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1. Constraints on metastable superheavy dark matter coupled to sterile neutrinos with the Pierre Auger Observatory

   https://doi.org/10.1103/PhysRevD.109.L081101  

   Abdul_Halim, A ; Abreu, P ; Aglietta, M ; Allekotte, I ; Almeida_Cheminant, K ; Almela, A ; Aloisio, R ; Alvarez-Muñiz, J ; Ammerman_Yebra, J ; Anastasi, G A ; et al ( April 2024 , Physical Review D)

   Dark matter particles could be superheavy, provided their lifetime is much longer than the age of the Universe. Using the sensitivity of the Pierre Auger Observatory to ultrahigh energy neutrinos and photons, we constrain a specific extension of the Standard Model of particle physics that meets the lifetime requirement for a superheavy particle by coupling it to a sector of ultralight sterile neutrinos. Our results show that, for a typical dark coupling constant of 0.1, the mixing angle${\theta }_m$between active and sterile neutrinos must satisfy, roughly,${\theta }_m\lesssim 1.5\times {10}^{-6}(M_X/{10}^9\mathrm{GeV}{)}^{-2}$for a mass$M_X$of the dark-matter particle between${10}^8\mathrm{GeV}$and${10}^{11}\mathrm{GeV}$.

   Published by the American Physical Society2024 

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2. Observation of the J/ψ→μ+μ−μ+μ− decay in proton-proton collisions at s=13  TeV

   https://doi.org/10.1103/PhysRevD.109.L111101  

   Hayrapetyan, A ; Tumasyan, A ; Adam, W ; Andrejkovic, J W ; Bergauer, T ; Chatterjee, S ; Damanakis, K ; Dragicevic, M ; Hussain, P S ; Jeitler, M ; et al ( June 2024 , Physical Review D)

   The$J/\psi \to {\mu }^{+}{\mu }^{-}{\mu }^{+}{\mu }^{-}$decay has been observed with a statistical significance in excess of five standard deviations. The analysis is based on an event sample of proton-proton collisions at a center-of-mass energy of 13 TeV, collected by the CMS experiment in 2018 and corresponding to an integrated luminosity of$33.6{\mathrm{fb}}^{-1}$. Normalizing to the$J/\psi \to {\mu }^{+}{\mu }^{-}$decay mode leads to a branching fraction of$[{10.1}_{-2.7}^{+3.3}(\mathrm{stat})\pm 0.4(\mathrm{syst})]\times {10}^{-7}$, a value that is consistent with the standard model prediction.