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1. Enantioselective One-Photon Excitation of Formic Acid

   https://doi.org/10.1103/PhysRevLett.133.093002  

   Tsitsonis, D; Trinter, F; Williams, J B; Fehre, K; Demekhin, Ph V; Jahnke, T; Dörner, R; Schöffler, M S (August 2024, Physical Review Letters)

   We use one-photon excitation to promote $K$-shell electrons of formic acid (which has a planar equilibrium structure) to an antibonding ${\pi }^{*}$orbital. The excited molecule is known to have a (chiral) pyramidal equilibrium structure. In our experiment, we determine the handedness of the excited molecule by imaging the momenta of charged fragments, which occur after its Coulomb explosion triggered by Auger-Meitner decay cascades succeeding the excitation. We find that the handedness of the excited molecule depends on its spatial orientation with respect to the propagation (or polarization) direction of the exciting photon. The effect is largely independent of the exact polarization properties of the light driving the $1s\to {\pi }^{*}$excitation. Published by the American Physical Society2024 

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2. Measurement of the branching fraction and $CP$ -violating asymmetry of the decay $B^0\to {\pi }^0{\pi }^0$ using 387 million $\mathrm{\Upsilon }\left(4S\right)$ decays in Belle II data

   https://doi.org/10.1103/PhysRevD.111.L071102  

   Adachi, I; Aggarwal, L; Ahmed, H; Aihara, H; Alhakami, M; Aloisio, A; Althubiti, N; Anh_Ky, N; Asner, D M; Atmacan, H; et al (April 2025, Physical Review D)

   We measure the branching fraction and $CP$-violating flavor-dependent rate asymmetry of $B^0\to {\pi }^0{\pi }^0$decays reconstructed using the Belle II detector in an electron-positron collision sample containing $387\times {10}^6\mathrm{\Upsilon }\left(4S\right)$mesons. Using an optimized event selection, we find $125\pm 20$signal decays in a fit to background-discriminating and flavor-sensitive distributions. The resulting branching fraction is $(1.25\pm 0.23)\times {10}^{-6}$and the $CP$-violating asymmetry is $0.03\pm 0.30$. Published by the American Physical Society2025 

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3. State selectivity in core ionization of methane

   https://doi.org/10.1103/PhysRevResearch.7.L022021  

   Rajput, J; Stindl, J; Cassimi, A; Gervais, B; Kircher, M; Kastirke, G; McGinnis, O D; Enoki, R; Williams, J B; Davis, V; et al (April 2025, Physical Review Research)

   A clear experimental signature of the population of the lowest triplet state ${}^{3}T_1$of the methane dication is identified in a photoionization experiment. This state is populated only in valence ionization and is absent when the dication is formed by core ionization followed by Auger-Meitner decay. For valence ionization, the total internal energy of the ${\mathrm{CH}}_3^{+}$fragment, formed during the deprotonation of ${\mathrm{CH}}_4{}^{2+}$, is evaluated. Notably, the distribution of this internal energy peaks at the same value regardless of the initially populated electronic state of ${\mathrm{CH}}_4{}^{2+}$. We find that excited electronic states of ${\mathrm{CH}}_3^{+}$are predominantly populated with significant rovibrational excitation. Published by the American Physical Society2025 

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4. Heavy Neutral Leptons via Axionlike Particles at Neutrino Facilities

   https://doi.org/10.1103/PhysRevLett.133.261802  

   Abdullahi, Asli M; de_Gouvêa, André; Dutta, Bhaskar; Shoemaker, Ian M; Tabrizi, Zahra (December 2024, Physical Review Letters)

   Heavy neutral leptons (HNLs) are often among the hypothetical ingredients behind nonzero neutrino masses. If sufficiently light, they can be produced and detected in fixed-target-like experiments. We show that if the HNLs belong to a richer—but rather generic—dark sector, their production mechanism can deviate dramatically from expectations associated with the standard-model weak interactions. In more detail, we postulate that the dark sector contains an axionlike particle (ALP) that naturally decays into HNLs. Since ALPs mix with the pseudoscalar hadrons, the HNL flux might be predominantly associated with the production of neutral mesons (e.g., ${\pi }^0$, $\eta$) as opposed to charge hadrons (e.g., ${\pi }^{\pm }$, $K^{\pm }$). In this case, the physics responsible for HNL production and decay are not directly related and experiments like DUNE might be sensitive to HNLs that are too weakly coupled to the standard model to be produced via weak interactions, as is generically the case of HNLs that play a direct role in the type-I seesaw mechanism. Published by the American Physical Society2024 

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5. First Search for Dark-Trident Processes Using the MicroBooNE Detector

   https://doi.org/10.1103/PhysRevLett.132.241801  

   Abratenko, P; Alterkait, O; Andrade_Aldana, D; Arellano, L; Asaadi, J; Ashkenazi, A; Balasubramanian, S; Baller, B; Barr, G; Barrow, D; et al (June 2024, Physical Review Letters)

   We present a first search for dark-trident scattering in a neutrino beam using a dataset corresponding to $7.2\times {10}^{20}$protons on target taken with the MicroBooNE detector at Fermilab. Proton interactions in the neutrino target at the main injector produce ${\pi }^0$and $\eta$mesons, which could decay into dark-matter (DM) particles mediated via a dark photon $A^{\prime }$. A convolutional neural network is trained to identify interactions of the DM particles in the liquid-argon time projection chamber (LArTPC) exploiting its imagelike reconstruction capability. In the absence of a DM signal, we provide limits at the 90% confidence level on the squared kinematic mixing parameter ${ϵ}^2$as a function of the dark-photon mass in the range $10\le M_{A^{\prime }}\le 400\mathrm{MeV}$. The limits cover previously unconstrained parameter space for the production of fermion or scalar DM particles $\chi$for two benchmark models with mass ratios $M_{\chi }/M_{A^{\prime }}=0.6$and 2 and for dark fine-structure constants $0.1\le {\alpha }_D\le 1$. Published by the American Physical Society2024 

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