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.

We present the development, realization and setup of dielectric resonators, for the purpose of measuring the surface impedance at microwave frequencies of superconducting thin films. We focus on resonators designed to operate in dc magnetic fields, optimized for the measurements of the variation of the surface impedance with the applied field. Two resonators, operating at 8 and 48 GHz, are presented. We discuss different approaches to the measurement of the resonator parameters, with particular attention to the nonidealities of real setups in a cryogenic environment. Finally, we present some sample measurement of high-T _c and low-T _c superconducting films.

Dielectric loaded resonators, by virtue of their high sensitivity, are a de facto standard for the measurement of the microwave surface impedance Z of good conductors, including superconductors. However, new perspective applications of superconductors request measurements in increasingly extreme conditions: cryogenic and magnetic environments, often combined together. Careful evaluations of the dielectric resonator (DR) design are necessary to operate in these conditions. Moreover, the evaluation of the uncertainties and the issues related to an appropriate calibration become problematic. We present here a performance analysis of DRs designed for cryogenic temperature and high magnetic field operation and some sample experimental results on Z measurements on the most technologically interesting superconductors.

Measurements of anisotropic transport properties (dc and high-frequency regime) of driven vortex matter in YBa₂Cu₃O_7−x with elongated strong-pinning sites (c-axis aligned, self-assembled BaZrO₃ nanorods) are used to demonstrate that the effective-mass angular scaling takes place only in intrinsic physical quantities (flux-flow resistivity), and not in pinning-related Labusch parameter and critical currents. Comparison of the dynamics at different time scales shows evidence for a transition of the vortex matter toward a Mott phase, driven by the presence of nanorods. The strong pinning in dc arises partially from a dynamic effect.

The high frequency vortex motion in Nb ₃ Sn was analyzed in this work up to 12 T. We used a dielectric loaded resonator tuned at 15 GHz to evaluate the surface impedance Z of a Nb ₃ Sn bulk sample (24.8 at.%Sn). From the field induced variation of Z , the high frequency vortex parameters (the pinning constant k _p , the depinning frequency ν _p and the flux flow resistivity ρ _ff ) were obtained over a large temperature and field range; their field and temperature dependencies were analyzed. Comparison with other superconducting materials shows that high frequency applications in strong magnetic fields are also feasible with Nb ₃ Sn. In the present work, we report the first measurements about the microwave response in Nb ₃ Sn in strong magnetic fields.

In structures made up of alternating superconducting and ferromagnet layers (S/F/S heterostructures), it is known that the macroscopic quantum wave function of the ground state changes its phase difference across the F layer from 0 to $\pi$ under certain temperature and geometrical conditions, hence the name “$0–\pi$” for this crossover. We present here a joint experimental and theoretical demonstration that $0–\pi$ is a true thermodynamic phase transition. Microwave measurements of the temperature dependence of the London penetration depth in $\mathrm{Nb}/{\mathrm{Pd}}_{0.84}{\mathrm{Ni}}_{0.16}/\mathrm{Nb}$ trilayers reveal a sudden, unusual decrease of the density of the superconducting condensate (square modulus of the macroscopic quantum wave function) with decreasing temperature, which is predicted by the theory here developed as a transition from the 0 state to the $\pi$ state. Our result for the jump of the amplitude of the order parameter is a thermodynamic manifestation of such a temperature-driven quantum transition.