Tue·Mar 27, 2018Tuesday·March 27, 2018

1. 01*

   The nuclear symmetry energy and the breaking of the isospin symmetry: how do they reconcile with each other?

   X. Roca-Maza (1)🇮🇹 · G. Colo' (1)🇮🇹 · H. Sagawa (2) ((1) Universita' degli Studi and INFN, Via Celoria 16, 20133 Milano, Italy (2) RIKEN Nishina Center, Wako 351-0198, Japan and University of Aizu, Aizu-Wakamatsu, Fukushima 965-8560, Japan)🇯🇵

   We analyze and propose a solution to the apparent inconsistency between our current knowledge of the Equation of State of asymmetric nuclear matter, the energy of the Isobaric Analog State (IAS) in a heavy nucleus such as 208Pb, and the isospin symmetry breaking forces in the nuclear medium. This is achieved by performing state-of-the-art Hartree-Fock plus Random Phase Approximation calculations of the IAS that include all isospin symmetry breaking contributions. To this aim, we propose a new effective interaction that is successful in reproducing the IAS excitation energy without compromising other properties of finite nuclei.

   ↳ nucl-thnucl-exPRL(2018)·54 citations
2. 02*

   COHERENT 2018 at the Spallation Neutron Source

   D. Akimov🇷🇺 · J.B. Albert🇺🇸 · P. An🇺🇸 · C. Awe🇺🇸 · P.S. Barbeau🇺🇸 · B. Becker🇺🇸 · V. Belov🇷🇺 · M.A. Blackston🇺🇸 · A. Bolozdynya🇷🇺 · A. Brown🇺🇸 · A. Burenkov🇷🇺 · B. Cabrera-Palmer🇺🇸 and 67 other authors

   The primary goal of the COHERENT collaboration is to measure and study coherent elastic neutrino-nucleus scattering (CEvNS) using the high-power, few-tens-of-MeV, pulsed source of neutrinos provided by the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory (ORNL). The COHERENT collaboration reported the first detection of CEvNS [Akimov:2017ade] using a CsI[Na] detector. At present the collaboration is deploying four detector technologies: a CsI[Na] scintillating crystal, p-type point-contact germanium detectors, single-phase liquid argon, and NaI[Tl] crystals. All detectors are located in the neutron-quiet basement of the SNS target building at distances 20-30 m from the SNS neutrino source. The simultaneous measurement in all four COHERENT detector subsystems will test the $N^2$ dependence of the cross section and search for new physics. In addition, COHERENT is measuring neutrino-induced neutrons from charged- and neutral-current neutrino interactions on nuclei in shielding materials, which represent a non-negligible background for CEvNS as well as being of intrinsic interest. The Collaboration is planning as well to look for charged-current interactions of relevance to supernova and weak-interaction physics. This document describes concisely the COHERENT physics motivations, sensitivity, and next plans for measurements at the SNS to be accomplished on a few-year timescale.

   ↳ physics.ins-dethep-exnucl-ex109 citations
3. 03*

   On an attempt to optically excite the nuclear isomer in Th-229

   Simon Stellmer · Georgy Kazakov · Matthias Schreitl · Hendrik Kaser · Michael Kolbe · Thorsten Schumm

   We aim to perform direct optical spectroscopy of the Th-229 nuclear isomer to measure its energy and lifetime, and to demonstrate optical coupling to the nucleus. To this end, we develop Th-doped CaF2 crystals, which are transparent at the anticipated isomer wavelength. Such crystals are illuminated by tunable VUV undulator radiation for direct excitation of the isomer. We scan a 5 sigma region around the assumed isomer energy of 7.8(5) eV and vary the excitation time in sequential scans between 30 and 600 seconds. Suffering from an unforeseen strong photoluminescence of the crystal, the experiment is sensitive only to radiative isomer lifetimes between 0.2 and 1.1 seconds. For this parameter range, and assuming radiative decay as the dominant de-excitation channel, we can exclude an isomer with energy between 7.5 and 10 eV at the 95% confidence level.

   ↳ physics.atom-phnucl-exPRA(2018)·36 citations
4. 04*

   Nucleon internal degrees of freedom and the uniqueness of the Gamow-Teller state

   N. Auerbach🇮🇱

   The Gamow-Teller strength in nuclei can be strongly affected by the internal degrees of freedom of the nucleon. It is demonstrated that this feature is unique to the Gamow-Teller. Excitation modes that involve spatial degrees of freedom are much less influenced by the internal excitation of nucleons. The fact that the observed Gamow-Teller strength is quenched by 30-40 percent in all nuclei suggests that indeed this is due to the nucleon excitation in nuclei.

   ↳ nucl-thnucl-ex1 citation
5. 05*

   Accurate nucleon electromagnetic form factors from dispersively improved chiral effective field theory

   J. M. Alarcón🇺🇸 · C. Weiss🇺🇸

   We present a theoretical parametrization of the nucleon electromagnetic form factors (FFs) based on a combination of chiral effective field theory and dispersion analysis. The isovector spectral functions on the two-pion cut are computed using elastic unitarity, chiral pion-nucleon amplitudes, and timelike pion FF data. Higher-mass isovector and isoscalar t-channel states are described by effective poles, whose strength is fixed by sum rules (charges, radii). Excellent agreement with the spacelike proton and neutron FF data is achieved up to Q^2 \sim 1 GeV^2. Our parametrization provides proper analyticity and theoretical uncertainty estimates and can be used for low-Q^2 FF studies and proton radius extraction.

   ↳ hep-phhep-latnucl-exPLB(2018)·30 citations
6. 06*

   Measurement of ambient neutrons in an underground laboratory at Kamioka Observatory

   Keita Mizukoshi🇯🇵 · Ryosuke Taishaku🇯🇵 · Keishi Hosokawa🇯🇵 · Kazuyoshi Kobayashi🇯🇵 · Kentaro Miuchi🇯🇵 · Tatsuhiro Naka🇯🇵 · Atsushi Takeda🇯🇵 · Masashi Tanaka🇯🇵 · Yoshiki Wada🇯🇵 · Kohei Yorita🇯🇵 · Sei Yoshida🇯🇵

   Ambient neutrons are one of the most serious backgrounds for underground experiments searching for rare events. The ambient neutron flux in an underground laboratory of Kamioka Observatory was measured using a ${}^3\mathrm{He}$ proportional counter with various moderator setups. Since the detector response largely depends on the spectral shape, the energy spectra of the neutrons transported from the rock to the laboratory are estimated by Monte-Carlo simulations. The ratio of the thermal neutron flux to the total neutron flux was found to depend on the thermalizing efficiency of the rock. Therefore, the ratio of the count rate without a moderator to that with a moderator was used to determine this parameter. Consequently, the most-likely neutron spectrum predicted by the simulations for the parameters determined by the experimental results was obtained. The result suggests an interesting spectral shape, which has not been indicated in previous studies. The total ambient neutron flux is $(23.52\pm 0.68{{}_{stat.}}_{-2.13}^{+1.87}{}_{sys.})\times 10^{-6}$ cm${}^{-2}$ s${}^{-1}$. This result, especially the energy spectrum information, could be a new and important input for estimating the background in current and future experiments in the underground laboratory at Kamioka Observatory.

   ↳ physics.ins-dethep-exnucl-exPTEP(2018)·11 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.