High Energy Description of Processes with Multiple Hard Jets

TL;DR

Problem: Multi-jet final states at the LHC are shaped by large hard radiative corrections that fixed-order or parton showers struggle to describe across large rapidity gaps. Approach: The paper reviews and applies High Energy Jets (HEJ), an all-order perturbative framework based on $t$-channel currents and Lipatov-inspired virtual corrections, with fixed-order matching for low jet multiplicities. Contributions: New HEJ predictions for dijet production and for W production with at least three jets show the amount of hard radiation grows with rapidity span and depends on initial-state parton flux (e.g., $gg$ vs $qg$); observables such as $d\sigma/d\phi_{fb}$, $d\sigma/dy_{fb}$, and the $H_T$ distribution are sensitive to these effects. Significance: The work improves SM background predictions in jet-rich channels and informs new physics searches by identifying where all-order corrections are essential for stable final-state descriptions.

Abstract

High Energy Jets (HEJ) is a new framework for approximating the all-order perturbative corrections to multi-jet processes, with a focus on the hard, wide-angle QCD emissions, which underpins the perturbative description of hard jets. In this contribution we review the basic concepts of HEJ, and present some new predictions for observables in dijet-production, and for W-boson production in association with at least 3 jets.

Figures (3)

• Figure 1: The average number of hard jets ($p_\perp>40$ GeV) in events with a Higgs boson and at least two jets at a 10 TeV $pp$-machine, as a function of the rapidity difference $\Delta y_{ab}$ between the most forward and most backward hard jet. The predictions from three different models are compared: Fixed order NLO by MCFMCampbell:2010cz (green), the SHERPA shower Monte CarloGleisberg:2008ta, including CKKW-matching with processes for a Higgs-boson and up to 4 final state partons (red), and finally the all-order framework of High Energy JetsAndersen:2008ueAndersen:2008gcAndersen:2009nuAndersen:2009he (blue). See Ref.Binoth:2010ra for more details.
• Figure 2: Top: The average number of hard jets ($p_\perp>75$GeV) in dijet events at the LHC (7 TeV). Bottom: The increasing weight of hard, radiative corrections for increasing rapidity spans between the forward/backward hard jet leads to the distribution on the azimuthal angle between these jets to be less peaked at the back-to-back configuration.
• Figure 3: Results obtained with HEJ for $W$-production in association with at least three jets.