A Comparison of Three-jet Events in p-pbar Collisions to Predictions from a Next-to-leading Order QCD Calculation

Contacts: Sally Seidel (seidel@phys.unm.edu) and Igor Gorelov (gorelov@fnal.gov)

Abstract

Features of the Run 1b inclusive three-jet sample are compared to predictions by the NLO Monte Carlo event generator of Kilgore and Giele (hep-ph/0009193). This analysis is documented in CDF notes 4948, 5419, 5977, 6124, 6225, and 6275. The draft of the paper is CDF note 7003.

Data selection and validation

Distributions of the data after all cuts have been applied

pic_x3x4_raw.mnypts.03.eps Paper Figure 1: The three-jet data, after all selection requirements have been applied but unsmearing has not yet been applied. The figures at the corners of the distribution represent typical three-jet topologies in those regions of the Dalitz plane.

pic_x3x4_unsm.03.eps Paper Figure 2: The event density in the Dalitz plane for the data (a), and as predicted by the NLO Monte Carlo calculation with CTEQ4M (b), normalized to luminosity.

Unsmearing and checks with HERWIG

k.eps The unsmearing factor, K, for bins of size (0.02 x 0.02) in the Dalitz plane.

x3utt.eps The fractional difference between the unsmeared simulated independent HERWIG sample's $X_3$ distribution and its true $X_3$ distribution.

x4utt.eps The fractional difference between the unsmeared simulated independent HERWIG sample's $X_4$ distribution and its true $X_4$ distribution.

totnjets_hw60.eps The number of jets in each event for the data and for HERWIG.

X3X4DatHerw60.eps The number of events in the data and in the HERWIG simulation as a function of $X_3$ (upper) and $X_4$ (lower) for events with three-jet mass $M_{\rm 3jet} > 500$ GeV/c$^2$.

totsetjet_hw60.eps The $\sum {\rm E_{T}}$ in each event after application of all event selection criteria to the data and to the HERWIG events.

Tabulated unsmearing factors.

Luminosity and multiple interactions correction

lum.eps Instantaneous luminosity for the CDF data used in this analysis. The total integrated luminosity is 86~$\pm$~4~pb$^{-1}$.

lumfrac.eps The fraction of events with two or more vertices in the $\sum {\rm E_{T}}$ data sample as a function of instantaneous luminosity.

vertcut.eps The change in the number of vertices in the data due to the rejection of resolved multiple interactions.

lumimul_z.eps Instantaneous luminosity (left) and jet multiplicity (right) for the Run 1b three-jet event sample with resolved (upper) secondary interaction vertices and for the remainder (``unresolved'') of the dataset.

multprof_y.eps Jet multiplicity as a function of instantaneous luminosity for resolved (lower) and unresolved (upper) subsamples. Linear fits to the data are shown.

Systematics

tot1_2_l.eps The total systematic uncertainty on the Dalitz variables as a function of X$_{3}$ for 0.74$<$X$_{4} \leq$0.98.

tot3_4_l.eps The total systematic uncertainty on the Dalitz variables as a function of X$_{3}$ for 0.50$<$X$_{4} \leq$0.74.

Tabulated systematic uncertainty information.

Cross section measurements and predictions

tables.ps

Comparison of data to theory using CTEQ4

CTEQ4A Results

dnc4m_abs_fig4567.332.eps Paper Figure 4: The fractional difference between corrected data and the NLO prediction, using the CTEQ4M parton distribution function, as a function of $X_3$ for various $X_4$ bins. Error bars reflect statistical uncertainty in cases in which it is larger than the size of the symbol used. Shaded bands indicate systematic uncertainty. The prediction is normalized to the luminosity of the data.

xc4a1.eps The event density in the Dalitz plane as predicted by the NLO calculation with CTEQ4A1.

xc4a2.eps The event density in the Dalitz plane as predicted by the NLO calculation with CTEQ4A2.

xc4m.eps The event density in the Dalitz plane as predicted by the NLO calculation with CTEQ4M.

xc4a4.eps The event density in the Dalitz plane as predicted by the NLO calculation with CTEQ4A4.

xc4a5.eps The event density in the Dalitz plane as predicted by the NLO calculation with CTEQ4A5.

pic_av3frac_10.14.eps Paper Figure 3: The fractional difference between the data and the theoretical prediction, using CTEQ4M, as a function of $X_4$, averaged over $X_3$. The vertical bands show the systematic uncertainties. The error bars show the statistical uncertainties. The prediction is normalized to the data to facilitate a comparison of the shapes of the distributions.

chi2_dat_c4.eps The $\chi^{2}$ between the data and the NLO calculation for different values of $\alpha_{\rm S}$, using appropriate parton distribution functions from the CTEQ4 family. This definition of the $\chi^2$ includes the experimental and theoretical statistical uncertainties but does not include the systematics associated with absence of the higher order terms in the perturbation series, with the choice of scale, and with the choice of PDF.

Last updated May 12, 2004