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1. Fine structure of the isoscalar giant monopole resonance in ${}^{58}\mathrm{Ni}, {}^{90}\mathrm{Zr}, {}^{120}\mathrm{Sn}$ , and ${}^{208}\mathrm{Pb}$

   https://doi.org/10.1103/PhysRevC.109.014325  

   Bahini, A; von_Neumann-Cosel, P; Carter, J; Usman, I T; Arsenyev, N N; Severyukhin, A P; Litvinova, E; Fearick, R W; Neveling, R; Adsley, P; et al (January 2024, Physical Review C)

   na (Ed.)

   Background: Over the past two decades high energy-resolution inelastic proton scattering studies were used to gain an understanding of the origin of fine structure observed in the isoscalar giant quadrupole resonance (ISGQR) and the isovector giant dipole resonance (IVGDR). Recently, the isoscalar giant monopole resonance (ISGMR) in 58 Ni , 90 Zr , 120 Sn , and 208 Pb was studied at the iThemba Laboratory for Accelerator Based Sciences (iThemba LABS) by means of inelastic 𝛼-particle scattering at very forward scattering angles (including 0∘). The good energy resolution of the measurement revealed significant fine structure of the ISGMR. Objective: To extract scales by means of wavelet analysis characterizing the observed fine structure of the ISGMR in order to investigate the role of different mechanisms contributing to its decay width. Methods: Characteristic energy scales are extracted from the fine structure using continuous wavelet transforms. The experimental energy scales are compared to different theoretical approaches performed in the framework of quasiparticle random phase approximation (QRPA) and beyond-QRPA including complex configurations using both non-relativistic and relativistic density functional theory. Results: All models highlight the role of Landau fragmentation for the damping of the ISGMR especially in the medium-mass region. Models which include the coupling between one-particle–one-hole (1p-1h) and two-particle–two-hole (2p-2h) configurations modify the strength distributions and wavelet scales indicating the importance of the spreading width. The effect becomes more pronounced with increasing mass number. Conclusions: Wavelet scales remain a sensitive measure of the interplay between Landau fragmentation and the spreading width in the description of the fine structure of giant resonances. The case of the ISGMR is intermediate between the IVGDR, where Landau damping dominates, and the ISGQR, where fine structure originates from coupling to low-lying surface vibrations. 

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2. Proton emission in ultraperipheral Pb-Pb collisions at $\sqrt{s_{NN}}=5.02$ TeV

   https://doi.org/10.1103/PhysRevC.111.054906  

   Acharya, S; Agarwal, A; Aglieri_Rinella, G; Aglietta, L; Agnello, M; Agrawal, N; Ahammed, Z; Ahmad, S; Ahn, S U; Ahuja, I; et al (May 2025, Physical Review C)

   The first measurements of proton emission accompanied by neutron emission in the electromagnetic dissociation (EMD) of ${}^{208}\mathrm{Pb}$ nuclei in the ALICE experiment at the Large Hadron Collider are presented. The EMD protons and neutrons emitted at very forward rapidities are detected by the proton and neutron zero degree calorimeters of the ALICE experiment. The emission cross sections of zero, one, two, and three protons accompanied by at least one neutron were measured in ultraperipheral ${}^{208}\mathrm{Pb}\text{−}{}^{208}\mathrm{Pb}$ collisions at a center-of-mass energy per nucleon pair $\sqrt{s_{NN}}=5.02\mathrm{TeV}$ . The 0p and 3p cross sections are described by the RELDIS model within their measurement uncertainties, while the 1p and 2p cross sections are underestimated by the model by 17–25%. According to this model, these 0p, 1p, 2p, and 3p cross sections are associated, respectively, with the production of various isotopes of Pb, Tl, Hg, and Au in the EMD of ${}^{208}\mathrm{Pb}$ . The cross sections of the emission of a single proton accompanied by the emission of one, two, or three neutrons in EMD were also measured. The data are significantly overestimated by the RELDIS model, which predicts that the (1p,1n), (1p,2n), and (1p,3n) cross sections are very similar to the cross sections for the production of the thallium isotopes ${}^{206,205,204}\mathrm{Tl}$ . ©2025 CERN, for the ALICE Collaboration2025CERN 

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3. Reduction of spectroscopic overlap across the $Z=8$ shell in neutron-rich nuclei

   https://doi.org/10.1103/PhysRevC.109.054325  

   Redpath, T; Guèye, P; Baumann, T; Brown, B A; Cunningham, A; DeYoung, P A; Frank, N; Hoffman, C R; Kuchera, A N; Godoy, B Monteagudo; et al (May 2024, Physical Review C)

   Zhang, Lin (Ed.)

   The recent discovery and spectroscopic measurements of ${}^{27}\mathrm{O}$ and ${}^{28}\mathrm{O}$ suggests the disappearance of the $N=20$ shell structure in these neutron-rich oxygen isotopes. We measured one- and two-proton removal cross sections from ${}^{27}\mathrm{F}$ and ${}^{29}\mathrm{Ne}$ , respectively, extracting spectroscopic factors and comparing them to shell model overlap functions coupled with eikonal reaction model calculations. The invariant mass technique was used to reconstruct the two-body ( ${}^{24}\mathrm{O}+n$ ) and three-body ( ${}^{24}\mathrm{O}+2n$ ) decay energies from knockout reactions of ${}^{27}\mathrm{F}$ (106.2 MeV/u) and ${}^{29}\mathrm{Ne}$ (112.8 MeV/u) beams impinging on a ${}^9\mathrm{Be}$ target. The one-proton removal from ${}^{27}\mathrm{F}$ strongly populated the ground state of ${}^{26}\mathrm{O}$ and the extracted cross section of $3.4_{-1.5}^{+0.3}$ mb agrees with eikonal model calculations that are normalized by the shell model spectroscopic factors and account for the systematic reduction factor observed for single nucleon removal reactions within the models used. For the two-proton removal reaction from ${}^{29}\mathrm{Ne}$ an upper limit of 0.08 mb was extracted for populating states in ${}^{27}\mathrm{O}$ decaying though the ground state of ${}^{26}\mathrm{O}$ . The measured upper limit for the population of the ground state of ${}^{26}\mathrm{O}$ in the two-proton removal reaction from ${}^{29}\mathrm{Ne}$ indicates a significant difference in the underlying nuclear structure of ${}^{27}\mathrm{F}$ and ${}^{29}\mathrm{Ne}$ . Published by the American Physical Society2024 

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4. Direct measurement of the ${}^{3}P_0$ clock state natural lifetime in ${}^{87}\mathrm{Sr}$

   https://doi.org/10.1103/f6pt-flnt  

   Dolde, Jonathan; Ganapathy, Dhruva; Zheng, Xin; Ma, Shuo; Beloy, Kyle; Kolkowitz, Shimon (August 2025, Physical Review A)

   Optical lattice clocks based on the narrow $(5s^2){}^{1}S_0\text{−}\left(5s5p\right){}^{3}P_0$ transition in neutral strontium (Sr) are among the most precise and accurate measurement devices in existence. Although this transition is completely forbidden by selection rules, state mixing from the hyperfine interaction in ${}^{87}\mathrm{Sr}$ provides a weakly allowed transition that can be coherently driven with practical clock laser intensities. While the coherent interrogation times of optical clocks are typically set by the linewidth of the probe laser, this limitation can be overcome in synchronous differential comparisons between ensembles. In such measurements the natural lifetime of the ${}^{1}S_0–{}^{3}P_0$ clock transition becomes the fundamental limiting factor to the duration of a single run of the experiment. However, a direct measurement of the decay rate of the clock excited state is quite challenging due to the competing effects of other loss channels such as Raman scattering, inelastic collisions, and atom loss due to background gas. In this work, we monitor the decay of Sr atoms trapped in an optical lattice and initialized in the ${}^{3}P_0$ state. By making measurements of high and low density ensembles of both ${}^{87}\mathrm{Sr}$ and ${}^{88}\mathrm{Sr}$ across varying lattice trap depths, we isolate radiative decay, which accounts for a significant fraction of the observed decays at low depths. We obtain a natural radiative decay lifetime of ${167}_{-40}^{+79}$ s for the ${}^{3}P_0$ clock state in ${}^{87}\mathrm{Sr}$ , a value that is consistent with previously reported measurements and theoretical predictions. We also introduce an additional measurement scheme that involves repeated measurements of the ground-state population within a single experimental sequence, validating our model and the consistency of the measured rates. We expect that the techniques introduced in this work are applicable to lifetime measurements of long-lived metastable states in other atoms and ions used for clocks and quantum computing. The results presented in this work inform performance estimates of proposed gravitational wave detectors and long-baseline atom interferometers making use of ${}^{87}\mathrm{Sr}$ . 

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5. Full-dimensional quantum scattering calculations of rovibrationally excited HD+HD collisions

   https://doi.org/10.1063/5.0318268  

   Mandal, Bikramaditya; Jóźwiak, Hubert; Wcisło, Piotr; Balakrishnan, Naduvalath (March 2026, The Journal of Chemical Physics)

   Full-dimensional quantum scattering calculations are reported for rovibrational transitions in HD+HD collisions using a highly accurate interaction potential for the H2–H2 system. Several near-resonant rovibrational transitions are identified that conserve the overall rotational angular momentum and nearly conserve the internal energy of the collision partners. Key anisotropic terms that drive the rotational transitions and angular momentum partial waves that contribute to low-energy resonant features in the energy dependence of the cross-sections are identified. The computed results agree with total cross-sections reported in previous experimental results, including resonant features in the energy dependence of the cross-section. In particular, low-energy cross-sections show a strong resonant feature associated with an l = 3 partial wave in the incident channel. Rate coefficients for several inelastic rotational and rovibrational transitions are reported for temperatures ranging from 0.1 to 200 K, and they display a maximum between 1 and 10 K, reflecting the important contributions from the l = 3 shape resonance that occurs around 2.5 K. 

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