Wed·Feb 19, 2025Wednesday·February 19, 2025

1. 01*

   Extreme Shape Coexistence Observed in ${}^{70}$Co

   Cade Dembski · Artemis Spyrou🇺🇸 · B. Alex Brown🇺🇸 · Sean N. Liddick🇺🇸 · Hannah C. Berg🇺🇸 · Darren L. Bleuel🇺🇸 · Katherine Childers · Benjamin P. Crider · Alexander C. Dombos · Erin C. Good🇺🇸 · Caley Harris🇺🇸 · Ann-Cecilie Larsen🇳🇴 and 13 other authors

   The shape of the atomic nucleus is a property which underpins our understanding of nuclear systems, impacts the limits of nuclear existence, and enables probes of physics beyond the Standard Model. Nuclei can adopt a variety of shapes, including spheres, axially deformed spheroids, and pear shapes. In some regions of the nuclear chart where a spherical nucleus would naively be expected, deformed nuclear states can result from collective action of constituent protons and neutrons. In a small subset of nuclei both spherical and deformed nuclear states have been experimentally observed, a phenomenon termed shape coexistence. We present spectroscopic evidence for the coexistence of $J^{\pi }=1+$ spherical and deformed states in ${}^{70}$Co, separated by less than 275~keV. This close degeneracy of levels with the same $J^{\pi }$ and different shapes demonstrates an extreme example of shape coexistence resulting from the interplay of independent particle motion and collective behavior in highly unstable nuclear systems and identifies the Co isotopes as a transition point between deformed ground states observed in the Cr isotopes and spherical configurations observed in the closed-shell Ni isotopes.

   nucl-exnucl-thCommun.Phys.(2025)·1 citation
2. 02*

   Search for medium effects using jet axis decorrelation in inclusive jets from PbPb collisions at $\sqrt{s_{\text{NN}}}$ = 5.02 TeV

   CMS Collaboration

   The jet axis decorrelation in inclusive jets is studied using lead-lead (PbPb) collisions at a center-of-mass energy per nucleon pair of 5.02 TeV. The jet axis decorrelation is defined as the angular difference between two definitions of the jet axis. It is obtained by applying two recombination schemes on all the constituents of a given jet reconstructed by the anti-$k_{\mathrm{T}}$ sequential algorithm with a distance parameter of $R$ = 0.4. The data set, corresponding to an integrated luminosity of 0.66 nb${}^{-1}$, was collected in 2018 with the CMS detector at the CERN LHC. The jet axis decorrelations are examined across collision centrality selections and intervals of jet transverse momentum. A centrality dependent evolution of the measured distributions is observed, with a progressive narrowing seen in more central events. This narrowing could result from medium-induced modification of the internal jet structure or reflect color charge effects in energy loss. This new measurement probes jet substructure in previously unexplored kinematic domains and show great promise for providing new insights on the color charge dependence of energy loss to jet-quenching models.

   nucl-exhep-exJHEP(2025)·6 citations
3. 03*

   Towards metrology with highly charged isomeric ions from antiproton annihilation

   Sara Alfaro🇦🇹 · Lorenz Panzl🇦🇹 · Jakub Zieliński🇵🇱 · Sankarshan Choudapurkar🇩🇪 · Fredrik Parnefjord Gustafsson🇨🇭 · Matthias Germann🇨🇭 · Tommaso Faorlin🇦🇹 · Yannick Weiser🇦🇹 · Thomas Lafenthaler🇦🇹 · Thomas Monz🇦🇹 · Michael Doser🇨🇭 · Georgy Kornakov🇵🇱 · Giovanni Cerchiari🇩🇪

   We describe how the annihilation of antiprotons can be utilized to generate highly charged isomeric ions in an ion-trap setup. We identify optical transitions in the hyperfine splitting of Hydrogen-like atoms composed of an isomer and a single electron in the ground state. We identify promising candidates in the isomers of Y, Nb, Rh, In, and Sb, for which the hyperfine transition lies in the infrared and whose excited state level lifetime is in the hundreds of milliseconds, which is suitable for metrology applications.

   ↳ physics.atom-phhep-exnucl-exquant-phJ.Phys.A(2025)·2 citations
4. 04*

   Initial-state-driven spin correlations in high-energy nuclear collisions

   Giuliano Giacalone🇨🇭 · Enrico Speranza🇨🇭

   In the study of spin-polarization phenomena in heavy-ion collisions, it is typically assumed that final-state particles are polarized through thermal vorticity and shear. In this sense, polarization is a final-state effect. Here, we propose a different mechanism. We postulate that the collision of spin-carrying nucleons generates an initial transverse spin density, inducing a net polarization of the QCD fireball along a random direction. If the net spin is conserved throughout the evolution of the fireball, the final-state particles should exhibit measurable polarization. Within a wounded nucleon picture, we estimate that initial-state fluctuations induce a net polarization of $\Lambda$ baryons which is around $1\%$ in central collisions and over $10\%$ in noncentral collisions, significantly exceeding the contributions from thermal vorticity and shear. We introduce a two-particle angular correlation observable designed to reveal initial net-spin fluctuations, and emphasize the main signatures to look for in experiments. We argue that the discovery of these phenomena would have profound implications for nuclear structure and our understanding of spin in relativistic hydrodynamics.

   ↳ nucl-thhep-exhep-phnucl-ex12 citations
5. 05*

   Nuclear effects in proton decay

   Denis Barbu🇷🇴 · Mihaela Parvu🇷🇴 · Ionel Lazanu🇷🇴

   Proton decay detection could put in evidence physics beyond the Standard Model (BSM). In this context, multiple projects are searching for such events. We focused our work on two of the expected decay modes, $p\to {\pi }^{+}+\bar{\nu }$ and $p\to K^{+}+\bar{\nu }$. Neutrinos are particles that interact very weakly with matter, so they are not of interest in our work. The detector materials investigated in this study include liquid argon (LAr), liquid xenon (LXe), and water (H${}_2$O). Our analysis focuses on two key effects relevant to this decay process: the Fermi motion of nucleons and final state interactions. In addition to these effects, we have also examined the nuclear interaction of particles with the nuclei of the medium. This paper presents values for nucleon energy distribution, cross sections, mean free paths and interaction probabilities.

   ↳ hep-phhep-exnucl-exMod.Phys.Lett.A(2025)·1 citation

* 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.