Jet Charge at the LHC

TL;DR

A systematically improvable method is developed to calculate moments of these charge distributions by combining multihadron fragmentation functions with perturbative jet functions and pertubative evolution equations, which can provide a validation tool for data independent of Monte Carlo fragmentation models.

Abstract

Knowing the charge of the parton initiating a light-quark jet could be extremely useful both for testing aspects of the Standard Model and for characterizing potential beyond-the-Standard-Model signals. We show that despite the complications of hadronization and out-of-jet radiation such as pile-up, a weighted sum of the charges of a jet's constituents can be used at the LHC to distinguish among jets with different charges. Potential applications include measuring electroweak quantum numbers of hadronically decaying resonances or supersymmetric particles, as well as Standard Model tests, such as jet charge in dijet events or in hadronically-decaying W bosons in t-tbar events. We develop a systematically improvable method to calculate moments of these charge distributions by combining multi-hadron fragmentation functions with perturbative jet functions and pertubative evolution equations. We show that the dependence on energy and jet size for the average and width of the jet charge can be calculated despite the large experimental uncertainty on fragmentation functions. These calculations can provide a validation tool for data independent of Monte-Carlo fragmentation models.

Figures (6)

• Figure 1: Distributions of ${\mathcal{Q}}_\kappa^i$ for various parton flavors obtained from $pp\to W'\to \bar{q}q$ or $pp\to gg$ events with $p_T^{\rm jet} = 500$ GeV and $\kappa=0.5,1$.
• Figure 2: Distinguishing $W'$ from $Z'$ with a log-likelihood discriminant, for different values of $\kappa$. Even with only 50 events the samples are extremely well separated.
• Figure 3: Top: final state composition in dijet production. Bottom: Sum of the two jet charges in dijet events, for various $\kappa$. The growth with dijet invariant mass reflects the larger fraction of valence quark PDFs at large $x$ and corresponding decrease in $gg$ final states.
• Figure 4: Sum of jet charges of the two non $b$-jets in semi-leptonic $t\bar{t}$ events with a positively (solid) or negatively (dashed) charged lepton.
• Figure 5: Comparison of $W'$ vs. $Z'$ discrimination subject to contamination from initial state radiation (ISR), multiple interactions (MI), and pile-up events. We also show the result with and without jet trimming ($R_{\rm sub}=0.2$, $f_{\rm cut} = 0.02$).