The energy distribution of subjets and the jet shape

Abstract

We present a framework that describes the energy distribution of subjets of radius r within a jet of radius R. We consider both an inclusive sample of subjets as well as subjets centered around a predetermined axis, from which the jet shape can be obtained. For r R we factorize the physics at angular scales r and R to resum the logarithms of r/R. For central subjets, we consider both the standard jet axis and the winner-take-all axis, which involve double and single logarithms of r/R, respectively. All relevant one-loop matching coefficients are given, and an inconsistency in some previous results for cone jets is resolved. Our results for the standard jet shape differ from previous calculations at next-to-leading logarithmic order, because we account for the recoil of the standard jet axis due to soft radiation. Numerical results are presented for an inclusive subjet sample for pp → jet + X at next-to-leading order plus leading logarithmic order.

Hadron-in-jet production at partonic threshold

“…The other ones which are multiplied by ∼ P dc (z h ) are resummed by evaluating the fragmentation function at the jet scale µ J ∼ p T R, see [9], whereas at fixed order the scale is chosen as µ H ∼ p T . Thus, the two DGLAP evolutions achieve the resummation of both sets of logarithms of the jet radius R. The relevant results for the cone algorithm can be found in [52]. We note that the threshold resummation discussed in this work does not depend on the choice of the jet algorithm to the accuracy we are working at.…”

“…We start with the hard matching coefficients functions H cd at the jet scale. The same functions appear in the refactorization of the cross section of other jet substructure observables which were first calculated in [42,52]. For completeness, we list the results here including the singularities:…”

“…We start with the evolution equations of the hard-matching functions H cd which are given by [42,52]…”

Using hadron-in-jet data in a global analysis of D* fragmentation functions

“…Currently, the only available data set for D ÃAE -mesons within jets is provided by the ATLAS Collaboration [26] for which the anti-k T algorithm was used with a jet-size parameter of R ¼ 0.6. However, the results for cone [46] and J E T [47] jets are also available in the literature [23,24,48].…”

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.…”