Study of Jet Shapes in Inclusive Jet Production in ppbar Collisions at sqrt{s} = 1.96 TeV

TL;DR

This paper presents a detailed measurement of differential and integrated jet shapes in inclusive jet production from CDF II Run II data, spanning jets with $37\le P_T^{\rm jet} \le 380$ GeV/c and central rapidities. By unfolding CAL jet shapes to the hadron level and comparing to LO MC predictions, the study demonstrates that PYTHIA-Tune A, which includes enhanced initial-state radiation and multiple parton interactions, best describes the data across the full $P_T^{\rm jet}$ range, while default PYTHIA and HERWIG have notable discrepancies tied to soft-gluon and underlying-event modeling. The results reveal that jet broadening is driven by the gluon/quark jet mix and the running of $\alpha_s$, with gluon jets dominating at low $P_T$ and diminishing at high $P_T$, offering stringent constraints on phenomenological models of soft QCD and the underlying event. Overall, jet-shape observables provide a sensitive probe of parton cascades and UE dynamics in hadron-hadron collisions and help refine MC tools used in high-energy physics analyses.

Abstract

We report on a study of jet shapes in inclusive jet production in $p \bar{p}$ collisions at $\sqrt{s} = 1.96 {\rm TeV}$ using the upgraded Collider Detector at Fermilab in Run II (CDF II) based on an integrated luminosity of $170 \rm pb^{-1}$. Measurements are carried out on jets with rapidity $0.1 < |Y^{\rm jet}| < 0.7$ and transverse momentum 37 GeV/c $< P_T^{\rm jet} < 380$ GeV/c. The jets have been corrected to the hadron level. The measured jet shapes are compared to leading-order QCD parton-shower Monte Carlo predictions as implemented in the PYTHIA and HERWIG programs. PYTHIA, tuned to describe the underlying event as measured in CDF Run I, provides a better description of the measured jet shapes than does PYTHIA or HERWIG with their default parameters.

Figures (9)

• Figure 1: Longitudinal view of half of the CDF II detector.
• Figure 2: The measured differential jet shape, $\rho(r/R)$, in inclusive jet production for jets with $0.1 < |Y^{\rm jet}| < 0.7$ and $37 \ {\rm GeV/c} < P_T^{\rm jet} < 148 \ {\rm GeV/c}$, is shown in different $P_T^{\rm jet}$ regions. Error bars indicate the statistical and systematic uncertainties added in quadrature. The predictions of PYTHIA-Tune A (solid lines) and HERWIG (dashed lines) are shown for comparison.
• Figure 3: The measured differential jet shape, $\rho(r/R)$, in inclusive jet production for jets with $0.1 < |Y^{\rm jet}| < 0.7$ and $148 \ {\rm GeV/c} < P_T^{\rm jet} < 380 \ {\rm GeV/c}$, is shown in different $P_T^{\rm jet}$ regions. Error bars indicate the statistical and systematic uncertainties added in quadrature. The predictions of PYTHIA-Tune A (solid lines) and HERWIG (dashed lines) are shown for comparison.
• Figure 4: The measured integrated jet shape, $\Psi(r/R)$, in inclusive jet production for jets with $0.1 < |Y^{\rm jet}| < 0.7$ and $37 \ {\rm GeV/c} < P_T^{\rm jet} < 148 \ {\rm GeV/c}$, is shown in different $P_T^{\rm jet}$ regions. Error bars indicate the statistical and systematic uncertainties added in quadrature. The predictions of PYTHIA-Tune A (solid lines), PYTHIA (dashed-dotted lines), PYTHIA-(no MPI) (dotted lines) and HERWIG (dashed lines) are shown for comparison.
• Figure 5: The measured integrated jet shape, $\Psi(r/R)$, in inclusive jet production for jets with $0.1 < |Y^{\rm jet}| < 0.7$ and $148 \ {\rm GeV/c} < P_T^{\rm jet} < 380 \ {\rm GeV/c}$, is shown in different $P_T^{\rm jet}$ regions. Error bars indicate the statistical and systematic uncertainties added in quadrature. The predictions of PYTHIA-Tune A (solid lines), PYTHIA (dashed-dotted lines), PYTHIA-(no MPI) (dotted lines) and HERWIG (dashed lines) are shown for comparison.