 · Yong-Jia Wang🇨🇳 · Maria Colonna🇮🇹 · Pawel Danielewicz🇺🇸 · Akira Ono🇯🇵 · Betty Tsang🇺🇸 · Hermann Wolter🇩🇪 · Jun Xu🇨🇳 · Lie-Wen Chen🇨🇳 · Dan Cozma🇷🇴 · Zhao-Qing Feng🇨🇳 · Subal Das Gupta🇨🇦 and 18 other authors

   Simulations by transport codes are indispensable to extract valuable physics information from heavy ion collisions. In order to understand the origins of discrepancies between different widely used transport codes, we compare 15 such codes under controlled conditions of a system confined to a box with periodic boundary, initialized with Fermi-Dirac distributions at saturation density and temperatures of either 0 or 5 MeV. In such calculations, one is able to check separately the different ingredients of a transport code. In this second publication of the code evaluation project, we only consider the two-body collision term, i.e. we perform cascade calculations. When the Pauli blocking is artificially suppressed, the collision rates are found to be consistent for most codes (to within $1\%$ or better) with analytical results, or completely controlled results of a basic cascade code after eliminating the correlations within the same pair of colliding particles. In calculations with active Pauli blocking, the blocking probability was found to deviate from the expected reference values. The reason is found in substantial phase-space fluctuations and smearing tied to numerical algorithms and model assumptions in the representation of phase space. This results in the reduction of the blocking probability in most transport codes, so that the simulated system gradually evolves away from the Fermi-Dirac towards a Boltzmann distribution. As a result of this investigation, we are able to make judgements about the most effective strategies in transport simulations for determining the collision probabilities and the Pauli blocking. Investigation in a similar vein of other ingredients in transport calculations, like the mean field propagation or the production of nucleon resonances and mesons, will be discussed in the future publications.

   ↳ nucl-thnucl-exPRC(2018)·168 citations
2. 02*

   Can one ever prove that neutrinos are Dirac particles?

   Martin Hirsch🇪🇸 · Rahul Srivastava🇪🇸 · José W. F. Valle🇪🇸

   According to the "Black Box" theorem the experimental confirmation of neutrinoless double beta decay ($0\nu 2\beta$) would imply that at least one of the neutrinos is a Majorana particle. However, a null $0\nu 2\beta$ signal cannot decide the nature of neutrinos, as it can be suppressed even for Majorana neutrinos. In this letter we argue that if the null $0\nu 2\beta$ decay signal is accompanied by a $0\nu 4\beta$ quadruple beta decay signal, then at least one neutrino should be a Dirac particle. This argument holds irrespective of the underlying processes leading to such decays.

   ↳ hep-phhep-exnucl-exnucl-thPLB(2018)·57 citations
3. 03*

   Measurements and Monte-Carlo simulations of the particle self-shielding effect of B4C grains in neutron shielding concrete

   D. D. DiJulio🇸🇪 · C. P. Cooper-Jensen · I. Llamas-Jansa · S. Kazi🇳🇴 · P. M. Bentley

   A combined measurement and Monte-Carlo simulation study was carried out in order to characterize the particle self-shielding effect of B4C grains in neutron shielding concrete. Several batches of a specialized neutron shielding concrete, with varying B4C grain sizes, were exposed to a 2 Å neutron beam at the R2D2 test beamline at the Institute for Energy Technology located in Kjeller, Norway. The direct and scattered neutrons were detected with a neutron detector placed behind the concrete blocks and the results were compared to Geant4 simulations. The particle self-shielding effect was included in the Geant4 simulations by calculating effective neutron cross-sections during the Monte-Carlo simulation process. It is shown that this method well reproduces the measured results. Our results show that shielding calculations for low-energy neutrons using such materials would lead to an underestimate of the shielding required for a certain design scenario if the particle self-shielding effect is not included in the calculations.

   ↳ physics.ins-detnucl-exRadiat.Phys.Chem.(2018)·2 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.