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The Future Circular Electron–Positron Collider (FCC-ee) is planned to be the world’s largest particle collider and a precision instrument to study the heaviest known particles. Achieving substantial physics results requires producing high amounts of integrated luminosity, which calls for sufficient machine availability. Although the operational availability of lepton colliders has been high, the increased complexity of the new infrastructure creates a challenge to maintain this. At the early stage of research, the main activity of an availability study should be to identify the causes that potentially have the most significant effect on downtime. This paper identifies critical systems of the FCC-ee based on available failure data. The paper further presents an operation model for the FCC-ee that can be used for assessing the effect of unavailability on overall performance. Special attention is given to systems with built-in redundancies as this design concept has been proven to increase accelerator availability.

The effect on particle physics processes by intense electromagnetic fields in the charge bunch collisions at future lepton colliders is considered. Since the charge bunch fields are tied to massive sources (the $e^{+}e^{-}$ charges), a reference frame is chosen in which the fields appear to be co-propagating. Solutions of the Dirac equation minimally coupled to the electromagnetic fields reasonably associated with two intense overlapping charge bunches are obtained and found to be a Volkov solution with respect to a null 4-vector whose 3-vector part lies in the common propagation direction. These solutions are used within the Furry interaction picture to calculate the beamstrahlung transition rate for electron radiation due to interaction with the electromagnetic fields of two colliding charge bunches. New analytic expressions are obtained and compared numerically with the beamstrahlung in the electromagnetic field of one charge bunch. The techniques developed will be applied to other collider physics processes in due course., Comment: 7 pages, 5 figures, Phys Lett B preprint

International audience; Top-up injection is an essential ingredient for the future circular lepton collider (FCC-ee) to maximize the integrated luminosity and it determines the design performance. In ttbar operation mode, with a beam energy of 175 GeV, the design lifetime of ∼ 1 h is the shortest of the four anticipated operational modes, and the beam lifetime may be even shorter in actual operation. A highly robust top-up injection scheme is consequently imperative. Various top-up methods are investigated and a number of suitable schemes are considered in developing alternative designs for the injection straight section of the collider ring. For the first time, we consider multipole-kicker off-energy injection, for minimizing detector background in top-up operation, and the use of a thin wire septum in a lepton storage ring, for maximizing the luminosity.

Following the recommendations of the European Strategy Group for High Energy Physics, CERN launched the Future Circular Collider Study (FCC) to investigate the feasibility of large-scale circular colliders for future high energy physics research. This thesis presents the considerations taken into account during the design process of the magnetic lattice in the arc sections of the electron-positron version FCC-ee. The machine is foreseen to operate at four different centre-of-mass energies in the range of 90 to 350$\,$GeV. Different beam parameters need to be achieved for every energy, which requires a flexible lattice design in the arc sections. Therefore methods to tune the horizontal beam emittance without re-positioning machine components are implemented. In combination with damping and excitation wigglers a precise adjustment of the emittance can be achieved. A very first estimation of the vertical emittance arising from lattice imperfections is performed. Special emphasis is put on the optimisation of the chromaticity correction scheme based on a multi-family sextupole scheme in the arcs. In order to obtain a momentum acceptance of $\pm2\,\%$, which is required because of the severe energy loss due to beamstrahlung, it is not sufficient to correct only the linear chromaticity. The very strong focussing in the final focus quadrupoles requires the correction of higher-order terms as well. Methods to deal with this issue are investigated. A systematic study of the higher-order chromaticity and the optimisation of the sextupole scheme to gain highest possible momentum acceptance is presented.

We study the effects of the initial state radiation on the $s$-channel Higgs boson resonant production at $\mu^+\mu^-$ and $e^+e^-$ colliders by convoluting with the beam energy spread profile of the collider and the Breit-Wigner resonance profile of the signal. We assess their impact on both the Higgs signal and SM backgrounds for the leading decay channels $h\rightarrow b\bar b,\ WW^*$. Our study improves the existing analyses of the proposed future resonant Higgs factories and provides further guidance for the accelerator designs with respect to the physical goals., Comment: 15 pages, 3 figures and 3 tables

Particle Flow Algorithms (PFAs) have been applied to existing detectors to improve the measurement of hadronic jets in colliding beam experiments. For future experiments, such as a TeV lepton collider, detector concepts optimized for the application of PFAs are being developed. These concepts require so-called imaging calorimeters, with unprecedented granularity. We will review the various recent developments of such highly granular calorimeters.