Calculating Track Thrust with Track Functions

TL;DR

This paper introduces a novel calculation of track thrust in e+e- collisions using track functions within soft-collinear effective theory, revealing a surprising similarity to calorimeter thrust distributions due to non-perturbative effects.

Contribution

It presents the first theoretical calculation of track thrust incorporating track functions and resummation, bridging a gap between perturbative predictions and experimental measurements.

Findings

Track thrust distribution matches experimental data from ALEPH and DELPHI.

Partial cancellation of non-perturbative parameters explains similarity to calorimeter thrust.

First application of track functions in soft-collinear effective theory for event shapes.

Abstract

In e+e- event shapes studies at LEP, two different measurements were sometimes performed: a "calorimetric" measurement using both charged and neutral particles, and a "track-based" measurement using just charged particles. Whereas calorimetric measurements are infrared and collinear safe and therefore calculable in perturbative QCD, track-based measurements necessarily depend on non-perturbative hadronization effects. On the other hand, track-based measurements typically have smaller experimental uncertainties. In this paper, we present the first calculation of the event shape track thrust and compare to measurements performed at ALEPH and DELPHI. This calculation is made possible through the recently developed formalism of track functions, which are non-perturbative objects describing how energetic partons fragment into charged hadrons. By incorporating track functions into soft-collinear effective theory, we calculate the distribution for track thrust with next-to-leading logarithmic resummation. Due to a partial cancellation between non-perturbative parameters, the distributions for calorimeter thrust and track thrust are remarkably similar, a feature also seen in LEP data.