Fri·May 8, 2020Friday·May 8, 2020

1. 01*

   First Penning trap mass measurement of ${}^{36}$Ca

   J. Surbrook🇺🇸 · G. Bollen🇺🇸 · M. Brodeur🇺🇸 · A. Hamaker🇺🇸 · D. Pérez-Loureiro🇺🇸 · D.Puentes🇺🇸 · C. Nicoloff🇺🇸 · M. Redshaw🇺🇸 · R. Ringle🇺🇸 · S. Schwarz🇺🇸 · C.S. Sumithrarachchi🇺🇸 · L.J. Sun🇺🇸 and 4 other authors

   Isobaric quintets provide the best test of the isobaric multiplet mass equation (IMME) and can uniquely identify higher order corrections suggestive of isospin symmetry breaking effects in the nuclear Hamiltonian. The Generalized IMME (GIMME) is a novel microscopic interaction theory that predicts an extension to the quadratic form of the IMME. Only the $A=20,32$ $T=2$ quintets have the exotic $T_z=-2$ member ground state mass determined to high-precision by Penning trap mass spectrometry. In this work, we establish $A=36$ as the third high-precision $T=2$ isobaric quintet with the $T_z=-2$ member ground state mass measured by Penning trap mass spectrometry and provide the first test of the predictive power of the GIMME. A radioactive beam of neutron-deficient ${}^{36}$Ca was produced by projectile fragmentation at the National Superconducting Cyclotron Laboratory. The beam was thermalized and the mass of ${}^{36}$Ca${}^{+}$ and ${}^{36}$Ca${}^{2+}$ measured by the Time of Flight - Ion Cyclotron Resonance method in the LEBIT 9.4 T Penning trap. We measure the mass excess of ${}^{36}$Ca to be ME$=-6483.6(56)$ keV, an improvement in precision by a factor of 6 over the literature value. The new datum is considered together with evaluated nuclear data on the $A=36$, $T=2$ quintet. We find agreement with the quadratic form of the IMME given by isospin symmetry, but only coarse qualitative agreement with predictions of the GIMME. A total of three isobaric quintets have their most exotic members measured by Penning trap mass spectrometry. The GIMME predictions in the $T=2$ quintet appear to break down for $A=32$ and greater.

   nucl-exPRC(2021)·15 citations
2. 02*

   New measurement of ${}^{12}$C+${}^{12}$C fusion reaction at astrophysical energies

   W. P. Tan🇺🇸 · A. Boeltzig🇮🇹 · C. Dulal · R. J. deBoer🇺🇸 · B. Frentz · S. Henderson🇺🇸 · K. B. Howard🇺🇸 · R. Kelmar · J. J. Kolata · J. Long🇺🇸 · K. T. Macon🇺🇸 · S. Moylan🇺🇸 and 10 other authors

   Carbon and oxygen burning reactions, in particular, ${}^{12}$C+${}^{12}$C fusion, are important for the understanding and interpretation of the late phases of stellar evolution as well as the ignition and nucleosynthesis in cataclysmic binary systems such as type Ia supernovae and x-ray superbursts. A new measurement of this reaction has been performed at the University of Notre Dame using particle-$\gamma$ coincidence techniques with SAND (a silicon detector array) at the high-intensity 5U Pelletron accelerator. New results for ${}^{12}$C+${}^{12}$C fusion at low energies relevant to nuclear astrophysics are reported. They show strong disagreement with a recent measurement using the indirect Trojan Horse method. The impact on the carbon burning process under astrophysical scenarios will be discussed.

   nucl-exPRL(2020)·79 citations
3. 03*

   Energy dependence of longitudinal flow decorrelation from STAR

   Maowu Nie (for the STAR Collaboration)🇨🇳

   Measurements of longitudinal flow decorrelations for charged particles are presented in the pseudorapidity range $|\eta |<1$ using a reference detector at 2.1 $<|{\eta }_{\mathrm{ref}}|<$ 5.1 in Au+Au collisions at $\sqrt{s_{NN}}$ = 27 GeV by STAR. The flow decorrelation for $v_2$ shows a strong centrality dependence, while a weak centrality dependence for $v_3$. Results are compared with the results in Au+Au collisions at 200 GeV as a function of $\eta$ scaled by beam-rapidity, i.e. $\eta /y_{beam}$. No energy dependence is observed for $v_2$ decorrelation, but clear energy dependence for $v_3$ decorrelation. These results provide new insights into the longitudinal structure of the initial-state geometry in heavy-ion collisions.

   nucl-exNPA(2021)·18 citations
4. 04*

   Probing dense QCD matter in the laboratory: The CBM experiment at FAIR

   Peter Senger (for the CBM Collaboration)🇩🇪

   The Facility for Antiproton and Ion Research (FAIR) in Darmstadt will provide unique research opportunities for the investigation of fundamental open questions related to nuclear physics and astrophysics, including the exploration of QCD matter under extreme conditions, which governs the structure and dynamics of cosmic objects and phenomena like neutron stars, supernova explosions, and neutron star mergers. The physics program of the Compressed Baryonic Matter (CBM) experiment is devoted to the production and investigation of dense nuclear matter, with a focus on the high-density equation-of-state (EOS), and signatures for new phases of dense QCD matter. According to the present schedule, the CBM experiment will receive the first beams from the FAIR accelerators in 2025. This article reviews promising observables, outlines the CBM detector system, and presents results of physics performance studies.

   nucl-exPhys.Scripta(2020)·14 citations
5. 05*

   Search for ${\eta }^{\prime }$ bound nuclei in the ${}^{12}\mathrm{C}(\gamma ,p)$ reaction with simultaneous detection of decay products

   N. Tomida · N. Muramatsu · M. Niiyama · J. K. Ahn · W. C. Chang · J. Y. Chen · M. L. Chu · S. Daté · T. Gogami · H. Goto · H. Hamano · T. Hashimoto and 51 other authors

   We measured missing mass spectrum of the ${}^{12}\mathrm{C}(\gamma ,p)$ reaction for the first time in coincidence with potential decay products from ${\eta }^{\prime }$ bound nuclei. We tagged an ($\eta +p$) pair associated with the ${\eta }^{\prime }N\to \eta N$ process in a nucleus. After applying kinematical selections to reduce backgrounds, no signal events were observed in the bound-state region. An upper limit of the signal cross section in the opening angle $\cos {\theta }_{lab}^{\eta p}<-0.9$ was obtained to be 2.2 nb/sr at the 90$\%$ confidence level. It is compared with theoretical cross sections, whose normalization ambiguity is suppressed by measuring a quasifree ${\eta }^{\prime }$ production rate. Our results indicate a small branching fraction of the ${\eta }^{\prime }N\to \eta N$ process and/or a shallow ${\eta }^{\prime }$-nucleus potential.

   nucl-exPRL(2020)·25 citations
6. 06*

   Investigating the dependence of collective dynamics on n/p asymmetry for light nuclei

   R.T. deSouza🇺🇸 · Varinderjit Singh🇺🇸 · S. Hudan🇺🇸 · Z. Lin🇺🇸 · C.J. Horowitz🇺🇸

   The dynamics present in the fusion of neutron-rich nuclei is explored through the comparison of experimental cross-sections at above-barrier energies with measurements of the interaction cross-section at relativistic energies. The increase of fusion dynamics with increasing neutron excess is clearly demonstrated. Experimental cross-sections are compared with the predictions of a Sao Paulo model using relativistic mean field density distributions and the impact of different interactions is explored.

   nucl-exnucl-th0 citations
7. 07*

   Effect of an electric field on liquid helium scintillation produced by fast electrons

   N. S. Phan🇺🇸 · V. Cianciolo🇺🇸 · S. M. Clayton🇺🇸 · S. A. Currie🇺🇸 · R. Dipert🇺🇸 · T. M. Ito🇺🇸 · S. W. T. MacDonald🇺🇸 · C. M. O'Shaughnessy🇺🇸 · J. C. Ramsey🇺🇸 · G. M. Seidel🇺🇸 · E. Smith🇺🇸 · E. Tang🇺🇸 · Z. Tang🇺🇸 · W. Yao🇺🇸

   The dependence on applied electric field ($0-40$ kV/cm) of the scintillation light produced by fast electrons and $\alpha$ particles stopped in liquid helium in the temperature range of 0.44 K to 3.12 K is reported. For both types of particles, the reduction in the intensity of the scintillation signal due to the applied field exhibits an apparent temperature dependence. Using an approximate solution of the Debye-Smoluchowski equation, we show that the apparent temperature dependence for electrons can be explained by the time required for geminate pairs to recombine relative to the detector signal integration time. This finding indicates that the spatial distribution of secondary electrons with respect to their geminate partners possesses a heavy, non-Gaussian tail at larger separations, and has a dependence on the energy of the primary ionization electron. We discuss the potential application of this result to pulse shape analysis for particle detection and discrimination.

   ↳ physics.ins-detcond-mat.otherhep-exnucl-ex+1PRC(2020)·15 citations
8. 08*

   Quantifying Uncertainties on Fission Fragment Mass Yields With Mixture Density Networks

   A.E. Lovell🇺🇸 · A.T. Mohan · P. Talou🇺🇸

   Probabilistic machine learning techniques can learn both complex relations between input features and output quantities of interest as well as take into account stochasticity or uncertainty within a data set. In this initial work, we explore the use of one such probabilistic network, the Mixture Density Network (MDN), to reproduce fission yields and their uncertainties. We study mass yields for the spontaneous fission of ${}^{252}$Cf, exploring the number of training samples needed for converged predictions, how different levels of uncertainty propagate from the training set to the MDN predictions, and how well physical constraints of the yields - such as normalization and symmetry - are upheld by the algorithm. Finally, we test the ability of the MDN to interpolate between and extrapolate beyond samples in the training set using energy-dependent mass yields for the neutron-induced fission on ${}^{235}$U. The MDN provides a reliable way to include and predict uncertainties and is a promising path forward for supplementing sparse sets of nuclear data.

   ↳ nucl-thnucl-exJ.Phys.G(2020)·32 citations
9. 09*

   Correlations Between Fission Fragment and Neutron Anisotropies in Neutron-Induced Fission

   A.E. Lovell🇺🇸 · P. Talou🇺🇸 · I. Stetcu🇺🇸 · K.J. Kelly🇺🇸

   Several sources of angular anisotropy for fission fragments and prompt neutrons have been studied in neutron-induced fission reactions. These include kinematic recoils of the target from the incident neutron beam and the fragments from the emission of the prompt neutrons, preferential directions of the emission of the fission fragments with respect to the beam axis due to the population of particular transition states at the fission barrier, and forward-peaked angular distributions of pre-equilibrium neutrons which are emitted before the formation of a compound nucleus. In addition, there are several potential sources of angular anisotropies that are more difficult to disentangle: the angular distributions of prompt neutrons from fully accelerated fragments or from scission neutrons, and the emission of neutrons from fission fragments that are not fully accelerated. In this work, we study the effects of the first group of anisotropy sources, particularly exploring the correlations between the fission fragment anisotropy and the resulting neutron anisotropy. While kinematic effects were already accounted for in our Hauser-Feshbach Monte Carlo code, $\mathtt{CGMF}$, anisotropic angular distributions for the fission fragments and pre-equilibrium neutrons resulting from neutron-induced fission on ${}^{233,234,235,238}$U, ${}^{239,241}$Pu, and ${}^{237}$Np have been introduced for the first time. The effects of these sources of anisotropy are examined over a range of incident neutron energies, from thermal to 20 MeV, and compared to experimental data from the Chi-Nu liquid scintillator array. The anisotropy of the fission fragments is reflected in the anisotropy of the prompt neutrons, especially as the outgoing energy of the prompt neutrons increases, allowing for an extraction of the fission fragment anisotropy to be made from a measurement of the neutrons.

   ↳ nucl-thnucl-exPRC(2020)·11 citations
10. 10*

    Hartree-Fock-Bogoliubov theory for odd-mass nuclei with a time-odd constraint and application to deformed halo nuclei

    Haruki Kasuya🇯🇵 · Kenichi Yoshida🇯🇵

    We show that the lowest-energy solution of the Hartree-Fock-Bogoliubov (HFB) equation has the even particle-number parity as long as the time-reversal symmetry is conserved in the HFB Hamiltonian without null eigenvalues. Based on this finding, we give a rigorous foundation of a method for solving the HFB equation to describe the ground state of odd-mass nuclei by employing a time-reversal anti-symmetric constraint operator to the Hamiltonian, where one obtains directly the ground state as a self-consistent solution of the cranked-HFB-type equation. Numerical analysis is done for the neutron-rich Mg isotopes with a reasonable choice for the operator, and it is demonstrated that the anomalous increase in the matter radius of ${}^{37}$Mg is well described when the last neutron occupies a low angular-momentum orbital in the framework of the nuclear energy-density-functional method, revealing the deformed halo structure.

    ↳ nucl-thnucl-exPTEP(2021)·30 citations
11. 11*

    Heavy flavor quenching and flow: the roles of initial condition, pre-equilibrium evolution and in-medium interaction

    Shu-Qing Li🇨🇳 · Wen-Jing Xing🇨🇳 · Feng-Lei Liu🇨🇳 · Shanshan Cao🇺🇸 · Guang-You Qin🇨🇳

    Within an advanced Langevin-hydrodynamics framework coupled to a hybrid fragmentation-coalescence hadronization model, we study heavy flavor quenching and flow in relativistic heavy-ion collisions. We investigate how the initial heavy quark spectrum, the energy loss and hadronization mechanisms of heavy quarks in medium, the evolution profile of pre-equilibrium stage, the flow of medium and the temperature dependence of heavy quark diffusion coefficient influence the suppression and elliptic flow of heavy mesons at RHIC and the LHC. Our result shows that different modeling of initial conditions, pre-equilibrium evolution and in-medium interaction can individually yield about 10-40% uncertainties in D meson suppression and flow at low transverse momentum. We also find that a proper combination of collisional versus radiative energy loss, coalescence versus fragmentation in hadronization, and the inclusion of medium flow are the most important factors for describing the suppression and elliptic flow of heavy mesons.

    ↳ nucl-thhep-phnucl-exCPC(2020)·29 citations
12. 12*

    Inclusive and effective bulk viscosities in the hadron gas

    J.-B. Rose🇩🇪 · J. M. Torres-Rincon🇩🇪 · H. Elfner🇩🇪

    We estimate the temperature dependence of the bulk viscosity in a relativistic hadron gas. Employing the Green-Kubo formalism in the SMASH (Simulating Many Accelerated Strongly-interacting Hadrons) transport approach, we study different hadronic systems in increasing order of complexity. We analyze the (in)validity of the single exponential relaxation ansatz for the bulk-channel correlation function and the strong influence of the resonances and their lifetimes. We discuss the difference between the inclusive bulk viscosity of an equilibrated, long-lived system, and the effective bulk viscosity of a short-lived mixture like the hadronic phase of relativistic heavy-ion collisions, where the processes whose inverse relaxation rate are larger than the fireball duration are excluded from the analysis. This clarifies the differences between previous approaches which computed the bulk viscosity including/excluding the very slow processes in the hadron gas. We compare our final results with previous hadron gas calculations and confirm a decreasing trend of the inclusive bulk viscosity over entropy density as temperature increases, whereas the effective bulk viscosity to entropy ratio, while being lower than the inclusive one, shows no strong dependence to temperature.

    ↳ hep-phnucl-exnucl-thJ.Phys.G(2020)·31 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.