Abstract
Track-assisted mass is a proxy for jet mass that only uses direction information from charged particles, allowing it to be measured at the Large Hadron Collider with very fine angular resolution. In this paper, we introduce a generalization of track-assisted mass and analyze its performance in both parton shower generators and resummed calculations. For the original track-assisted mass, the track-only mass is rescaled by the charged energy fraction of the jet. In our generalization, the rescaling factor includes both per-jet and ensemble-averaged information, facilitating a closer correspondence to ordinary jet mass. Using the track function formalism in electron-positron collisions, we calculate the spectrum of generalized track-assisted mass to next-to-leading-logarithmic order with leading-order matching. These resummed calculations provide theoretical insight into the close correspondence between track-assisted mass and ordinary jet mass. With the growing importance of jet grooming algorithms, we also calculate track-assisted mass on soft-drop groomed jets.
Highlights
Products can become so collimated that their separation is even below the typical hadronic calorimeter resolution of 0.1 × 0.1 (0.02 × 0.02) in the rapidity-azimuth plane
Track-assisted mass is a proxy for jet mass that only uses direction information from charged particles, allowing it to be measured at the Large Hadron Collider with very fine angular resolution
In the spirit of ref. [99], this same generalized track-assisted mass (GTAM) philosophy could be applied to situations where both tracking and electromagnetic calorimeter information is used to determine jet mass, but hadronic calorimeter information is only used to determine jet pT
Summary
The ordinary jet mass (Mcalo) and jet transverse momentum (pT,calo) are defined analogously, with the sum running over all particles in a jet. An observable that is more closely related to the ordinary jet mass can be constructed using a re-weighting factor involving pT,calo and pT,track. This is the motivation for trackassisted mass in eq (1.1) and our generalized version in eq (1.2), repeated for convenience: MT(1A,0) ≡ MTA. The charged particle momentum fraction is rather scale insensitive, so averaging over a wide pT and rapidity range turns out to not have much of an effect This is true even accounting for differences in the quark/gluon composition of the ensemble; see further discussion in appendix A.
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