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Christopher Neu on behalf of the CDF and D  Collaborations

W/Z + Jets and W/Z + Heavy Flavor Jets at the Tevatron. Christopher Neu on behalf of the CDF and D  Collaborations XLIIIrd Rencontres de Moriond QCD and High Energy Interactions 12 March 2008 La Thuile - Aosta Valley, Italy. Outline:. Importance of W/Z + jets

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Christopher Neu on behalf of the CDF and D  Collaborations

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  1. W/Z + Jets and W/Z + Heavy Flavor Jets at the Tevatron Christopher Neu on behalf of the CDF and D Collaborations XLIIIrd Rencontres de Moriond QCD and High Energy Interactions 12 March 2008 La Thuile - Aosta Valley, Italy Outline: • Importance of W/Z + jets • Recent Tevatron progress • Summary and future

  2. Importance of W/Z + Jet Physics Why study W/Z +jet production? q • Important tests of Quantum Chromodynamics (QCD) • Recent LO and NLO simulations need experimental verification • Signature shared with top production, Higgs, other searches at Tevatron, LHC q q(‘) q’ q’ V q q q q V q(’) V=W or Z Christopher Neu

  3. The CDF and D Experiments Common features: Christopher Neu Charged particle tracking in magnetic field Electromagnetic and hadroniccalorimetry Muon detection Luminosity monitoring Three level event trigger

  4. W + Inclusive Jets W+jets signal Fake W bkgd Real W bkgd W+jets signal Fake W bkgd Real W bkgd S/B ~ 10/1 W+jets signal Fake W bkgd Real W bkgd W+jets signal Fake W bkgd Real W bkgd S/B ~ 1.2/1 • W selection: seek W e  • e: ET > 20 GeV, || < 1.1 • : missing energy MET> 30 GeV • MT (W) > 20 GeV/c2 • Jet definition: • Corrected ET > 20 GeV, || < 2.0 • Cone algorithm, R= 0.4 Christopher Neu

  5. W + Inclusive Jets PRD 77, 011108(R) MCFM : MCFM (NLO) MLM : ALPGEN (LO) + Herwig (shower) + MLM matching SMPR : MadGraph (LO) + Pythia (shower) + CKKW matching Total cross section for jet multiplicity, n: NLO prediction more accurate than LO! Relative rates within each prediction consistent with data. Christopher Neu

  6. W + Inclusive Jets PRD 77, 011108(R) MCFM : MCFM (NLO) MLM : ALPGEN (LO) + Herwig (shower) + MLM matching Can examine differential cross sections within each multiplicity bin…. SMPR : MadGraph (LO) + Pythia (shower) + CKKW matching Total cross section for jet multiplicity, n: NLO prediction more accurate than LO! Relative rates within each prediction consistent with data. Christopher Neu

  7. W + Inclusive Jets W+2 jets PRD 77, 011108(R) MCFM : MCFM (NLO) MLM : ALPGEN (LO) + Herwig (shower) + MLM matching SMPR : MadGraph (LO) + Pythia (shower) + CKKW matching At LO, MadGraph+Pythia+CKKW provides better performance. Christopher Neu • LO calculation procedure: Generate ppW+Npartons at tree level, ignore loop corrections, employ parton shower • Ambiguities arise: • Possibility for double counting if Nparton  Njet • SMPR and MLM refer to algorithms for avoiding/removing overlaps

  8. Z /* + Inclusive Jets hep-ex/0711.3717 (Submitted to PRL) Can’t see the NLO prediction points - close overlap with data! NLO prediction once again more accurate than LO! Christopher Neu • Validity of NLO predictions borne out in Z /*+jets? • Z /* selection: seek Z /*e+e- • Two ET > 25 GeV electrons • 66 < Mee < 116 GeV/c2 • Jet definition: • Corrected pT > 30, |y| < 2.1 • Cone algorithm w/ R=0.7 • Major backgrounds: S/B ~ 7/1 • QCD multijets • W + jets • ttbar, diboson • Z+, Z

  9. hep-ex/0711.3717 (Submitted to PRL) Z /* + Inclusive Jets Christopher Neu • Differential cross section: • No LO comparison here NLO prediction reliable – as inW+jets • Analysis would benefit from increased statistics to further populate the Z+2-jets sample • NLO for Z+3-jets would be valuable as well.

  10. Z /* + Inclusive Jets Pythia Sherpa Christopher Neu • DZ /*(ee)+jets analysis: 950/pb • Purpose here: compare Pythia(ppW+1+ internal PS)and Sherpa (ppW+N+ internal PS + CKKW matching) event generators • Test of different prediction techniques • Some confidence in CKKW from CDF W+jets LO studies…true here as well?

  11. Z /* + Inclusive Jets Pythia Sherpa Sherpa + CKKW represents data better than Pythia - pT of jet 1,2,3 - Z pT, Jet multiplicity - (jet, jet), (jet, jet) Not unexpected given the nature of Pythia’s calculation. Christopher Neu

  12. top pair production s-channel single top W/Z H production Summary so far… ℓ / ℓ,  / ℓ,  W/Z W/Z • W/Z+1,2 jet NLO predictions from MCFM look reliable • NLO predictions not yet in hand for W/Z+3 jet • Technique of calculating/generating ppW+N+ parton shower + matching scheme (ala ALPGEN, MadGraph, Sherpa) superior to Pythia+PS alone • Differences among available tools still need to be understood • W/Z + heavy flavor (b,c) jets also important • background to top, Higgs, others • W+c production has unique features Christopher Neu

  13. Tagging:b’s and Non-b’s Tag efficiency for b jets Tagging of real b jet: long lifetime+ large boost = secondary vertex Displaced tracks Secondary vertex Fractional  L2d > 0 Primary vertex Prompt tracks Jet ET (GeV) Displaced tracks Tag efficiency for u/d/s/g jets Spurious tagging of light flavor jet: “mistag” Fractional  Secondary vertex Primary vertex Prompt tracks L2d<0 Jet ET (GeV) Christopher Neu

  14. Vertex Mass Shapes = u/d/s/g W + b-Jets From simulation • MB-hadrons > MC-hadrons > MLF-hadrons • so • Mbvert > Mcvert > MLFvert • Goals: • Measure W+b-jet production cross section • Use measurement to improve background estimate for Higgs search • W and jets selection here similar to W + inclusive jets analysis • key difference: 1 or 2 jets only • Here we need to identify jets that are likely b’s (via high purity tagging) and determine how many are really b’s via vertex mass: - invariant mass of charged particle tracks in secondary vertex Christopher Neu

  15. W + b-Jets High purity b-tagging at work! New result! x3.5 mismatch ~1000 tagged jets among which ~700 are consistent with coming from a b quark NB: This cross section is for b jets from W+b-jet production in events with a high pT central lepton, high pT neutrino and 1 or 2 total jets. Publication in preparation. • Largest backgrounds: S/B ~ 3/1 • ttbar (40% of total bkgd) • single top (30%) • Fake W (15%) • WZ (5%) • Total contribution: ~180 tagged b jets • Result: xBR = 2.74  0.27 (stat)  0.42 (syst) pb • Prediction: xBR = 0.78 pb (ALPGEN ) Christopher Neu

  16. Z + b-Jets • Differential cross sections with comparisons to LO, NLO predictions • Dividing by (Z) puts LO, NLO on equal footing • Pythia does a good job at low jet ET Christopher Neu • Similar CDF analysis for Z+b-jets: 2/fb • Utilize Zeeand  • Similar jet definition • Corrected ET > 20 GeV, || < 1.5 • Cone algorithm with R=0.7 • Secondary vertex tags

  17. Z + b-Jets • ALPGEN (LO) and MCFM (NLO) undershoot data in several bins • Pythia surprisingly on target in some regimes – LO predictions are in other analyses low (eg, Z+jets). Publication in preparation. Christopher Neu

  18. W/Z + b-Jets: Summary Raw NLO predictions corrected for underlying event and hadronization effects. • More studies for W+b-jets are forthcoming • Need to understand NLO predictions • In Z+b-jets it is strange that the NLO prediction undershoots data • Borne out in W+b-jets? Christopher Neu

  19. W + Single c Production c c hep-ex/0711.2901 - submitted to PRL W- s(90%) or d(10%) Different tagging algorithm: Soft Muon Identification used to identify charm hadron decays! μ • Result:xBR = 28.5  8.2 (stat)  4.4 (syst)  1.7 (lum)pb • Prediction: ALPGEN • xBR = 22.2  1.2 (PDF)  3.8 (scale) pb Good agreement! Christopher Neu • W+singlec production unique • no W+singleb analogue at Tevatron • Exploit feature: charm semileptonic daughter and W have opposite charge

  20. W + Single c Production LO prediction reasonably good. Impact of systematic errors drawn on theory curve. Statistical uncertainty drawn for data points . Publication in preparation. Christopher Neu • Similar analysis completed at D: 1/fb • Measures which can be compared to the LO prediction: 0.040  0.003 (PDF)

  21. Conclusions • W/Z + jets physics plays an important role in current collider physics programs • Current NLO predictions for W/Z + look to be accurate, higher multiplicities desirable • W/Z+b-jets studies have indicated deficiencies in both LO and NLO predictions; more study and more data is needed • W+singlec studies indicate good agreement with LO predictions Christopher Neu

  22. Backup Slides Christopher Neu

  23. W + Inclusive Jets MCFM : MCFM (NLO) MLM : ALPGEN (LO) + Herwig (shower) + MLM matching SMPR : MadGraph (LO) + Pythia (shower) + CKKW matching Christopher Neu

  24. Identifying b Jets • Bhadron lifetime: ~1.5 ps • Large boost (v ~ 0.95c) means the B lifetime is long in the lab frame • B travels macroscopic distance before decaying which we can detect • Exploit the long lifetime - • Reconstruct charged particle tracks • See if they intersect at a common point • Require the common point be significantly displaced from the primary p-p collision point Long-lifetime yields secondary decay vertex “b-tagging” Displaced tracks Secondary vertex d0 L2d Prompt tracks Primary vertex, aka p/pbar collision point Christopher Neu

  25. W + b-Jets Christopher Neu

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