Soft-drop thrust

Abstract

Soft drop, a technique originally developed in the context of jet physics in proton-proton collisions in order to reduce the contamination from non-perturbative effects, is applied to event shapes in electron-positron annihilation. In particular, we study the thrust distribution at the Z pole and show that the region where non-perturbative corrections due to the hadronisation process are small is considerably extended if soft drop is applied. Therefore, we argue that the use of soft drop to reduce hadronisation effects is potentially of great benefit in the context of strong coupling determination using event shapes, which would be otherwise characterised by a strong correlation between α s and nonperturbative parameters. However, reduced sensitivity to hadronisation corrections is only one of the aspects that need to be considered. In this context, we show that perturbative calculability, especially away from the soft and collinear region of the event-shape spectrum, has a nontrivial interplay with the soft-drop observable of choice. To this purpose, besides thrust, we investigate the behaviour of the hemisphere mass as well as the jet mass. We find that the latter shows the most promising behaviour in the intermediate region of the spectrum, especially if small jet radii are considered.

Fitting the strong coupling constant with soft-drop thrust

“…An important difference between this definition and what was presented in the first version of Ref. [19] is the rescaling factor in front of the observable. This additional factor ensures collinear safety for the case β = 0.…”

“…In Ref. [19] the resummation of soft-drop thrust at NLL accuracy has been presented. The calculation is based on the factorisation of the differential distribution in hard, soft and collinear pieces, derived using Soft Collinear Effective Theory [32].…”

“…In recent studies [19,20], some of us put forward the idea of exploiting techniques developed in jet physics to improve on the determination of the strong coupling. Jet substructure techniques are primarily developed to search for boosted massive particles decaying hadronically.…”

“…The soft-drop algorithm [24] is particularly well-suited for this task and in Ref. [19] soft-dropped versions of thrust, and related event shapes, where discussed in detail. In this paper we continue the analysis of soft-drop thrust and, in particular, focus on the effects that soft drop has on the impact of nonperturbative corrections in the extraction of α s .…”

The soft drop groomed jet radius at NLL

“…In this work, we focus on the soft drop grooming algorithm of [4]. Both on the experimental [5][6][7][8] and the theoretical side [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24], significant progress has been made recently in improving our understanding of soft drop groomed jet observables. In the heavy-ion community, soft drop groomed jet substructure observables have also received increasing attention from both experiment [25][26][27][28] and theory [29][30][31][32][33][34][35][36][37][38][39].…”