The Catchment Area of Jets (0802.1188v2)

Abstract: The area of a jet is a measure of its susceptibility to radiation, like pileup or underlying event (UE), that on average, in the jet's neighbourhood, is uniform in rapidity and azimuth. In this article we establish a theoretical grounding for the discussion of jet areas, introducing two main definitions, passive and active areas, which respectively characterise the sensitivity to pointlike or diffuse pileup and UE radiation. We investigate the properties of jet areas for three standard jet algorithms, k_t, Cambridge/Aachen and SISCone. Passive areas for single-particle jets are equal to the naive geometrical expectation \pi R^2, but acquire an anomalous dimension at higher orders in the coupling, calculated here at leading order. The more physically relevant active areas differ from \pi R^2 even for single-particle jets, substantially so in the case of the cone algorithms like SISCone with a Tevatron Run-II split--merge procedure. We compare our results with direct measures of areas in parton-shower Monte Carlo simulations and find good agreement with the main features of the analytical predictions. We furthermore justify the use of jet areas to subtract the contamination from pileup.

• The paper establishes a theoretical foundation for jet areas by introducing passive and active definitions to quantify pileup contamination.
• It evaluates jet area characteristics across k_t, Cambridge/Aachen, and SISCone algorithms, revealing deviations from the naive πR² expectation.
• Monte Carlo simulation results align with analytical predictions, providing critical insights for enhancing jet p_t corrections in collider experiments.

Analysis of "The Catchment Area of Jets"

In the paper "The Catchment Area of Jets," the authors present a rigorous exploration of jet area definitions within the context of high-energy physics, focusing on their susceptibility to radiation from pileup and the underlying event (UE). The main objective is to establish solid theoretical foundations for the concept of jet areas, which are instrumental in quantifying the influence of soft radiation on jet observables at collider experiments such as the LHC and Tevatron.

Definitions and Motivation

The paper introduces two primary definitions of jet areas: passive and active. These concepts serve to characterize the jet's vulnerability to UE and pileup contaminations. Passive areas are determined by the integration of ghost particles into a jet, evaluating the susceptibility to contamination by isolated particles. Meanwhile, active areas are identified by introducing a dense grid of ghost particles and measuring their clustering within a jet, giving insight into the sensitivity to diffuse radiation.

Methodology and Evaluation of Algorithms

The paper evaluates the properties of jet areas for three standard jet algorithms: the $k_t$, Cambridge/Aachen, and SISCone algorithms. These algorithms were chosen due to their prominence in theoretical and experimental high-energy physics applications.

1. Passive Areas:
   • For single-particle jets, passive areas coincide with the naive geometrical expectation, $\pi R^2$.
   • For higher-order emissions, passive areas acquire an anomalous dimension, indicative of their scaling behavior with respect to the jet's transverse momentum ($p_t$).
2. Active Areas:
   • Active areas differ from $\pi R^2$, even for single-particle jets, revealing significant discrepancies, especially with cone algorithms like SISCone.

The paper recognizes that passive and active areas provide complementary insights, yet both highlight the limitations of assuming $\pi R^2$ as a universal jet area.

Results and Simulation Comparisons

The authors compare the theoretical predictions with direct measures of areas from parton-shower Monte Carlo simulations, observing substantial alignment with the significant features deduced analytically. Discrepancies are addressed through the notion of back-reaction effects, where UE and PU particles alter the jet constituents both directly and indirectly.

Implications and Future Directions

The results hold substantial implications for the subtraction of pileup contamination in analyses of jet observables at colliders. Understanding jet areas enables more precise jet $p_t$ corrections, enhancing the accuracy of high-energy physics measurements.

The paper also underscores the potential for refining jet algorithms to minimize UE/PU effects and improve infrared safety. Future research could extend these concepts to investigate jet areas at higher orders or explore their implications in different collider environments and energy scales.

In conclusion, "The Catchment Area of Jets" provides a rigorous and analytical foundation for jet area definitions, crucial for accurate data interpretation in collider physics. These insights have the potential to significantly enhance the precision and reliability of theoretical predictions and experimental analyses in high-energy particle physics.