We present a new preliminary measurement of the inclusive jet cross section
in pp-bar collisions based on a integrated luminosity of about 0.8 fb-1. The
data were acquired using the D0 detector between 2002 and 2005. Jets are
reconstructed using an iterative cone algorithm with radius R_cone = 0.7. The
inclusive jet cross section is presented as a function of transverse jet
momentum and rapidity. Predictions from perturbative QCD in next-to-leading
order, plus threshold corrections in 2-loop accuracy describe the shape in the
transverse jet momentum.Comment: 4 pages, 4 figures; proceedings of the DIS 2006 worksho

Voutilainen, M.

English

arXiv

We present a new preliminary measurement of the inclusive jet cross section in pp collisions based on a integrated luminosity of about 0.8 fb-1. The data were acquired using the DØ detector between 2002 and 2005. Jets are reconstructed using an iterative cone algorithm with radius Rcone = 0:7. The inclusive jet cross section is presented as a function of transverse jet momentum and rapidity. Predictions from perturbative QCD in next-to-leading order, plus threshold corrections in 2-loop accuracy describe the shape in the transverse jet momentum

DigitalCommons@University of Nebraska

University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Faculty Publications, Department of Physics and Astronomy Research Papers in Physics and Astronomy 2006 INCLUSIVE JET CROSS SECTION MEASUREMENT AT DØ M. Voutilainen Follow this and additional works at: https://digitalcommons.unl.edu/physicsfacpub This Article is brought to you for free and open access by the Research Papers in Physics and Astronomy at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Faculty Publications, Department of Physics and Astronomy by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. June 30, 2006 17:9 Proceedings Trim Size: 9in x 6in hfs-voutilainenINCLUSIVE JET CROSS SECTION MEASUREMENT AT DØM. VOUTILAINEN FOR THE DØ COLLABORATIONUNIVERSITY OF NEBRASKA IN LINCOLN,HELSINKI INSTITUTE OF PHYSICSFermilab — DØ M.S. 357,Batavia, IL 60510-0500, USAE-mail: mavoutil@fnal.govWe present a new preliminary measurement of the inclusive jet cross section inpp¯ collisions based on a integrated luminosity of about 0.8 fb−1. The data wereacquired using the DØ detector between 2002 and 2005. Jets are reconstructedusing an iterative cone algorithm with radius Rcone = 0.7. The inclusive jet crosssection is presented as a function of transverse jet momentum and rapidity. Predic-tions from perturbative QCD in next-to-leading order, plus threshold correctionsin 2-loop accuracy describe the shape in the transverse jet momentum.1. IntroductionThe production of particle jets in hadron collisions is described by thetheory of Quantum Chromodynamics (QCD). When the transverse jet mo-mentum with respect to the hadron beam direction (pT ) is large, the contri-butions from long-distance physics processes with low pT are small and theproduction rates of jets can be predicted by perturbative QCD (pQCD).The inclusive jet cross section in pp¯ collisions at large pT is directly sensi-tive to the strong coupling constant (αs) and the parton density functions(PDFs) of the proton. Furthermore, potential deviations from the pQCDprediction at high pT , not explained by PDFs, may indicate new physicsbeyond the Standard Model.2. Jet energy scaleThe inclusive jet cross section is measured in two central rapidity regions|yjet| < 0.4 and 0.4 < |yjet| < 0.8. We note that the data are corrected forunderlying events when the jet energy scale is computed usingEptcl =Ecal −OR · S , (1)1FERMILAB-CONF-06-342-EJune 30, 2006 17:9 Proceedings Trim Size: 9in x 6in hfs-voutilainen2where O is the offset contribution, R is the response of the particle jet andS is the net showering due to detector effects. The jet energy scale correctsfor “offset” energies measured using zero-bias events which correspond touranium noise (jets are measured with a liquid Argon-Uranium calorime-ter), pile-up effects and underlying events because these effects cannot bedistinguished experimentally. The electromagnetic calorimeter is calibratedusing the Z peak in Z→ e+e− events. The energy scale of the electromag-netic calorimeter is transferred to photons in γ+jets events, with photonpurity and relative photon–electron energy scale mostly compensating eachother. The absolute jet energy scale is assigned using the transverse mo-mentum balance between the jet and the photon in the γ+jets events. Thedetector pseudorapidity dependence of the jet energy scale was determinedusing both dijet and isolated photon plus jet events. Detector effects causesome of the particle jets energy to be showered outside the cone, or outsideenergy to be showered inside the cone. The net effect is accounted for bymeasuring the energy density profile around the jet, subtracting from thisthe contribution to the showering due to physics effects from Monte Carlo.3. Jet pT resolution and unfoldingJet pT resolution is measured on a subsample of the same dataset as is usedfor cross section measurement using dijet asymmetryA =|pT,1 − pT,2|pT,1 + pT,2, (2)which is corrected for soft radiation of additional jets below jet reconstruc-tion threshold and for particle level imbalance.Spectra in pT are fit, in an iterative procedure, with parameterizedansatz functions,f(N, α, β, γ) = N(pT /GeV)−α(1− 2 cosh(ymin)pT√s)βexp(−γpT ), (3)where ymin is the minimum absolute rapidity in the bin and√s is thecenter-of-mass energy, and folded with resolutions determined from data.Ratios of the original to the folded ansatz functions are used to correct thedata for folding of resolution effects. The results were cross-checked withanother method using PYTHIA1 smeared according to the jet pT and yresolutions.June 30, 2006 17:9 Proceedings Trim Size: 9in x 6in hfs-voutilainen34. ResultsThe cross section is measured using seven different jet triggers, as shownin Fig. 1. The different triggers are matched together using relative triggerefficiencies and the cross section is corrected for jet identification and eventselection efficiencies. The partially corrected spectrum and the final resultcorrected for pT resolution are shown in Fig. 1. The measurement is nor-malized to theory at pT =100 GeV/c in |yjet| < 0.4 to remove luminosityuncertainty. The agreement with pQCD is good over the wide pT regionexplored. (GeV/c)Tp0 100 200 300 400 500 600 700 (pb/(GeV/c))T/dpσpartially corrected d-410-310-210-110110210310410510610Jet 8 GeV, P=26142Jet 15 GeV, P=6186Jet 25 GeV, P=306Jet 45 GeV, P=21Jet 65 GeV, P=4.9Jet 95 GeV, P=1.3Jet 125 GeV, P=1-1L ~ 0.8 fb| < 0.4jet|yDØ Run II preliminary (GeV/c)Tp50 100 200 300dy (pb/(GeV/c))T/dpσ2 d-410-310-210-110110210310410510| < 0.4 (x10)jet |y| < 0.8jet 0.4 < |yNLO pQCDplus threshold corrections (2-loop)Hadronization corrections appliedT = pFµ = RµCTEQ6.1M      = 1.96 TeVs-1L ~ 0.8 fb = 0.7coneRDØ Run II preliminaryFigure 1. Partially corrected inclusive jet cross section in central rapidity, measuredwith different jet triggers at different pT thresholds (left). The inclusive jet cross section,measured in two regions of jet rapidity (right). Error bars show the total measurementuncertainty. The predictions from pQCD are corrected for hadronization effects and areoverlaid on the data as lines.The cross section measurement is compared to next-to-leading order(NLO) theory with threshold corrections in 2-loop approximation2 in Fig. 2in two regions of jet rapidity. The NLO calculations were performed us-ing NLOJet++3 and FastNLO4. The PDF uncertainty from CTEQ6.1M5is overlaid as dashed red lines, showing that the measurement is gettingprecise enough to constrain the PDFs at high pT . Most of the PDF uncer-tainty at high pT is coming from the uncertainty in the gluon PDFs at highmomentum fraction x. The next-to-leading order theory without thresholdcorrections is also shown as a dash-dotted blue line.June 30, 2006 17:9 Proceedings Trim Size: 9in x 6in hfs-voutilainen4 (GeV/c)Tp0 100 200 300 400 500 600 700data / theory00.511.522.5data / theory = 0.7cone  CTEQ6.1M   RT = pR,FµNLO  Hadronization corrections appliedData scaled to theory for CTEQ6.1M|<0.4jet=100 GeV/c at |yTat pto remove luminosity uncertainty with threshold corrections PDF uncertainty without threshold corrections| < 0.4jet|y -1L ~ 0.8 fbDØ Run II preliminary (GeV/c)Tp0 100 200 300 400 500 600data / theory00.511.522.5data / theory = 0.7cone  CTEQ6.1M   RT = pR,FµNLO  Hadronization corrections appliedData scaled to theory for CTEQ6.1M|<0.4jet=100 GeV/c at |yTat pto remove luminosity uncertainty with threshold corrections PDF uncertainty without threshold corrections| < 0.8jet0.4 < |y -1L ~ 0.8 fbDØ Run II preliminaryFigure 2. Inclusive jet cross section over theory, measured in two regions of jet rapidity.Error bars and band show statistical and systematic uncertainty, respectively.5. ConclusionPreliminary results on the inclusive jet cross section measurements at DØwere shown with 0.8 fb−1 of collected luminosity. The results are in goodagreement with the next-to-leading order perturbative QCD calculations.The measurement is sensitive to the quark and gluon contents in the protonand allows one to reduce the gluon density uncertainty at high momentumfraction. This is one of the leading limitations of beyond Standard Modelsearches at the Tevatron and the LHC.AcknowledgementsI thank my colleagues at DØ and acknowledge support from the GraduateSchool in Particle and Nuclear Physics, the Finnish Cultural Foundationand Magnus Ehrnrooth Foundation.References1. T. Sjo¨strand et al., Comp. Phys. Comm. 135, 238 (2001).2. N. Kidonakis, J.F. Owens, Phys. Rev. D63, 054019 (2001)3. Z. Nagy, Phys. Rev. Lett. 88, 122003 (2002);Z. Nagy, Phys. Rev. D 68, 094002 (2003).4. T. Kluge, K. Rabbertz, M. Wobisch, publication in preparation,http://hepforge.cedar.ac.uk/fastnlo/5. J. Pumplin et al., JHEP 0207, 12 (2002);D. Stump et al., JHEP 0310, 046 (2003).

INCLUSIVE JET CROSS SECTION MEASUREMENT AT DØ

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