Higgs and top physics reconstruction challenges and opportunities at FCC-ee

Abstract

The Higgs bosons and the top quark decay into rich and diverse final states, containing both light and heavy quarks, gluons, photons as well as W and Z bosons. This article reviews the challenges involved in reconstructing Higgs and top events at the FCC-ee and identifies the areas where novel developments are needed. The precise identification and reconstruction of these final states at the FCC-ee rely on the capability of the detector to provide excellent flavour tagging, jet energy and angular resolution, and global kinematic event reconstruction. Excellent flavour tagging performance requires low-material vertex and tracking detectors, and advanced machine learning techniques as successfully employed in LHC experiments. In addition, the Z pole run will provide abundant samples of heavy flavour partons that can be used for calibration of the tagging algorithms. For the reconstruction of jets, leptons, and missing energy, particle-flow algorithms are crucial to explore the full potential of the highly granular tracking and calorimeter systems, and give access to excellent energy–momentum resolution and precise identification of heavy bosons in their hadronic decays. This enables, among many other key elements, the reconstruction of Higgsstrahlung processes with leptonically and hadronically decaying Z bosons, and an almost background-free identification of top quark pair events. Exploiting the full available kinematic constraints together with exclusive jet clustering algorithms will allow for the optimisation of global event reconstruction with kinematic fitting techniques.

The Future Circular Collider: a Summary for the US 2021 Snowmass Process

“…As pointed out in Ref. [104], using kinematic constraints in the event reconstruction can improve reconstructed invariant masses and utilizing new techniques, including machine-learning with particle-flow reconstruction, can provide enhanced jet and event reconstruction. These will contribute to increase the sensitivity in FCNC searches compared to the existing limit projections that utilize more traditional analysis approaches [104].…”

High-precision QCD physics at FCC-ee

“…One of the most exciting (but challenging) prospects in pp collisions is light-quark gluon discrimination. Being able to efficiently identify the flavour of the parton which initiates the jet is critical for the success of the physics program of future EW factories [5]. An accurate light quarkgluon discrimination would allow precise Beyond the Standard Model (BSM) searches for signals without leptons, b-or top-quarks, as well as would produce an enhancement of light quark-rich signals i.e.…”

Jet Flavour Tagging for Future Colliders with Fast Simulation

“…In particular, the measurement of the Higgs couplings to bottom (b) and charm (c) quarks, and gluons (g) [7][8][9][10][11][12][13], the Higgs self-coupling [14] and the precise characterisation of top quark properties, such as the top quark mass [15] and its electroweak couplings [16,17] require an efficient reconstruction and identification of hadronic final states. Being able to efficiently identify the flavour of the parton that initiated the formation of a jet, known as jet flavour tagging, is therefore critical for the success of the physics program of future electroweak factories [18]. The large statistics of hadronic Z boson decays at both lepton circular machines and future hadron machines would provide copious control samples to calibrate jet tagging algorithms in data.…”