Effect of PYTHIA8 tunes on event shapes and top-quark reconstruction in $e^+e^-$ annihilation at CLIC

TL;DR

This study investigates how different PYTHIA8 tunes influence event shape variables and top-quark mass reconstruction in simulated electron-positron collisions at CLIC energies, revealing tune-dependent effects especially in boosted top scenarios.

Contribution

It provides a detailed analysis of PYTHIA8 tune impacts on event shapes and top mass reconstruction at high energies, highlighting significant shifts in boosted regimes.

Findings

No significant top mass variation at 380 GeV.

A 700 MeV shift in top mass at 3 TeV with the Montull tune.

Increased particle multiplicity correlates with mass shifts.

Abstract

This paper describes the effect of PYTHIA8 tunes on event simulation of $e^+e^-$ collisions with center-of-mass (CM) energies of 380 GeV and 3 TeV at the proposed CLIC collider. Event shapes, such as thrust, thrust major, thrust minor, oblateness, as well as particle multiplicities have been analyzed and relative differences with respect to the default PYTHIA8 tune were determined. The effect of tunes on top-mass reconstruction in the resolved and boosted regimes was analyzed. No statistically significant variation for reconstructed top masses using invariant masses of three jets was found for events with a CM energy of 380 GeV. For the fully boosted top reconstruction at a CM energy of 3 TeV, a significant shift in reconstructed top mass of about 700 MeV for the "Montull" tune was observed. This shift correlates with an increase in particle multiplicity compared to all other PYTHIA8 tunes.