Tue·Aug 28, 2018Tuesday·August 28, 2018

1. 01*

   Stellar ${}^{36,38}$Ar$(n,\gamma {)}^{37,39}$Ar reactions and their effect on light neutron-rich nuclide synthesis

   M. Tessler🇮🇱 · M. Paul🇮🇱 · S. Halfon🇮🇱 · B. S. Meyer🇺🇸 · R. Pardo🇺🇸 · R. Purtschert · K. E. Rehm🇺🇸 · R. Scott · M. Weigand🇩🇪 · L. Weissman🇮🇱 · S. Almaraz-Calderon · M. L. Avila and 13 other authors

   The ${}^{36}$Ar$(n,\gamma {)}^{37}$Ar ($t_{1/2}$ = 35 d) and ${}^{38}$Ar$(n,\gamma {)}^{39}$Ar (269 y) reactions were studied for the first time with a quasi-Maxwellian ($kT\sim 47$ keV) neutron flux for Maxwellian Average Cross Section (MACS) measurements at stellar energies. Gas samples were irradiated at the high-intensity Soreq applied research accelerator facility-liquid-lithium target neutron source and the ${}^{37}$Ar/${}^{36}$Ar and ${}^{39}$Ar/${}^{38}$Ar ratios in the activated samples were determined by accelerator mass spectrometry at the ATLAS facility (Argonne National Laboratory). The ${}^{37}$Ar activity was also measured by low-level counting at the University of Bern. Experimental MACS of ${}^{36}$Ar and ${}^{38}$Ar, corrected to the standard 30 keV thermal energy, are 1.9(3) mb and 1.3(2) mb, respectively, differing from the theoretical and evaluated values published to date by up to an order of magnitude. The neutron capture cross sections of ${}^{36,38}$Ar are relevant to the stellar nucleosynthesis of light neutron-rich nuclides; the two experimental values are shown to affect the calculated mass fraction of nuclides in the region A=36-48 during the weak $s$-process. The new production cross sections have implications also for the use of ${}^{37}$Ar and ${}^{39}$Ar as environmental tracers in the atmosphere and hydrosphere.

   nucl-exPRL(2018)·15 citations
2. 02*

   Directed flow in an extended multiphase transport model

   Chong-Qiang Guo🇨🇳 · He Liu🇨🇳 · Jun Xu🇨🇳

   We have studied the rapidity-odd directed flow in ${}^{197}$Au+${}^{197}$Au collisions in the beam energy range from $\sqrt{s_{NN}}$ = 7.7 to 39 GeV within the framework of an extended multiphase transport model with both partonic and hadronic mean-field potentials incorporated. Effects of the partonic scatterings, mean-field potentials, hadronization, and hadronic evolution on the directed flow are investigated, and it is found that the final directed flow is mostly sensitive to the partonic scatterings and the hadronization mechanism. Our study shows that a negative slope of the proton directed flow does not necessarily need the equation of state with a first-order phase transition.

   ↳ nucl-thhep-exnucl-exPRC(2018)·9 citations
3. 03*

   Validity of the distorted-wave impulse-approximation description of ${}^{40}$Ca$(e,e^{\prime }p{)}^{39}$K data using only ingredients from a nonlocal dispersive optical model

   M. C. Atkinson🇨🇦 · H.P. Blok🇳🇱 · L. Lapikás · R. J. Charity🇺🇸 · W. H. Dickhoff🇺🇸

   The nonlocal implementation of the dispersive optical model (DOM) provides all the ingredients for distorted-wave impulse-approximation (DWIA) calculations of the $(e,e^{\prime }p)$ reaction. It provides both the overlap function, including its normalization, and the outgoing proton distorted wave. This framework is applied to describe the knockout of a proton from the $0\text{d}\frac{3}{2}$ and $1\text{s}\frac{1}{2}$ orbitals in ${}^{40}$Ca with fixed normalizations of 0.71 and 0.60, respectively. Data were obtained in parallel kinematics for three outgoing proton energies: 70, 100, and 135 MeV. Agreement with the data is as good as, or better than, previous descriptions employing local optical potentials and overlap functions from Woods-Saxon potentials - both with standard nonlocality corrections - whose normalization (spectroscopic factor) and radius were fitted to the data. The present analysis suggests that slightly larger spectroscopic factors are obtained when nonlocal optical potentials are employed than those generated with local potentials. The results further suggest that the chosen kinematical window around 100 MeV proton energy provides the best and cleanest method to employ the DWIA for the analysis of this reaction. The conclusion that substantial ground-state correlations cannot be ignored when describing a closed-shell atomic nucleus is therefore confirmed in detail. To reach these conclusions, it is essential to have a complete description of the nucleon single-particle propagator that accounts for all elastic nucleon-scattering observables in a wide energy domain up to 200 MeV. The current nonlocal implementation of the DOM fulfills this requirement.

   ↳ nucl-thnucl-exPRC(2018)·33 citations
4. 04*

   Polarization and Entanglement in Baryon-Antibaryon Pair Production in Electron-Positron Annihilation

   BESIII Collaboration: M. Ablikim · M. N. Achasov · S. Ahmed · M. Albrecht · M. Alekseev · A. Amoroso · F. F. An · Q. An · Y. Bai · O. Bakina · R. Baldini Ferroli · Y. Ban and 456 other authors

   Using a sample of $1.31\times 10^9$ $J/\psi$ events collected with the BESIII detector, we report the first observation of spin polarization of $\Lambda$ and $\bar{\Lambda }$ hyperons from the coherent production in the $J/\psi \to \Lambda \bar{\Lambda }$ decay. We measure the phase between the hadronic form factors to be $\Delta \Phi =(42.4\pm 0.6\pm 0.5{)}^{\circ }$. The decay parameters for $\Lambda \to p{\pi }^{-}$ (${\alpha }_{-}$), $\bar{\Lambda }\to \bar{p}{\pi }^{+}$ (${\alpha }_{+}$) and $\bar{\Lambda }\to \bar{n}{\pi }^0$ (${\bar{\alpha }}_0$) are measured to be ${\alpha }_{-}=0.750\pm 0.009\pm 0.004$, ${\alpha }_{+}=-0.758\pm 0.010\pm 0.007$ and ${\bar{\alpha }}_0=-0.692\pm 0.016\pm 0.006$, respectively. The obtained value of ${\alpha }_{-}$ is higher by $(17\pm 3)\%$ than the current world average. In addition, the $CP$ asymmetry of $-0.006\pm 0.012\pm 0.007$ is extracted with substantially improved precision. The ratio ${\bar{\alpha }}_0/{\alpha }_{+}=0.913\pm 0.028\pm 0.012$ is also measured.

   ↳ hep-exnucl-exNat.Phys.(2019)·284 citations
5. 05*

   Neutron Dark Matter Decays and Correlation Coefficients of Neutron Beta Decays

   A. N. Ivanov🇦🇹 · R. Höllwieser🇦🇹 · N. I. Troitskaya🇦🇹 · M. Wellenzohn🇦🇹 · Ya. A. Berdnikov🇷🇺

   As we have pointed out in (arXiv:1806.10107 [hep-ph]), the existence of neutron dark matter decay modes "n -> chi + anything", where "chi" is a dark matter fermion, for the solution of the neutron lifetime problem changes priorities and demands to describe the neutron lifetime "tau_n = 888.0(2.0)s", measured in beam experiments and defined by the decay modes "n -> p + anything", in the Standard Model (SM). The latter requires the axial coupling constant "lambda" to be equal to "lambda = - 1.2690" (arXiv:1806.10107 [hep-ph]). Since such an axial coupling constant is excluded by experimental data reported by the PERKEO II and UCNA Collaborations, the neutron lifetime "tau_n = 888.0(2.0)s" can be explained only by virtue of interactions beyond the SM, namely, by the Fierz interference term of order "b ~ - 10^{-2}" dependent on scalar and tensor coupling constants. We give a complete analysis of all correlation coefficients of the neutron beta decays with polarized neutron, taking into account the contributions of scalar and tensor interactions beyond the SM with the Fierz interference term "b ~ - 10^{-2}". We show that the obtained results agree well with the contemporary experimental data that does not prevent the neutron with the rate of the decay modes "n -> p + anything", measured in beam experiments, to have dark matter decay modes "n -> chi + anything".

   ↳ hep-phgr-qcnucl-exNPB(2019)·25 citations
6. 06*

   Women Scientists Who Made Nuclear Astrophysics

   C. V. Hampton🇺🇸 · M. Lugaro🇭🇺 · P. Papakonstantinou🇰🇷 · P. G. Isar🇷🇴 · B. Nordström🇩🇰 · N. Özkan🇹🇷 · M. Aliotta🇬🇧 · A. Ćiprijanović🇷🇸 · S. Curtis🇺🇸 · M. Di Criscienzo🇮🇹 · J. den Hartogh🇭🇺 · A. S. Font🇬🇧 and 15 other authors

   Female role models reduce the impact on women of stereotype threat, i.e., of being at risk of conforming to a negative stereotype about one's social, gender, or racial group. This can lead women scientists to underperform or to leave their scientific career because of negative stereotypes such as, not being as talented or as interested in science as men. Sadly, history rarely provides role models for women scientists; instead, it often renders these women invisible. In response to this situation, we present a selection of twelve outstanding women who helped to develop nuclear astrophysics.

   ↳ physics.hist-phastro-ph.EPastro-ph.GAastro-ph.HE+3Springer Proc.Phys.(2019)·0 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.