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Seeing in Color: Jet Superstructure

Jason Gallicchio, Matthew D. Schwartz

TL;DR

A new class of observables is introduced which aims to characterize the superstructure of an event, that is, features, such as color flow, which are not determined by the jet four-momenta alone, which can be used on an event-by-event basis as a tool for distinguishing previously irreducible backgrounds at the Tevatron and the LHC.

Abstract

A new class of observables is introduced which aims to characterize the superstructure of an event, that is, features, such as color flow, which are not determined by the jet four-momenta alone. Traditionally, an event is described as having jets which are independent objects; each jet has some energy, size, and possible substructure such as subjets or heavy flavor content. This description discards information connecting the jets to each other, which can be used to determine if the jets came from decay of a color singlet object, or if they were initiated by quarks or gluons. An example superstructure variable, pull, is presented as a simple handle on color flow. It can be used on an event-by-event basis as a tool for distinguishing previously irreducible backgrounds at the Tevatron and the LHC.

Seeing in Color: Jet Superstructure

TL;DR

A new class of observables is introduced which aims to characterize the superstructure of an event, that is, features, such as color flow, which are not determined by the jet four-momenta alone, which can be used on an event-by-event basis as a tool for distinguishing previously irreducible backgrounds at the Tevatron and the LHC.

Abstract

A new class of observables is introduced which aims to characterize the superstructure of an event, that is, features, such as color flow, which are not determined by the jet four-momenta alone. Traditionally, an event is described as having jets which are independent objects; each jet has some energy, size, and possible substructure such as subjets or heavy flavor content. This description discards information connecting the jets to each other, which can be used to determine if the jets came from decay of a color singlet object, or if they were initiated by quarks or gluons. An example superstructure variable, pull, is presented as a simple handle on color flow. It can be used on an event-by-event basis as a tool for distinguishing previously irreducible backgrounds at the Tevatron and the LHC.

Paper Structure

This paper contains 2 equations, 5 figures.

Figures (5)

  • Figure 1: Possible color connections for signal ($pp\to H\to b\bar{b}$) and for background ($pp\to g \to b\bar{b}$).
  • Figure 2: Accumulated $p_T$ after showering a particular partonic phase space point 3 million times. Left has the $b$ and $\bar{b}$ color-connected to each other (signal) and right has the $b$ and $\bar{b}$ color-connected to the beams (background). Contours represent factors of 2 increase in radiation.
  • Figure 3: Event-by-event density plot of the pull vector of the $b$ jet in polar coordinates. The signal (connected to $\bar{b}$ jet) is on the left, the background (connected to the left-going, $y=-\infty$ beam) is on the right. $10^5$ events are shown.
  • Figure 4: Distribution of the pull angle (for the $b$ jet) with $\Delta y_{b\bar{b}} = 1$ and $\Delta \phi_{b\bar{b}} = 2$, for signal and background, showered $10^5$ times with different Monte Carlos.
  • Figure 5: Pull angles in the $b$ or $\bar{b}$ jet in $HZ\to Z b\bar{b}$ signal events and their $Z+b \bar{b}$ backgrounds. For each event, $\Delta \theta_t=0$ is defined to point toward the other $b$ jet. $3\times10^5$ events are shown.