Fri·May 17, 2019Friday·May 17, 2019

1. 01*

   Search for stabilizing effects of $\mathbf{Z}=82$ shell closure against fission

   J. Gehlot · S. Nath · Tathagata Banerjee · Ish Mukul🇮🇱 · R. Dubey · A. Shamlath · P. V. Laveen · M. Shareef · Md. Moin Shaikh🇮🇳 · A. Jhingan🇮🇳 · N. Madhavan · T. Rajbongshi · P. Jisha · Santanu Pal

   Presence of closed proton and/or neutron shells causes deviation from macroscopic properties of nuclei which are understood in terms of the liquid drop model. It is important to investigate experimentally the stabilizing effects of shell closure, if any, against fission. This work aims to investigate probable effects of proton shell ($Z=82$) closure in the compound nucleus, in enhancing survival probability of the evaporation residues formed in heavy ion-induced fusion-fission reactions. Evaporation residue cross sections have been measured for the reactions ${}^{19}$F+${}^{180}$Hf, ${}^{19}$F+${}^{181}$Ta and ${}^{19}$F+${}^{182}$W from $\simeq 9\%$ below to $\simeq 42\%$ above the Coulomb barrier, leading to formation of compound nuclei with same number of neutrons ($N=118$) but different number of protons across $Z=82$. Measured excitation functions have been compared with statistical model calculation, in which reduced dissipation coefficient is the only adjustable parameter. Evaporation residue cross section, normalized by capture cross section, is found to decrease gradually with increasing fissility of the compound nucleus. Measured evaporation residue cross sections require inclusion of nuclear viscosity in the model calculations. Reduced dissipation coefficient in the range of 1\textendash3 $\times$ $10^{21}$ s${}^{-1}$ reproduces the data quite well. No abrupt enhancement of evaporation residue cross sections has been observed in the reaction forming compound nucleus with $Z=82$. Thus, this work does not find enhanced stabilizing effects of $Z=82$ shell closure against fission in the compound nucleus. One may attempt to measure cross sections of individual exit channels for further confirmation of our observation.

   nucl-exnucl-thPRC(2019)·7 citations
2. 02*

   Resonance $d^{\ast }(2380)$ and higher isospin states

   E. A. Doroshkevich🇷🇺

   A new isoscalar state in the two-baryon system with mass 2380 MeV and width 80 MeV denoted now $d^{\ast }(2380)$ has been detected in the experiments at the Juelich Cooler Synchrotron (COSY). Existence or influence of states with higher isospin is a subject of the experiment for studing of the ${\pi }^{+}{\pi }^{-}$ production in $pp$ collisions. Calculations taking into account isotensor dibaryon resonance in the $\Delta N$ with $I(J^p)=2(1^{+})$ provide a good description of the $pp\to pp{\pi }^{+}{\pi }^{-}$ total and differential cross sections.

   nucl-exJ.Phys.Conf.Ser.(2019)·0 citations
3. 03*

   Quantitative description of the ${}^{20}$Ne($p$,$p\alpha$)${}^{16}$O cross section as a means of probing the surface $\alpha$ amplitude

   Kazuki Yoshida🇯🇵 · Yohei Chiba🇯🇵 · Masaaki Kimura🇯🇵 · Yasutaka Taniguchi🇯🇵 · Yoshiko Kanada-En'yo🇯🇵 · Kazuyuki Ogata🇯🇵

   The proton-induced $\alpha$ knockout reaction has been utilized for decades to investigate the $\alpha$ cluster states of nuclei, of the ground state in particular. However, even in recent years, it is reported that the deduced $\alpha$ spectroscopic factors from $\alpha$ knockout experiments and reaction analyses with a phenomenological $\alpha$ cluster wave function diverge depending on the kinematical condition of the reaction. In the present study we examine the theoretical description of the ${}^{20}$Ne($p$,$p\alpha$)${}^{16}$O cross section based on the antisymmetrized molecular dynamics and the distorted wave impulse approximation by comparing with existing experimental data. We also investigate the correspondence between the $\alpha$ cluster wave function and the $\alpha$ knockout cross section. The existing ${}^{20}$Ne($p$,$p\alpha$)${}^{16}$O data at 101.5 MeV is well reproduced by the present framework. Due to the peripherality of the reaction, the surface region of the cluster wave function is selectively reflected to the knockout cross section. A quantitatively reliable $\alpha$ cluster wave function, $p$-$\alpha$ cross section, and distorting potentials between scattering particles, $\alpha$-${}^{16}$O in particular, are crucial for the quantitative description of the ($p$,$p\alpha$) cross section. Due to the peripherality of the reaction, the ($p$,$p\alpha$) cross section is a good probe for the surface $\alpha$ amplitude.

   ↳ nucl-thnucl-exPRC(2019)·28 citations
4. 04*

   The onset of $\Lambda \Lambda$ hypernuclear binding

   L. Contessi🇮🇱 · M. Schäfer🇨🇿 · N. Barnea🇮🇱 · A. Gal🇮🇱 · J. Mareš🇨🇿

   Binding energies of light, $A\le 6$, $\Lambda \Lambda$ hypernuclei are calculated using the stochastic variational method in a pionless effective field theory (EFT) approach at leading order with the purpose of assessing critically the onset of binding in the strangeness S=-2 hadronic sector. The EFT input in this sector consists of (i) a $\Lambda \Lambda$ contact term constrained by the $\Lambda \Lambda$ scattering length $a_{\Lambda \Lambda }$, using a range of values compatible with $\Lambda \Lambda$ correlations observed in relativistic heavy ion collisions, and (ii) a $\Lambda \Lambda N$ contact term constrained by the only available $A\le 6$ $\Lambda \Lambda$ hypernucler binding energy datum of ${}_{\Lambda \Lambda }^6$He. The recently debated neutral three-body and four-body systems ${}_{\Lambda \Lambda }^3$n and ${}_{\Lambda \Lambda }^4$n are found unbound by a wide margin. A relatively large value of $|a_{\Lambda \Lambda }|\gtrsim 1.5$ fm is needed to bind ${}_{\Lambda \Lambda }^4$H, thereby questioning its particle stability. In contrast, the particle stability of the $A=5$ $\Lambda \Lambda$ hypernuclear isodoublet ${}_{\Lambda \Lambda }^5$H--${}_{\Lambda \Lambda }^5$He is robust, with $\Lambda$ separation energy of order 1 MeV.

   ↳ nucl-thhep-phnucl-exPLB(2019)·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.