Multiple Jet Production at Low Transverse Energies in p-pbar Collisions at Root(s) = 1.8 TeV

TL;DR

This study probes multi-jet production at low transverse energy $E_T$ in $p\bar{p}$ collisions at $\sqrt{s}=1.8$ TeV, comparing parton-shower QCD predictions from PYTHIA and HERWIG to next-to-leading order results from JETRAD across 1–4 jets. The authors find that shower-based Monte Carlos reproduce the data well after tuning (notably enhancing multiple parton interactions), while the NLO approach struggles to describe angular distributions in three-jet events. Key observables include leading-jet $E_T$ spectra, azimuthal separations, and $Q_T^2$ distributions, all indicating a significant role for the underlying event and higher-order radiation in low-$E_T$ jet production. The results support the necessity of accurate modeling of multiple parton interactions in interpreting low-$E_T$ jet data at hadron colliders.

Abstract

We present data on multiple production of jets with transverse energies near 20 GeV in p-pbar collisions at Root(s) = 1.8 TeV. QCD calculations in the parton-shower approximation of PYTHIA and HERWIG and the next-to-leading order approximation of JETRAD are compared to the data for one, two, three, and four jet inclusive production. Transverse energy spectra and multiple jet angular and summed transverse-energy distributions are adequately described by the shower approximation while next-to-leading order calculations describe the data poorly.

Figures (7)

• Figure 1: The transverse energy distributions of the leading jet for (a) single-inclusive, (b) two-jet inclusive, (c) three-jet inclusive, and (d) four-jet inclusive events. Solid histograms show the pythia simulation normalized (with a factor of 0.75) to the inclusive two-jet sample for $E_T$$>$ 40 GeV. Dotted histograms are similarly normalized herwig results (increased by a factor of 1.6).
• Figure 2: (Data $-$pythia)/ pythia as a function of the transverse energy of the leading jet for (a) single-jet inclusive, (b) two-jet inclusive, (c) three-jet inclusive, and (d) four-jet inclusive event samples. The relative systematic uncertainties in the cross section corresponding to the energy calibration added in quadrature with 15% uncertainty in luminosity are shown by the solid lines. The uncertainty in the ratio (Data $-$ MC) / MC from energy and angle smearing is shown by the dashed lines. The total uncertainty on the ratio is shown by the dotted lines.
• Figure 3: (Data $-$herwig)/ herwig as a function of the transverse energy of the leading jet for (a) single-jet inclusive, (b) two-jet inclusive, (c) three-jet inclusive, and (d) four-jet inclusive event samples. The relative systematic uncertainties in the cross section corresponding to the energy calibration added in quadrature with 15% uncertainty in luminosity are shown by the solid lines. The uncertainty in the ratio (Data $-$ MC) / MC from energy and angle smearing is shown by the dashed lines. The total uncertainty on the ratio is shown by the dotted lines.
• Figure 4: Distributions of the relative azimuthal angle between two jets in (a) two-jet inclusive events and in three-jet inclusive events (b--d). Jets are ordered by their transverse energies. The pythia predictions are indicated by the solid histograms and the herwig predictions by the dotted histograms.
• Figure 5: Distributions of the square of the summed vector transverse momenta $Q_{T}^2$, for (a) two-jet inclusive, (b) three-jet inclusive, and (c) four-jet inclusive event samples. The pythia predictions are indicated by the solid histograms and the herwig predictions by the dotted histograms.