Ilya Feige, Matthew Schwartz, Iain Stewart, Jesse Thaler
Jet substructure has emerged as a critical tool for LHC searches, but studies so far have relied heavily on shower Monte Carlos, which formally approximate QCD at leading-log level. We demonstrate that systematic higher-order QCD computations of jet substructure can be carried out by boosting global event shapes by a large momentum Q, and accounting for effects due to finite jet size, initial state radiation (ISR), and underlying event (UE) as 1/Q corrections. In particular, we compute the 2-subjettiness substructure distribution for boosted Z -> q qbar events at the LHC at next-to-next-to-next-to-leading log order. The calculation is greatly simplified by recycling known results for the thrust distribution in e+ e- collisions. The 2-subjettiness distribution quickly saturates, becoming Q independent for Q > 400 GeV. Crucially, the effects of jet contamination from ISR/UE can be subtracted out analytically at large Q, without knowing their detailed form. Amusingly, the Q=infinity and Q=0 distributions are related by a scaling by e, up to next-to-leading log order.
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http://arxiv.org/abs/1204.3898
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