Fri·Jun 30, 2023Friday·June 30, 2023

1. 01*

   Experimental study of excited states of ${}^{62}$Ni via one-neutron $(d,p)$ transfer up to the neutron-separation threshold and characteristics of the pygmy dipole resonance states

   M. Spieker🇺🇸 · L.T. Baby🇺🇸 · A.L. Conley🇺🇸 · B. Kelly🇺🇸 · M. Müscher · R. Renom · T. Schüttler · A. Zilges

   The degree of collectivity of the Pygmy Dipole Resonance (PDR) is an open question. Recently, Ries {\it et al.} have suggested the onset of the PDR beyond $N=28$ based on the observation of a significant $E1$ strength increase in the Cr isotopes and proposed that the PDR has its origin in a few-nucleon effect. Earlier, Inakura {\it et al.} had predicted by performing systematic calculations using the random-phase approximation (RPA) with the Skyrme functional SkM* that the $E1$ strength of the PDR strongly depends on the position of the Fermi level and that it displays a clear correlation with the occupation of orbits with orbital angular momenta less than $3\hslash$ $(l\le 2)$. To further investigate the microscopic structures causing the possible formation of a PDR beyond the $N=28$ neutron shell closure, we performed a ${}^{61}$Ni$(d,p){}^{62}$Ni experiment at the John D. Fox Superconducting Linear Accelerator Laboratory of Florida State University. To determine the angular momentum transfer populating possible $J^{\pi }=1^{-}$ states and other excited states of ${}^{62}$Ni, angular distributions and associated single-neutron transfer cross sections were measured with the Super-Enge Split-Pole Spectrograph. A number of $J^{\pi }=1^{-}$ states were observed below the neutron-separation threshold after being populated through $l=2$ angular momentum transfers. A comparison to available $(\gamma ,{\gamma }^{\prime })$ data for ${}^{58,60}$Ni provides evidence that the $B(E1)$ strength shifts further down in energy. The $(d,p)$ data clearly prove that $l=0$ strength, i.e., the neutron $(2p_{3/2}{)}^{-1}(3s_{1/2}{)}^{+1}$ one-particle-one-hole configuration plays only a minor role for $1^{-}$ states below the neutron-separation threshold in ${}^{62}$Ni.

   nucl-exPRC(2023)·14 citations
2. 02*

   $\gamma$-ray Angular Distributions in Single Nucleon Transfer Reactions with Exotic Strontium Isotopes

   R. Jain🇮🇳

   $\gamma$-ray angular distributions help assign spin and parity to excited energy levels in nuclei. The spectroscopy of ${}^{94,96}$Sr studied through the single neutron transfer reactions with ${}^{95}$Sr beam in inverse kinematics [${}^{95}$Sr(d,p)${}^{96}$Sr; ${}^{95}$Sr(d,t)${}^{94}$Sr] revealed a rich nuclear structure with many excited states. While the spin-parities were assigned to low lying states through techniques like particle angular distributions and angular momentum transfer, those for higher lying states were ambiguous. The goal of this project is to develop the Gamma-ray angular distributions and correlations techniques to assign spin-parity to these states. In this work, the $\gamma$-ray angular distributions for 815 keV transition from the first excited state to ground state $(2^{+}\to 0^{+})$ in ${}^{96}$Sr are measured. The alignment of this state is calculated from these measurements and compared to the theoretically calculated alignment for this state which is determined by coupling the spins of reactants and the orbital angular momentum transfered. The values agree within experimental limits justifying the technique. It is then applied to some other transitions and important results are discussed. Angular correlations cannot be performed with this data since statistics turn out to be limiting factor at the crystal level.

   nucl-ex0 citations
3. 03*

   Nucleosynthesis of light nuclei and hypernuclei in central Au+Au collisions at $\sqrt{s_{NN}}$=3 GeV

   N. Buyukcizmeci🇹🇷 · T. Reichert🇩🇪 · A. S. Botvina🇩🇪 · M. Bleicher🇩🇪

   We analyze the experimental data on nuclei and hypernuclei yields recently obtained by the STAR collaboration. The hybrid dynamical and statistical approaches which have been developed previously are able to describe the experimental data reasonably. We discuss the intriguing difference between the yields of normal nuclei and hypernuclei which may be related to the properties of hypermatter at subnuclear densities. Most importantly new (hyper-)nuclei could be detected via particle correlations, and such measurements are relevant to pin down the production mechanism.

   ↳ nucl-thnucl-exPRC(2023)·18 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.