Jet Timing

TL;DR

This paper investigates methods to define and measure the arrival time of jets in particle detectors, finding that a transverse momentum weighted sum of constituents' times offers superior resolution and potential for new insights into jet physics.

Contribution

It introduces an optimal jet time definition based on transverse momentum weighting and analyzes its performance and dependencies in detail.

Findings

Transverse momentum weighted sum yields ten times better jet time resolution.

Jet time performance depends on jet trajectory and origin, especially for delayed jets.

Proper calibration of jet time definitions enhances understanding of jet behavior in the time domain.

Abstract

The measurement of the arrival time of a particle, such as a lepton, a photon, or a pion, reaching the detector provides valuable information. A similar measurement for a hadronic final state, however, is much more challenging as one has to extract the relevant information from a collection of particles. In this paper, we explore various possibilities in defining the time of a jet through the measurable arrival times of the jet constituents. We find that a definition of jet time based on a transverse momentum weighted sum of the times of the constituents has the best performance. For prompt jets, the performance depends on the jet trajectory. For delayed jets, the performance depends on the trajectory of the jet, the trajectory of the mother particle, and the location of the displaced vertex. Compared to the next-best-performing jet time definition, the transverse momentum weighted sum has roughly a factor of ten times better jet time resolution. We give a detailed discussion of the relevant effects and characterize the full geometrical dependence of the performance. These results highlight the critical importance of using a proper definition of jet time with its corresponding detector-dependent calibration and the exciting possibility of deepening our understanding of jets in the time domain.