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b-Jets production at Tevatron

b-Jets production at Tevatron. Sandro De Cecco INFN Roma. European Physical Society meeting Strong Interactions session Manchester, 20-07-2007. Outline. B-jets production introduction B-Jets Energy Scale and Z  bb at Tevatron Inclusive B-Bbar Jets production at Tevatron

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b-Jets production at Tevatron

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  1. b-Jets production at Tevatron Sandro De Cecco INFN Roma European Physical Society meeting Strong Interactions session Manchester, 20-07-2007 Sandro De Cecco - EPS, Manchester 20-07-07

  2. Outline • B-jets production introduction • B-Jets Energy Scale and Zbb at Tevatron • Inclusive B-Bbar Jets production at Tevatron • B-Jets associate production with gauge bosons and its impact on Tevatron and LHC physics • Heavy Flavor Jet + g at Tevatron • W / Z + Heavy Flavour production at Tevatron • Recent CDF developments on Jet Flavor taggers • first application to Z + Heavy Flavors Sandro De Cecco - EPS, Manchester 20-07-07

  3. bb pairs production in hadronic collisions Leading Order and Next to Leading Order Q g Q g g g Flavor excitation and … radiative corrections Flavor creation Gluon splitting … but:b/c-jets or B/D hadrons are the observables rather than b/c-quark Observed Proton structure Fragmentation NLO QCD Factorizes into a calculable part and a non-calculable but universal piece Sandro De Cecco - EPS, Manchester 20-07-07

  4. Inclusive bcross section - low PT • Run I: b cross-section ~ 3x old NLO QCD • Theoretical approaches: Next-to-Leading-log resummations, non perturbative fragmentation function from LEP, new factorization schemes… • Experimentally: unbinned maximum likelihood fit to the J/y decay timein the R- plane to extract the b fraction Run II: Bottom Quark Production cross-section: PRD 71, 032001 (2005) Good agreement  Sandro De Cecco - EPS, Manchester 20-07-07

  5. High PT Jets and b tagging • Secondary Vertex b-tag Algorithm (CDF SecVtx) • Select tracks within the Jet Cone • Reconstruct 2 or 3 tracks vertex • Cut on vertex displacement significance to reduce light Jets rate • Secondary vertex mass has some separating power between light, charm and b Flavors mass Sandro De Cecco - EPS, Manchester 20-07-07

  6. Inclusive bb di-jets production • Specific Trigger based on L2 SVT (Secondary Vertex Trigger) used. • Sensitive to the different production mechanisms • Flavor creation at high  • Flavor excitation or gluon splitting at low  Purity ~ 85 % :extracted from data using shape of secondary vertex mass Sandro De Cecco - EPS, Manchester 20-07-07

  7. b-Jets Energy Scale and Zbb • Generic Jet Energy Calibration of the Detector needs specific correction for b-Jets • Reduction of uncertainty in b-JES important for Top mass measurement • Test algorithms to improve b-jet energy resolution is crucial for low mass Higgs search. • Use of L2 SVT based b-tag di-jet trigger  Extract a signal, measure data/MC b-JES Result on 600 pb-1 b-jet Data/MC Energy Scale Factor = 0.974 ± 0.020 Zbb signal templates for 0.9<SF<1.09 N(Zbb)~5600 Sandro De Cecco - EPS, Manchester 20-07-07 Background template

  8. W / Z /g bosons + HF Jets production • The study of W / Z / g + Jets production is very relevant: • to QCD: • High q2 ( ~Mboson) interactions, perturbative theory • Less leading diagrams ( wrt pure Jets production) • Test Monte Carlo generators (ALPGEN…) • Probe for protons PDF (in particular W/Z + H.F. ) • for many high pT analysis where W/Z+HF is a main background: • Top quark cross section and mass • Single Top cross section • Search for low mass Higgs boson • Several SUSY searches … and also crucial process at LHC ! Sandro De Cecco - EPS, Manchester 20-07-07

  9. W+HF backgrounds in WHl bb = 1 jet tagged jet sample signal region Mjj • Expectations based on: • MC predictions for EW and top backgrounds • Fake tags (mistag matrix) applied to light jets • Heavy Flavor background: • admixture of MC and data driven procedure Sandro De Cecco - EPS, Manchester 20-07-07

  10. Z + HF x-section from Tevatron to LHC from hep-ph/0312024 - Tevatron : pT 15 GeV, │h│< 2, DRjj > 0.7 Tevatron Sandro De Cecco - EPS, Manchester 20-07-07

  11. LHC example: b quark PDF from Z+b bb->Z @ LHC is ~5% of entire Z production Spread of existing pdf’s gives a 10% spread in the prediction of the SM Higgs cross section Even bigger impact on MSSM Higgs production (sensitive to bb coupling) Sandro De Cecco - EPS, Manchester 20-07-07

  12. W + bb production results In secondary-vertex-tagged sample, fit for light, c, b contributions CDF measure: 0.90±0.32 pb for Wbb (ET(j)>20 GeV, ||<2.0 LO calculation (ALPGEN): 0.74±0.18 pb Sandro De Cecco - EPS, Manchester 20-07-07

  13. g + b Jet production results • Probes heavy-quark PDFs • Background for SUSY (light stop) • Experimentally difficult because of large background from 0 decays SVT+  dataset Inclusive  dataset Sandro De Cecco - EPS, Manchester 20-07-07

  14. b-tagged jet Z+b production (old) results Campbell, et al.(hep-ph/0510362) (<1.5): (Z+b)/(Z+j) = 0.0237 ± 0.0085 (<2.5): (Z+b)/(Z+j) = 0.024 ± 0.007 (  assuming b/c ratio from MC ) Sandro De Cecco - EPS, Manchester 20-07-07

  15. Z+b jets new CDF analysis • Luminosity from 330 pb-1 1.5 fb-1 • Improved selection, higher • acceptance from 7.7%  9.6% • Improved systematics Mℓℓ Z+≥1 b tag Inclusive Jets, Cone DR=0.7 Ask for the Jet to have a Secondary Vertex Tag and …exploit light,charm to b separation from sec.vtx. Mass  ET(jet) Sandro De Cecco - EPS, Manchester 20-07-07

  16. Z+b jets new CDF result Sec. Vtx mass fit in events with at least 1 tagged Jet: Systematic table MSecVtx • Overall precision improved by almost a factor of 2. • s(Z+b) is 2s away from MCFM NLO preliminary calculation by Campbell Sandro De Cecco - EPS, Manchester 20-07-07

  17. A new CDF H.F. Neural Network Tagger Roma NN b-tag M.C. • The underlying idea is improving the ability to boost performance exploiting as much information as possible: • number of vertices (not just A SINGLE secondary vertex a’ la SecVtx) and their masses; • displaced but un-vertexed tracks (tracks not belonging neither to secondary vertex nor to the primary); • Soft leptons, JetProb,global jet variables • Best to combine all info together in a single discriminant: use (a series of) Neural Networks (NN) • NN training performed on generic sample to be used in different analysis (top, single top, low mass Higgs, …) uds c b • A Continuous tagging variable allow weighting events to get the most of it in terms of search sensitivity • GOOD b-c-udsstatistical separation allows the fraction of c jet to be studied as well, HIGH Jet taggability: ~ 75% • Increased per-jet efficiency at same background rate than SecVtx: Sandro De Cecco - EPS, Manchester 20-07-07

  18. Z+HF fractions with Roma NN b-tagging Roma NN b-tag output fit in Z+jets events, L= 1.6 fb-1 Toy MC estimate on b, c fractions uncertainty CDF Run II Preliminary L = 1.6 fb-1 MC Roma NN output DATA Fit -Blind- • Could allow for the first time a simultaneous measurement of Z+c and Z+b cross sections. • Application of the Roma NN tagger to other samples: one could fit top/higgs cross section together with the W/Z+HF background as a function of jet multiplicity. Sandro De Cecco - EPS, Manchester 20-07-07

  19. Summary: • W/Z + HF processes not yet fully studied, now starting to characterize at the Tevatron. • Many Tevatron results on bb and W/g/Z + b-jet productions • New Z+b-jet measurement from CDF • New generation NN Jet Flavor Tagger being developed at CDF and being tested in Z+b, Z+c measurement • … lot of knowledge progresses on HF production processes will be an important Tevatron legacy to the LHC Sandro De Cecco - EPS, Manchester 20-07-07

  20. Backup Sandro De Cecco - EPS, Manchester 20-07-07

  21. jet Jets outside acceptance Small contribution Higher order in αs ME Monte Carlo issues Naïve: W+n p (ME)+(PS) ~ W + ≥ N jet W+(n+1) p (ME)+(PS) ~ W + ≥ N+1 jet ... Soft radiation PS Hard scattering ME shower 2 topologies ~ O(α) Same jet multiplicity parton double counting Problems: how to generate the whole n jet spectrum avoiding double counting ? how be sure that the selected jet is coming from the ME and not PS ? Goal: have a prescription to safely merge different MC multiplicity samples Sandro De Cecco - EPS, Manchester 20-07-07

  22. Tracks info PV info Jet info JetProb info SecVtx info SLTm info Vertices NN Tracks NN b-q c-q bb-b cc-c b-c NN tagger structure New Vertexing multiple verticies reconstruction (based on CTVMFT) NeuroBayesTM 3 flavour NN 5 flavour NN TMultiLayerPerceptron outputs Sandro De Cecco - EPS, Manchester 20-07-07

  23. New CDF Jet Flavor Tagger - Outlook There is some separation power between single and double b Jet • Further possibility: building block are there to try to tackle also the b/bbar (c/ccbar) jet content and more closely investigate the b production mechanisms CDF Monte Carlo Roma NN b-tag Sandro De Cecco - EPS, Manchester 20-07-07

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