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1. First on-line commissioning experiments at the St. Benedict facility

   https://doi.org/10.1088/1402-4896/adeed8  

   Porter, William_Samuel; Brodeur, Maxime; Bruce, Olivia; Burdette, Daniel_P; Clark, Jason; Eversole, Olivia; Gallant, Aaron_T; Houff, Alicen_M; Kolata, James_J; Markel, Erin; et al (July 2025, Physica Scripta)

   Abstract Nuclear beta decays provide an excellent probe of fundamental symmetries due to their mediation by the weak interaction. In particular, precise measurements of these decays provide constraints on the unitarity of the Cabbibo-Kobayashi-Maskawa (CKM) quark-mixing matrix. While superallowed pure Fermi decays currently set the most precise limits, the alternative suite of superallowed mixed mirror decays has been ill-studied. These nuclei can provide an important consistency check of calculation and measurement methods employed for the pure Fermi decays, more critically needed now in the wake of a 2.4σ deviation from unitarity of the CKM matrix. In order to remedy the gap in data for mirror decays, the Superallowed Transition Beta-Neutrino Decay Ion Coincidence Trap (St. Benedict) facility is being commissioned at the University of Notre Dame's Nuclear Science Laboratory (NSL). In this paper, we present first results of the commissioning of the St. Benedict facility on-line at the TwinSol radioactive beam facility. The results of initial commissioning experiments involving the St. Benedict gas catcher, RF carpet, RFQ ion guide and RFQ cooler-buncher will be presented. 

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2. Weak Interaction Physics at TwinSol

   https://doi.org/10.1051/epjconf/202125203001  

   Kolata’, J. J.; Brodeur, Maxime; Ahn, Tan; Bardayan, Dan; O’Malley, Patrick; Randhawa, J. S. (January 2021, EPJ Web of Conferences)

   Pakou, A.; Bonatsos, D.; Lalazissis, G.; Souliotis, G. (Ed.)

   A program to investigate the unitarity of the Cabibbo-Kobayashi-Maskawa (CKM) quark-mixing matrix by studying super-allowed mixed mirror β decays has been initiated at the TwinSol facility at Notre Dame. These mixed Fermi/Gamow-Teller (F-GT) decays, occurring between T=1/2 isospin doublets in mirror nuclei, provide a complimentary check on the data from super-allowed pure Fermi decays from 0 + to 0 + states. The first part of the program, involving the measurement of the lifetimes of the relevant nuclei to the required accuracy of one part in 10 3 or better, has nearly been completed. However, the additional complication introduced by F-GT mixing requires the use of an ion trap to measure the mixing ratio ρ with similar accuracy. The lifetime measurements, as well as progress in installing an ion trap at TwinSol , will be discussed. In addition, since the ion trap will require a dedicated beam line for its operation, an opportunity presented itself to greatly improve the performance of TwinSol for reaction studies with exotic nuclei. This took the form of an added dipole switching magnet coupled to a third solenoid to form the new TriSol facility currently under construction. The expected properties of TriSol , and its application to reaction studies of interest for nuclear astrophysics, will also be discussed. 

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3. On-line installation of the Superallowed Transition Beta-Neutrino Decay Ion Coincidence Trap

   https://doi.org/10.1051/epjconf/202430102002  

   Brodeur, M; Bardayan, DW; Bruce, O; Bualuan, R; Burdette, DP; Clark, JA; Gallant, AT; Gan, D; Guillet, D; Houff, AM; et al (January 2024, EPJ Web of Conferences)

   Bijker, R; Marín_Lámbarri, DJ; Yépez_Martínez, TC (Ed.)

   The Cabibbo-Kobayashi-Maskawa quark mixing matrix currently does not satisfy unitarity at the 2σ-level. This could be the result of an inaccurate value of one or both of its largest matrix elementsV_usandV_ud. In the case ofV_ud, the most precise measurement is obtained from thef t-value measurements of superallowed beta-transitions between 0⁺states. The accuracy of this determination can, in turn, be tested by extractingV_udin other transitions including superallowed transitions between mirror nuclei. The Superallowed Transition Beta-Neutrino Decay Ion Coincidence Trap (St. Benedict) is currently under construction at the Nuclear Science Laboratory of the University of Notre Dame to perform such a determination, with the goal of shedding more light on this tension with unitarity. St. Benedict will take a radioactive ion beam produced byTwinSol, thermalize it in a large volume gas catcher, then transport it in two separate differentially-pumped volumes using a radio-frequency (RF) carpet and a radio-frequency quadrupole (RFQ) ion guide before injecting it in an RFQ trap to create cool ion bunches for injection in the measurement Paul trap. In this paper, we detail the installation of the beam preparation components of St. Benedict, and present the results of the first RIBs successfully stopped and extracted from its gas catcher. 

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4. The Nab experiment: A precision measurement of unpolarized neutron beta decay

   https://doi.org/10.1051/epjconf/201921904002  

   Fry, J.; Alarcon, R.; Baeßler, S.; Balascuta, S.; Palos, L. Barrón; Bailey, T.; Bass, K.; Birge, N.; Blose, A.; Borissenko, D.; et al (January 2019, EPJ Web of Conferences)

   Neutron beta decay is one of the most fundamental processes in nuclear physics and provides sensitive means to uncover the details of the weak interaction. Neutron beta decay can evaluate the ratio of axial-vector to vector coupling constants in the standard model, λ = g A / g V , through multiple decay correlations. The Nab experiment will carry out measurements of the electron-neutrino correlation parameter a with a precision of δ a / a = 10 −3 and the Fierz interference term b to δ b = 3 × 10 −3 in unpolarized free neutron beta decay. These results, along with a more precise measurement of the neutron lifetime, aim to deliver an independent determination of the ratio λ with a precision of δλ/λ = 0.03% that will allow an evaluation of V ud and sensitively test CKM unitarity, independent of nuclear models. Nab utilizes a novel, long asymmetric spectrometer that guides the decay electron and proton to two large area silicon detectors in order to precisely determine the electron energy and an estimation of the proton momentum from the proton time of flight. The Nab spectrometer is being commissioned at the Fundamental Neutron Physics Beamline at the Spallation Neutron Source at Oak Ridge National Lab. We present an overview of the Nab experiment and recent updates on the spectrometer, analysis, and systematic effects. 

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5. Penning-Trap Mass Measurements in Atomic and Nuclear Physics

   https://doi.org/10.1146/annurev-nucl-102711-094939  

   Dilling, Jens; Blaum, Klaus; Brodeur, Maxime; Eliseev, Sergey (October 2018, Annual Review of Nuclear and Particle Science)

   Penning-trap mass spectrometry in atomic and nuclear physics has become a well-established and reliable tool for the determination of atomic masses. In combination with short-lived radioactive nuclides it was first introduced at ISOLTRAP at the Isotope Mass Separator On-Line facility (ISOLDE) at CERN. Penning traps have found new applications in coupling to other production mechanisms, such as in-flight production and separation systems. The applications in atomic and nuclear physics range from nuclear structure studies and related precision tests of theoretical approaches to description of the strong interaction to tests of the electroweak Standard Model, quantum electrodynamics and neutrino physics, and applications in nuclear astrophysics. The success of Penning-trap mass spectrometry is due to its precision and accuracy, even for low ion intensities (i.e., low production yields), as well as its very fast measurement cycle, enabling access to short-lived isotopes. The current reach in relative mass precision goes beyond δ m/ m=10 −8 , the half-life limit is as low as a few milliseconds, and the sensitivity is on the order of one ion per minute in the trap. We provide a comprehensive overview of the techniques and applications of Penning-trap mass spectrometry in nuclear and atomic physics. 

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