Top-quark physics at the first CLIC stage

TL;DR

This paper explores the potential of the first stage of CLIC for precision top-quark measurements, including mass, couplings, and rare decay searches, using detailed simulations and various analysis methods.

Contribution

It provides detailed simulation-based projections for top-quark property measurements and rare decay searches at the initial CLIC energy stage, highlighting the collider's physics reach.

Findings

Top-quark mass can be measured with ~50 MeV precision.

Sensitivity to top-quark couplings to electroweak bosons beyond 10 TeV.

Exclusion limits for rare top decays down to BR of 4.7×10⁻⁵.

Abstract

The Compact Linear Collider (CLIC) is a mature option for a future electron-positron collider operating at centre-of-mass energies of up to 3 TeV. CLIC will be built and operated in a staged approach with three centre-of-mass energies currently assumed to be 380 GeV, 1.5 TeV and 3 TeV. This contribution discusses the prospects for precision measurements of top-quark properties at the first stage of CLIC, based on detailed simulation studies, taking into account luminosity spectra and beam induced backgrounds, full detector simulation based on Geant4, final state reconstruction based on particle flow approach with PandoraPFA, jet clustering with the VLC algorithm as implemented in the FastJet package, and flavour tagging with LcfiPlus. Based on a dedicated centre-of-mass energy scan around the top-quark pair production threshold, the top-quark mass can be determined with a precision of about 50 MeV in a theoretically well-defined manner. This scan is also sensitive to the top-quark width and Yukawa coupling. Other approaches to extract the top-quark mass at the first stage of CLIC make use of ISR photons or the direct reconstruction of the top quarks. Precise measurements of the differential top-quark pair production cross sections at 380 GeV, for different electron beam polarisations, allow the study of top-quark couplings to electroweak gauge bosons sensitive to new physics mass scales beyond 10 TeV. The large number of top-quark pairs produced also allows competitive searches for Flavour Changing Neutral Current (FCNC) top-quark decays with charm quarks in the final state. Exclusion limits expected for 500 fb$^{-1}$ collected at the first stage of CLIC are presented for $t\rightarrow ch$, $t\rightarrow c\gamma$ and $t\rightarrow c E_{miss}$ channels, reaching down to $4.7 \cdot 10^{-5}$ for BR($t\rightarrow c\gamma$).