An overview of Run I jet physics at the ppbar Fermilab Tevatron Collider with
a particular emphasis on inclusive jet cross section measurements is given. The
impact of these studies on PDFs constrain from global fits is underlined.
Preliminary results on inclusive jet and di-jet mass cross section measurements
in Run II are then summarized.Comment: Presented at 15th Conference on High-Energy Physics (IFAE 2003),
  Lecce, Italy, 23-26 Apr 200

Latino, Giuseppe

English

arXiv

An overview of Run I jet physics at the p{bar p} Fermilab Tevatron Collider with a particular emphasis on inclusive jet cross section measurements is given. The impact of these studies on PDFs constrain from global fits is underlined. Preliminary results on inclusive jet and di-jet mass cross section measurements in Run II are then summarized

Latino, G.

UNT Digital Library

Fermilab FERMILAB-Conf-03/391-E  December 2003JET PHYSICS AT TEVATRONGiuseppe Latino1(On behalf of the CDF and D 6O Collaborations)Department of Physics and Astronomy, University of New Mexico,800 Yale Blvd. NE, Albuquerque NM 87131, USAAbstractAn overview of Run I jet physics at the pp Fermilab Tevatron Collider with aparticular emphasis on inclusive jet cross section measurements is given. Theimpact of these studies on PDFs constrain from global ts is underlined. Pre-liminary results on inclusive jet and di-jet mass cross section measurementsin Run II are then summarized.1 IntroductionJet measurements at the Fermilab Tevatron Collider represent a fundamentaltest of next-to-leading order perturbative QCD (NLO pQCD) at the highestcenter-of-mass energy so far probed. Consequently, they are potentially sen-sitive to new phenomena beyond the Standard Model, the existence of newparticles as well as of new interactions down to a distance scale of  10 19m being expected to be revealed by deviations from theory. Furthermore,these measurements allow the extraction on a wider kinematical range of thefundamental parameters of QCD: s and the parton distribution functions(PDFs).2 Run I Results: Inclusive Jet Cross SectionDuring Run I, the CDF [1] and D 6O [2] Collaborations performed several jetmeasurements as part of their physics program at the Tevatron. Stringent1latino@fnal.gov1tests of LO and NLO pQCD were obtained from the study of nal stateswith high ET jets: inclusive jet and di-jet dierential cross sections, di-jetmass, di-jet angular and multijet distributions as well as the Z/W + jetsproduction cross sections were among the most signicant measurements tobe compared with theory. In general, QCD predictions gave a reasonabledescription of the observed data.10-610-510-410-310-210-111010 250 100 150 200 250 300 350 400Transverse Energy  (GeV)nb/GeVNLO QCD prediction (EKS)cteq4m  µ=Et/2  Rsep=1.3Statistical Errors Only1994-951992-93Figure 1: Inclusive jet cross section as measured in CDF [5] (left) and D 6O [6](right) respectively using 87 and 95 pb 1 of Run I data atps = 1.8 TeV.However, great interest was raised when initial inclusive jet cross sectionmeasurements showed an excess of data at high ET over NLO theoreticalpredictions using then-current PDFs [3]. Global PDF analyses by CTEQ [4]have demonstrated that such excess can be explained in terms of a largerthan expected gluon distribution at high x, a kinematical region were itis not yet well constrained. Subsequent measurements performed with anincreased data sample [5, 6] (see g. 1) showed a better data-theory agreementwhen PDFs with an increased high x gluon contribution (CTEQ4HJ) wereconsidered in the NLO calculations. Given the exibility allowed by currentknowledge of PDFs, CDF and D 6O data were found to be consistent betweenthem, with previous results and with NLO pQCD.Furthermore, results from these analyses have been used in most recentglobal PDFs ts where an enhanced statistical weight was given to Tevatronhigh ET jet data in order to determine the high x gluon contribution. Inparticular, by involving jets in a range of rapidity intervals, the D 6O mea-surement allowed to constrain the partons over a much wider x range (seeg. 2: left). These new PDFs sets (CTEQ6 [7] and MRST01 [8]) representthe most complete information available for Run II jet predictions, but arestill characterized by a big uncertainty on high x gluon distributions (seeg. 2: right). Run II jet measurements are expected to reduce this uncer-tainty before the LHC era.Figure 2: Left: kinematical reach of CDF and D 6O in the x Q2 plane as comparedto other collider and xed target experiments [6]. Right: uncertainty band for thegluon distribution function at Q2 = 10 GeV2 in the CTEQ6M set [7]; comparisonsto CTEQ5M1 (solid), CTEQ5HJ (dashed) and MRST01 (dotted) are also shown.3 Preliminary Run II Jet MeasurementsQCD jet studies at Tevatron are expected to be greatly extended in RunII considering both the larger collected data samples and the higher crosssection which is related to the increase of the center-of-mass energyps from1.8 to 1.96 TeV. The improved performances of the upgraded CDF and D 6Odetectors are also expected to play a role.Both experiments have recently performed preliminary Run II measure-ments of the inclusive jet and di-jet mass cross sections. In order to comparethe results at dierentps, CDF adopted the same analysis techniques asin Run I. In particular, the same cone algorithm (JetClu [9], R = 0.7) andcorrection procedures (but Run II updated) were used in order to reconstructjets and to properly correct them by taking into account both detector andphysics eects. The same jet pseudorapidity ranges were also considered.D 6O performed two completely new analyses. For both of them, central (jj< 0.5) jets were reconstructed with an \optimized" cone algorithm (Mid-Point [10], R = 0.7) and then corrected with a new set of jet corrections asderived from -jet and di-jet balancing studies on data [11]. Results fromthe inclusive jet cross sections measurements are shown in g. 3: in both ex-periments, a reasonably good agreement is found within errors between dataand NLO pQCD theory using the latest CTEQ PDFs sets [7]2. A reasonable2Similar results were also found by D 6O using the MRST01 set [8].agreement was also observed, within errors, between data and theory for thedi-jet mass cross section measurement. Systematic uncertainties were foundto be dominanted by the error on jet energy scale in data and on high x gluondistribution function in theoretical calculations.Rened analysis techniques, a sensible increase in Run II data samplesand a better understanding of Run II CDF and D 6O detectors performances,are expected to update and improve the very preliminary results reportedhere. (GeV)TInclusive Jet E0 100 200 300 400 500 600 (nb/GeV)η dT / dEσ2d10-810-710-610-510-410-310-210-1110102CDF Run II PreliminaryIntegrated L = 85 pb -10.1 < |ηDet| < 0.7JetClu Cone R = 0.7Run II DataCTEQ 6.1 Uncertainty+/- 5% Energy Scale UncertaintyFigure 3: Inclusive jet cross section as measured in CDF (left) and D 6O (right)respectively analyzing 85 and 34 pb 1 of Run II data atps = 1.96 TeV. The resultsare compared to the NLO pQCD prediction from EKS [12] ( = EJT=2, CTEQ6.1MPDFs) in CDF and JETRAD [13] ( = EmaxT=2, CTEQ6M PDFs) in D 6O.References[1] F. Abe et al., (CDF Coll.), Nucl. Instr. and Meth. A 271, 387 (1988).[2] S. Abachi et al., (D 6O Coll.), Nucl. Instr. and Meth. A 338, 185 (1994).[3] F. Abe et al., (CDF Coll.), Phys. Rev. Lett. 77, 438 (1996).[4] H.L. Lai et al., Phys. Rev. D 55, 1280 (1997).H.L. Lai et al., Eur. Phys. J. C12, 375 (2000).[5] F. Aolder et al., (CDF Coll.), Phys. Rev. D 64, 032001 (2001).[6] B. Abbott et al., (D 6O Coll.), Phys. Rev. Lett. 86, 1707 (2001).[7] J. Pumplin et al., JHEP, 0207 (2002).D. Stump et al., hep-ph/0303013 (2003).[8] A.D. Martin et al., hep-ph/0110215 (2001); hep-ph/0211080 (2002).[9] F. Abe et al., (CDF Coll.), Phys. Rev. D 45, 1448 (1992).[10] G. C. Blazey et al., hep-ex/0005012 (2000).[11] B. Abbott et al., (D 6O Coll.), Nucl. Instr. and Meth. A 424, 352 (1999).[12] S.D. Ellis et al., Phys. Rev. Lett. 64, 2121 (1990).[13] W.T. Giele et al., Phys. Rev. Lett. 73, 2019 (1994).

Jet Physics at Tevatron

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Jet Physics at Tevatron

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