Search

A novel type of calorimeter based on grains of inorganic scintillating crystal readout by wave length shifting fibers is proposed. The concept and main features as well as the prototype design are introduced and the first results obtained using cosmic rays are presented. The number of photo-electrons generated by cosmic rays muons in the prototype detector is estimated to be of the order of 10000 photo-electrons per GeV, validating the concept of this next-generation shashlik calorimeter., Comment: 11 pages, 7 figures

This article surveys the important questions attached to unitarity tests of the Cabibbo-Kobayashi-Maskawa matrix, with a focus on the direct determinations of the magnitude of CKM matrix elements. The current CKM anomalies are discussed and the clear-cut prospects at LHCb and Belle II envisaged. The anticipated precision on $C\!P$-conserving and $C\!P$-violating observables at the projected upgrades of the LHCb and Belle~II experiments is examined from the point of view of the search for New Physics in $B$-meson mixing, addressing the bottlenecks in precision for the interpretation of the measurements for future experiments and highlighting the related theoretical and experimental challenges. The vibrant prospects at future $e^+e^-$ colliders running at the $Z^0$ pole and $W^+W^-$ are eventually discussed., Comment: 18 pages, 5 figures, submitted to the Proceedings of the US Community Study on the Future of Particle Physics (Snowmass 2021)

In this essay we discuss the possibilities and associated challenges concerning beyond the Standard Model searches at FCC-ee, such as rare decays of heavy-flavoured particles and long-lived particles. The Standard Model contains several suppression mechanisms, which cause a given group of processes to happen rarely, resulting in rare decays. The interest in these decays lies in the fact that the physics beyond the Standard Model does not need to be affected by the same suppression mechanism and therefore can naturally manifest in these decays. Their interest is reinforced by the recent report of several measurements of $b$-flavoured rare decays, showing deviations with respect to the Standard Model predictions. We will show how the FCC-ee project has unique capabilities to address these scientific questions and will consider the related detector design challenges to meet. Another group of processes discussed are those that produce new particles with relatively long lifetimes, that travel substantial distances inside the detectors before decaying. Models containing long-lived particles can give answers to many open questions of the Standard Model, such as the nature of dark matter, or the neutrino masses, among others; while providing an interesting experimental complement to mainstream searches. Long-lived particles often display unique experimental signatures, such as displaced tracks and vertices, disappearing tracks, or anomalously charged jets. Due to this, they are affected by very low background levels but in exchange, they often require dedicated reconstruction algorithms and triggers., Comment: Submitted to the EPJ Plus "Focus Point on A Future Higgs & Electroweak Factory (FCC): Challenges towards Discovery - Part II: Physics Opportunities and Challenges"

The abundant production of beauty and charm hadrons in the $5 \times 10^{12}$ $Z^0$ decays expected at FCC-ee offers outstanding opportunities in flavour physics that in general exceed those available at Belle II, and are complementary to the heavy-flavour programme of the LHC. A wide range of measurements will be possible in heavy-flavour spectroscopy, rare decays of heavy-flavoured particles and $C\!P$-violation studies, which will benefit from the low-background experimental environment, the high Lorentz boost, and the availability of the full spectrum of hadron species. This essay first surveys the important questions in heavy-flavour physics, and assesses the likely theoretical and experimental landscape at the turn-on of FCC-ee. From this certain measurements are identified where the impact of FCC-ee will be particularly important. A full exploitation of the heavy-flavour potential of FCC-ee places specific constraints and challenges on detector design, which in some cases are in tension with those imposed by the other physics goals of the facility. These requirements and conflicts are discussed., Comment: Accepted for publication in the EPJ Plus Focus Point on "A future Higgs and electroweak factory (FCC): challenges towards discovery". This version includes minor modifications and corrections following review

This document answers in simple terms many FAQs about FCC-ee, including comparisons with other colliders. It complements the FCC-ee CDR and the FCC Physics CDR by addressing many questions from non-experts and clarifying issues raised during the European Strategy symposium in Granada, with a view to informing discussions in the period between now and the final endorsement by the CERN Council in 2020 of the European Strategy Group recommendations. This document will be regularly updated as more questions appear or new information becomes available., Comment: Contribution to the European Particle Physics Strategy Update 2018-2020. Forty-five pages, six figures

A future high-luminosity $Z$-factory has the potential to investigate lepton flavour violation. Rare decays such as $Z \to \ell_1^\mp \ell_2^\pm$ can be complementary to low-energy (high-intensity) observables of lepton flavour violation. Here we consider two extensions of the Standard Model which add to its particle content one or more sterile neutrinos. We address the impact of the sterile fermions on lepton flavour violating $Z$ decays, focusing on potential searches at FCC-ee (TLEP), and taking into account experimental and observational constraints. We show that sterile neutrinos can give rise to contributions to BR($Z \to \ell_1^\mp \ell_2^\pm$) within reach of the FCC-ee. We discuss the complementarity between a high-luminosity $Z$-factory and low-energy charged lepton flavour violation facilities., Comment: 6 pages, 4 figures. Contribution to the proceedings of The European Physical Society Conference on High Energy Physics, 22-29 July 2015, Vienna (Austria)