Search for production of an invisible dark photon from π0 decays at NA62

A search for an invisible dark photon A' has been performed, exploiting the efficient photon-veto capability and high resolution tracking of the NA62 detector at CERN. The signal stems from the chain K+ → π+π0 followed by π0 → A'γ. No significant statistical excess has been identified. Upper limits on the dark photon coupling to the ordinary photon as a function of the dark photon mass have been set, improving on the previous limits over the mass range 60–110 MeV/c

Search for production of an invisible dark photon from π0 decays at NA62

A search for an invisible dark photon A' has been performed, exploiting the efficient photon-veto capability and high resolution tracking of the NA62 detector at CERN. The signal stems from the chain K+ → π+π0 followed by π0 → A'γ. No significant statistical excess has been identified. Upper limits on the dark photon coupling to the ordinary photon as a function of the dark photon mass have been set, improving on the previous limits over the mass range 60–110 MeV/c

Search for lepton number and flavour violation in K+ and π0 decays

The NA62 experiment at CERN collected a large sample of charged kaon decays into final states with multiple charged particles in 2016-2018. This sample provides sensitivities to rare decays with branching ratios as low as 10−11. Searches for the lepton number violating K+ → π−µ+e+ decay and the lepton flavour violating K+ → π+µ−e+ and π0 → µ−e+ decays are reported. No evidence for these decays is found and upper limits of the branching ratios are obtained at 90% confidence level. These results improve by one order of magnitude over previous results for these decay modes

Search for production of an invisible dark photon from π0 decays at NA62

A search for an invisible dark photon A' has been performed, exploiting the efficient photon-veto capability and high resolution tracking of the NA62 detector at CERN. The signal stems from the chain K+ → π+π0 followed by π0 → A'γ. No significant statistical excess has been identified. Upper limits on the dark photon coupling to the ordinary photon as a function of the dark photon mass have been set, improving on the previous limits over the mass range 60–110 MeV/c

Search for new phenomena using the invariant mass distribution of same-flavour opposite-sign dilepton pairs in events with missing transverse momentum in√s =13 TeV ppcollisions with the ATLAS detector

aJUTS: s We thank CERN for the very successful operation of the LHC, as well as the support staff from our institutions without whom ATLAS could not be operated efficiently. We acknowledge the support of EPLANET, ERC, ERDF, FP7, Horizon 2020 and Marie Skłodowska-Curie Actions, European Union; MINECO, Spain AND CERCA Programme Generalitat de Catalunya.A search for new phenomena in final states containing an or pair, jets, and large missing transverse momentum is presented. This analysis makes use of proton-proton collision data with an integrated luminosity of , collected during 2015 and 2016 at a centre-of-mass energy with the ATLAS detector at the Large Hadron Collider. The search targets the pair production of supersymmetric coloured particles (squarks or gluinos) and their decays into final states containing an or pair and the lightest neutralino () via one of two next-to-lightest neutralino () decay mechanisms: , where the Z boson decays leptonically leading to a peak in the dilepton invariant mass distribution around the Z boson mass; and with no intermediate resonance, yielding a kinematic endpoint in the dilepton invariant mass spectrum. The data are found to be consistent with the Standard Model expectation. Results are interpreted using simplified models, and exclude gluinos and squarks with masses as large as 1.85 and 1.3 at 95% confidence level, respectively