Thu·Apr 11, 2019Thursday·April 11, 2019

1. 01*

   First evidence of enhanced low-energy $\gamma$-ray strength from thermal neutron capture data

   L. Crespo Campo🇳🇴 · R. B. Firestone🇺🇸 · B. A. Brown🇺🇸 · M. Guttormsen🇳🇴 · R. Schwengner🇩🇪

   The $\gamma$-ray strength function, or average reduced $\gamma$-ray transition probability, is a fundamental input in the calculation of $(n,\gamma )$ cross sections used to simulate the nucleosynthesis of elements heavier than Fe. Since 2004, an enhanced probability of $\gamma$-decay with $\gamma$-ray energies below $\approx 2-4$ MeV has been measured in reaction data for numerous nuclei. This has been observed as an increase in the $\gamma$-ray strength with decreasing $\gamma$-ray energy, often referred to as the low-energy enhancement or \textit{upbend} in the $\gamma$-ray strength. Nevertheless, the available data confirming this enhancement corresponded solely to charged-particle included reactions and no low-energy enhancement had yet been confirmed from neutron-induced reaction measurements. In this work, we present the first evidence of low-energy $\gamma$-ray strength enhancement from neutron-capture reaction data. Gamma-ray spectra following thermal neutron capture on ${}^{58,60}$Ni have been used to determine the strength for primary and secondary $\gamma$-rays in ${}^{59,61}$Ni, showing an enhancement for $\gamma$-ray energies below $\approx 3$ MeV and $\approx 2$ MeV for ${}^{59,61}$Ni, respectively. For the first time, this enhancement is observed down to $\gamma$-ray energies of $\approx 0.2$ MeV. Further, available spin-parity assignments have been used to obtain the multipolarity and electromagnetic character of these transitions, showing that this low-energy enhancement is dominated by $M1$ and $E2$ strength, with $E1$ strength also exceeding Standard Lorentzian Model predictions. Finally, large-basis shell-model calculations have been performed, also predicting a strong $M1$ enhancement at low $\gamma$-ray energies.

   nucl-ex1 citation
2. 02*

   Fine structure in the $\alpha$ decay of ${}^{223}$U

   M.D. Sun · Z. Liu🇨🇳 · T.H. Huang · W.Q. Zhang · A.N. Andreyev🇬🇧 · B. Ding🇨🇳 · J.G. Wang🇨🇳 · X.Y. Liu🇹🇭 · H.Y. Lu🇺🇸 · D.S. Hou · Z.G. Gan🇨🇳 · L. Ma🇨🇳 and 20 other authors

   Fine structure in the $\alpha$ decay of ${}^{223}$U was observed in the fusion-evaporation reaction ${}^{187}$Re(${}^{40}$Ar, p3n) by using fast digital pulse processing technique. Two $\alpha$-decay branches of ${}^{223}$U feeding the ground state and 244 keV excited state of ${}^{219}$Th were identified by establishing the decay chain ${}^{223}$U $\stackrel{{\alpha }_1}{\to }$ ${}^{219}$Th $\stackrel{{\alpha }_2}{\to }$ ${}^{215}$Ra $\stackrel{{\alpha }_3}{\to }$ ${}^{211}$Rn. The $\alpha$-particle energy for the ground-state to ground-state transition of ${}^{223}$U was determined to be 8993(17) keV, 213 keV higher than the previous value, the half-life was updated to be 62${}_{-10}^{+14}$ $\mu$s. Evolution of nuclear structure for $N$ = 131 even-$Z$ isotones from Po to U was discussed in the frameworks of nuclear mass and reduced $\alpha$-decay width, a weakening octupole deformation in the ground state of ${}^{223}$U relative to its lighter isotones ${}^{219}$Ra and ${}^{221}$Th was suggested.

   nucl-exPLB(2020)·10 citations
3. 03*

   Delineating the properties of matter in cold, dense QCD

   Toru Kojo🇨🇳

   The properties of dense QCD matter are delineated through the construction of equations of state which should be consistent with QCD calculations in the low and high density limits, nuclear laboratory experiments, and the neutron star observations. These constraints, together with the causality condition of the sound velocity, are used to develop the picture of hadron-quark continuity in which hadronic matter continuously transforms into quark matter (modulo small 1st order phase transitions). For hadronic matter (at baryon density nB > ~2n0 with n0 ~ 0.16 fm^(-3) being the nuclear saturation density) we use equations of state by Togashi et al. based on microscopic variational many-body calculations, and for quark matter (nB > ~5n0) we construct equations of state using a schematic quark model (with strangeness) whose interactions are motivated by the hadron phenomenology. The region between hadronic and quark matters (~2n0 < nB < ~5n0), which is most difficult to calculate, is treated by highly constrained interpolation between nuclear and quark matter equations of state. The resultant unified equation of state at zero temperature and beta-equilibrium, which we call Quark-Hadron-Crossover (QHC18 and QHC19), is consistent with the measured properties of neutron stars and in addition gives us microscopic insights into the properties of dense QCD matter. In particular to ~10n0 the gluons can remain as non-perturbative as in vacuum and the strangeness can be as abundant as up- and down-quarks at the core of two-solar mass neutron stars. Within our modeling the maximum mass is found less than ~2.35 times solar mass and the baryon density at the core ranges in ~5-8n0.

   ↳ astro-ph.HEnucl-exnucl-thAIP Conf.Proc.(2019)·13 citations
4. 04*

   Pomeron, nucleon-resonance, and $(0^{+},0^{-},1^{+})$-meson contributions in $\varphi$-meson photoproduction

   Sang-Ho Kim🇰🇷 · Seung-il Nam🇰🇷

   We investigate the reaction mechanism of the $\varphi$-meson photoproduction off the proton target, i.e., $\gamma p\to \varphi p$, up to $\sqrt{s}=2.8$ GeV. For this purpose, we employ an effective Lagrangian approach in the tree-level Born approximation, and we employ various experimental and theoretical inputs. As a theoretical setup, the vectorlike Pomeron ($C=+1$) is taken into account as a parameterized two-gluon exchange contribution. We also consider $f_1(1285)$ axial-vector-meson, ($\pi ,\eta$) pseudoscalar-meson, and ($a_0,f_0$) scalar-meson exchanges in the $t$ channel, in addition to the experimentally confirmed nucleon resonances, such as $N^{\ast }(2000,5/2^{+})$ and $N^{\ast }(2300,1/2^{+})$, for the direct $\varphi$-meson radiations in the $s$ and $u$ channels. We provide numerical results for the total and differential cross sections as well as the spin-density matrices in the Gottfried-Jackson, Adair, and helicity frames. We observe that, together with the universally accepted pomeron contribution, the considered meson and nucleon-resonance contributions play significant roles in reproducing the experimental data for the forward and backward $\varphi$-meson scattering-angle regions, respectively, indicating the nontrivial interferences between mesonic and baryonic contributions.

   ↳ hep-phhep-exnucl-exnucl-thPRC(2019)·12 citations
5. 05*

   Studying nucleon structure via Double Deeply Virtual Compton Scattering (DDVCS)

   Shengying Zhao🇫🇷

   Study of the structure and dynamics of the nucleon has been deeply renewed with the advent of a parameterization of the partonic structure of the nucleon in terms of the Generalized Parton Distributions (GPDs). Encoding the correlations between the elementary constituents of the nucleon, GPDs allow a 3-dimensional imaging of the nucleon from the dynamical link between the transverse position and the longitudinal momentum of partons. Double Deeply Virtual Compton Scattering (DDVCS) corresponds to the scattering from the nucleon of a virtual photon that finally generates a lepton pair, where the final leptons can be either an electron or a muon pair. The virtuality of the final photon allows to investigate in a decorrelated way the initial and transferred momentum dependences of the GPDs. This unique feature of DDVCS is of relevance, among others, for the determination of the transverse parton densities and the distribution of nuclear forces. This proceeding discusses preliminary model-predicted DDVCS experimental projections at JLab12 and indicates the impact of potential DDVCS experiments.

   ↳ hep-phnucl-exPoS(2019)·5 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.