Mon·Jul 1, 2019Monday·July 1, 2019

1. 01*

   Gamma Ray Spectra from Thermal Neutron Capture on Gadolinium-155 and Natural Gadolinium

   Tomoyuki Tanaka🇯🇵 · Kaito Hagiwara🇯🇵 · Enrico Gazzola🇮🇹 · Takashi Sudo🇯🇵 · Mandeep Singh Reen🇯🇵 · Ajmi Ali🇯🇵 · Iwa Ou🇯🇵 · Rohit Dhir🇯🇵 · Pretam Kumar Das🇯🇵 · Yusuke Koshio🇯🇵 · Makoto Sakuda🇯🇵 · Atsushi Kimura🇯🇵 and 9 other authors

   Natural gadolinium is widely used for its excellent thermal neutron capture cross section, because of its two major isotopes: ${}^{155}$Gd and ${}^{157}$Gd. We measured the $\gamma$-ray spectra produced from the thermal neutron capture on targets comprising a natural gadolinium film and enriched ${}^{155}$Gd (in Gd${}_2$O${}_3$ powder) in the energy range from 0.11 MeV to 8.0 MeV, using the ANNRI germanium spectrometer at MLF, J-PARC. The freshly analysed data of the ${}^{155}$Gd(n, $\gamma$) reaction are used to improve our previously developed model (ANNRI-Gd model) for the ${}^{157}$Gd(n, $\gamma$) reaction, and its performance confirmed with the independent data from the ${}^{\mathrm{nat}}$Gd(n, $\gamma$) reaction. This article completes the development of an efficient Monte Carlo model required to simulate and analyse particle interactions involving the thermal neutron captures on gadolinium in any relevant future experiments.

   nucl-exhep-exphysics.ins-detPTEP(2020)·33 citations
2. 02*

   Elastic Antiproton-Nucleus Scattering from Chiral Forces

   Matteo Vorabbi🇨🇦 · Michael Gennari🇨🇦 · Paolo Finelli🇮🇹 · Carlotta Giusti🇮🇹 · Petr Navrátil🇨🇦

   Elastic scattering of antiprotons off ${}^4$He, ${}^{12}$C, and ${}^{16,18}$O is described for the first time with a totally microscopic approach based on the calculation of an optical potential (OP) describing the antiproton-target interaction. The OP is derived using the recent antiproton-nucleon ($\bar{p}N$) chiral interaction to calculate the $\bar{p}N$ $t$ matrix, while the target densities are computed with the ab initio no-core shell model using chiral interactions as well. Our results are in a good agreement with the existing experimental data and the results computed at different chiral orders of the $\bar{p}N$ interaction display the convergence pattern expected from the theory.

   ↳ nucl-thnucl-exPRL(2020)·15 citations
3. 03*

   $DK$, $DDK$, and $DDDK$ molecules--understanding the nature of the $D_{s0}^{\ast }(2317)$

   Tian-Wei Wu🇨🇳 · Ming-Zhu Liu🇨🇳 · Li-Sheng Geng🇨🇳 · Emiko Hiyama🇯🇵 · Manuel Pavon Valderrama🇨🇳

   The $DK$ interaction is strong enough to form a bound state, the $D_{s0}^{\ast }(2317)$. This in turn begs the question of whether there are bound states composed of several charmed mesons and a kaon. Previous calculations indicate that the three-body $DDK$ system is probably bound, where the quantum numbers are $J^P=0^{-}$, $I=\frac{1}{2}$, $S=1$ and $C=2$. The minimum quark content of this state is $cc\bar{q}\bar{s}$ with $q=u,d$, which means that, if discovered, it will be an explicitly exotic tetraquark. In the present work. we apply the Gaussian Expansion Method to study the $DDDK$ system and show that it binds as well. The existence of these three and four body states is rather robust with respect to the $DD$ interaction and subleading (chiral) corrections to the $DK$ interaction. If these states exist, it is quite likely that their heavy quark symmetry counterparts exist as well. These three-body $DDK$ and four-body $DDDK$ molecular states could be viewed as counterparts of atomic nuclei, which are clusters of nucleons bound by the residual strong force, or chemical molecules, which are clusters of atoms bound by the residual electromagnetic interaction.

   ↳ hep-phhep-exhep-latnucl-ex+1PRD(2019)·68 citations
4. 04*

   Suppression of elliptic flow without viscosity

   Adam Takacs🇳🇴 · Denes Molnar🇭🇺

   We investigate fluid-to-particle conversion using the usual Cooper-Frye approach but with more general local equilibrium distributions than the Boltzmann or Bose/Fermi distributions typically used. Even though we study ideal fluids (i.e., shear stress and bulk pressure are zero everywhere), we find a suppression of elliptic flow (v2) at high transverse momenta (pT>1.5 GeV/c), relative to results obtained with the traditional Boltzmann distributions. The non-viscous suppression shows qualitatively similar features to the well-known shear viscous suppression of v2; for example, it increases with pT, and it is smaller for heavier species as seen in self-consistent kinetic theory calculations. Our results question whether all of the v2 suppression seen in the data can be attributed to viscous effects, and indicate that shear viscosities extracted from RHIC and LHC elliptic flow data might be overestimated.

   ↳ nucl-thhep-exhep-phnucl-ex8 citations
5. 05*

   How AMPT generates large elliptic flow with small cross sections

   Denes Molnar (Dept. of Physics and Astronomy, Purdue University, West Lafayette, IN)🇺🇸

   We resolve the long-standing open question of how the transport model AMPT manages to generate sufficiently high elliptic flow (v2) in A+A reactions with only few-millibarn 2->2 partonic cross sections - in apparent contradiction with an early study by Molnar and Gyulassy. Through detailed comparisons with the covariant Molnar's Parton Cascade (MPC), we pinpoint which features of initial conditions, interactions, and dynamics encoded in the partonic stage of AMPT allow it to circumvent the "opacity puzzle" at RHIC.

   ↳ nucl-thhep-phnucl-ex9 citations
6. 06*

   Metastable Nuclear Isomers as Dark Matter Accelerators

   Maxim Pospelov🇨🇦 · Surjeet Rajendran🇺🇸 · Harikrishnan Ramani🇺🇸

   Inelastic dark matter and strongly interacting dark matter are poorly constrained by direct detection experiments since they both require the scattering event to deliver energy from the nucleus into the dark matter in order to have observable effects. We propose to test these scenarios by searching for the collisional de-excitation of meta-stable nuclear isomers by the dark matter particles. The longevity of these isomers is related to a strong suppression of $\gamma$- and $\beta$-transitions, typically inhibited by a large difference in the angular momentum for the nuclear transition. The collisional de-excitation by dark matter is possible since heavy dark matter particles can have a momentum exchange with the nucleus comparable to the inverse nuclear size, hence lifting tremendous angular momentum suppression of the nuclear transition. This de-excitation can be observed either by searching for the direct effects of the decaying isomer, or through the re-scattering or decay of excited dark matter states in a nearby conventional dark matter detector setup. Existing nuclear isomer sources such as naturally occurring ${}^{180m}$Ta, ${}^{137m}$Ba produced in decaying Cesium in nuclear waste, ${}^{177m}$Lu from medical waste, and ${}^{178m}$Hf from the Department of Energy storage can be combined with current dark matter detector technology to search for this class of dark matter.

   ↳ hep-phastro-ph.COhep-exnucl-ex+1PRD(2020)·48 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.