The jet mass distribution after Soft Drop

Abstract

We present a first-principle computation of the mass distribution of jets which have undergone the grooming procedure known as Soft Drop. This calculation includes the resummation of the large logarithms of the jet mass over its transverse momentum, up to next-to-logarithmic accuracy, matched to exact fixed-order results at next-toleading order. We also include non-perturbative corrections obtained from Monte-Carlo simulations and discuss analytic expressions for hadronisation and Underlying Event effects.Introduction The study of jets at the Large Hadron Collider (LHC) has recently taken a new turn with new substructure observables [1,2] amenable to precise theory calculations [3][4][5], including genuine theory uncertainty bands, and corresponding experimental measurements from both the CMS [6] and ATLAS [7] collaborations. The substructure techniques we concentrate on are usually referred to as grooming and they aim to reduce sensitivity to non-perturbative corrections and pileup.A first series of studies has focused on the jet mass after applying the (modified) MassDrop Tagger (mMDT) [1,8] in dijet events, as measured by the CMS collaboration [6]. On the theory side, the description of this observable requires to match a resummed calculation, important in the smallmass region, to fixed-order results, which are important for large masses. The former are obtained analytically, including to all orders terms enhanced by the large logarithms of p 2 t /m 2 with p t the jet transverse momentum and m the (groomed) jet mass. The latter is obtained from fixedorder Monte-Carlo simulations. To date, two theory calculations are available: a SCET-based next-to-leading logarithmic (NLL) resummation in the small z cut limit, matched to leading order (LO) results [4], and our previous study

Nonperturbative corrections to soft drop jet mass

“…For a numerical comparison of the m J -and β-dependence of our shift and boundary corrections with the corresponding results of Ref. [64] given in Eq. (7.2) we consider the quark jet case, and set Ω • • 1q = C F Λ had = 1 GeV, Υ q 1,0 = C A Λ had = 1 GeV, and Υ q 1,1 = 0 GeV.…”

“…Here we will make a comparison of our results with the analytic estimates for hadronization corrections from Refs. [50,55,64].…”

“…These estimates were extended to β > 0 in Ref. [64] where hadronization corrections were considered due to a shift in m J and a reduction in p T of soft subjets from nonperturbative particles, z)) is the effective radius of the jet formed by a single perturbative splitting, and Λ hadr ∼ Λ QCD is a nonperturbative parameter common to both the corrections. Eq.…”

“…(7.2), since Refs. [50,64] did not account for the additional β dependence from expanding the soft drop condition in their treatment of Eqs. (4.17) and (4.18).…”

Novel subjet observables for jet quenching in heavy-ion collisions

“…However, in all these measurements the treatment of the background originating from the copiously produced particles not associated to hard scatterings poses an experimental challenge for precise and unbiased measurements. Previous works that addressed the effect of filtering a e-mail: liliana@lip.pt b e-mail: guilherme.milhano@ist.utl.pt c e-mail: mploskon@lbl.gov d e-mail: xiaoming.zhang@cern.ch on subjet analysis [26] and the recent analytic calculations of the momentum distributions of subjets [27][28][29] and groomed jet mass distributions [30][31][32] that were recently measured in proton-proton collisions [33,34], provide a strong motivation for novel studies. In this writeup, following previous works [35], we propose observables that are sensitive to the internal jet structure but significantly alleviate the difficulties associated to the effects of the background.…”