Inclusive Jet Production at the Tevatron, PDFs, and the Search for New Physics

•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

Hung-Liang Lai

Taipei Municipal Teachers College, TAIWAN

Work in collaboration with: J. Huston, S. Kuhlmann, J. Owens, J. Pumplin, D. Stump, and W.K.Tung. (arXive: hep-ph/0303013)

Talk given at Hard QCD session, EPS03Hung-Liang Lai (hllai@tmtc.edu.tw)

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 uncertaintiesSystematic error propagation and uncertainty studies:

CTEQ: JHEP 2002 0207:012

HEPDATA: http://durpdg.dur.ac.uk/hepdata/pdf3.htmlMRST: hep- ph/ 0211080

– 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.

D0 D0 D0

D0

D0

Current Hadronic inclusive jet cross-section (Tevatron Run I) and Parton uncertainties (CTEQ6.1)

CDF

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

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

Calculation involves re-doing the global fits with the new interaction

= 1.6, 2.0, 2.4 TeV

• 8 orders of magnitude!

• Highest ET jets ever!

Comparison: prediction vs. first data from Tevatron Run II

(CDF collaboration, hep-ex/0304211)

Good agreement (within uncertainties)

Comparison: prediction vs. preliminary data -- linear plot

(D0 collaboration, hep-ex/0305072)

Summary

•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.

•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.