Resummation of heavy jet mass and comparison to LEP data

TL;DR

This paper advances the precision of heavy jet mass distribution calculations in e+e- collisions using NNNLL and NNLO accuracy, compares predictions with LEP data, and explores implications for alpha_s extraction and non-perturbative effects.

Contribution

It provides the first combined NNNLL and NNLO analysis of heavy jet mass, confirming resummed predictions with fixed order data and examining non-perturbative corrections.

Findings

Extracted alpha_s(m_Z)=0.1220 +/- 0.0031 from ALEPH data.

Combined heavy jet mass and thrust yields alpha_s(m_Z)=0.1193 +/- 0.0027.

Monte Carlo hadronization models are unreliable for power corrections at this precision.

Abstract

The heavy jet mass distribution in e+e- collisions is computed to next-to-next-to-next-to leading logarithmic (NNNLL) and next-to-next-to leading fixed order accuracy (NNLO). The singular terms predicted from the resummed distribution are confirmed by the fixed order distributions allowing a precise extraction of the unknown soft function coefficients. A number of quantitative and qualitative comparisons of heavy jet mass and the related thrust distribution are made. From fitting to ALEPH data, a value of alpha_s is extracted, alpha_s(m_Z)=0.1220 +/- 0.0031, which is larger than, but not in conflict with, the corresponding value for thrust. A weighted average of the two produces alpha_s(m_Z) = 0.1193 +/- 0.0027, consistent with the world average. A study of the non-perturbative corrections shows that the flat direction observed for thrust between alpha_s and a simple non-perturbative shape parameter is not lifted in combining with heavy jet mass. The Monte Carlo treatment of hadronization gives qualitatively different results for thrust and heavy jet mass, and we conclude that it cannot be trusted to add power corrections to the event shape distributions at this accuracy. Whether a more sophisticated effective field theory approach to power corrections can reconcile the thrust and heavy jet mass distributions remains an open question.