Tue·Oct 27, 2020Tuesday·October 27, 2020

1. 01*

   Investigating High-Energy Proton-Induced Reactions on Spherical Nuclei: Implications for the Pre-Equilibrium Exciton Model

   Morgan B. Fox (1)🇺🇸 · Andrew S. Voyles (1 and 2)🇺🇸 · Jonathan T. Morrell (1)🇺🇸 · Lee A. Bernstein (1 and 2) · Amanda M. Lewis (1)🇺🇸 · Arjan J. Koning (3)🇦🇹 · Jon C. Batchelder (1)🇺🇸 · Eva R. Birnbaum (4)🇺🇸 · Cathy S. Cutler (5)🇺🇸 · Dmitri G. Medvedev (5)🇺🇸 · Francois M. Nortier (4)🇺🇸 · Ellen M. O'Brien (4)🇺🇸 · Christiaan Vermeulen (4) ((1) Department of Nuclear Engineering, University of California, Berkeley (2) Lawrence Berkeley National Laboratory (3) International Atomic Energy Agency (4) Los Alamos National Laboratory (5) Brookhaven National Laboratory)🇺🇸

   A number of accelerator-based isotope production facilities utilize 100- to 200-MeV proton beams due to the high production rates enabled by high-intensity beam capabilities and the greater diversity of isotope production brought on by the long range of high-energy protons. However, nuclear reaction modeling at these energies can be challenging because of the interplay between different reaction modes and a lack of existing guiding cross section data. A Tri-lab collaboration has been formed among the Lawrence Berkeley, Los Alamos, and Brookhaven National Laboratories to address these complexities by characterizing charged-particle nuclear reactions relevant to the production of established and novel radioisotopes. In the inaugural collaboration experiments, stacked-targets of niobium foils were irradiated at the Brookhaven Linac Isotope Producer (E${}_p$=200 MeV) and the Los Alamos Isotope Production Facility (E${}_p$=100 MeV) to measure ${}^{93}$Nb(p,x) cross sections between 50 and 200 MeV. The measured cross-section results were compared with literature data as well as the default calculations of the nuclear model codes TALYS, CoH, EMPIRE, and ALICE. We developed a standardized procedure that determines the reaction model parameters that best reproduce the most prominent reaction channels in a physically justifiable manner. The primary focus of the procedure was to determine the best parametrization for the pre-equilibrium two-component exciton model. This modeling study revealed a trend toward a relative decrease for internal transition rates at intermediate proton energies (E${}_p$=20-60 MeV) in the current exciton model as compared to the default values. The results of this work are instrumental for the planning, execution, and analysis essential to isotope production.

   nucl-exnucl-thPRC(2021)·20 citations
2. 02*

   Absence of Low-Energy Shape Coexistence in ${}^{80}$Ge: The Nonobservation of a Proposed Excited 0${}_2^{+}$ Level at 639 keV

   F. H. Garcia🇨🇦 · C. Andreoiu🇨🇦 · G. C. Ball🇨🇦 · A. Bell🇨🇦 · A. B. Garnsworthy🇨🇦 · F. Nowacki🇫🇷 · C. M. Petrache🇫🇷 · A. Poves🇪🇸 · K. Whitmore🇨🇦 · F. A. Ali🇨🇦 · N. Bernier🇨🇦 · S. S. Bhattacharjee🇨🇦 and 19 other authors

   The ${}^{80}$Ge structure was investigated in a high-statistics $\beta$-decay experiment of ${}^{80}$Ga using the GRIFFIN spectrometer at TRIUMF-ISAC through $\gamma$, $\beta$-$e$, $e$-$\gamma$ and $\gamma$-$\gamma$ spectroscopy. No evidence was found for the recently reported 0${}_2^{+}$ 639-keV level suggested as evidence for low-energy shape coexistence in ${}^{80}$Ge. Large-scale shell model calculations performed in ${}^{78,80,82}$Ge place the $0_2^{+}$ level in ${}^{80}$Ge at 2\,MeV. The new experimental evidence combined with shell model predictions indicate that low-energy shape coexistence is not present in ${}^{80}$Ge.

   nucl-exPRL(2020)·24 citations
3. 03*

   Low-mass dielectron measurements in pp, p-Pb, and Pb-Pb collisions with ALICE at the LHC

   H. Sebastian Scheid (for the ALICE Collaboration)🇩🇪

   Dielectrons are an excellent probe for the QCD matter created in created in ultra-relativistic heavy-ion collisions, since they are emitted during the whole evolution of the collision and do not interact strongly with the medium. To isolate the QGP signals, measurement of the dielectron production in vacuum and its modifications due to the presence of cold nuclear matter is necessary. We present and discuss results from a low magnetic field detector setup in proton-proton collisions at $\sqrt{s}=13$ TeV, as well as the measurement of dielectron production in pp, p-Pb, and Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5$ TeV.

   nucl-exhep-exNPA(2021)·2 citations
4. 04*

   Measurement of heavy-quark production via dielectrons in pp and p-Pb collisions with ALICE at the LHC

   Horst Sebastian Scheid (for the ALICE Collaboration)🇩🇪

   Heavy quarks are useful probes to investigate the properties of the Quark-Gluon Plasma (QGP) produced in heavy-ion collisions at the LHC, since they are produced in initial hard scattering processes. To single out the signals that are characteristic of the QGP, it is nevertheless crucial to understand the primordial heavy-quark production in vacuum, and to disentangle hot from cold nuclear matter effects. Moreover, observations of collective effects in high-multiplicity pp and p-Pb collisions show surprising similarities with those in heavy-ion collisions. Heavy-flavour production in such collisions could give further insight into the underlying processes. The heavy-flavour production can be studied with ${\mathrm{e}}^{+}{\mathrm{e}}^{-}$ pairs from correlated semileptonic decays of heavy-flavour hadrons. Compared to single heavy-flavour measurements, the dielectron yield contains information about the initial kinematical correlations between the charm and anti-charm quarks, which is otherwise not accessible, and is sensitive to soft heavy-flavour production. We report results on correlated ${\mathrm{e}}^{+}{\mathrm{e}}^{-}$ pairs in pp collisions recorded by the ALICE detector at different collision energies. The production of heavy quarks is discussed by comparing the yield of dielectrons from heavy-flavour hadron decays as a function of invariant mass, pair transverse momentum and distance of closest approach to the primary vertex with different Monte Carlo event generators. The heavy-flavour production cross sections are also presented. Results from high-multiplicity pp collisions at $\sqrt{s}=13$ TeV and the status of the p-Pb analysis at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV are reported as well.

   nucl-exhep-exPoS(2020)·0 citations
5. 05*

   First Measurement of the Asymmetry and the Gerasimov-Drell-Hearn Integrand from $\overrightarrow{{}^{3}He}(\vec{\gamma },p)d$ reaction at the Incident Photon Energy of 29 MeV

   G.Laskaris · W.Ji · X.Yan · J.Zhou · W.R.Zimmerman · M.W.Ahmed · T.Averett · A.Deltuva · A.C.Fonseca · H.Gao · J.Golak · A.Kafkarkou and 12 other authors

   The first measurement of the $\overrightarrow{{}^{3}He}(\vec{\gamma },p)d$ process was performed at the High Intensity $\gamma$-ray Source (HI$\gamma$S) facility at Triangle Universities Nuclear Laboratory (TUNL) using a circularly polarized, monoenergetic $\gamma$-ray beam and a longitudinally polarized ${}^3$He target. The spin-dependent asymmetry and the contribution from the two-body photodisintegration to the ${}^3$He Gerasimov-Drell-Hearn integrand are extracted and compared with state-of-the-art three-nucleon system calculations at the incident photon energy of 29.0 MeV. The data are in general agreement with the various theoretical predictions based on the Siegert theorem or on explicit inclusion of meson-exchange currents.

   nucl-exPRC(2021)·6 citations
6. 06*

   Coupled-channels treatment of ${}^7\mathrm{Be}(p,\gamma {)}^8\mathrm{B}$ in effective field theory

   Renato Higa🇧🇷 · Pradeepa Premarathna🇺🇸 · Gautam Rupak🇺🇸

   The E1 and M1 contributions to ${}^7\mathrm{Be}(p,\gamma {)}^8\mathrm{B}$ at low energies are calculated in halo effective field theory. The excited ${}^7{\mathrm{Be}}^{\star }$ core is included as an explicit degree of freedom in a coupled-channels calculation. The E1 transition is calculated up to next-to-next-to-leading order. The leading contribution from M1 transition that gives significant contribution in a narrow energy region around the $1^{+}$ resonance state of ${}^8$B is included. We compare our results with previous halo effective field theory calculations that also included the ${}^7{\mathrm{Be}}^{\star }$ as an explicit degree of freedom. We disagree with these previous calculations in both the formal expressions and also in the analysis. Bayesian inference of the data gives $S_{17}(0)=21.0(7)$ eV b when combined with the expected theory error.

   ↳ nucl-thastro-ph.SRnucl-exPRC(2022)·12 citations
7. 07*

   Comprehensive analysis of beta decays within and beyond the Standard Model

   Adam Falkowski🇫🇷 · Martín González-Alonso🇪🇸 · Oscar Naviliat-Cuncic🇫🇷

   Precision measurements in allowed nuclear beta decays and neutron decay are reviewed and analyzed both within the Standard Model and looking for new physics. The analysis incorporates the most recent experimental and theoretical developments. The results are interpreted in terms of Wilson coefficients describing the effective interactions between leptons and nucleons (or quarks) that are responsible for beta decay. New global fits are performed incorporating a comprehensive list of precision measurements in neutron decay, superallowed $0^{+}\to 0^{+}$ transitions, and other nuclear decays that include, for the first time, data from mirror beta transitions. The results confirm the $V$-$A$ character of the interaction and translate into updated values for $V_{ud}$ and $g_A$ at the $10^{-4}$ level. We also place new stringent limits on exotic couplings involving left-handed and right-handed neutrinos, which benefit significantly from the inclusion of mirror decays in the analysis.

   ↳ hep-phnucl-exnucl-thJHEP(2021)·126 citations
8. 08*

   Independent Normalization for $\gamma$-ray Strength Functions: The Shape Method

   M. Wiedeking🇿🇦 · M. Guttormsen🇳🇴 · A.C. Larsen🇳🇴 · F. Zeiser🇳🇴 · A. Görgen🇳🇴 · S. N. Liddick🇺🇸 · D. Mücher🇨🇦 · S. Siem🇳🇴 · A. Spyrou

   The Shape method, a novel approach to obtain the functional form of the $\gamma$-ray strength function ($\gamma$SF) in the absence of neutron resonance spacing data, is introduced. When used in connection with the Oslo method the slope of the Nuclear Level Density (NLD) is obtained simultaneously. The foundation of the Shape method lies in the primary $\gamma$-ray transitions which preserve information on the functional form of the $\gamma$SF. The Shape method has been applied to ${}^{56}$Fe, ${}^{92}$Zr, ${}^{164}$Dy, and ${}^{240}$Pu, which are representative cases for the variety of situations encountered in typical NLD and $\gamma$SF studies. The comparisons of results from the Shape method to those from the Oslo method demonstrate that the functional form of the $\gamma$SF is retained regardless of nuclear structure details or $J^{\pi }$ values of the states fed by the primary transitions.

   ↳ physics.data-annucl-exnucl-thPRC(2021)·38 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.