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1. Proposal for a Ramsey Neutron-Beam Experiment to Search for Ultralight Axion Dark Matter at the European Spallation Source

   https://doi.org/10.1103/PhysRevLett.133.181001  

   Fierlinger, P; Holl, M; Milstead, D; Santoro, V; Snow, W M; Stadnik, Y V (October 2024, Physical Review Letters)

   High-intensity neutron beams, such as those available at the European Spallation Source (ESS), provide new opportunities for fundamental discoveries. Here, we discuss a novel Ramsey neutron-beam experiment to search for ultralight axion dark matter through its coupling to neutron spins, which would cause the neutron spins to rotate about the velocity of the neutrons relative to the dark matter halo. We estimate that experiments at the HIBEAM beamline with a 50 m free flight path at the ESS can improve the sensitivity to the axion-neutron coupling compared to the current best laboratory limits by up to 2–3 orders of magnitude over the axion mass range ${10}^{-22}\mathrm{eV}–{10}^{-16}\mathrm{eV}$ . Published by the American Physical Society2024 

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2. Neutrino yield and neutron shielding calculations for a high-power target installed in an underground setting

   https://doi.org/10.1088/1748-0221/21/02/P02010  

   Bungau, Adriana; Alonso, Jose; Barlow, Roger; Bartoszek, Larry; Conrad, Janet; Shaevitz, Michael; Spitz, Joshua; Winklehner, Daniel (February 2026, Journal of Instrumentation)

   Abstract With the ever increasing beam power at particle accelerator-based facilities for nuclear and particle physics, radioactive isotope production, and nuclear engineering, it becomes increasingly important to have targets that can withstand this power, and shielding to block the secondary particles produced. Here we present Monte Carlo (MC) calculations using the well-established Geant4 software to predict the antineutrino yield of a⁸Li Decay-At-Rest (DAR) source. The source relies on 600 kW of beam power from a continuous wave proton beam impinging on a beryllium target, where spallation neutrons are captured by⁷Li to produce the⁸Li. We further present an in-depth treatment of the neutron shielding surrounding this target. We show that we can produce the high antineutrino flux needed for the discovery-level experiment IsoDAR, searching for “sterile” neutrinos (predicted new fundamental particles) and other beyond standard model physics, while maintaining a neutron flux in the detector that is below natural backgrounds. The methods presented in this paper are easily transferable to other high-power targets and their associated shielding. 

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3. Measurement of the neutron lifetime using a magneto-gravitational trap and in situ detection

   https://doi.org/10.1126  

   Pattie, R.W.; Callahan, N.B.; Cude-Woods, C.; Adamek, E.R.; Broussard, L.J.; Clayton, S.M.; Currie, S.A.; Dees, E.B.; Ding, X.; Engel, E.M.; et al (May 2018, Science)

   The precise value of the mean neutron lifetime, tau_n, plays an important role in nuclear and particle physics and cosmology. It is used to predict the ratio of protons to helium atoms in the primordial universe and to search for physics beyond the Standard Model of particle physics. We eliminated loss mechanisms present in previous trap experiments by levitating polarized ultracold neutrons above the surface of an asymmetric storage trap using a repulsive magnetic field gradient so that the stored neutrons do not interact with material trap walls. As a result of this approach and the use of an in situ neutron detector, the lifetime reported here [877.7 +/- 0.7 (stat) +0.4/-0.2 (sys) seconds] does not require corrections larger than the quoted uncertainties. 

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4. The neutron electric dipole moment experiment at the Spallation Neutron Source

   https://doi.org/10.1051/epjconf/201921902005  

   Leung, K.K.H.; Ahmed, M.; Alarcon, R.; Aleksandrova, A.; Baeßler, S.; Barrón-Palos, L.; Bartoszek, L.; Beck, D.H.; Behzadipour, M.; Bessuille, J.; et al (January 2019, EPJ Web of Conferences)

   Novel experimental techniques are required to make the next big leap in neutron electric dipole moment experimental sensitivity, both in terms of statistics and systematic error control. The nEDM experiment at the Spallation Neutron Source (nEDM@SNS) will implement the scheme of Golub & Lamoreaux [Phys. Rep., 237, 1 (1994)]. The unique properties of combining polarized ultracold neutrons, polarized 3 He, and superfluid 4 He will be exploited to provide a sensitivity to ∼ 10 −28   e  · cm. Our cryogenic apparatus will deploy two small (3 L) measurement cells with a high density of ultracold neutrons produced and spin analyzed in situ. The electric field strength, precession time, magnetic shielding, and detected UCN number will all be enhanced compared to previous room temperature Ramsey measurements. Our 3 He co-magnetometer offers unique control of systematic effects, in particular the Bloch-Siegert induced false EDM. Furthermore, there will be two distinct measurement modes: free precession and dressed spin. This will provide an important self-check of our results. Following five years of “critical component demonstration,” our collaboration transitioned to a “large scale integration” phase in 2018. An overview of our measurement techniques, experimental design, and brief updates are described in these proceedings. 

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5. Characterization of low energy argon recoils with ReD and ReD+

   https://doi.org/10.1088/1748-0221/20/06/C06062  

   Ave, M; Ahmad, I; Albergo, S; Albuquerque, I; Atzori_Corona, M; Bottino, B; Cadeddu, M; Caminata, A; Canci, N; Cesarano, R; et al (June 2025, Journal of Instrumentation)

   Abstract The Recoil Directionality project (ReD) within the DarkSide-20k Collaboration characterizedthe response of a liquid argon (LAr) dual-phase Time Projection Chamber (TPC) to neutron induced nuclear recoils,to measure the ionization yield at low-energy. The ionization yield is a critical parameter for the experiments searchingfor Dark Matter in the form of low-mass WIMPs and measurements in Ar below 10 keV are scarce in theliterature. ReD was designed to cover the gap down to 2 keV. The ReD data taking took place in 2023 at the INFNSezione di Catania. The TPC was irradiated by neutrons from an intense²⁵²Cf fission source in orderto produce Ar recoils inthe energy range of interest. The energy of the nuclear recoils produced within the TPC by (n,n')scattering was determined by detecting the outgoing neutrons with a dedicated neutron spectrometermade of 18 plastic scintillators. The kinetic energy of neutrons interacting in the TPC was evaluatedevent-by-event by measuring the time of flight. ReD collected and characterized a sample of nuclearrecoils down to 2 keV, thus meeting its design goal.The ReD effort will be further extended by a new project, ReD+, funded by a PRIN grant from theItalian Ministry of Research. ReD+ is designed to push the sensitivity down to 0.5 keV, by using thesame conceptual design of ReD and improved components. A new TPC is being re-designed andoptimized in order to increase the signal rate and the signal-to-background ratio, which limited thesensitivity of ReD. 

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