The MEG experiment took data at the Paul Scherrer Institute in the years 2009–2013 to test the violation of the lepton flavor conservation law, which originates from an accidental symmetry that the Standard Model of elementary particle physics has, and published the most stringent limit on the charged lepton flavor violating decay ${\mathsf{\mu }}^{+}\to {\mathrm{e}}^{+}\mathsf{\gamma }$: BR(${\mathsf{\mu }}^{+}\to {\mathrm{e}}^{+}\mathsf{\gamma }$) $<4.2\times {10}^{-13}$ at $90\%$ confidence level. The MEG detector has been upgraded in order to reach a sensitivity of $6\times {10}^{-14}$. The basic principle of MEG II is to achieve the highest possible sensitivity using the full muon beam intensity at the Paul Scherrer Institute ($7\times {10}^7$ muons/s) with an upgraded detector. The main improvements are better rate capability of all sub-detectors and improved resolutions while keeping the same detector concept. In this paper, we present the current status of the preparation, integration and commissioning of the MEG II detector in the recent engineering runs.

Volume 1 of the FCC Feasibility Report presents an overview of the physics case, experimental programme, and detector concepts for the Future Circular Collider (FCC). This volume outlines how FCC would address some of the most profound open questions in particle physics, from precision studies of the Higgs and EW bosons and of the top quark, to the exploration of physics beyond the Standard Model. The report reviews the experimental opportunities offered by the staged implementation of FCC, beginning with an electron-positron collider (FCC-ee), operating at several centre-of-mass energies, followed by a hadron collider (FCC-hh). Benchmark examples are given of the expected physics performance, in terms of precision and sensitivity to new phenomena, of each collider stage. Detector requirements and conceptual designs for FCC-ee experiments are discussed, as are the specific demands that the physics programme imposes on the accelerator in the domains of the calibration of the collision energy, and the interface region between the accelerator and the detector. The report also highlights advances in detector, software and computing technologies, as well as the theoretical tools/reconstruction techniques that will enable the precision measurements and discovery potential of the FCC experimental programme. The content and structure of this report are guided by the scope and priorities defined in the mandate of the FCC Feasibility Study. It is therefore not intended to serve as an exhaustive review of the full physics potential of FCC. Several topics, already covered in earlier reports such as the FCC CDR, are not reiterated here or are addressed only briefly, in alignment with the study’s focus. This volume reflects the outcome of a global collaborative effort involving hundreds of scientists and institutions, aided by a dedicated community-building coordination, and provides a targeted assessment of the scientific opportunities and experimental foundations of the FCC programme.

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 $$1.4 \times 10^{17}$$ 1.4 × 10 17 protons on dump collected in 2021. No evidence of a New Physics signal is observed, excluding new regions of parameter spaces of multiple models.

A bstract: Results from the study of the rare decays $$ {K}^{+}\to {\pi}^{+}\nu \overline{\nu} $$ K + → π + ν ν ¯ , K ⁺ → π ⁺ μ ⁺ μ ⁻ and K ⁺ → π ⁺ γγ at the NA62 experiment at CERN are interpreted in terms of improved limits for $$ \mathcal{B}\left({K}^{+}\to {\pi}^{+}X\right) $$ B K + → π + X and coupling parameters of hidden-sector models, where X is a mediator. World-leading limits are achieved for dark photon, dark scalar and axion-like particle models.

Electric dipole moments (EDM) of fundamental particles inherently violate time-reversal (T) and the combined charge-conjugation and parity symmetry (CP). We aim to measure the EDM of the muon using the frozen-spin technique within a compact storage trap. This method exploits the high effective electric field, $$E\approx {165\,\mathrm{MV/m}}$$ E ≈ 165 MV / m , experienced in the rest frame of the muon with a momentum of about $${23\,\mathrm{MeV/}}c$$ 23 MeV / c when it passes through a solenoidal magnetic field of $$|\vec {B}|={2.5\,\textrm{T}}$$ | B → | = 2.5 T . In this paper, we outline the fundamental considerations for a muon EDM search and present a conceptual design for a demonstration experiment to be conducted at secondary muon beamlines of the Paul Scherrer Institute in Switzerland. In Phase I, with an anticipated data acquisition period of 200 days, the expected sensitivity to a muon EDM is $$\sigma (d)\le {4E-21\,\mathrm{{\text {e}}\!\cdot \!\text {cm}}}$$ σ ( d ) ≤ 4 E - 21 e · cm . In a subsequent phase, Phase II, we propose to improve the sensitivity to $$\sigma (d)\le {6E-23\,\mathrm{{\text {e}}\!\cdot \!\text {cm}}}$$ σ ( d ) ≤ 6 E - 23 e · cm using a dedicated instrument installed on a different beamline that produces muons of momentum 125 $$\textrm{MeV}\!/\!{ c}$$ MeV / c .