Thu·May 14, 2020Thursday·May 14, 2020

1. 01*

   On the inversion of isobaric-analogue states in nuclei

   J. Henderson🇨🇦 · S. R. Stroberg🇺🇸

   Isospin is an approximate symmetry in atomic nuclei, arising from the rather similar properties of protons and neutrons. Perhaps the clearest manifestation of isospin within nuclei is in the near-identical structure of excited states in mirror nuclei: nuclei with inverted numbers of protons and neutrons. Isospin symmetry, and therefore mirror-symmetry, is broken by electromagnetic interactions and the difference in the masses of the up and down quarks. A recent study by Hoff and collaborators presented evidence that the ground-state spin of ${}^{73}$Sr is different from that of its mirror, ${}^{73}$Br, due to an inversion of the ground- and first-excited states, separated by only 27 keV in the ${}^{73}$Br system. In this brief note, we place this inversion within the necessary context of the past half-century of experimental and theoretical work, and show that it is entirely consistent with normal behaviour, and affords no new insight into isospin-symmetry breaking. The essential point is that isospin-breaking effects due to the Coulomb interaction frequently vary from level to level within a given medium-mass nucleus by as much as 200 keV. Any level splitting smaller than this is liable to manifest a level inversion in the mirror partner which, absent disagreement with an appropriate nuclear model, does not challenge our understanding. While we note the novelty of an inversion in nuclear ground states, we emphasize that in the context of isospin there is nothing specifically illuminating about the ground state, or a level inversion.

   nucl-exnucl-thPRC(2020)·13 citations
2. 02*

   Neutron-$\gamma$ discrimination with organic scintillators: Intrinsic pulse shape and light yield contributions

   M. Sénoville🇫🇷 · F. Delaunay🇫🇷 · M. Pârlog🇫🇷 · N. L. Achouri🇫🇷 · N. A. Orr🇫🇷

   A comparative study of the neutron-$\gamma$ Pulse Shape Discrimination (PSD) with seven organic scintillators is performed using an identical setup and digital electronics. The scintillators include plastics (EJ-299-33 and a plastic prototype), single crystals (stilbene and the recent doped $p$-terphenyl) and liquids (BC501A, NE213 and the deuterated liquid BC537). First, the overall PSD performance of the different scintillators is compared and threshold neutron energies for a given discrimination quality are determined. Then, using statistical arguments, two intrinsic contributions to the PSD capability of the scintillating materials are disentangled: the light yield and the specific pulse shapes induced by neutrons and $\gamma$-rays. This separation provides additional insight into the behaviour of organic scintillators and allows a detailed comparison of the discrimination performance of the various materials. On the basis of this analysis, limitations of current organic scintillators and of recently proposed alternative scintillators are discussed.

   ↳ physics.ins-detnucl-exNucl.Instrum.Meth.A(2020)·8 citations
3. 03*

   Search for the Chiral Magnetic Effect with the ALICE detector

   Sizar Aziz🇫🇷

   In non-central heavy-ion collisions, spectator protons that do not participate in the interaction create strong magnetic fields. The strength of these fields allows testing an effect based on the hypothesized properties of QCD. The presence of so-called topological configurations can give rise to domains that carry net chirality. Coupled with the aforementioned magnetic fields, they may induce a charge separation of the particles generated in the collisions. This charge separation is called the Chiral Magnetic Effect (CME) and can be measured through charged-particle angular correlations. Measurements of the ${\gamma }_{1,1}$ correlator, which is sensitive to the CME, are shown for Pb--Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV as well as for Xe--Xe collisions at $\sqrt{s_{\mathrm{NN}}}=5.44$ TeV. These are found to have a significant charge dependence between opposite-sign and same-sign charge pairs. This behavior is consistent with a CME-like signal. However, the ${\delta }_1$ correlator, which measures charge correlations unrelated to any symmetry plane (i.e. background), was measured in Xe--Xe collisions and also shows a significant charge dependence. This prevents a clear interpretation of the ${\gamma }_{1,1}$ correlator. Novel methods to constrain the CME contribution to the ${\gamma }_{1,1}$ correlator are necessary.

   ↳ hep-exnucl-exNPA(2021)·12 citations
4. 04*

   Symmetries Created by Random Interactions- Ultimacy of "More Is Different"

   Takaharu Otsuka🇯🇵 · Noritaka Shimizu🇯🇵

   The dominance (preponderance) of the 0+ ground state for random interactions is shown to be a consequence of certain random interactions with chaotic features. These random interactions, called chaotic random interactions, impart a symmetry property to the ground-state wave function: an isotropy under an appropriate transformation, such as zero angular momentum for rotation. Under this mechanism, the ground-state parity and isospin can also be predicted in such a manner that positive parity is favored over negative parity and the isospin T = 0 is favored over higher isospins. As chaotic random interaction is a limit with no particular dynamics at the level of two interacting particles, this realization of isotropic symmetry in the ground state can be considered as the ultimate case of many-body correlations. A possible relation to the isotropy of the early universe is mentioned.

   ↳ nucl-thnucl-exquant-ph0 citations
5. 05*

   Recent design studies for the novel momentum spectrometer NoMoS

   Daniel Moser · Waleed Khalid · Raluca Jiglau · Torsten Soldner Manfred Valentan · Johann Zmeskal · Gertrud Konrad

   NoMoS is a novel momentum spectrometer with which we aim to measure the spectra of the charged neutron beta decay products with high precision. The shape of the proton and electron spectra can inter alia be used for the determination of the electron-antineutrino correlation coefficient $a$ and the Fierz interference term $b$, respectively. These observables can in turn be used to test the Standard Model of Particle Physics and to search for extensions thereof. NoMoS utilizes the $R\times B$ drift effect present in curved magnetic fields, which disperses charged particles according to their momentum. In this paper, we report on selected recent investigations that were conducted with regard to the magnet design and the detection system.

   ↳ physics.ins-detnucl-exJ.Phys.Conf.Ser.(2020)·3 citations
6. 06*

   Sensitivity of a tonne-scale NEXT detector for neutrinoless double beta decay searches

   NEXT Collaboration: C. Adams🇺🇸 · V. Álvarez🇪🇸 · L. Arazi🇮🇱 · I.J. Arnquist🇺🇸 · C.D.R Azevedo🇵🇹 · K. Bailey🇺🇸 · F. Ballester🇪🇸 · J.M. Benlloch-Rodríguez🇪🇸 · F.I.G.M. Borges🇵🇹 · N. Byrnes🇺🇸 · S. Cárcel🇪🇸 · J.V. Carrión🇪🇸 and 86 other authors

   The Neutrino Experiment with a Xenon TPC (NEXT) searches for the neutrinoless double-beta decay of Xe-136 using high-pressure xenon gas TPCs with electroluminescent amplification. A scaled-up version of this technology with about 1 tonne of enriched xenon could reach in less than 5 years of operation a sensitivity to the half-life of neutrinoless double-beta decay decay better than 1E27 years, improving the current limits by at least one order of magnitude. This prediction is based on a well-understood background model dominated by radiogenic sources. The detector concept presented here represents a first step on a compelling path towards sensitivity to the parameter space defined by the inverted ordering of neutrino masses, and beyond.

   ↳ physics.ins-detnucl-exJHEP(2021)·108 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.