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AGATA Collaboration(Siciliano, M. et al), Gadea, A., Perez-Vidal, R. M., & Domingo-Pardo, C. (2020). Pairing-quadrupole interplay in the neutron-deficient tin nuclei: First lifetime measurements of low-lying states in Sn-106,Sn-108. Phys. Lett. B, 806, 135474–7pp.
Abstract: The lifetimes of the low-lying excited states 2(+) and 4(+) have been directly measured in the neutron-deficient Sn-106,Sn-108 isotopes. The nuclei were populated via a deep-inelastic reaction and the lifetime measurement was performed employing a differential plunger device. The emitted gamma rays were detected by the AGATA array, while the reaction products were uniquely identified by the VAMOS++ magnetic spectrometer. Large-Scale Shell-Model calculations with realistic forces indicate that, independently of the pairing content of the interaction, the quadrupole force is dominant in the B(E2; 2(1)(+) -> 0(g.s)(+)) values and it describes well the experimental pattern for Sn104-114 ; the B(E2;(+)(4) -> 2(1)(+)) values, measured here for the first time, depend critically on a delicate pairing-quadrupole balance, disclosed by the very precise results in Sn-108.
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AGATA Collaboration(Avigo, R. et al), Domingo-Pardo, C., Gadea, A., & Gonzalez, V. (2020). Low-lying electric dipole gamma-continuum for the unstable Fe-62(,)64 nuclei: Strength evolution with neutron number. Phys. Lett. B, 811, 135951–6pp.
Abstract: The gamma-ray emission from the nuclei Fe-62,Fe-64 following Coulomb excitation at bombarding energy of 400-440 AMeV was measured with special focus on E1 transitions in the energy region 4-8 MeV. The unstable neutron-rich nuclei Fe-62,Fe-64 were produced at the FAIR-GSI laboratories and selected with the FRS spectrometer. The gamma decay was detected with AGATA. From the measured gamma-ray spectra the summed E1 strength is extracted and compared to microscopic quasi-particle phonon model calculations. The trend of the E1 strength with increasing neutron number is found to be fairly well reproduced with calculations that assume a rather complex structure of the 1(-) states (three-phonon states) inducing a strong fragmentation of the E1 nuclear response below the neutron binding energy.
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Pasqualato, G. et al, Gadea, A., & Jurado, M. (2023). An alternative viewpoint on the nuclear structure towards 100Sn: Lifetime measurements in 105Sn. Phys. Lett. B, 845, 138148–7pp.
Abstract: This work aims at presenting an alternative approach to the long standing problem of the B(E2) values in Sn isotopes in the vicinity of the N=Z double-magic nucleus Sn-100, until now predominantly measured with relativistic and intermediate-energy Coulomb excitation reactions. The direct measurement of the lifetime of low-lying excited states in odd-even Sn isotopes provides a new and precise guidance for the theoretical description of the nuclear structure in this region. Lifetime measurements have been performed in Sn-105 for the first time with the coincidence Recoil Distance Doppler Shift technique. The lifetime results for the 7/2(1)(+) first excited state and the 11/2(1)(+) state, 2(+)(Sn-104) circle times nu 1g(7/2) multiplet member, are discussed in comparison with state-of-the-art shell model and mean field calculations, highlighting the crucial contribution of proton excitation across the core of Sn-100. The reduced transition probability B(E2) of the 11/2(1)(+) core-coupled state points out an enhanced staggering with respect to the B(E2; 2(1)(+) -> 0(1)(+)) in the even-mass Sn-104 and Sn-106 isotopes.
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Alvarez-Ruso, L. et al, & Nieves, J. (2018). NuSTEC White Paper: Status and challenges of neutrino-nucleus scattering. Prog. Part. Nucl. Phys., 100, 1–68.
Abstract: The precise measurement of neutrino properties is among the highest priorities in fundamental particle physics, involving many experiments worldwide. Since the experiments rely on the interactions of neutrinos with bound nucleons inside atomic nuclei, the planned advances in the scope and precision of these experiments require a commensurate effort in the understanding and modeling of the hadronic and nuclear physics of these interactions, which is incorporated as a nuclear model in neutrino event generators. This model is essential to every phase of experimental analyses and its theoretical uncertainties play an important role in interpreting every result. In this White Paper we discuss in detail the impact of neutrino-nucleus interactions, especially the nuclear effects, on the measurement of neutrino properties using the determination of oscillation parameters as a central example. After an Executive Summary and a concise Overview of the issues, we explain how the neutrino event generators work, what can be learned from electron-nucleus interactions and how each underlying physics process – from quasi-elastic to deep inelastic scattering – is understood today. We then emphasize how our understanding must improve to meet the demands of future experiments. With every topic we find that the challenges can be met only with the active support and collaboration among specialists in strong interactions and electroweak physics that include theorists and experimentalists from both the nuclear and high energy physics communities.
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Gomez-Cadenas, J. J., Martin-Albo, J., Menendez, J., Mezzetto, M., Monrabal, F., & Sorel, M. (2024). The search for neutrinoless double-beta decay. Riv. Nuovo Cimento, 46, 619–692.
Abstract: Neutrinos are the only particles in the Standard Model that could be Majorana fermions, that is, completely neutral fermions that are their own antiparticles. The most sensitive known experimental method to verify whether neutrinos are Majorana particles is the search for neutrinoless double-beta decay. The last 2 decades have witnessed the development of a vigorous program of neutrinoless double-beta decay experiments, spanning several isotopes and developing different strategies to handle the backgrounds masking a possible signal. In addition, remarkable progress has been made in the understanding of the nuclear matrix elements of neutrinoless double-beta decay, thus reducing a substantial part of the theoretical uncertainties affecting the particle-physics interpretation of the process. On the other hand, the negative results by several experiments, combined with the hints that the neutrino mass ordering could be normal, may imply very long lifetimes for the neutrinoless double-beta decay process. In this report, we review the main aspects of such process, the recent progress on theoretical ideas and the experimental state of the art. We then consider the experimental challenges to be addressed to increase the sensitivity to detect the process in the likely case that lifetimes are much longer than currently explored, and discuss a selection of the most promising experimental efforts.
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