Mon·Feb 19, 2018Monday·February 19, 2018

1. 01*

   A Search for Possible Long Range Spin Dependent Interactions of the Neutron From Exotic Vector Boson Exchange

   Christopher C. Haddock · Joseph Amadio · Eamon Anderson · Libertad Barron-Palos · Bret Crawford · Daniel Esposito · Walter Fox · Ian Francis · Jason Fry · Hanna Gardiner · Adam Holley · Kirill Korsak and 17 other authors

   We present a search for possible spin dependent interactions of the neutron with matter through exchange of spin 1 bosons with axial vector couplings as envisioned in possible extensions of the Standard Model. This was sought using a slow neutron polarimeter that passed transversely polarized slow neutrons by unpolarized slabs of material arranged so that this interaction would tilt the plane of polarization and develop a component along the neutron momentum. The result for the rotation angle, ${\varphi }_{V_5}^{\prime }=[2.8\pm 4.6(stat.)\pm 4.0(sys.)]\times 10^{-5}\text{mbox}rad/m$ is consistent with zero. This result improves the upper bounds on the neutron-matter coupling $g_A^2$ from such an interaction by about three orders of magnitude for force ranges in the mm-$\mu$m regime.

   nucl-exhep-exphysics.ins-detPLB(2018)·27 citations
2. 02*

   Impacts of nuclear-physics uncertainties in the s-process determined by Monte-Carlo variations

   N. Nishimura🇬🇧 · G. Cescutti · R. Hirschi🇬🇧 · T. Rauscher🇬🇧 · J. den Hartogh🇭🇺 · A. St. J. Murphy🇬🇧

   The s-process, a production mechanism based on slow-neutron capture during stellar evolution, is the origin of about half the elements heavier than iron. Abundance predictions for s-process nucleosynthesis depend strongly on the relevant neutron-capture and $\beta$-decay rates, as well as on the details of the stellar model being considered. Here, we have used a Monte-Carlo approach to evaluate the nuclear uncertainty in s-process nucleosynthesis. We considered the helium burning of massive stars for the weak s-process and low-mass asymptotic-giant-branch stars for the main s-process. Our calculations include a realistic and general prescription for the temperature dependent uncertainty for the reaction cross sections. We find that the adopted uncertainty for ($\mathrm{n},\gamma$) rates, tens of per cent on average, effects the production of s-process nuclei along the line of $\beta$-stability, and that the uncertainties in $\beta$-decay from excited state contributions, has the strongest impact on branching points.

   ↳ astro-ph.SRnucl-exnucl-thJAEA-Conf 2018-001·5 citations
3. 03*

   Sensitivity to neutron captures and beta-decays of the enhanced s-process in rotating massive stars at low metallicities

   N. Nishimura🇬🇧 · R. Hirschi🇬🇧 · T. Rauscher🇬🇧

   The s-process in massive stars, producing nuclei up to $A\approx 90$, has a different behaviour at low metallicity if stellar rotation is significant. This enhanced s-process is distinct from the s-process in massive stars around solar metallicity, and details of the nucleosynthesis are poorly known. We investigated nuclear physics uncertainties in the enhanced s-process in metal-poor stars within a Monte-Carlo framework. We applied temperature-dependent uncertainties of reaction rates, distinguishing contributions from the ground state and from excited states. We found that the final abundance of several isotopes shows uncertainties larger than a factor of 2, mostly due to the neutron capture uncertainties. A few nuclei around branching points are affected by uncertainties in the $\beta$-decay.

   ↳ astro-ph.SRnucl-exnucl-thJ.Phys.Conf.Ser.(2018)·1 citation
4. 04*

   Decay Modes of the Hoyle State in ${}^{12}C$

   H. Zheng🇮🇹 · A. Bonasera🇺🇸 · M. Huang🇨🇳 · S. Zhang🇨🇳

   Recent experimental results give an upper limit less than 0.043\% (95\% C.L.) to the direct decay of the Hoyle state into 3$\alpha$ respect to the sequential decay into ${}^8${Be}+$\alpha$. We performed one and two-dimensional tunneling calculations to estimate such a ratio and found it to be more than one order of magnitude smaller than experiment depending on the range of the nuclear force. This is within high statistics experimental capabilities. Our results can also be tested by measuring the decay modes of high excitation energy states of ${}^{12}$C where the ratio of direct to sequential decay might reach 10\% at $E^{\ast }$(${}^{12}$C)=10.3 MeV. The link between a Bose Einstein Condensate (BEC) and the direct decay of the Hoyle state is also addressed. We discuss a hypothetical `Efimov state' at $E^{\ast }$(${}^{12}$C)=7.458 MeV, which would mainly {\it sequentially} decay with 3$\alpha$ of {\it equal energies}: a counterintuitive result of tunneling. Such a state, if it would exist, is at least 8 orders of magnitude less probable than the Hoyle's, thus below the sensitivity of recent and past experiments.

   ↳ nucl-thnucl-exPLB(2018)·25 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.