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IDS Collaboration(Dyszel, P. et al), Algora, A., & Nacher, E. (2025). First β-Delayed Two-Neutron Spectroscopy of the r-Process Nucleus 134In and Observation of the i13/2 Single-Particle Neutron State in 133Sn. Phys. Rev. Lett., 135(15), 152501–8pp.
Abstract: This manuscript reports on the direct observation of a beta-delayed two-neutron emission in a study of In-134 at the ISOLDE Decay Station using neutron spectroscopy. We also report on the first measurement in beta(-) decay of the long-sought 13/2(+) excited state in Sn-133, attributed to be the neutron single-particle i(13/2) orbital. The observation of sequential neutron emission is used to extract the relative population of the i(13/2) state, which was found to be much smaller than the predictions of the statistical model. The experiment was possible because of the innovative use of a neutron array with neutron discrimination and interaction tracking capabilities. This is the first study of the details of the two-neutron emission for a nucleus, which belongs to the r-process path. Understanding beta-delayed two-neutron emission probabilities is essential to validate models used in astrophysical r-process nucleosynthesis calculations. Observing two-neutron emissions in beta(-) decay paves the way for new experiments to study energy and angular correlations for ssdelayed multineutron emitters.
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Gomez Dumm, D., Noguera, S., & Scoccola, N. N. (2025). Charged pion decay in a laser field. Phys. Rev. D, 112(11), 114035–23pp.
Abstract: We study the decays n+ -> l+vl in the presence of a background electromagnetic plane wave with circular polarization. We find that, in the presence of this background, the number of hadronic form factors required to describe the pion-to-vacuum amplitude increases from one to four. Three of these form factors are associated with the axial vector current and one with the vector piece, which is in general different from zero. We obtain analytical expressions for the corresponding contributions to the decay width, considering in particular some range of values of interest for the frequency and amplitude of the external wave. For laser frequencies ri of the order of the eV, it is seen that the main correction to the result obtained in absence of the external field is proportional to the vector form factor, carrying a suppression factor of order similar to(ri/mn)4/3. In addition, we show that our expressions can be connected with the Kroll-Watson formula, which provides the differential cross section for the scattering of a charged particle by some potential in the presence of a strong external electromagnetic wave. Our analytical results are also compatible with previous numerical calculations obtained in the limit of low amplitude laser fields, offering new insight on some characteristics of these results.
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ISOLDE Collaboration(Parra, S. et al), Nacher, E., Rubio, B., Agramunt, J., Algora, A., Morales, A. I., et al. (2025). Isospin mixing in 64,66Ga reexamined via total absorption spectroscopy. Phys. Rev. C, 112(6), 064328–9pp.
Abstract: New measurements of the ,B decay of 64Ga and 66Ga have been carried out using total absorption spectroscopy at CERN-ISOLDE. The purpose of the study was to determine whether systemic effects such as Pandemonium have affected previous measurements and also determine the degree of isospin mixing in these proton-rich nuclei. Our results show that the ,B strength distribution of 64Ga was previously underestimated, while that of 66Ga agrees well with previous high-resolution measurements. The results allowed us to determine the amount of isospin mixing in the 0+ -> 0+ transitions to the ground states of the daughter nuclei. From the extracted log ft values, we determined the isospin mixing parameter a for the two cases. They were found to be consistent with values for similar transitions in other nuclei. 64Ga exhibits the largest amount of isospin mixing in such nuclei. These findings improve our understanding of beta decay and have implications for nuclear structure models and medical applications of 66Ga in PET imaging.
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Wang, W. F., Xu, J. Y., Zhou, S. H., & Shi, P. P. (2026). Contributions of ρ(770,1450)→ωπ to Cabibbo-favored D→hωπ decays. Chin. Phys. C, 50(2), 023111–10pp.
Abstract: Recently, the BESIII Collaboration observed the three-body decays D-s(+) -> eta omega pi(+), D+ -> Kappa(0)(S)pi(+)omega, and D-0 -> Kappa pi(+)omega. In this study, we investigate the contributions of the subprocesses rho(+) -> omega pi(+) in these Cabibbo-favored decays D -> h omega pi, with rho(+) = {rho(770)(+),rho(1450)(+),rho(770)(+)&rho(1450)(+)} and h = {eta, Kappa(0)(S), K- }, by introducing these subprocesses into the decay amplitudes of the relevant decay processes via the vector form factor F-omega pi, which has been measured in the related rand e(+)e(-) processes. We provide the first theoretical predictions for the branching fractions of the quasi-two-body decays D-s(+) -> eta[rho(+) -> ] omega pi(+), D+ -> Kappa(0)(S) [rho* ->]omega pi(+), and D-0 -> Kappa(-)[rho(+) ->]omega pi(+). Our findings reveal that the contributions from the subprocess rho(770)(+) omega pi(+) are significant in these observed three-body decays D-s(+) -> eta omega pi(+), D+ -> Kappa(0)(S)omega pi(+), and D-0 -> Kappa(-)omega pi(+), notwithstanding the contributions originating from the Breit-Wigner tail effect of rho(770)(+). The numerical results of this study suggest that the dominant resonance contributions for the three-body decays D-s(+) -> eta omega pi(+) and D+ -> Kappa(0)(S)omega pi(+) originate from the P-wave intermediate states rho(770), rho(1450) and their interference effects.
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Di Luzio, L., Landini, G., Mescia, F., & Susic, V. (2026). High-quality Peccei-Quinn symmetry from the interplay of vertical and horizontal gauge symmetries. Eur. Phys. J. C, 86(1), 5–55pp.
Abstract: We explore a class of axion models where an accidental U(1) Peccei-Quinn (PQ) symmetry automatically emerges from the interplay of vertical (grand-unified) and horizontal (flavor) gauge symmetries. We study a specific Pati-Salam realization in detail, and aim to generalize the conclusions. We show that our specific model offers protection from PQ-violating operators to high dimension, and demonstrate that the model can reproduce the Standard Model flavor structure. A distinctive feature of the vertical-horizontal setup is the presence of parametrically light fermions, known as anomalons, which are introduced to cancel the gauge anomalies of the flavor symmetry. We also identify a major challenge to building a fully realistic model, most notably that of Landau poles in gauge couplings before the Planck scale. For the specific model investigated, the pre-inflationary PQ-breaking scenario predicts the axion mass window to be ma is an element of [2 x 10(-8,) 10(-3)] eV. Conversely, a high-quality axion may be obtained instead in the post-inflationary scenario, with axion mass ma >= 0.01 eV, and anomalon masses predicted below the eV scale. We elaborate on anomalons' cosmological production in the early universe, highlighting how measurements of Delta N-eff could serve as a low-energy probe of the ultraviolet dynamics addressing the PQ quality problem.
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