Thu·Sep 3, 2020Thursday·September 3, 2020

1. 01*

   Shell structure of ${}^{43}$S and collapse of the $N=28$ shell closure

   S. Momiyama🇯🇵 · K. Wimmer🇯🇵 · D. Bazin🇺🇸 · J. Belarge · P. Bender · B. Elman · A. Gade🇺🇸 · K. W. Kemper🇺🇸 · N. Kitamura🇯🇵 · B. Longfellow🇺🇸 · E. Lunderberg🇺🇸 · M. Niikura🇯🇵 and 4 other authors

   The single-particle structure of the $N=27$ isotones provides insights into the shell evolution of neutron-rich nuclei from the doubly-magic ${}^{48}$Ca toward the drip line. ${}^{43}$S was studied employing the one-neutron knockout reaction from a radioactive ${}^{44}$S beam. Using a combination of prompt and delayed $\gamma$-ray spectroscopy the level structure of ${}^{43}$S was clarified. Momentum distributions were analyzed and allowed for spin and parity assignments. The deduced spectroscopic factors show that the ${}^{44}$S ground-state configuration has a strong intruder component. The results were confronted with shell model calculations using two effective interactions. General agreement was found between the calculations, but strong population of states originating from the removal of neutrons from the $2p_{3/2}$ orbital in the experiment indicates that the breakdown of the $N=28$ magic number is more rapid than the theoretical calculations suggest.

   nucl-exPRC(2020)·11 citations
2. 02*

   ${}^{25}$Si ${\beta }^{+}$-decay spectroscopy

   L. J. Sun🇺🇸 · M. Friedman🇺🇸 · T. Budner🇺🇸 · D. Pérez-Loureiro🇺🇸 · E. Pollacco🇫🇷 · C. Wrede🇺🇸 · B. A. Brown🇺🇸 · M. Cortesi🇺🇸 · C. Fry🇺🇸 · B. E. Glassman🇺🇸 · J. Heideman🇺🇸 · M. Janasik🇺🇸 and 6 other authors

   $\beta$-decay spectroscopy provides valuable information on exotic nuclei and a stringent test for nuclear theories beyond the stability line. To search for new $\beta$-delayed protons and $\gamma$ rays of ${}^{25}$Si to investigate the properties of ${}^{25}$Al excited states. ${}^{25}$Si $\beta$ decays were measured by using the Gaseous Detector with Germanium Tagging system at the National Superconducting Cyclotron Laboratory. The protons and $\gamma$ rays emitted in the decay were detected simultaneously. A Monte Carlo method was used to model the Doppler broadening of ${}^{24}$Mg $\gamma$-ray lines caused by nuclear recoil from proton emission. Shell-model calculations using two newly developed universal \textit{sd}-shell Hamiltonians, USDC and USDI, were performed. The most precise ${}^{25}$Si half-life to date has been determined. A new proton branch at 724(4)~keV and new proton-$\gamma$-ray coincidences have been identified. Three ${}^{24}$Mg $\gamma$-ray lines and eight ${}^{25}$Al $\gamma$-ray lines are observed for the first time in ${}^{25}$Si decay. The first measurement of the ${}^{25}$Si $\beta$-delayed $\gamma$ ray intensities through the ${}^{25}$Al unbound states is reported. All the bound states of ${}^{25}$Al are observed to be populated in the $\beta$ decay of ${}^{25}$Si. Several inconsistencies between the previous measurements have been resolved, and new information on the ${}^{25}$Al level scheme is provided. An enhanced decay scheme has been constructed and compared to the mirror decay of ${}^{25}$Na and the shell-model calculations. The measured excitation energies, $\gamma$-ray and proton branchings, log~$ft$ values, and Gamow-Teller transition strengths for the states of ${}^{25}$Al populated in the $\beta$ decay of ${}^{25}$Si are in good agreement with the shell-model calculations, offering gratifyingly consistent insights into the fine nuclear structure of ${}^{25}$Al.

   nucl-exPRC(2021)·10 citations
3. 03*

   Estimation of CP violating EDMs from known mechanisms in the SM

   Prajwal Mohanmurthy🇺🇸 · Jeff A. Winger🇺🇸

   New sources of CP violation, beyond the known sources in the standard model (SM), are required to explain the baryon asymmetry of the universe. Measurement of a non-zero permanent electric dipole moment (EDM) for fundamental particles, such as in an electron or a neutron, or in nuclei or atoms, can help us gain a handle on the sources of CP violation, both in SM and beyond. Multiple mechanisms within the SM can generate CP violating EDMs, viz.\ through the CKM matrix in the weak sector or through the QCD $\bar{\theta }$ parameter in the strong sector. We will estimate the maximum possible EDMs of leptons, certain baryons, select atoms and molecules in the (CKM$⨁\bar{\theta }$) framework, assuming that the EDM wholly originates from either of the two SM mechanisms, independently. These estimates have been presented in light of the current experimental upper limits on the EDMs, in the following systems - leptons: $e^{-}$, ${\mu }^{-}$, ${\tau }^{-}$, ${\nu }_e^0$, ${\nu }_{\mu }^0$, ${\nu }_{\tau }^0$, baryons: $n^0$, $p^{+}$, ${\Lambda }^0$, ${\Sigma }^0$, ${\Xi }^0$, ${\Lambda }_c^{+}$, ${\Xi }_c^{+}$, atoms: ${}^{85}$Rb, ${}^{133}$Cs, ${}^{210}$Fr, ${}^{205}$Tl, ${}^{199}$Hg, ${}^{129}$Xe, ${}^{225}$Ra, ${}^{223}$Rn, and molecules: HfF${}^{+}$, PbO, YbF, ThO, RaF, TlF. Particularly, to drive home the point that EDMs in different systems constrain CP-violating interactions differently, we show that the same measured constraint on the EDM in two different systems may not actually be equally constraining on CP violating parameters, and to emphasize the need to measure a non-zero EDM in multiple systems before understanding the origins of these CP-violating EDMs.

   nucl-exnucl-thPoS(2021)·4 citations
4. 04*

   The percolation phase transition and statistical multifragmentation in finite systems

   T. Pietrzak🇵🇱 · A. S. Botvina🇩🇪 · J. Brzychczyk🇵🇱 · N. Buyukcizmeci🇹🇷 · A. Le Fèvre🇩🇪 · J. Łukasik🇵🇱 · P. Pawłowski🇵🇱 · C. Sfienti🇩🇪 · W. Trautmann🇩🇪 · A. Wieloch🇵🇱

   The cumulant ratios up to fourth order of the $Z$ distributions of the largest fragment in spectator fragmentation following ${}^{107,124}$Sn+Sn and ${}^{124}$La+Sn collisions at 600 MeV/nucleon have been investigated. They are found to exhibit the signatures of a second-order phase transition established with cubic bond percolation and previously observed in the ALADIN experimental data for fragmentation of ${}^{197}$Au projectiles at similar energies. The deduced pseudocritical points are found to be only weakly dependent on the $A/Z$ ratio of the fragmenting spectator source. The same holds for the corresponding chemical freeze-out temperatures of close to 6 MeV. The experimental cumulant distributions are quantitatively reproduced with the Statistical Multifragmentation Model and parameters used to describe the experimental fragment multiplicities, isotope distributions and their correlations with impact-parameter related observables in these reactions. The characteristic coincidence of the zero transition of the skewness with the minimum of the kurtosis excess appears to be a generic property of statistical models and is found to coincide with the maximum of the heat capacity in the canonical thermodynamic fragmentation model.

   nucl-exPLB(2020)·5 citations
5. 05*

   Accessing the Single-Particle Structure of the Pygmy Dipole Resonance in ${}^{208}$Pb

   M. Spieker🇺🇸 · A. Heusler · B. A. Brown🇺🇸 · T. Faestermann🇩🇪 · R. Hertenberger🇩🇪 · G. Potel🇺🇸 · M. Scheck🇬🇧 · N. Tsoneva · M. Weinert🇩🇪 · H.-F. Wirth🇩🇪 · A. Zilges🇩🇪

   New experimental data on the neutron single-particle character of the Pygmy Dipole Resonance (PDR) in ${}^{208}$Pb are presented. They were obtained from $(d,p)$ and resonant proton scattering experiments performed at the Q3D spectrograph of the Maier-Leibnitz Laboratory in Garching, Germany. The new data are compared to the large suite of complementary, experimental data available for ${}^{208}$Pb and establish $(d,p)$ as an additional, valuable, experimental probe to study the PDR and its collectivity. Besides the single-particle character of the states, different features of the strength distributions are discussed and compared to Large-Scale-Shell-Model (LSSM) and energy-density functional (EDF) plus Quasiparticle-Phonon Model (QPM) theoretical approaches to elucidate the microscopic structure of the PDR in ${}^{208}$Pb.

   nucl-exnucl-thPRL(2020)·31 citations
6. 06*

   Microscopic investigation of the ${}^8$Li($n,\gamma$)${}^9$Li reaction

   Callum McCracken🇨🇦 · Petr Navratil🇨🇦 · Anna McCoy🇨🇦 · Sofia Quaglioni🇺🇸 · Guillaume Hupin🇫🇷

   The ${}^8$Li($n,\gamma$)${}^9$Li reaction plays an important role in several astrophysics scenarios. It cannot be measured directly and indirect experiments have so far provided only cross section limits. Theoretical predictions differ by an order of magnitude. In this work we study the properties of ${}^9$Li bound states and low-lying resonances and calculate the ${}^8$Li($n,\gamma$)${}^9$Li cross section within the no-core shell model with continuum (NCSMC) with chiral nucleon-nucleon and three-nucleon interactions as the only input. The NCSMC is an ab initio method applicable to light nuclei that provides a unified description of bound and scattering states well suited to calculate low-energy nuclear scattering and reactions. Our calculations reproduce the experimentally known bound states as well as the lowest $5/2^{-}$ resonance of ${}^9$Li. We predict a $3/2^{-}$ spin-parity assignment for the resonance observed at 5.38 MeV. In addition to the a very narrow $7/2^{-}$ resonance corresponding presumably to the experimental 6.43 MeV state, we find several other broad low-lying resonances. Our calculated ${}^8$Li($n,\gamma$)${}^9$Li cross section is within the limits derived from the 1998 National Superconducting Cyclotron Laboratory Coulomb-dissociation experiment [Phys. Rev. C {\bf 57}, 959 (1998)]. However, it is higher than cross sections obtained in recent phenomenological studies. It is dominated by a direct E1 capture to the ground state with a resonant contribution at $\sim 0.2$ MeV due to E2/M1 radiation enhanced by the $5/2^{-}$ resonance.

   ↳ nucl-thnucl-exPRC(2021)·17 citations
7. 07*

   The mean square radius of the neutron distribution and the skin thickness derived from electron scattering

   Haruki Kurasawa · Toshimi Suda🇯🇵 · Toshio Suzuki🇯🇵

   The second-order moment of the nuclear charge density($R_c^2$) is dominated by the mean square radius(msr) of the point proton distribution($R_p^2$), while the fourth-order moment($Q_c^4$) depends on the msr of the point neutron one($R_n^2$) also. Moreover, $R_n^2$ is strongly correlated to $R_c^2$ in nuclear models. According to these facts, the linear relationship between various moments in the nuclear mean field models are investigated with use of the least squares method for ${}^{40}$Ca, ${}^{48}$Ca and ${}^{208}$Pb. From the intersection points of the obtained straight lines with those of the experimental values for $R_c^2$ and $Q_c^4$ determined through electron scattering, the values of $R_p$ and $R_n$ are estimated. Since relativistic and non-relativistic models provide different lines, the obtained values of $R_n$ and the skin thickness($R_n-R_p$) differ from each other in the two frameworks.

   ↳ nucl-thnucl-exPTEP(2021)·19 citations
8. 08*

   Reanalyses for ${}^{42-51}$Ca scattering on a ${}^{12}$C target at $280$ MeV/nucleon based on chiral $g$ folding mode with Gogny-D1S Hartree-Fock-Bogoliubov densities (published in Results in Physics)

   Maya Takechi · Tomotsugu Wakasa · Shingo Tagami Jun Matsui · Masanobu Yahiro

   In the previous paper, we predicted reaction cross sections ${\sigma }_{\mathrm{R}}$ for ${}^{40-60,62,64}$Ca+${}^{12}$C scattering at $280$~MeV/nucleon, since Tanaka {\it el al.} measured interaction cross sections ${\sigma }_{\mathrm{I}}$ for ${}^{42-51}$Ca in RIKEN and determined neutron skin $r_{\mathrm{skin}}(\mathrm{RIKEN})$ using the optical limit of the Glauber model with the Woos-Saxon densities. Our purpose is to reanalyze the $r_{\mathrm{skin}}$ from the ${\sigma }_{\mathrm{I}}$. Our analysis is superior to theirs, since the chiral $g$-matrix folding model (the GHFB and GHFB+AMP densities) is much better than the optical limit of the Glauber model (the Woos-Saxon densities). Our model is the chiral $g$-matrix folding model with the densities scaled from the GHFB and GHFB+AMP densities. We scale the GHFB and GHFB+AMP densities so that the ${\sigma }_{\mathrm{R}}$ of the scaled densities can agree with the central values of ${\sigma }_{\mathrm{I}}$ under the condition that the proton radius of the scaled proton density equals the data determined from the isotope shift based on the electron scattering. The $r_{\mathrm{skin}}$ thus determined are close to their results $r_{\mathrm{skin}}^{42-51}(\mathrm{RIKEN})$. For ${}^{48}$Ca, our value $r_{\mathrm{skin}}^{48}$ is 0.105 $\pm$ 0.06~fm, while their value is $r_{\mathrm{m}}^{48}(\mathrm{RIKEN})=0.146\pm 0.06$~fm. We take the weighted mean and its error of $r_{\mathrm{skin}}^{48}({\sigma }_{\mathrm{I}})=0.105\pm 0.06$~fm and $r_{\mathrm{skin}}^{48}(E1\mathrm{pE})=0.17\pm 0.03$~fm of the high-resolution $E1$ polarizability experiment (E1{\rm pE}). Our final result is $r_{\mathrm{skin}}^{48}=0.157\pm 0.027$~fm. Our conclusion is $r_{\mathrm{skin}}^{48}=0.157\pm 0.027$~fm for ${}^{48}$Ca. For ${}^{42-47,49-51}$Ca, our results on $r_{\mathrm{skin}}$ are similar to theirs. Our result for ${}^{48}$Ca is related to CREX.

   ↳ nucl-thnucl-exResults Phys.(2021)·5 citations
9. 09*

   GW190814: Circumstantial Evidence for Up-Down Quark Star

   Zheng Cao🇨🇳 · Lie-Wen Chen🇨🇳 · Peng-Cheng Chu🇨🇳 · Ying Zhou🇨🇳

   Within a confining quark matter model which considers phenomenologically the quark confinement and asymptotic freedom as well as the chiral symmetry restoration and quark deconfinement at high baryon density, we find that if the up-down quark matter ($ud$QM) is more stable than nuclear matter and strange quark matter (SQM), the maximum mass of static quark stars with $ud$QM is $2.87M_{\odot }$ under agreement with both the constraints on star tidal deformability from gravitational wave signal GW170817 and the mass-radius of PSR J0030+0451 and PSR J0740+6620 measured by NICER. In contrast, the conventional strange quark star with the SQM that is more stable than nuclear matter while the nuclear matter is more stable than $ud$QM, has a maximum static mass of only $1.87M_{\odot }$ and its radius significantly deviates from NICER's constraint. Our results thus provide circumstantial evidence suggesting the recently reported GW190814's secondary component with a mass of $2.59_{-0.09}^{+0.08}{M}_{\odot }$ could be an up-down quark star.

   ↳ astro-ph.HEhep-exhep-phnucl-ex+1PRD(2022)·65 citations
10. 10*

    Left-right symmetry and leading contributions to neutrinoless double beta decay

    Gang Li🇺🇸 · Michael Ramsey-Musolf🇨🇳 · Juan Carlos Vasquez🇺🇸

    We study the impact of the mixing (LR mixing) between the standard model $W$ boson and its hypothetical, heavier right-handed parter $W_R$ on the neutrinoless double beta decay ($0\nu \beta \beta$-decay) rate. Our study is done in the minimal left-right symmetric model assuming type-II dominance scenario with charge conjugation as the left-right symmetry. We then show that the $0\nu \beta \beta$-decay rate may be dominated by the contribution proportional to this LR mixing, which at the hadronic level induces the leading-order contribution to the interaction between two pions and two charged leptons. The resulting long-range pion exchange contribution can significantly enhance the decay rate compared to previously considered short-range contributions. Finally, we find that even if future cosmological experiments rule out the inverted hierarchy for neutrino masses, there are still good prospects for a positive signal in the next generation of $0\nu \beta \beta$-decay experiments.

    ↳ hep-phnucl-exnucl-thPRL(2021)·46 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.