Based on JHEP 1008:058,2010(arXiv:1005.1644)Yang-Ting Chein and Matthew D. Schwartz

Heavy jet mass is an event shape similar to thrust. It can also be computing to high precision in the threshold region using Soft-Collinear Effective Theory.

Comparing the fits for heavy jet mass and thrust, we find that thrust is a much better fit.

The values of alpha_s consequently have somewhat larger uncertainty than from thrust

The average value of alpha_s from ALEPH data using NNLO + NNNLL accuracty, without power corrections, is alpha_s = 0.1220 +/- 0.0031.

Work is in progress to understand power corrections. Some interesting preliminary observations are about a sensitivity to the profile functions and the scheme used for boundary conditions at the kinematically limiting value of thrust.

Profile dependence