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1. Confined variational calculation of low-energy Ps- ${\mathrm{Li}}^{+}$ scattering

   https://doi.org/10.1103/PhysRevA.109.042801  

   Zhao, D-X; Wu, M-S; Zhang, J-Y; Yan, Z-C; Varga, K (April 2024, Physical Review A)

   A theoretical investigation is conducted on the s- and p-wave elastic scatterings of positronium by a lithium ion Li+ with the scattering energy below 1.41 eV, corresponding to the threshold of the e+-Li channel. The confined variational method is applied to serve as the theoretical framework for this study. To accurately account for correlations between involved particles, explicitly correlated Gaussians are employed as basis functions, which are optimized through a hybrid approach combining stochastic variational and energy-gradient-based methods. Additionally, a straightforward yet effective algorithm is developed for the automatic adjustment of confining potentials. The s-wave zero-energy pickoff annihilation parameter 1Zeff,0 is accurately determined to be 0.126 ± 0.002, which yields an enhancement factor of 1.88 compared with the value 0.067 obtained using the fixed-core stochastic variational method [Phys. Rev. A 65, 034709 (2002)]. Finally, a broad p-wave resonance structure is predicted at the incident energy of approximately 0.27 eV, with the annihilation parameter 1Zeff,1 at the resonance center estimated to be around 0.034. 

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2. Coincidence Doppler Broadening Spectroscopy of Multilayer Graphene on Copper Surface Using a Variable Energy Positron Beam

   https://doi.org/10.4028/p-hleO2T  

   Mahdy, H; Chirayath, Varghese Anto; Lotfimarangloo, Sima; Gladen, RW; Chrysler, M; Fairchild, AJ; Sau, Pratyanik; Koymen, Ali R; Weiss, Alex H (July 2025, Solid State Phenomena)

   The use of Coincidence Doppler-Broadened (CDB) positron annihilation spectra for surface analysis requires ensuring that a significant fraction of the annihilation signal originates from positrons annihilating at the surface. We present measurements of CDB spectra obtained using a high-purity germanium (HPGe) detector in coincidence with a sodium iodide (NaI) detector for a series of incident positron beam energies ranging from 2 eV to 20 keV on multilayer graphene (6–8 layers) on copper. The CDB data were analyzed by fitting the Doppler spectra using a linear combination of spectra derived from measured data obtained at the incident beam energies mentioned together with a Gaussian function representing the spectrum associated with para-positronium decay. These fits were used to determine the fraction of incident positrons that annihilate at the surface and in the bulk. We compare the results obtained from fitting the full Doppler-broadened spectra with those derived from a VEPFIT analysis of the S parameters as a function of beam energy, using the same set of Doppler spectra. Both approaches indicate that most annihilation events occur at the surface for beam energies below 5 keV. However, the results from full spectrum fitting suggest a significantly larger bulk annihilation fraction than VEPFIT in the 100 eV to 5 keV range, highlighting the importance of accounting for bulk contributions when using CDB for surface analysis at beam energies above 100 eV. 

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3. Neutron Elastic Scattering Differential Cross Sections on ¹³ C

   https://doi.org/10.1051/epjconf/202532905004  

   Vanhoy, JR; Perkoff, AS; Hicks, SF; Vajdic, S; Araya, DS; Crider, BP; Marsh, JC; Peters, EE; Xiao, Y; Yates, SW (January 2025, EPJ Web of Conferences)

   Jentschel, M (Ed.)

   Neutron elastic scattering cross sections on natural carbon serve as a reference standard in the incident energy range 10 eV to 1.8 MeV. The 2017 standards evaluation [1, 2] is 0.5 to 2.0% higher in that energy range than the 2006 standards evaluation [3]. In addition the ENDF/B-VIII.0 release split the natural carbon cross sections into the isotopes¹²C,¹³C, and¹⁴C for the first time. These details call for the re-measurement of the¹³C cross sections in sensitive regions. Ten elastic scattering angular distributions were recently measured for incident neutron energies between 0.5 and 3.25 MeV at the University of Kentucky Accelerator Laboratory (www.pa.uky.edu/accelerator/) using nanosecond pulsed beams and time-of-flight techniques. An overview of neutron production and detection, the new digital data acquisition system, and data analysis will be presented. Results are compared with data from previous measurements and database evaluations. 

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4. Neutrino constraints on inelastic dark matter captured in the Sun

   https://doi.org/10.1088/1475-7516/2024/01/030  

   Chauhan, Bhavesh; Reno, Mary Hall; Rott, Carsten; Sarcevic, Ina (January 2024, Journal of Cosmology and Astroparticle Physics)

   Abstract The flux of neutrinos from annihilation of gravitationally captured dark matter in the Sun has significant constraints from direct-detection experiments. However, these constraints are relaxed for inelastic dark matter as inelastic dark matter interactions generate less energetic nuclear recoils compared to elastic dark matter interactions. In this paper, we explore the possibility for large volume underground neutrino experiments to detect the neutrino flux from captured inelastic dark matter in the Sun. The neutrino spectrum has two components: a mono-energetic “spike” from pion and kaon decays at rest and a broad-spectrum “shoulder” from prompt primary meson decays. We focus on detecting the shoulder neutrinos from annihilation of hadrophilic inelastic dark matter with masses in the range 4–100 GeV and the mass splittings in up to 300 keV. We determine the event selection criterion for DUNE to identify GeV-scale muon neutrinos and anti-neutrinos originating from hadrophilic dark matter annihilation in the Sun, and forecast the sensitivity from contained events. We also map the current bounds from Super-Kamiokande and IceCube on elastic dark matter, as well as the projected limits from Hyper-Kamiokande, to the parameter space of inelastic dark matter. We find that there is a region of parameter space that these neutrino experiments are more sensitive to than the direct-detection experiments. For dark matter annihilation to heavy-quarks, the projected sensitivity of DUNE is weaker than current (future) Super (Hyper) Kamiokande experiments. However, for the light-quark channel, only the spike is observable and DUNE will be the most sensitive experiment. 

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5. Improved Formulae for Low-Frequency Ultrasonic Attenuation in Metals

   https://doi.org/10.32548/2024.me-04422  

   Roy, Anubhav; Kube, Christopher (June 2024, Materials Evaluation)

   A range of ultrasonic techniques associated with the nondestructive evaluation of metals involves the propagation of low-frequency elastic waves. Metals that are isotropic and homogeneous in the macroscopic length scale contain elastic heterogeneities, such as grain boundaries within the microstructures. Ultrasonic waves propagating through such microstructures get scattered from the grain boundaries. As a result, the propagating ultrasound attenuates. The mass density and the elastic anisotropy in each constituent grain govern the degree of heterogeneity in the polycrystalline aggregates. Existing elastodynamic models consider first-order scattering effects from grain boundaries. This paper presents the improved attenuation formulae, for the first time, by including the next order of grain scattering effects. Results from investigating 759 polycrystals reveal a positive correlation between the effects of higher-order scattering from grain boundaries and the degree of heterogeneity. Thus, higher-order grain scattering effects are now known. These results motivate further investigation into higher frequencies and strongly scattering alloys in the future. 

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