Inclusive Jet Production at the Tevatron and the Search for

							    Inclusive Jet Production at the Tevatron, PDFs,
            and the Search for New Physics
                              Hung-Liang Lai
         Taipei Municipal Teachers College, TAIWAN
 •Motivation/Introduction
 •Uncertainty analysis of the inclusive jet x-section
 at the Tevatron
 •Reliability of NLO prediction
 •Room for new Physics
 •Prediction for Run II
 •Summary

Work in collaboration with: J. Huston, S. Kuhlmann, J. Owens, J. Pumplin,
D. Stump, and W.K.Tung. (arXive: hep-ph/0303013)
Hung-Liang Lai (hllai@tmtc.edu.tw)             Talk given at Hard QCD session, EPS03
                   Motivation/Introduction

 • Jet production cross-sections at hadron colliders probe the
   shortest distances available in the laboratories.
• Jet X-section is sensitive to Gluon distribution.

• Better determination of G(x,Q) provides better predictions
  of many new physics processes at higher energies.

• Any deviation from QCD predictions at high energies can
  indicate signals for new physics.
Uncertainties of PDFs:   CTEQ6
Subprocess contributions to jet production
                      Quantifying uncertainties
        Systematic error propagation and uncertainty studies:

– Effective (Hessian and Lagrangian) methods in the Global Analysis
  context developed by Pumplin, Stump, et.al. (CTEQ): These were first
  applied to the CTEQ5/6 analyses (2001/2002);
– They have now also been adopted by the MRST2002 analysis.



                                                                CTEQ: JHEP
                                                                2002 0207:012




MRST: hep- ph/                       HEPDATA: http://durpdg.dur.ac.uk/hepdata/pdf3.html
0211080
        Current Hadronic inclusive jet cross-section
     (Tevatron Run I) and Parton uncertainties (CTEQ6.1)

D0                    D0                    D0




             D0




                                                    CDF
             D0
Range of gluon distribution spanned by
    eigenvector sets 15- and 15+
        Theoretical uncertainties on Jet Inclusive Xsec

                               (effect is largest at large rapidities)




“NLO + 2-loop”: based on threshold resummation results of:
Comparison of gluon distributions fitted in
            different scales
                       Limits on New Physics




                                                     L = 1.6, 2.0,
                                                         2.4 TeV


Curves: New Physics with (effective) contact term interactions.

Calculation involves re-doing the global fits with the new interaction
Comparison: prediction vs. first data from Tevatron Run II




• 8 orders of magnitude!
• Highest ET jets ever!    (CDF collaboration, hep-ex/0304211)
Comparison: prediction vs. preliminary data -- linear plot




  Good agreement (within uncertainties)
(D0 collaboration, hep-ex/0305072)
                          Summary

•The uncertainties on the jet cross section predictions still
remain sizable, primarily due to the uncertainty on gluon.
They are comparable to current experimental uncertainties.

•With better consistency between experimental data and
theoretical calculations, we have produced an improved
version of the CTEQ6 PDFs --- CTEQ6.1.

•Scale dependence and higher order corrections are
estimated to be well within the PDF uncertainty band.

•The allowed range for any new physics such as compositeness
model must have a scale larger than 1.6 TeV, given the Run 1
jet data.