Universality of 1Q corrections to jet-shape observables rescued Original Research Article

We address the problem of potential non-universality of the leading 1Q power corrections to jet shapes emerging from the non-inclusive character of these observables. We consider the thrust distribution as an example and analyse the non-inclusive contributions which emerge at the two-loop level. Although formally subleading in αs, they modify the existing naïve one-loop result for the expected magnitude of the power term by a factor of order unity. Such a promotion of a subleading correction into a numerical factor is natural since the non-perturbative power terms are explicitly proportional to powers of the QCD scale Λ which can be fixed precisely only at the two-loop level. The “jet-shape scaling factor” depends on the observable but remains perturbatively calculable. Therefore it does not undermine the universal nature of 1Q power corrections, which remain expressible in terms of the universal running coupling and universal soft-gluon emission.