Wed·Jun 27, 2018Wednesday·June 27, 2018

1. 01*

   Nuclear level densities and $\gamma$-ray strength functions of ${}^{87}\mathrm{Kr}$ -- First application of the Oslo Method in inverse kinematics

   V. W. Ingeberg (1)🇳🇴 · S. Siem (1)🇳🇴 · M. Wiedeking (2)🇿🇦 · K. Sieja (3 and 4)🇫🇷 · D. L. Bleuel (5)🇺🇸 · C. P. Brits (2 and 6)🇿🇦 · T. D. Bucher (2)🇿🇦 · T. S. Dinoko (2)🇿🇦 · J. L. Easton (2 and 7)🇿🇦 · A. Görgen (1)🇳🇴 · M. Guttormsen (1)🇳🇴 · P. Jones (2)🇿🇦 and 17 other authors

   The $\gamma$-ray strength function ($\gamma$SF) and nuclear level density (NLD) have been extracted for the first time from inverse kinematic reactions with the Oslo Method. This novel technique allows measurements of these properties across a wide range of previously inaccessible nuclei. Proton-$\gamma$ coincidence events from the $\mathrm{d}{(}^{86}\mathrm{Kr},\mathrm{p}\gamma {)}^{87}\mathrm{Kr}$ reaction were measured at iThemba LABS and the $\gamma$SF and NLD in ${}^{87}\mathrm{Kr}$ obtained. The low-energy region of the $\gamma$SF is compared to Shell Model calculations which suggest this region to be dominated by M1 strength. The $\gamma$SF and NLD are used as input parameters to Hauser-Feshbach calculations to constrain $(\mathrm{n},\gamma )$ cross sections of nuclei using the TALYS reaction code. These results are compared to ${}^{86}\mathrm{Kr}(n,\gamma )$ data from direct measurements.

   nucl-exEPJA(2020)·34 citations
2. 02*

   Are the Muonic Hydrogen and Electron Scattering Experiments Measuring the Same Observable?

   T.W. Donnelly🇺🇸 · D.K. Hasell🇺🇸 · R.G. Milner🇺🇸

   Elastic scattering of relativistic electrons from the nucleon yields Lorentz invariant form factors that describe the fundamental distribution of charge and magnetism. The spatial dependence of the nucleon's charge and magnetism is typically interpreted in the Breit reference frame which is related by a Lorentz boost from the laboratory frame, where the nucleon is at rest. We construct a model to estimate how the Sachs electric and magnetic form factors can be corrected for the effects of relativistic recoil. When the corrections are applied, the ratio of the proton's Sachs form factors is approximately flat with $Q^2$, i.e. the spatial distributions of the proton's intrinsic charge and magnetization are similar. Further, we estimate the correction due to recoil that must be applied to the determination of the proton charge radius from elastic electron scattering before it can be compared to the value determined using the Lamb shift in hydrogen. Application of the correction brings the two values of the proton charge radius into significantly closer agreement. Predicted corrections based on the model are provided for the rms charge radii of the deuteron, the triton, and the helium isotopes.

   nucl-ex0 citations
3. 03*

   Neutron Dark Matter Decays

   A. N. Ivanov🇦🇹 · R. Höllwieser🇦🇹 · N. I. Troitskaya🇦🇹 · M. Wellenzohn🇦🇹 · Ya. A. Berdnikov🇷🇺

   We analyse the discrepancy between the neutron lifetimes measured in the bottle and beam experiments. Following Fornal and Grinstein (Phys. Rev. Lett. 120, 191801 (2018)) we propose an explanation of such a puzzle by the dark matter channels of the neutron decay. However, unlike Fornal and Grinstein in addition to the dark matter decay channel n -> \chi + e^- + e^+, where \chi is a dark matter Dirac fermion and (e^-e^+) is an electron--positron pair, we assume the existence of the dark matter channel n -> chi + \nu_e + \bar{\nu}_e, where \nu_e \bar{\nu}_e is the electron neutrino-antineutrino pair. This allows to describe the discrepancy between the measurements of the neutron lifetime even in case of an unobservability of the dark matter decay channel n -> \chi + e^- + e^+, which may be below the reaction threshold. The existence of the coupling n -> \chi + e^- + e^+ can be observed experimentally by measuring electron-neutron scattering e^- + n -> \chi + e^- at very low electron energies, induced with the strength as of the decay n -> \chi + \nu_e + \bar{\nu}_e$. We propose a gauge invariant quantum field theory model with SU_L(2)\times U_R(1) \times U_R'(1)\times U''_L(1) symmetry for the UV completion of the effective (n\chi \ell \bar{\ell}) interaction, where \ell(\bar{\ell}) is electron (positron) or neutrino(antineutrino).

   ↳ hep-phgr-qcnucl-ex20 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.