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tt Production Cross Section at CDF

-. tt Production Cross Section at CDF. Petra Merkel – Purdue University For the CDF Collaboration Frontiers in Contemporary Physics III Vanderbilt University – 05/26/05. Top @ Tevatron. Top is the only quark at weak scale  window to EWSB ?

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tt Production Cross Section at CDF

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  1. - tt Production Cross Section at CDF Petra Merkel – Purdue University For the CDF Collaboration Frontiers in Contemporary Physics III Vanderbilt University – 05/26/05

  2. Top @ Tevatron • Top is the only quark at weak scale •  window to EWSB ? • New physics may appear in production (e.g. topcolor) or in decay (e.g. charged Higgs) • Top mainly produced in pairs at Tevatron • s(top pairs) ~ 6.7 pb : 85% qq annihilation + 15% gg fusion • cf s(single top) ~ 3 pb • Extremely rare process (smallest cross section measured so far) • About 1 tt event in 1010 inelastic pp collisions ! P.Merkel - 05/26/05 : TTBAR PRODUCTION CROSS SECTION AT CDF - -

  3. CDF @ Tevatron - • 1.96 TeV pp collisions are collected for top physics by triggering on one high-Pt lepton, on jets or on missing Et • Presenting measurements with data collected up to 09/2004, corresponding to up to ~350 pb-1 • (cf ~108 pb-1 in RunI) P.Merkel - 05/26/05 : TTBAR PRODUCTION CROSS SECTION AT CDF

  4. Final States Dileptons: BR=11% (ee/em/mm only = 5%) cleanest sample, lowest statistics Lepton+Jets: BR=44% (e/m + jets = 29%) golden channel w/ high statistics and reasonable S/B All-Hadronic: BR=44%, most challenging channel w/ high statistics but large backgrounds l- - b W- n - t X p t p - p b q W+ - q’ Top Production and Decay P.Merkel - 05/26/05 : TTBAR PRODUCTION CROSS SECTION AT CDF SM: Cacciari et al., JHEP0404, 068 (2004) Kidonakis and Vogt, Phys. Rev. D68, 114014 (2004)

  5. B Jet Tagging Algorithms 2ndary Vertex Tag Soft Muon Tag Jet Probability Tag Determine probability for jet to originate from b or c or light quarks based on signed impact parameter distribution of all tracks in the jet Displaced vertex reconstruction with silicon detector: B hadrons travel ~3mm before decay w/ large track multiplicity look for relatively low momentum m in or near the jets that result from semileptonic decays of B hadrons P.Merkel - 05/26/05 : TTBAR PRODUCTION CROSS SECTION AT CDF Top Event Tag Efficiency 58-63% False Tag Rate (QCD jets) 0.8% Top Event Tag Efficiency 15% False Tag Rate (QCD jets) 3.6% Top Event Tag Efficiency 57% False Tag Rate (QCD jets) 1.2%

  6. NEW ! Lepton+Jets Channel:2ndary Vertex b-tag 318 pb-1 • 1 isolated high-Pt e or m (Et(Pt)>20 GeV) • Missing Et > 20 GeV accounting for escaping n • ≥3 jets (Et>15 GeV) w/ ≥1 b-tags • b-tag: 2ndary vertex tagger • Optimize S:B by cuts on Mt>20 GeV (leptonic W) and Ht>200 GeV (scalar sum of total energy in event) P.Merkel - 05/26/05 : TTBAR PRODUCTION CROSS SECTION AT CDF

  7. stt (≥1 b-tag) 7.9 ± 0.9 (stat) ± 0.9 (syst) pb stt (≥2 b-tags) 8.7 ± 1.7 (stat) ± 1.5 (syst) pb Results (previously published with 162 pb-1 in PRD 71, 052003) ≥1 b-tag ≥2 b-tags signal region signal region P.Merkel - 05/26/05 : TTBAR PRODUCTION CROSS SECTION AT CDF

  8. NEW ! Lepton+Jets Channel:Event Kinematics + Neural Net Fit 347 pb-1 • Independent of b-tagging • Select events w/ 1 e or m, MEt and 3 jets • Neural Net: feed forward, 7 input variables, 7 hidden nodes, 1 output node • Input variables: Aplanarity, Max-Jet-Rapidity, Min-Dijet-Separation, Ht, Sjet(3,4,5)Et, SPz/SEt, Min-Dijet-Mass •  3-Jet Sample: • a priori most sensitive •  4-Jet Sample: • better S:B  cross check P.Merkel - 05/26/05 : TTBAR PRODUCTION CROSS SECTION AT CDF

  9. Results (hep-ex/0504053, submitted to PRD) Fit: tt and W-like float QCD fixed to 4.6% s vs mtop P.Merkel - 05/26/05 : TTBAR PRODUCTION CROSS SECTION AT CDF evolution of result w/ mt

  10. 162 pb-1 Lepton+Jets Channel:2ndary Vertex b-tag + EtleadJet Fit (Published in PRD 71, 072005) • Use semileptonic b-tagged tt events with 3 jets • Take signal and background shapes in leading jet Et from MC and data • Fit leading jet Et distribution in data to templates: • signal fraction: in 57 events P.Merkel - 05/26/05 : TTBAR PRODUCTION CROSS SECTION AT CDF

  11. Lepton+Jets Channel:Soft Muon b-tag 200 pb-1 signal region • In events w/ 1 e or m, MEt and 3 jets require 1 b-tag • b-tag: soft muon tag • Reduce background by Ht>200 GeV cut (scalar sum of total energy) P.Merkel - 05/26/05 : TTBAR PRODUCTION CROSS SECTION AT CDF

  12. Lepton+Jets Channel:Jet Probability b-tag 162 pb-1 • In events w/ 1 e or m, MEt and 3 jets require 1 b-tag • b-tag: jet probability tag: P.Merkel - 05/26/05 : TTBAR PRODUCTION CROSS SECTION AT CDF signal region

  13. (Published in PRL 93, 142001) Dilepton Channel:Counting Experiments 200 pb-1 Tight selection • Two well identified leptons (e or m): ee, em, mm • Large MEt • 2 jets, no b-tagging Loose selection • One well identified lepton (e or m) + isolated track: e+track, m+track • Large MEt • 2 jets, no b-tagging P.Merkel - 05/26/05 : TTBAR PRODUCTION CROSS SECTION AT CDF signal region signal region

  14. 193 pb-1 Dilepton Channel:Global Fit • Global fit to isolated high-Pt dilepton data (ee/em/mm) in Njet - MEt plane • Fit data to shapes from templates from SM processes • Signal(s) floating in fit: tt, WW, Ztt • Backgrounds fixed in fit: WZ, ZZ, Zee, Zmm, bb, Wg, W+jets P.Merkel - 05/26/05 : TTBAR PRODUCTION CROSS SECTION AT CDF

  15. All-Hadronic Channel:2ndary Vertex b-tag 165 pb-1 • Use dedicated trigger: 4 jets w/ Et>15 GeV and SEtevent>125 GeV • S:B of 1:2500 increased to 1:24 with SEtjets and topological cuts (aplanarity, centrality) • Require 6 – 8 jets, and 1 b-tag (using the 2ndary vertex algorithm) P.Merkel - 05/26/05 : TTBAR PRODUCTION CROSS SECTION AT CDF

  16. All CDF RunII results Observed cross sections consistent with each other and with the SM prediction P.Merkel - 05/26/05 : TTBAR PRODUCTION CROSS SECTION AT CDF Working on combination

  17. tt Cross Section vs Energy P.Merkel - 05/26/05 : TTBAR PRODUCTION CROSS SECTION AT CDF

  18. Conclusions & Outlook • All measurements consistent with SM • Current measurements will continue to improve • Doubled data set each year • Reduction of systematics through better understanding of detector • New techniques employed • Expect ~10% precision on s(tt) with 2 fb-1 (now ~20%) • Top is major background for new physics at LHC • Concise understanding of top sector before LHC turns on is crucial P.Merkel - 05/26/05 : TTBAR PRODUCTION CROSS SECTION AT CDF

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