Generalizing event shapes: In search of lost collider time

TL;DR

This paper introduces generalized event shapes in conformal field theories, providing a new way to analyze the longitudinal structure of collision states, with computations in super-Yang-Mills theory at various couplings.

Contribution

It defines a novel class of collider observables called generalized event shapes, connecting correlation functions and scattering amplitudes, and explores their properties at weak and strong coupling.

Findings

Generalized event shapes are infrared finite and interpolate to traditional event shapes.

At strong coupling, energy-energy correlations show longitudinal broadening.

Long-time tails in energy flux indicate quantum and stringy effects at strong coupling.

Abstract

We introduce a new class of collider-type observables in conformal field theories which we call generalized event shapes. They are defined as matrix elements of light-ray operators that are sensitive to the longitudinal, or time-dependent, structure of the state produced in the collision. Generalized event shapes can be studied using both correlation functions and scattering amplitudes. They are infrared finite and smoothly transit over to the familiar event shapes. We compute them in planar ${\cal N}=4$ super-Yang-Mills theory at weak and strong coupling, and study their physical properties. We show that at strong coupling both the stringy and quantum-gravitational corrections to the energy-energy correlation exhibit longitudinal broadening that manifests itself through the presence of long-time tails in the energy flux measured by the detectors.