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1. First Measurement of ${\nu }_e$ and ${\nu }_{\mu }$ Interaction Cross Sections at the LHC with FASER’s Emulsion Detector

   https://doi.org/10.1103/PhysRevLett.133.021802  

   Abraham, Roshan Mammen; Anders, John; Antel, Claire; Ariga, Akitaka; Ariga, Tomoko; Atkinson, Jeremy; Bernlochner, Florian U; Boeckh, Tobias; Boyd, Jamie; Brenner, Lydia; et al (July 2024, Physical Review Letters)

   The first results of the study of high-energy electron neutrino ( ${\nu }_e$) and muon neutrino ( ${\nu }_{\mu }$) charged-current interactions in the $\mathrm{FASER}\nu$emulsion-tungsten detector of the FASER experiment at the LHC are presented. A 128.8 kg subset of the $\mathrm{FASER}\nu$volume was analyzed after exposure to $9.5{\mathrm{fb}}^{-1}$of $\sqrt{s}=13.6\mathrm{TeV}$ $pp$data. Four (eight) ${\nu }_e$( ${\nu }_{\mu }$) interaction candidate events are observed with a statistical significance of $5.2\sigma$( $5.7\sigma$). This is the first direct observation of ${\nu }_e$interactions at a particle collider and includes the highest-energy ${\nu }_e$and ${\nu }_{\mu }$ever detected from an artificial source. The interaction cross section per nucleon $\sigma /E_{\nu }$is measured over an energy range of 560–1740 GeV (520–1760 GeV) for ${\nu }_e$( ${\nu }_{\mu }$) to be $\left({1.2}_{-0.7}^{+0.8}\right)\times {10}^{-38}{\mathrm{cm}}^2{\mathrm{GeV}}^{-1}$[ $(0.5\pm 0.2)\times {10}^{-38}{\mathrm{cm}}^2{\mathrm{GeV}}^{-1}$], consistent with standard model predictions. These are the first measurements of neutrino interaction cross sections in those energy ranges. Published by the American Physical Society2024 

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2. Properties of Cosmic Lithium Isotopes Measured by the Alpha Magnetic Spectrometer

   https://doi.org/10.1103/PhysRevLett.134.201001  

   Aguilar, M; Ambrosi, G; Anderson, H; Arruda, L; Attig, N; Bagwell, C; Barao, F; Barbanera, M; Barrin, L; Bartoloni, A; et al (May 2025, Physical Review Letters)

   We present the first measurement of cosmic-ray fluxes of ${}^6\mathrm{Li}$and ${}^7\mathrm{Li}$isotopes in the rigidity range from 1.9 to 25 GV. The measurements are based on $9.7\times {10}^5$ ${}^6\mathrm{Li}$and $1.04\times {10}^6$ ${}^7\mathrm{Li}$nuclei collected by the Alpha Magnetic Spectrometer on the International Space Station from May 2011 to October 2023. We observe that over the entire rigidity range the ${}^6\mathrm{Li}$and ${}^7\mathrm{Li}$fluxes exhibit nearly identical time variations and, above $\sim 4\mathrm{GV}$, the time variations of ${}^6\mathrm{Li}$, ${}^7\mathrm{Li}$, He, Be, B, C, N, and O fluxes are identical. Above $\sim 7\mathrm{GV}$, we find an identical rigidity dependence of the ${}^6\mathrm{Li}$and ${}^7\mathrm{Li}$fluxes. This shows that they are both produced by collisions of heavier cosmic-ray nuclei with the interstellar medium and, in particular, excludes the existence of a sizable primary component in the ${}^7\mathrm{Li}$flux. Published by the American Physical Society2025 

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3. Chiral Superfluid Helium-3 in the Quasi-Two-Dimensional Limit

   https://doi.org/10.1103/PhysRevLett.134.136001  

   Heikkinen, Petri J; Levitin, Lev V; Rojas, Xavier; Singh, Angadjit; Eng, Nathan; Casey, Andrew; Saunders, John; Vorontsov, Anton; Zhelev, Nikolay; Sebastian, Abhilash Thanniyil; et al (March 2025, Physical Review Letters)

   Anisotropic pair breaking close to surfaces favors the chiral $A$phase of the superfluid ${}^3\mathrm{He}$over the time-reversal invariant $B$phase. Confining the superfluid ${}^3\mathrm{He}$into a cavity of height $D$of the order of the Cooper pair size characterized by the coherence length ${\xi }_0$—ranging between 16 nm (34 bar) and 77 nm (0 bar)—extends the surface effects over the whole sample volume, thus allowing stabilization of the $A$phase at pressures $P$and temperatures $T$where otherwise the $B$phase would be stable. In this Letter, the surfaces of such a confined sample are covered with a superfluid ${}^4\mathrm{He}$film to create specular quasiparticle scattering boundary conditions, preventing the suppression of the superfluid order parameter. We show that the chiral $A$phase is the stable superfluid phase under strong confinement over the full $P\text{−}T$phase diagram down to a quasi-two-dimensional limit $D/{\xi }_0=1$, where $D=80\mathrm{nm}$. The planar phase, which is degenerate with the chiral $A$phase in the weak-coupling limit, is not observed. The gap inferred from measurements over the wide pressure range from 0.2 to 21.0 bar leads to an empirical ansatz for temperature-dependent strong-coupling effects. We discuss how these results pave the way for the realization of the fully gapped two-dimensional $p_x+i{p}_y$superfluid under more extreme confinement. Published by the American Physical Society2025 

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4. Measurements of the charge ratio and polarization of cosmic-ray muons with the Super-Kamiokande detector

   https://doi.org/10.1103/PhysRevD.110.082008  

   Kitagawa, H; Tada, T; Abe, K; Bronner, C; Hayato, Y; Hiraide, K; Hosokawa, K; Ieki, K; Ikeda, M; Kameda, J; et al (October 2024, Physical Review D)

   We present the results of the charge ratio ( $R$) and polarization ( $P_0^{\mu }$) measurements using decay electron events collected between September 2008 and June 2022 with the Super-Kamiokande detector. Because of its underground location and long operation, we are able to perform high-precision measurements by accumulating cosmic-ray muons. We measured the muon charge ratio to be $R=1.32\pm 0.02(\mathrm{stat}+\mathrm{syst})$at $E_{\mu }\cos {\theta }_{\text{Zenith}}={0.7}_{-0.2}^{+0.3}\mathrm{TeV}$, where $E_{\mu }$is the muon energy and ${\theta }_{\text{Zenith}}$is the zenith angle of incoming cosmic-ray muons. This result is consistent with the Honda flux model while indicating a tension with the $\pi K$model of $1.9\sigma$. We also measured the muon polarization at the production location to be $P_0^{\mu }=0.52\pm 0.02(\mathrm{stat}+\mathrm{syst})$at the muon momentum of ${0.9}_{-0.1}^{+0.6}\mathrm{TeV}/c$at the surface of the mountain; this also suggests a tension with the Honda flux model of $1.5\sigma$. This is the most precise measurement ever to experimentally determine the cosmic-ray muon polarization near $1\mathrm{TeV}/c$. These measurement results are useful to improve atmospheric neutrino simulations. Published by the American Physical Society2024 

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5. Properties of Cosmic Deuterons Measured by the Alpha Magnetic Spectrometer

   https://doi.org/10.1103/PhysRevLett.132.261001  

   Aguilar, M; Alpat, B; Ambrosi, G; Anderson, H; Arruda, L; Attig, N; Bagwell, C; Barao, F; Barbanera, M; Barrin, L; et al (June 2024, Physical Review Letters)

   Precision measurements by the Alpha Magnetic Spectrometer (AMS) on the International Space Station of the deuteron ( $D$) flux are presented. The measurements are based on $21\times {10}^6$ $D$nuclei in the rigidity range from 1.9 to 21 GV collected from May 2011 to April 2021. We observe that over the entire rigidity range the $D$flux exhibits nearly identical time variations with the $p$, ${}^3\mathrm{He}$, and ${}^4\mathrm{He}$fluxes. Above 4.5 GV, the $D/{}^4\mathrm{He}$flux ratio is time independent and its rigidity dependence is well described by a single power law $\propto R^{\mathrm{\Delta }}$with ${\mathrm{\Delta }}_{D/{}^4\mathrm{He}}=-0.108\pm 0.005$. This is in contrast with the ${}^3\mathrm{He}/{}^4\mathrm{He}$flux ratio for which we find ${\mathrm{\Delta }}_{{}^3\mathrm{He}/{}^4\mathrm{He}}=-0.289\pm 0.003$. Above $\sim 13\mathrm{GV}$we find a nearly identical rigidity dependence of the $D$and $p$fluxes with a $D/p$flux ratio of $0.027\pm 0.001$. These unexpected observations indicate that cosmic deuterons have a sizable primarylike component. With a method independent of cosmic ray propagation, we obtain the primary component of the $D$flux equal to $9.4\pm 0.5\%$of the ${}^4\mathrm{He}$flux and the secondary component of the $D$flux equal to $58\pm 5\%$of the ${}^3\mathrm{He}$flux. Published by the American Physical Society2024 

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