Singular observation of shape and spin hindrance in metastable nuclear decay of $^{197}$Au

S. K. Tandel; D. Rathore; M. Hemalatha; Subhrajit Sahoo; P. C. Srivastava; P. Chowdhury; R. V. F. Janssens; F. G. Kondev; M. P. Carpenter; T. Lauritsen; D. Seweryniak

arXiv · 2610.25915

Singular observation of shape and spin hindrance in metastable nuclear decay of $^{197}$Au

S. K. Tandel·D. Rathore·M. Hemalatha·Subhrajit Sahoo·P. C. Srivastava·P. Chowdhury·R. V. F. Janssens·F. G. Kondev·M. P. Carpenter·T. Lauritsen·D. Seweryniak

View original source ↗Read source document ↗Export metadata ↓

Abstract

A $I^π$ = (29/2$^{+}$) metastable state with $T_{1/2}$ $ > $ 10 s at $E_{x}$ = 2102 keV has been identified in the stable nucleus, $^{197}$Au. Its decay exhibits the unusual coexistence of a strongly hindered $E2$ transition and a competing $E4$ branch with comparable intensity, indicating the simultaneous presence of shape- and spin-related hindrance mechanisms. Such a decay pattern has not previously been identified in a long-lived nuclear state and serves as a sensitive probe of the interplay between shell structure, configuration mixing, and collective degrees of freedom. This result establishes an important benchmark for modern nuclear-structure models, for which a unified description of all observables remains challenging.

Explore related subjects

nucl-ex

Keep this discovery

Explore connections, maps & timelines

BibTeX RIS

S. K. Tandel, D. Rathore, M. Hemalatha, Subhrajit Sahoo, P. C. Srivastava, P. Chowdhury, R. V. F. Janssens, F. G. Kondev, M. P. Carpenter, T. Lauritsen, D. Seweryniak. 2026-10-19. Singular observation of shape and spin hindrance in metastable nuclear decay of $^{197}$Au. https://arxiv.org/abs/2610.25915

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2026

Measurements of local polarization of $Λ$ hyperons with event shape engineering in Au+Au collisions at RHIC-STAR

Anisotropic flow is expected to generate local vorticities along the beam direction, which in turn lead to local polarization of produced particles. Although the local polarization of hyperons has already been observed at RHIC and the LHC, its mechanism is not yet understood: model calculations indicate that the shear-induced and vorticity-induced contributions can have opposite signs and may substantially cancel, so that the resulting polarization depends sensitively on the theoretical implementation. Since both are driven by the anisotropic flow, we employ the Event Shape Engineering (ESE) method, which selects events with different flow magnitudes within a narrow centrality range, to measure the local polarization as a function of the elliptic flow at a fixed multiplicity. We report the measurements of the elliptic flow ($v_2$) and the local polarization ($P_{z,2}$) of $Λ$ and $\barΛ$ as a function of the reduced flow vector magnitude $q_2$ used for the ESE event selection, in Au+Au collisions at $\sqrt{s_{\rm NN}} = 19.6~{\rm GeV}$ from the STAR experiment. The $v_2$ shows a clear positive dependence on $q_2$, while $P_{z,2}$ indicates a weak positive dependence on $q_2$ and $v_2$. This is the first measurement to directly investigate the relation between anisotropic flow and local polarization, providing new insight into the origin of local polarization.

nucl-ex↗

arXiv2026

First measurement of kaonic deuterium X-ray transitions

The study of the strong interaction among hadrons at low energies remains one of the key challenges in fundamental physics because of its non-perturbative nature, which makes theoretical descriptions strongly dependent on experimental input. Although substantial progress has been made for systems involving up and down quarks, theoretical models in the strangeness sector continue to face limitations due to the lack of experimental data. Kaonic atoms provide a powerful tool to study the low-energy strong interaction with strangeness through the energy shifts and widths induced on their lowest atomic levels. In this context, kaonic deuterium X-ray spectroscopy has long represented one of the major open challenges in hadronic-atom physics because of its extremely low X-ray yield. This measurement is particularly important because it gives access to the poorly constrained $K^-n$ interaction at threshold. Here, we report the first observation of kaonic deuterium X-ray transitions, performed with the SIDDHARTA-2 experiment at the DA$Φ$NE collider. We determine the strong-interaction shift and width of the $1s$ level to be $\varepsilon_{1s}=-810.9\pm24.5\,(\mathrm{stat})\pm2.1\,(\mathrm{syst})\,\mathrm{eV}$ and $Γ_{1s}=812\pm97\,(\mathrm{stat})\pm33\,(\mathrm{syst})\,\mathrm{eV}$, respectively. This measurement constitutes the most precise experimental determination of the $K^-d$ strong interaction at threshold and allows discrimination among competing theoretical models. Combined with the kaonic hydrogen measurement, this result provides the experimental input required to determine the isospin-dependent $K^-N$ scattering lengths, with implications for the description of the nature of the molecular interpretation of the $Λ(1405)$, and neutron-rich matter.

nucl-ex↗

arXiv2026

Short-range correlated pair formation and nuclear shell structure

Short-range correlated (SRC) nucleon pairs, caused by brief, high-momentum interactions between two nucleons, are dominated by neutron-proton pairs with large relative and smaller center-of-mass momenta. However, which nucleons form pairs is not fully understood. Measurements of 40,48Ca and 54Fe showed that intra-shell pairing was much stronger than inter-shell pairing. We measured high- missing-momentum protons knocked out in electron scattering from selected nuclei with a range of shell configurations, A, and N/Z, including 9Be, 10,11B, 12C, 40,48Ca, 54Fe, and 197Au, focusing on the four light nuclei. Unexpectedly, we found that adding one proton to 9Be (to make 10B) increased the number of correlated protons far more than adding one neutron to 10B or adding one proton to 11B, perhaps due to the large spin (J = 3) of 10B or the unusual structure of 9Be. In addition, the increase in pairing probability from 9Be to 12C and from 40Ca to 54Fe was much steeper than the increase from 9Be to 197Au. This shows the importance of low-momentum nuclear structure on the probability of high-momentum nucleon pairing.

nucl-ex↗