Recent QCD jet production measurements in p-pbar collisions at sqrt(s)=1.96
TeV at the Tevatron Collider at Fermilab are presented. Preliminary: inclusive
jet, dijet, isolated photon + jet and Z + jets measurements are compared to
available perturbative QCD models.Comment: 4 pages, 5 figures, to appear in the proceedings of 42nd Recontres de
  Moriond on QCD and high energy hadronic interactions, La Thuile, Aosta
  Valley, Italy, 17-24 March 200

Cwiok, Mikolaj

English

arXiv

Recent QCD jet production measurements in p{bar p} collisions at {radical}s = 1.96 TeV at the Tevatron Collider at Fermilab are presented. Preliminary: inclusive jet, dijet, isolated photon + jet and Z + jets measurements are compared to available perturbative QCD models

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FERMILAB-CONF-07-208-ELATEST JET RESULTS FROM THE TEVATRONM. C´WIOK a(on behalf of CDF and DØ collaborations)University College Dublin, School of Physics, Belfield, Dublin 4, IrelandRecent QCD jet production measurements in pp¯ collisions at√s = 1.96 TeV at the TevatronCollider at Fermilab are presented. Preliminary: inclusive jet, dijet, isolated photon + jet andZ + jets measurements are compared to available perturbative QCD models.The production of particle jets with high transverse momenta in hadronic collisions is de-scribed in perturbative Quantum Chromodynamics (pQCD) as resulting from the hard scatteringof strongly interacting constituents of the colliding hadrons.Inclusive jet rates observed in hadronic collisions at high values of transverse momenta pro-vide a basic test of pQCD. The DØ and CDF collaborations1,2 have measured the inclusive jetproduction cross section using midpoint cone and kT algorithms3 using data corresponding tothe integrated luminosities of about 1 fb−1. The DØ result4 is shown in Figure 1 for two regionsof rapidityb (closed and open circles). The error bars correspond to the total measurement un-certainty. The data are corrected for the jet energy scale (JES) determined from isolated photonplus jets events, selection efficiencies and migrations due to pT resolution (an ansatz functionconvoluted with the jet pT resolution measured directly in data). The JES is the dominantsource of systematic uncertainty. The integrated luminosity is known with accuracy of 6%.The data are compared to the next-to-leading order (NLO) pQCD predictions computed usingNLOJET++5 with parton density functions (PDFs) from CTEQ6.1M,6 after applying thresholdcorrections at 2-loop (next-to-next-leading-logarithm) accuracy.7 The same jet algorithm wasused in the calculations and the pQCD predictions are also corrected for hadronization effectsusing PYTHIA.8 The theory describes the data well over the whole measured pT range in allaPresented at 42nd Recontres de Moriond on QCD and high energy hadronic interactions, La Thuile, AostaValley, Italy, 17-24 March 2007.bThe rapidity y is defined as y = − 12ln E+pzE−pzwhere E and pz denote the energy and the momentum componentalong the proton beam direction, respectively. (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 = 0.9 fb = 0.7coneRDØ Run II preliminary]2 [GeV/cjjM200 400 600 800 1000 1200 1400Data / Theory00.511.522.53-1 = 1.13 fbint|<1, Ljet1,2Midpoint, R=0.7, |y=1.3)sep, R0µ(jet1,2)/2=meanT=pµData / NLO (CTEQ6.1M, Systematic uncertaintiesPDF uncertainty from CTEQ(CTEQ6.1M)σ(MRST2004) / σ)0µ(σ) / 0µ(2 x σ=1.3)sep(Rσ) / sep(without RσCDF Run II Preliminary6 % luminosity uncertainty not included±Figure 1: The inclusive jet differential cross sectionmeasured in two regions of jet rapidity.Figure 2: The data/theory ratio for dijet inclusive crosssections as a function of the dijet invariant mass.rapidity regions. The experimental uncertainties are competitive with those from the protonPDFs and the data therefore further constrain the gluon density functions at high-x. Inclusivejet spectra measured by CDF are also in good agreement with the NLO pQCD predictions.9The rate of dijet event produced in hadronic collisions not only provides a test of pQCD butalso is sensitive to new physics such as compositeness and massive particles decays. The ratioof the dijet cross section measured by CDF to theory is shown as a function of dijet invariantmass (Mjj) in Figure 2. The measurement corresponds to 1.13 fb−1 and centrally producedjets. The jets were selected using midpoint cone algorithm.3 The error bars and shaded bandsrepresent the statistical and systematic uncertainties respectively. Theoretical predictions werecalculated using NLOJET++5 with PDFs from CTEQ6.1M6 and corrected to the hadron level.The systematic errors are comparable to the PDF uncertainties and NLO pQCD predictions areconsistent with the data over the whole measured Mjj range.The production rates of bb¯ jet pairs have also been studied by CDF using a data sample of260 pb−1. Such a measurement provides insight into b-quark direct production, flavour excitationand gluon splitting mechanisms and also allows a test of radiative gluon corrections. The selectedevents were first required to contain two jets with transverse energy above 20 GeV associated totwo displaced vertex tracks at the trigger level. A Run I cone algorithm3 was used to identifythe jets. Jets having a positively displaced secondary with respect to the jet axis were tagged as“SVT b-jets”. Two positively tagged jets with central pseudorapiditiesc and transverse energiesof a leading and a second jet above 35 and 32 GeV respectively were required. The invariantmass of the tracks associated to the secondary vertex was fitted using signal and backgroundMonte Carlo templates to determine the bb¯ purity of the final event sample. The resulting puritywas about 80%. The differential cross section measured as a function of the azimuthal anglebetween two jets (∆φjj), unfolded to the hadron level, is shown in Figure 3 (full squares). Theerror bars and shaded bands correspond to the measured statistical and systematic uncertaintiesrespectively. The data are compared to three theoretical models: two predictions at leadingorder (LO) from PYTHIA8 (Tune A) and HERWIG10 with PDFs from CTEQ5L11 and a NLOprediction from MC@NLO12 using CTEQ6.1M6 PDFs and with multiple parton interactionssimulated by JIMMY.13 The ∆φjj spectrum is sensitive to contributions arising from soft gluonradiation and therefore only the NLO pQCD model describes data reasonably well even at largedepartures from a back-to-back jet topology.cPseudorapidity η is defined as η = − ln tan θ2, where θ is the polar angle w.r.t. the proton beam direction. (rad)φ ∆0 0.5 1 1.5 2 2.5 3) [pb/rad]φ ∆ d(η/dσ2 d10210310410Data - systematicsPythia Tune A (CTEQ5L)Herwig (CTEQ5L)MC@NLO + Jimmy (CTEQ6.1M)-1 = 1.96 TeV, L = 260 pbs|<1.21.2η=0.4, |coneJetClu R>32 GeVT,2>35 GeV, ET,1ECDF Run II PreliminaryFigure 3: The differential bb¯ cross section as a function of the azimuthal angle between two jets.Photons produced directly in parton-parton QCD interactions arrive unaltered at the elec-tromagnetic calorimeter and carry clean information of the dynamics of the hard scatter. Atthe Tevatron prompt photon production is dominated by the Compton scattering subpro-cess qg → γq for photon transverse momenta pγT . 150GeV/c. The differential cross sectiond3σ/(dpγT dηγ dηjet) for the production of a photon and a jet measured by DØ using a 1.1 fb−1data sample is shown in Figure 4.14 The jets were reconstructed using a midpoint cone algorithm3and were required to have: transverse momenta pjetT > 15GeV/c and pseudorapidities either inthe central calorimeter (“CC”, |ηjet| < 0.8) or in the end cap (forward) calorimeter region (“EC”,1.5 < |ηjet| < 2.5). Photons were selected with transverse momenta 30 < pγT < 300GeV/c andcentral pseudorapidities |ηγ | < 1. Strong isolation criteria were imposed on photon candidatesin order to filter background events with neutral hadrons decaying to photons in the final state.The purity of the resulting sample was estimated with the help of an artificial neural networktrained to distinguish between direct photons and background. The measured cross section iscorrected for the finite resolution of the calorimeter. Events with a leading jet and a photoncontained in the same hemisphere in terms of their pseudorapidities are denoted as “SS” (samesign) while the remaining ones as “OS” (opposite sign). The four curves overlaid on the datarepresent the NLO pQCD predictions from JETPHOX15 with the choice of CTEQ6.1M6 PDFsand fragmentation functions.16 The theory qualitatively reproduces the data in some kinematicregions.Jets accompanied by W or Z vector bosons in pp¯ collisions constitute an important back-ground for top quark production, Higgs and SUSY searches. Their production rates are alsosensitive to physics beyond the Standard Model (compositeness and decays of heavy objects). Inaddition, Z+jets events are suitable for testing phenomenological models of the underlying eventin pp¯ collisions by studying integrated and differential jet shapes or energy flow with respect tothe momentum of a Z boson. The CDF collaboration studied production of Z+jets events withZ bosons decaying into e+e− pair using 1.1 fb−1 of data. Such a channel provides much cleanerexperimental signature than W+jets one, albeit has 10 times smaller cross section. The anal-ysis covered the following kinematic region: jets reconstructed using midpoint cone algorithm3having pjetT > 30GeV/c and |ηjet| < 2.1, electrons with Ee 1,2T > 25GeV, |ηe 1| < 1, |ηe 2| < 2.8and isolated from jet cones. The acceptance window for the invariant mass of an e+e− pairwas taken to be 66 to 116GeV/c2 to suppress background. The cross section as a function ofthe transverse momentum of a leading jet is shown in Figure 5 (closed circles) and is comparedto the NLO prediction using MCFM17 with CTEQ6.1M6 PDFs after corrections to the hadronlevel (open circles). The data/theory ratio is consistent with unity, although statistical errorsdominate at pjetT > 100GeV/c region. (GeV)γTp0 50 100 150 200 250 300   (pb/GeV) jetηdγ ηd Tγ dp⁄  σ 3 d-410-310-210-110110210310 & jet in CC, SSγ Region 1:    & jet in CC, OSγ Region 2:    in CC, jet in EC, SSγ Region 3:    in CC, jet in EC, OSγ Region 4:    Region 1 Region 2 Region 3 Region 4 -1L = 1.1 fbDØ dataNLO QCD=pT*f(y*)R,F,fµCTEQ 6M, DØ RunII Preliminary  [fb/(GeV/c)]   jetT/dpσd-210-110110210310-1 Data  L = 1.1 fb Systematic uncertainties NLO MCFM CTEQ6.1M Corrected to hadron level=1.3sep(Z), R2T + p2Z = M20µ  PDF uncertaintiesCDF Run II Preliminaryee + jets→Z2 < 116 GeV/cee66 < M| < 1e1η > 25 GeV, |eTE| < 2.8e2η| < 1  ||  1.2 < |e2η|| < 2.1jet > 30 GeV/c, |yjetTpR(e,jet) > 0.7  [GeV/c]  jetTp30 100 200   Figure 4: The differential γ+jet cross sections as afunction of photon pT for four rapidity regions.Figure 5: The differential Z(→ e+e−)+ jets cross sec-tion as a function of jet pT .Present experimental data on QCD jets from the Tevatron Collider are reasonably welldescribed by existing next-to-leading calculations after applying parton-to-hadron level correc-tions. The CDF and DØ collaborations have now collected about 2.2 fb−1 of data on tape andanticipate up to 8 fb−1 by end of 2009. This should make possible even higher precision tests ofpQCD theory over extended kinematic regions.AcknowledgmentsI would like thank the staffs at Fermilab and collaborating institutions and acknowledge supportfrom SFI (Ireland) and EU Marie Curie Programme.References1. DØ Collaboration: S. Abachi et al., Nucl. Instr. Methods A338, 185 (1994); V.M. Abazovet al., Nucl. Instr. Methods A565, 463 (2006)2. CDF Collaboration: F. Abe et al., Nucl. Instr. Methods A271, 387 (1988); R. Blair et al.,FERMILAB-PUB-96/390-E; D. Acosta et al., Phys. Review D71, 032001 (2005)3. G.C. Blazey et al., hep-ex/00050124. V.M. Abazov et al. [DØ Collaboration], DØ NOTE 5087 (2007)5. Z. Nagy, Phys. Rev. Letters 88, 122003 (2002); Z. Nagy, Phys. Review D68, 094002 (2003)6. D. Stump et al., JHEP 10, 046 (2003)7. N. Kidonakis & J.F. Owens, Phys. Review D63, 054019 (2001)8. T. Sjo¨strand et al., Comput. Phys. Commun. 135, 238 (2001)9. O. Norniella [for CDF Collaboration], this Conference10. G. Corcella et al., JHEP 01, 010 (2001)11. H.L. Lai et al., Eur. Phys. J. C12, 375 (2000)12. S. Frixione, P. Nason & B.R. Webber, JHEP 08, 007 (2003)13. J.M. Butterworth, J.R. Forshaw & M.H. Seymour, Z. Phys. C7, 637 (1996)14. V.M. Abazov et al. [DØ Collaboration], DØ NOTE 5369-CONF (2007)15. S. Catani et al., JHEP 05, 028 (2002)16. L. Bourhis, M. Fontannaz & J.P. Guillet, Eur. Phys. J. C2, 529 (1998)17. J. Campbell & R.K. Ellis, http://mcfm.fnal.gov

Latest Jet Results from the Tevatron

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