
Primary contacts:
Kenichi Hatakeyama^{1}, Anwar Bhatti^{1},
Robert Harris^{2}
Rockefeller University^{1}
Fermilab^{2}
for the CDF Collaboration
Submitted to PRD:
arXiv:0812.4036
FIG. 1: (a) The measured dijet mass spectrum for both jets
to have y < 1 compared to the NLO pQCD prediction obtained
using the CTEQ6.1 PDFs. (b) The ratio of the data
to the NLO pQCD prediction. The experimental systematic
uncertainties, theoretical uncertainties from PDF, the ratio of
MRST2004/CTEQ6.1, and the dependence on the choice of
renormalization and factorization scales are also shown.
An additional 6% uncertainty in the determination of the luminosity
is not shown. [eps gif]  
FIG. 2: (a) The measured dijet mass spectrum (points) fitted
to Eq. (2) (dashed curve). The binbybin unfolding corrections
is not applied. Also shown are the predictions from the
excited quark, q^{*}, simulations for masses of 300, 500, 700,
900, and 1100 GeV/c2, respectively (solid curves). (b) The
fractional difference between the measured dijet mass distri
bution and the fit (points) compared to the predictions for
q^{*} signals divided by the fit to the measured dijet mass spec
trum (curves). The inset shows the expanded view in which
the vertical scale is restricted to +/0.04. [eps gif]  
FIG. 3: Dijet mass distributions for simulated signals of the
q^{*}, RS graviton, W', and Z' with the mass of 800
GeV/c^{2}. [eps gif]  
FIG. 4: Observed 95% C.L. upper limits on new particle
production cross sections times the branching fraction to dijets
obtained with the signal shapes from (a) W', (b) Z', (c) RS
graviton, and (d) q^{*} production. Also shown are
the cross section predictions for the production of W', Z', RS graviton,
#rho_{T8}, q^{*}, axigluon, flavoruniversal coloron,
and E6 diquark for the set of parameters described in the text.
The limits and theoretical predictions are for events in which both of
the leading two jets have y < 1. [eps gif] 
Dijet mass distributions from QCD and expected signals  

Excited quark: Dijet mass spectrum expected from QCD and excited quark production with excited quark mass=300, 500, 700, 900, and 1100 GeV/c^{2}. The excited quark decaying to a quarkgluon pait is simulated with Pythia with f=f'=f_{s}=1. [eps gif] W': The W' production is simulated with Pythia with SM couplings. The W' production cross section is multiplied by a factor of 1.3 to account for the kfactor. [eps gif] Z': The Z' production is simulated with Pythia with SM couplings. The Z' production cross section is multiplied by a factor of 1.3 to account for the kfactor. [eps gif] RandallSundrum graviton: The RS graviton production is simulated with Pythia with k/M_{PL}=0.1. The RS graviton production cross section is multiplied by a factor of 1.3 to account for the kfactor. [eps gif]  
Dijet mass distribution from four models that produce dijet mass resonances  
Dijet mass distribution from four models that produce dijet
mass resonances.
[eps gif]  
Test of a parametrization form used for modeling QCD production with Pythia and Herwig dijet MC samples  
The dijet mass spectra from Pythia and Herwig Monte Carlo
and fits to the parametrization form: Pythia [eps gif] Herwig [eps gif] (Note: these spetra are the "detectorlevel" dijet mass distributions, not corrected to the particlelevel.)  
Dijet mass distribution from data and fit to a parametrization form  
The measured dijet mass spectrum and results of a fit to the
parametrization form: [eps gif] No significant indication of resonant structure is observed. (Note: this measured spetrum is the "detectorlevel" dijet mass distribution, not corrected to the particlelevel.)  
Effect of systematic uncertainties on limits for new particle production decaying into dijets.  

The four parameters in the parametrization form (shown above)
are not a priori
determined. When forming likelihood distributions as function
of signal cross sections at each new particle mass, the
likelihood is maximized keeping these four parameters free
(profiling). The other systematic uncertainties from (1) jet energy scale (JES), (2) jet energy resolution, (3) luminosity, (4) trigger prescale, and (5) trigger efficiency are folded into the likelihood by the Bayesian approach. The effects of these systematic uncertainties on the limits are shown in: top [eps gif] bottom [eps gif] 
Limits on production of new particles decaying into dijets.  

[top]
95% C.L. limits on the RandallSundrum graviton and coloroctet
technirho producion (red), and limits on the
excited quark, axigluon, flavoruniversal coloron,
and E_{6} diquark (black), compared with
the theoretical predictions for these particle
production. [eps gif] [bottom] 95% C.L. limits on the W' and Z' production compared with their theoretical predictions. [eps gif] The shown cross section predictions and limits are for the total particle production cross section times branching fraction to dijets times the kinematic acceptance that the leading two particlelevel jets are within y(jet1,2)<1. 
Observed mass exclusion range  Model description 
260870 GeV/c^{2}  Excited quark (f=f'=fs=1) 
2601100 GeV/c^{2}  Coloroctet technirho [topcolorassistedtechnicolor (TC2) couplings, M'_{8}=0, M(pi_{22}^{8})=5M(rho)/6, M(pi_{22}^{1})=M(pi_{22}^{8})/2, M_{8}=5M(rho)/6] 
2601250 GeV/c^{2}  Axigluon and flavoruniversal coloron (mixing of two SU(3)'s, cot(theta)=1) 
290630 GeV/c^{2}  E_{6} diquark 
280840 GeV/c^{2}  W' (SM couplings) 
320740 GeV/c^{2}  Z' (SM couplings) 