Abstract
The hard-scatter processes in hadronic collisions are often largely contaminated with soft background coming from pileup in proton-proton collisions, or underlying event in heavy-ion collisions. This paper presents a new background subtraction method for jets and event observables (such as missing transverse energy) which is based on the previously published Constituent Subtraction algorithm. The new subtraction method, called Iterative Constituent Subtraction, applies event-wide implementation of Constituent Subtraction iteratively in order to fully equilibrate the background subtraction across the entire event. Besides documenting the new method, we provide guidelines for setting the free parameters of the subtraction algorithm. Using particle-level simulation, we provide a comparison of Iterative Constituent Subtraction with several existing methods from which we conclude that the new method has a significant potential to improve the background mitigation in both proton-proton and heavy-ion collisions.
Highlights
Using particle-level simulation, we provide a comparison of Iterative Constituent Subtraction with several existing methods from which we conclude that the new method has a significant potential to improve the background mitigation in both proton-proton and heavy-ion collisions
We presented a new background mitigation method for jet kinematics, jet substructure observables, and event observables, called Iterative Constituent Subtraction
This method is applicable to both pileup effects in proton-proton collisions and underlying event contributions in heavy-ion collisions
Summary
The CS algorithm described in ref. [8] corrects individual jets which were already clustered using a certain jet algorithm. Background subtraction in the Shape-expansion and Jet-by-jet CS methods In all these methods, their property of infinite softness is essential to not modify the jet clustering sequence. For the Event-wide CS, this property is irrevelant and each ghost pT is directly set to pgT ≡ Ag · ρ Such ghosts already represent the expected background contribution in the given event, and can be used to correct particles via the Event-wide. Any operation can be done on these output particles — most commonly jet clustering, evaluation of global event shapes or missing transverse energy. A detailed discussion of the choice of the free CS parameters is provided in appendix A
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