For tau decay identifications, DL techniques have been used since 1992 at LEP however, complex multivariate analysis (MVA) using observably motivated by the QCD theory is usually preferred in the modern experiments. The image-based approach achieved high performances using convolutional neural networks (CNNs) developed in the computer vision area. Representation can be crucial to highlight peculiar characteristics of an object or a pattern jets have been studied viewing them as two- or three-dimensional images, as sequences, trees, or graphs of particles. In the jet tagging context, where the task is to identify the elementary particle that originated the jet, several machine learning methods have been explored with great results. In the last few years, deep learning (DL) algorithms have dramatically improved the state of the art in many fields, such as speech recognition, visual object recognition, and object detection, and have also been successfully applied to the analysis of data collected in high-energy physics experiments. For these reasons, Tau identification and reconstruction can play a relevant role for new physics search in the Higgs sector at FCC-ee. In particular, the branching ratio of H → ττ is ∼ 6.3 %, a factor 100 or 10 larger than the BR( H → μμ) ∼ 0.02 %, or the BR( H → γγ) of ∼ 0.22 %, used in the Higgs discovery. Tau provides an optimal channel for Higgs precision measurements, since a significant fraction of the SM Higgs boson decays into the di- τ channel. Several experiments leverage this property in order to find discrepancies with the theory that could lead to new physics beyond the Standard Model, like the charged lepton flavor violation (cLFV) processes, the violation of the lepton universality, or the tau polarization. These decay modes, unlike the ones originated from quarks and gluons, can be described and predicted by the weak interaction decay theory and quantum chromodynamics, since tau decays as a free, isolated particle. Tau is the charged elementary particle belonging to the third lepton generation its mass, around 15 times larger than the muon mass, makes the τ the only lepton that can decay into hadrons. Several detector concepts have been studied to fully exploit the high energy and the great luminosity that new colliders will reach, like the IDEA (Innovative Detector for Electron–positron Accelerators) concept, that will provide an innovative calorimeter, based on the dual-readout method, that is expected to guarantee great performances in the event reconstruction. FCC-ee is expected to produce ∼ 1 0 12 events Z → ττ around the Z pole, the largest sample of ττ events foreseen at any lepton collider. In the first phase as an electron–positron collider, FCC-ee is designed to deliver the highest possible statistics and ultimate precision of Z, W, and Higgs bosons and the top quark. The Future Circular Collider (FCC) is a proposed design for a new research infrastructure that will host a 100 km particle accelerator, in order to extend the research currently being conducted at the LHC, once the high-luminosity phase (HL-LHC) reaches its conclusion in 2040.
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