4 Search Results

The NA62 experiment at CERN has the capability to collect data in a beam-dump mode, where 400 GeV protons are dumped on an absorber. In this configuration, New Physics particles, including dark photons, dark scalars, and axion-like particles, may be produced in the absorber and decay in the instrumented volume beginning approximately 80 m downstream of the dump. A search for these particles decaying in flight to hadronic final states is reported, based on an analysis of a sample of 1.4 x 10¹⁷ protons on dump collected in 2021. No evidence of a New Physics signal is observed, excluding newmore » regions of parameter spaces of multiple models.« less

The NA62 experiment at CERN utilises a differential Cherenkov counter with achromatic ring focus (CEDAR) for tagging kaons within an unseparated monochromatic beam of charged hadrons. The CEDAR-H detector was developed to minimise the amount of material in the path of the beam by using hydrogen gas as the radiator medium. The detector was shown to satisfy the kaon tagging requirements in a test-beam before installation and commissioning at the experiment. The CEDAR-H performance was measured using NA62 data collected in 2023.

A sample of 3984 candidates of the $$K^{+} → π^{+} γγ$$ decay, with an estimated background of 291 ± 14 events, was collected by the NA62 experiment at CERN during 2017–2018. In order to describe the observed di-photon mass spectrum, the next-to-leading order contribution in chiral perturbation theory was found to be necessary. The decay branching ratio in the full kinematic range is measured to be (9.61 ± 0.17) x 10^-7. The first search for production and prompt decay of an axion-like particle with gluon coupling in the process $$K^{+} → π^{+} a$$, $a → γγ$ is also reported.

The first search for ultra-rare K⁺ decays into the π⁺e⁺e^-e⁺e^- final state is reported, using a dataset collected by the NA62 experiment at CERN in 2017–2018. An upper limit of 1.4 x 10^-8 at 90% CL is obtained for the branching ratio of the K⁺ → π⁺e⁺e^-e⁺e^- decay, predicted in the Standard Model to be (7.2 ± 0.7) x 10^-11 . Upper limits at 90% CL are obtained at the level of 10^-9 for the branching ratios of two prompt decay chains involving pair-production of hidden-sector mediators: K⁺ → π⁺ aa,a → e⁺e^- and K⁺ → π⁺ S,S → A'A',A'more » → e⁺e^-.« less