Mon·Feb 4, 2019Monday·February 4, 2019

1. 01*

   Key ${}^{19}$Ne states identified affecting $\gamma$-ray emission from ${}^{18}$F in novae

   M.R. Hall · D.W. Barbadian · T. Baugher🇺🇸 · A. Lepailleur🇫🇷 · S.D. Pain🇺🇸 · A. Ratkiewicz · S. Ahn🇺🇸 · J.M. Allen🇺🇸 · J.T. Anderson🇺🇸 · A.D. Ayangeakaa🇺🇸 · J.C. Blackmon🇺🇸 · S. Burcher🇺🇸 and 25 other authors

   Detection of nuclear-decay $\gamma$ rays provides a sensitive thermometer of nova nucleosynthesis. The most intense $\gamma$-ray flux is thought to be annihilation radiation from the ${\beta }^{+}$ decay of ${}^{18}$F, which is destroyed prior to decay by the ${}^{18}$F($p$,$\alpha$)${}^{15}$O reaction. Estimates of ${}^{18}$F production had been uncertain, however, because key near-threshold levels in the compound nucleus, ${}^{19}$Ne, had yet to be identified. This Letter reports the first measurement of the ${}^{19}$F(${}^3$He,$t\gamma$)${}^{19}$Ne reaction, in which the placement of two long-sought 3/2${}^{+}$ levels is suggested via triton-$\gamma$-$\gamma$ coincidences. The precise determination of their resonance energies reduces the upper limit of the rate by a factor of $1.5-17$ at nova temperatures and reduces the average uncertainty on the nova detection probability by a factor of 2.1.

   nucl-exPRL(2019)·11 citations
2. 02*

   $s$-wave scattering lengths for the ${}^7$Be+p system from an $\text{R}$-matrix analysis

   S. N. Paneru (1)🇺🇸 · C. R. Brune (1)🇺🇸 · R. Giri (1) · R. J. Livesay (2) · U. Greife (2)🇺🇸 · J. C. Blackmon (3)🇺🇸 · D. W. Bardayan (4) · K. A. Chipps (5)🇺🇸 · B. Davids (6 and 7)🇨🇦 · D. S. Connolly (6) · K. Y. Chae (8)🇰🇷 · A. E. Champagne (9)🇺🇸 and 14 other authors

   The astrophysical $S$-factor for the radiative proton capture reaction on ${}^7$Be ($S_{17}$) at low energies is affected by the $s$-wave scattering lengths. We report the measurement of elastic and inelastic scattering cross sections for the ${}^7$Be+p system in the center-of-mass energy range 0.474 - 2.740 MeV and center-of-mass angular range of 70${}^{\circ }$- 150${}^{\circ }$. A radioactive ${}^7$Be beam produced at Oak Ridge National Laboratory's (ORNL) Holifield Radioactive Ion Beam Facility was accelerated and bombarded a thin polypropylene (CH${}_2$)${}_{\text{n}}$ target. Scattered ions were detected in the segmented Silicon Detector Array. Using an $\text{R}$-matrix analysis of ORNL and Louvain-la-Neuve cross section data, the $s$-wave scattering lengths for channel spins 1 and 2 were determined to be 17.34${}_{-1.33}^{+1.11}$ and -3.18${}_{-0.50}^{+0.55}$ fm, respectively. The uncertainty in the $s$-wave scattering lengths reported in this work is smaller by a factor of 5-8 compared to the previous measurement, which may reduce the overall uncertainty in $S_{17}$ at zero energy. The level structure of ${}^8$B is discussed based upon the results from this work. Evidence for the existence of 0${}^{+}$ and 2${}^{+}$ levels in ${}^8$B at 1.9 and 2.21 MeV, respectively, is observed.

   nucl-exastro-ph.SRnucl-thPRC(2019)·12 citations
3. 03*

   Nucleon and $\Delta$ isobar in a strong magnetic field

   Ulugbek Yakhshiev🇰🇷 · Hyun-Chul Kim🇰🇷 · Makoto Oka🇯🇵

   We investigate the static properties of the nucleon in the presence of strong magnetic fields and discuss the consequent changes of the nucleon structure, based on the Skyrme model. The results show that at large values of the magnetic field ($\sim 10^{17}$ to $10^{18}\mathrm{G}$), which is supposed to appear in heavy-ion collision experiments at RHIC energies, the soliton starts to deviate from the spherically symmetric form and its size starts to change. At extremely large values of the magnetic field ($\sim 10^{19}$ G), which may be found at the LHC experiments, the soliton becomes more compact than in free space. The results also show that in the presence of the external magnetic field, the mass of the nucleon tends to increase in general and the mass degeneracy of the $\Delta$ isobars from isospin symmetry will be lifted. We also discuss the changes in the mass difference between the $\Delta$ and the nucleon, $\Delta m_{\Delta \mathrm{N}}$, due to the influence of the external magnetic field. We find that $\Delta m_{\Delta \mathrm{N}}$ increases as the strength of the magnetic field grows.

   ↳ hep-phhep-exnucl-exnucl-thPRD(2019)·14 citations
4. 04*

   Evidence for Triangular D'(3h) Symmetry in 13C

   R. Bijker🇲🇽 · F. Iachello🇺🇸

   We derive the rotation-vibration spectrum of a 3alpha+1 neutron (proton) configuration with triangular D(3h) symmetry by exploiting the properties of the double group D'(3h), and show evidence for this symmetry to occur in the rotation-vibration spectra of 13C. Our results, based on purely symmetry considerations, provide benchmarks for microscopic calculations of the cluster structure of light nuclei.

   ↳ nucl-thnucl-exPRL(2019)·31 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.