Konstantin Mashtakov | Study of the Pygmy Dipole Resonance in ^{96}Zr following the beta decay of ^{96}Y |
Skyler Degenkolb | Searching for permanent electric dipole moments |
Jack Wilson | Space-Based Measurement of the Neutron Lifetime using Data from the Neutron Spectrometers on NASA's MESSENGER and Lunar Prospector Missions |
Antonio Márquez Romero | Proton-neutron pairing description using symmetry-restored mean-field methods |
David O'Donnell | Measurements of the low-energy dipole strength in actinide nuclei |
Ragnar Stroberg | Can we do all of nuclear physics ab initio? |
Pieter Van Isacker | The Structure of Octupole Phonons in Nuclei |
Mark Spieker | Isospin symmetry around 56Ni |
Ruben Pieter De Groote | New frontiers in optical spectroscopy of radioactive nuclei |
Kaitlin Cook | Halo structure of the neutron-dripline nucleus 19B |
Manuela Cavallaro | Nuclear Reactions for neutrinoless double beta decay |
Ruth Newton | Quantum Entanglement in PET imaging |
Sergio Cristallo | The cosmic nucleosynthesis competition between low mass stars and neutron stars mergers |
Carlo Barbieri | Ab Initio Computations of Ground State Correlations and Optical Potentials in Nuclei |
Robin Smith | Nuclear structure and astrophysics with TPC detectors and gamma beams |
Ryo Taniuchi | In-beam gamma-ray spectroscopy of 78Ni revealed its double magicity and shape-coexistence |
Daniel Doherty | Shape Evolution and Triaxiality in Hitherto Inaccessible Regions of the Nuclear Chart |
Lindsay Michelle Donaldson | Resolving discrepancies between (p,p') and (γ,xn) reactions |
Kyle Leach | The BeEST Experiment: A Search for keV-Scale Neutrinos in the EC Decay of ^{7}Be with Superconducting Quantum Sensors |
David Sharp | Probing single-particle structure near the Island of Inversion with the ISOLDE Solenoidal Spectrometer |
Michael Bowry | The Search for Nuclear Pear Shapes |
Gregory Christian | Particle-Gated Transfer Reactions to Understand Stellar Nucleosynthesis |
Kelly Chipps | Experimental Approaches for Constraining Nuclear Contributions to R-Process Uncertainties |
Jack Henderson | Testing modern microscopic calculations: Coulomb excitation of mirror pairs in the sd-shell |
Benjamin Kay | Solenoidal spectrometer techniques: HELIOS, ISS, and SOLARIS |
Alessandro Pastore | Neurons, Trees and Forests: A different approach to simple nuclear structure problems |
The pygmy dipole resonance (PDR) is a nuclear phenomenon which is associated with the movement of the ‘neutron skin’ of a nucleus against an isospin saturated proton-neutron core. The nature of the PDR is of particular interest due to its importance in many areas of nuclear and astrophysics. Current experimental techniques used to study this phenomenon produce inconsistent results. This is mostly due to the unknown branching behaviour of the J^{π} =1^{−} levels, which form the PDR. The nuclear resonance fluorescence (NRF) technique, which is widely used to study low-lying E1 strength in stable nuclei, loses decay branches to lower-lying excited states to the atomic background. The latter effect leads to underestimated values of E1 strength of the PDR. Recently it was realised that electric dipole levels associated with the PDR could also be excited following the β decay of certain nuclei. The novel approach of using β decay to populate high-lying 1^{−} states allows the extraction of branching transitions previously not resolved in NRF, which will recover missing E1 strength associated with the PDR. In this work, the nature of the high-lying final levels of the ^{96}Y_{gs} beta decay, one of the three most important contributors to the high-energy reactor antineutrino spectrum, has been investigated in high-resolution gamma-ray spectroscopy following the beta decay as well as in a campaign of inelastic photon scattering experiments. The combined data represents a comprehensive approach to the wavefunction of the 1^{−} levels below the Qbeta value (7.1 MeV), which are also studied in the Quasiparticle Phonon Model. The calculations reveal that the components populated in beta decay contribute only with small amplitudes to the complex wavefunction of these 1^{−} levels. A comparison of the beta decay results to data from total absorption gamma-ray spectroscopy demonstrates that high-resolution spectroscopy using modern detector arrays is capable to resolve the pandemonium effect. |
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Discrete symmetries provide a powerful means of classifying and constraining models in nuclear and particle physics, including the Standard Model. Although the Standard Model predicts finite values for CP-violating electromagnetic moments (both for fundamental particles and for composite systems), today's experiments are insufficiently sensitive -- by several orders of magnitude -- to test these predictions. Nevertheless, experimental limits consistent with zero have played an important role in constraining Standard Model parameters and extended models with new sources of CP violation. In particular, searches for permanent electric dipole moments (EDMs) test the Standard Model at high precision, provide diagnostic power for new sources of CP violation, and connect deeply to the symmetry-breaking mechanisms required for baryogenesis. I will survey the main target systems and experimental techniques that are employed in modern EDM measurements, with some emphasis on neutrons and the nuclei of diamagnetic atoms. I will also discuss the phenomenological interpretation of EDM limits, and in particular the "global analysis", or joint constraints, that are enabled by multiple experiments in complementary systems. |
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Precise knowledge of the free neutron lifetime, τ_{n}, is required to test the consistency of the standard model and uncertainties in τ_{n} dominate those in predicted primordial ^{4}He abundance from Big Bang nucleosynthesis. Presently, there exist two classes of experiments that have successfully made measurements of τ_{n}. The `Beam' class involves measuring the activation of cold neutron beams and the `Bottle' class uses storage (material, magnetic and/or gravitational) to trap neutrons and measure the rate of decay during storage. However, there currently exists a 4σ disagreement between the `beam' and `bottle' measurements. We have developed a new technique for using space-based neutron spectroscopy measurements to determine τ_{n}. Under this technique the change in planet-originating neutron flux with planet-to-spacecraft distance yields a measure of τ_{n}. Here, we will present an analysis of data from the neutron spectrometer on NASA's MESSENGER and Lunar Prospector missions as a proof-of-principle demonstration of a space-based τ_{n} measurement. Here I discuss the basis of the technique, statistical and systematic errors of the measurement, and presented the results that we have so far. |
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By means of a full restoration of particle-number (A), spin (S), and isospin (T) broken symmetries of paired mean-field quasiparticle states, we show that proton-neutron (pn) and like-nucleon pair condensates coexist. We use the Thouless representation for these states, parametrised by the normalised isovector (T=1) and isoscalar (T=0) pair amplitudes. Using a simple and well-known SO(8) pairing Hamiltonian, whose exact solutions are known, we minimize the energy calculated with the symmetry-restored paired states, that is, we use the so-called variation after projection (VAP) approach. The results obtained using this method are strikingly accurate in comparison with the exact results, and for all interaction strengths the isovector and isoscalar pairs coexist, in opposition of the pure mean-field approach. This study suggests that further work on properties of proton-neutron pairing should be carried out within the VAP approach to mean-field pairing methods. |
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Atomic nuclei with certain combinations of proton and neutron numbers can adopt reflection-asymmetric or octupole-deformed shapes at low excitation energy. These nuclei present a promising avenue in the search for a permanent atomic electric dipole moment — the existence of which has implications for physics beyond the Standard Model of particle physics. Theoretical studies have suggested that certain thorium isotopes may have large octupole deformation. However, due to experimental challenges, the extent of the octupole collectivity in the low-energy states in these thorium nuclei has not yet been demonstrated. Here, we report measurements of the lifetimes of low-energy states in the actinide nuclei ^{228}Th (Z = 90) and ^{234}U (Z = 92) with a direct electronic fast-timing technique, the mirror symmetric centroid difference method. From lifetime measurements of the low-lying J^{π} = 1^{-} and J^{π} = 3^{-} states, the E1 transition probability rates and the intrinsic dipole moments are extracted. Through comparisons with theoretical calculations, we have been able to estimate the extent of the octupole deformation of these nuclei. This study indicates that the nuclei ^{229}Th and ^{229}Pa (Z = 91) may be good candidates for the search for a permanent atomic electric dipole moment. |
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Over the past decade, developments in effective field theory and many-body theory have pushed the limits of ab initio calculations from the p-shell (A~10) up to A=100. This means that the structure of medium-mass nuclei can be addressed with a theory constrained in the few-body sector (e.g. up to A=4), with no additional parameters needed. I will present a conceptual introduction to modern ab initio theory, followed by some highlights from the past few years, including a quantitative understanding of the gA quenching problem in beta decay, prediction of the proton and neutron drip lines, and some insights about the nuclear shell model. Finally, I will discuss some ongoing efforts to extend the reach of ab initio calculations beyond A=100, and to provide meaningful theoretical error bars. |
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Nuclei with a closed-shell configuration for neutrons and protons exhibit low-energy excitations with angular momentum J=3 and negative parity. Such excitations are associated with nuclear shapes that break reflection symmetry and, in particular, with pear-like or octupole shapes. In this talk the shell-model structure of octupole excitations is discussed and the question of their phonon-like behaviour is addressed. It is shown that with some simple assumptions concerning single-particle energies and two-body interactions octupole phonons obey universal symmetry properties. The results of this schematic approach are compared with those of a realistic shell-model calculation for ^{208}Pb. Extensions to odd-mass and semi-magic nuclei are also discussed. |
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