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B-jet production cross section at CDF

B-jet production cross section at CDF. Monica D’Onofrio University of Geneva Wine&Cheese Seminar, September 9 th 2005. Study of events with b-quarks has led to important Tevatron results Discovery and study of the top quark

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B-jet production cross section at CDF

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  1. B-jet production cross section at CDF Monica D’Onofrio University of Geneva Wine&Cheese Seminar, September 9th 2005

  2. Study of events with b-quarks has led to important Tevatron results Discovery and study of the top quark B physics in general (spectroscopy, lifetimes measurement, sin 2b etc..) Measurement of quarkonium states and appreciation of color-octet-mediated production mechanisms These results mostly obtained when a factor 3 discrepancy was reported between theory predictions and experimental data by both CDF and DØ in b-hadron cross sections In the last 15 years… Wine&Cheese Seminar, Fermilab September 9th 2005

  3. « To claim that we need to understand b production in order to make new discoveries is therefore a bit exaggerated … .. Nevertheless, lack of confidence in the ability to describe properties of events containing b quarks, in addition to raising doubts over the general applicability of pQCD in hadronic collisions, does limit our potential for the discovery of possible subtle and unexpected new phenomena » (M.Mangano, HCP2004) Therefore, the study of b production properties should be one of the main priorities for RunII … …also considering high statistics.. Ecm=1.96 TeV s(bb) ~ 50 mb  few kHz event rate!! Wine&Cheese Seminar, Fermilab September 9th 2005

  4. Recent advances in the theory of b production cross sections in hadronic collisions and application to experimental results related to B-hadrons. Exploring b-jets at CDF: Inclusive b-jet cross section Event selection, experimental tools Results and preliminary comparison with theoretical calculations at Next-to-Leading order (NLO) More exclusive b-jet cross sections bb-jets correlations: to disentangle b production processes Z+b-jet cross section: to probe b content of the proton Conclusions Outline Wine&Cheese Seminar, Fermilab September 9th 2005

  5. The theory and recent developments

  6. B-quark production in hadron collisions Leading Order Next to Leading Order Q g Q g g g Flavor excitation other radiative corrections.. Flavor creation Gluon splitting Experimental inputs are B-Hadrons or b-jets rather than b-quark Observed Proton structure Fragmentation NLO QCD Factorization theorem: factorize physical observable into a calculable part and a non-calculable but universal piece Wine&Cheese Seminar, Fermilab September 9th 2005

  7. Proton structure: PDF Parton Distribution Functions (PDFs) are universal global fits to data on proton structure independent of the process  Momentum distributions of the partons inside proton gluon u d x Generally PDF uncertainties are estimated at ~ 15% Dominant contribution due to high x gluon distribution Uncertainty on gluon PDF (from CTEQ6) x Wine&Cheese Seminar, Fermilab September 9th 2005

  8. Fragmentation functions Db B Perturbative part: probability to find a hadron with fraction x’ of original parton momentum Hadronization: non perturbative QCD, need models Wine&Cheese Seminar, Fermilab September 9th 2005

  9. Recent theory advances • pQCD calculations: • resummation of aslog(pT/m) terms •  Fixed Order Next Leading Log (FONLL) • pT >> m  need large corrections • Moment analysis to treat Dmeas • for fragmentation • (new approach: Cacciari et. Al. 2002) • Cross section very dependent • on PDF evolution now <1994 sbNLO(|y|<1) (mb) Release date of PDF Wine&Cheese Seminar, Fermilab September 9th 2005

  10. J/   B+ K+ Testing FONLL: B hadron production • J/ decays of B-Hadrons used to • measure the b production cross section • Find J/y inclusive cross section • Extract fraction of J/y from decay of long-lived b-hadrons • Find b-hadrons cross section for pT(B) down to 0 considering |y(J/y)|<0.6  J/yfrom B  J/y X will be displaced B  J/y X shape from MC templates Maximum likelihood fit on flight path to extract b fractionas function of pT(J/y) Wine&Cheese Seminar, Fermilab September 9th 2005

  11. B hadron production cross section Good agreement with theory prediction Total inclusive single b-hadron (Hb) cross section considering Br(HbJ/yX) = 1.160.10% and Br(J/ymm) = 5.880.10% Wine&Cheese Seminar, Fermilab September 9th 2005

  12. Summary on theory advances • Reduction of discrepancy is due • to four basic points: • FONLL calculation brings 20% increase • in intermediate pT region • fragmentation step from perturbative • b quark to B hadron at small pT was • too strong: 20% increase in this pT • region • Peterson fragmentation function was • too soft: use new LEP data =0.002 • additional 20% increase • PDF evolution (> 20% increase) RunI RunII comparison with RunI data |y(Hb)| < 1, s(RunII) multiplied by B+ fragmentation=0.4 (Ecm rescaled) Data moved ~ 20% down(still within errors) Many little changes combined together  big effect in Data/Theory comparison Wine&Cheese Seminar, Fermilab September 9th 2005

  13. Why b-jets? • b-jets include most of quark fragmentation remnants •  small dependence on fragmentation • wide PT spectrum In RunI studies performed to measure bottom and charm fraction in inclusive jet samples +5 - 6 s(pT>pTmin, |y|<1)(nb) sb = 19 ± 2(stat) (syst) [nb] at PT> 35 GeV/c +3 - 1 PT(B) GeV/c In RunI differential b-jet cross section using semi-leptonic decays of the b (muon tagger) Wine&Cheese Seminar, Fermilab September 9th 2005

  14. Inclusive b-jet cross section at CDF

  15. The Tevatron in RunII • Peak luminosity in 2005 above 1032 cm-2 s-1 • CDF collected ~ 1 fb-1 on tape!! • (but 1.2 fb-1 already delivered) • Analysis shown here use ~ 300 pb-1 Wine&Cheese Seminar, Fermilab September 9th 2005

  16. Collider Detector Fermilab The CDF experiment • Muon Chamber (collision hall) • position and pT • 4 systems of scintillators and proportional chambers • min scattering resolution [12/p;25/p] cm/p • TOF • time • Scintillators • 100 ns resolution Solenoid (1.4 T) • CENTRAL and PLUG Calorimeter • energy and direction • 2 systems of passive layers-scintillators • COT • position • drift chamber • spatial resolution • 100 m • Silicon Detector • With 750,000 channels, the largest Silicon detector in the world! • position • 3 systems of single or double sided detector • down to 10 m spatial resolution (3D) Wine&Cheese Seminar, Fermilab September 9th 2005

  17. B-jet cross section • Nitaggedis the number of tagged jets • eib-tag is the b-tagging efficiency • fib is the fraction of b-jets among tagged jets • Ciunfold are correction factors from Monte Carlo for acceptance and smearing effects • DY is the rapidity range • DpiT is the size of bin in transverse momentum • ∫L is the integrated luminosity Wine&Cheese Seminar, Fermilab September 9th 2005

  18. Seed towers Only iterate over towers above certain threshold (3 GeV at CDF) MidPoint adds extra seed in centre of each pair of seeds  Infrared safe Ratcheting (JetClu only) All towers initially inside a cone must stay in a cone Jet reconstruction Final state partons are revealed through collimated flows of hadrons called jets Jet Beam remnants Hard scattering • Two main type of jet algorithms (in CDF): • Cone Algorithm •  JETCLU and MIDPOINT • - KT algorithm Multiple partons interaction • Merging/Splitting fmerge=0.75 Wine&Cheese Seminar, Fermilab September 9th 2005

  19. Path L1 L2 L3 Dataset Event selection • MIDPOINT jets, Rcone = 0.7, |Yjet|<0.7 • PT range 30-360 GeV/c  38-400 GeV/c for corrected PT jets use 5 samples with different ETjetthreshold • Total luminosity used ~ 300 pb-1 Trigger efficiency • Inclusive calorimetric triggers: • Level 1: selection based on ET of cal towers (EM+HAD) • Level 2: accept tower clusters with ET above a fixed threshold • Level 3: jets reconstructed (JETCLU, Rcone=0.7, Zv=0) • |Z primary vertex|<50 cm • to assure good energy measurement, vertexing capability • Cut on missing ET Significance ( = ET/√∑ET) • implemented to reject to cosmic rays Event Selection Wine&Cheese Seminar, Fermilab September 9th 2005

  20. Jet corrections: detector effects For each calorimeter jet in |Y|<0.7 look for the corresponding hadronic (particle) jet to remove dependence from detector effects • need inclusive correction that takes into account the • bias due to the tagger correction on tagged jets Time 20 ÷ 10% • b-quark-originated jets different from ordinary jets • account for smearing effects for detector resolution •  apply “unfolding” correction bin by bin for b-jet • from Monte Carlo hadronic b-jet Wine&Cheese Seminar, Fermilab September 9th 2005

  21. Jet Corrections: Pile up UEM (PT) = 0.932±0.002 GeV Main idea: measure PT in a random cone in Minimum Bias sample (central region) as a function of # primary vertices to define effect due to multiple interactions; Average number of primary vertices as a function of instantaneous luminosity Jet samples 6 different slices of Instantaneous luminosity Small dependence on Lum. Effects in jet PT: about -1 GeV/c per each additional primary vertex Wine&Cheese Seminar, Fermilab September 9th 2005

  22. B tagging algorithm In general b-tagging procedures take advantage of the long life-time of B hadrons ct ~ 450 mm • Looks for tracks associated with a jet • the track selection is based onon • measurement of impact parameter (d0) • with respect to primary vertex • Need ≥ two displaced tracks to reconstruct • a secondary vertex (made in 2 steps) • After secondary vertex reconstruction • require to be well separated from primary vertex in r-f space by looking at Lxy and its error: • Jets passing those selections: tagged Wine&Cheese Seminar, Fermilab September 9th 2005

  23. b-jet content after tagging F tag bjet Ntag+ mjet Fm bjet N m jet b-jet content before tagging  b jet= B tagging efficiency (1) • Use Monte Carlo simulation to cover the wide PT spectrum [38-400] GeV/c • Measure efficiency scale factor to take into account simulation imperfections (tracking efficiency&resolution, B hadron decay models…) • For this purpose, use independent dataset • Sample enhanced in b-jet content: • dijet events  one e/m jet + “away” jet tagged • look e.g. at eb-jet for the muon jet • Measure b-tagging efficiency in Data and MC b-jet content extract using PTrel muon-jet Wine&Cheese Seminar, Fermilab September 9th 2005

  24. B tagging efficiency (2) eData b-jet/eMCb-jet Scale Factor (SF) SF = 0.9090.06(stat+syst) • Systematic error due to hadronic VS semileptonic b-decay below 3% • Geometrical acceptance and energy dependence of the tagger  from simulation • Tagging rates parametrized as function of relevant variables to define systematic error on PT dependence  5% Wine&Cheese Seminar, Fermilab September 9th 2005

  25. b-fraction tagged jets • Extract fraction of b-tagged jets from data using shape of mass of secondary vertex as discriminating quantity • bin-by-bin as a function of jet pT • 2 component fit:b and non-b templates (Monte Carlo PYTHIA) 82 < pTjet < 90 GeV/c Wine&Cheese Seminar, Fermilab September 9th 2005

  26. Systematics errors JES only (%) Total Jet Reconstr. (%) 3% ES  Resolution  Smearing  effect on cross section ~ 20-40% • Main sources: • jet reconstruction • Secondary vertex mass templates • Uncertainty: • MC generator, fitting procedure • Heavy quark multiplicity in jets • Fragmentation Wine&Cheese Seminar, Fermilab September 9th 2005

  27. Systematics on Secondary vertex Mass • To estimate systematics: • Test fit stability depending on templates shape and statistic • - also PYTHIA/HERWIG comparison • effects of fluctuation in relative composition of 2b/1b and 2c/1c estimate from NLO calculation 1b/2b 1c/2c 148 < pT < 202 GeV/c • Check on templates variation due to fragmentation scheme: PYTHIA Lund model, =0.0025 (default) VS Peterson model, =0.006 Total systematic from fraction: from 10% to 30% (but for last bin ~ 50%) Wine&Cheese Seminar, Fermilab September 9th 2005

  28. b-jet cross section: results Differential b-jet cross section at particle level (range pT 38-400 GeV/c) Total systematic error ~ 25%  70% in the last bin Ratio Data/Pythia MC(CTEQ5L) Wine&Cheese Seminar, Fermilab September 9th 2005

  29. Preliminary comparison with NLO for inclusive b-jet cross section

  30. b-jets @ NLO • - NLO calculation for b-jets Mangano&Frixione • 2 3 process, so jets are very simple: 1 or 2 partons inside gg total Shape very sensitive to bb content from gluon splitting (more likely to have 2 b inside same jet) qg qq Wine&Cheese Seminar, Fermilab September 9th 2005

  31. Fraction of double b-quark ending up in the same jet depend on gluon splitting, only appearing at LO  Scale dependence of b-jets @ NLO Rate bb-jets / All jets ~ 45% ~ 30% Strong scale dependence Wine&Cheese Seminar, Fermilab September 9th 2005

  32. Hadronization Underlying events Hadronization and Underlying events Before comparison with theoretical expectations  correct NLO b-jets for hadronization and underlying events Corrections that need to be added to theory from PYTHIA Monte Carlo ~ 20% correction for lowest bin None for b-jets above 130 GeV/c Wine&Cheese Seminar, Fermilab September 9th 2005

  33. Preliminary Data VS NLO b-jets NLO theoretical expectation for b-jet corrected at particle level • in analogy to inclusive jet cross • section measurements • mb=4.75 GeV/c2 • PDF Uncertainty:7%  20% • Merging/splitting issue: Rtheory=Rdata*Rsep, Rsep=1.3  10% uncertainty • Include scale uncertainty • ~ from 40%  20% • (PTbjet>250 GeV/c) Wine&Cheese Seminar, Fermilab September 9th 2005

  34. Data/NLO ratio • Ratio up to 1.5 above 100 GeV/c jets • Poor agreement but still within systematics without considering scale uncertainty if considering scale uncertainty overlap region increase Wine&Cheese Seminar, Fermilab September 9th 2005

  35. Comparison with Run I D results • Use m=m0 for central theory value • data close to upper band of systematic (m=m0/2  PDF uncertainty) • direct comparison of data not possible (different center of mass energy s, different jet algorithm, different rapidity range …) For jets below 100 GeV/c, D0 data in RunI showed a similar pattern Wine&Cheese Seminar, Fermilab September 9th 2005

  36. Issues on high PT b-jets • Unknown impact of higher order contributions: • reduced scale dependence • event has more partons in the final state, thus closer • to the real world • better description of the transverse momentum of • final state due to double radiation of initial states • Logarithmic log(pT/m) enhancement of higher order contribution due to gluon splitting is not included in NLO calculations (neither in MC@NLO) •  at low PT effects are small (range of B-hadron cross section) •  at high PT arevery important andneed to be considered Experimentally: • study of bb-jets correlation •  to disentangle different production mechanisms • Z+b jets and g+b jets •  could help to constrain the b density in the proton Wine&Cheese Seminar, Fermilab September 9th 2005

  37. More exclusive bjet cross sections

  38. bb jets cross section • Small data sample used • still preliminary • Analysis with larger sample in progress • dijet events • JETCLU, Rcone=0.7 jets • ET1>30GeV, ET2>20GeV • |h jets| < 1.2 central jets: more likely to be • sensitive to flavor creation Flavor excitation Q g Flavor creation ( + radiative corrections) predominantly back-to-back Q g g g Gluon splitting • Jets corrected at particle level for b flavor jets • Tag 2 jets with b-tagging algorithm earlier described Wine&Cheese Seminar, Fermilab September 9th 2005

  39. bb jets cross section results b fraction from Mass secvtx fit (global fit all ET range) Fbb=0.830.04 Integrated cross section: Data results +10.3 - 10.7 = 34.5  1.8 nb A = trigger acceptance ~ 1 (stat.) (syst) Monte Carlo prediction: Need to add more statistics on MC@NLO with final Underlying Event tuning = 35.7 ± 2.0 nbwith preliminary UE tuning Wine&Cheese Seminar, Fermilab September 9th 2005

  40. bb jets correlations Differential cross section as function of Df jets • Predominantly back to back • Explains agreement in cross section with Pythia • LO MC deviates away at low Df (where statistics are still low) Linear scale Log scale Compared to MC@NLO Wine&Cheese Seminar, Fermilab September 9th 2005

  41. Z+b jet production In QCD, Z+b can help constrain b density in the proton Important background for new physics such as higgs search + Probe the heavy flavor content of proton With HERA Fbb2 data: CTEQ below MRST by down to 1/2 and below data  Z+b jets can help understand this picture Wine&Cheese Seminar, Fermilab September 9th 2005

  42. Analysis strategy • Leptonic decays for Z reconstruction:Z e+e-,m+m- • Signal defined as Z0,g*l+l- events with 66<Mll<116 GeV/c2 Muon channel equivalent •  Z associated with jets -Rcone jet = 0.7, |h|<1.5, ET>20 GeV • Backgrounds: - fake electrons/same-sign muons (Data) - Real signatures e+e-/m+m- + bjet (MC) Wine&Cheese Seminar, Fermilab September 9th 2005

  43. Mass of secondary vertex Fit • Look for tagged jets in Z events • same b-tagging algorithm as in previous analyses • extract fraction of b-tagged jets from secondary vertex Mass • Use negative tagged jets to better constrain light and c quarks • Make no assumption on the charm content  extract b:NbData/NbMC Main source of systematic uncertainty from dependence of mass templates on b/bb content in the jet Wine&Cheese Seminar, Fermilab September 9th 2005

  44. Z+bjets results Z+b jet cross section corrected at particle (hadron) level: b: NbData/NbMCin Z events SF : scale factor for b-tag NZ+bMCHad: MC particle b-jets in Z evts NZMCHad: total MC Z evts NZMC: MC evts passing Z cuts NZData: Data evts passing Z cuts meas(Z) : CDF Z cross section m=MZ Uncertainty ~10% changing scale Central value for Z+b cross section also above theoretical expectations Wine&Cheese Seminar, Fermilab September 9th 2005

  45. Summary and Conclusion • In the last year many advances in theory calculation for b production at intermediate and low PT • Good agreement with B-Hadron cross section • Big effort in study of b-jets production in CDF RunII • Inclusive b-jet cross section measurement done within a wide range in transverse momentum using ~300 pb-1 data • Similar behaviour to D RunI cross section w.r.t. theoretical expectations for jet PT below 100 GeV/c • Agreement with theory within uncertainties: NLO b-jet cross section calculation still shows big scale dependences • Study of more exclusive b-jet cross section could help: • bb correlations to disentangle production processes • Z+b to understand b content in the initial radiation Wine&Cheese Seminar, Fermilab September 9th 2005

  46. Back up

  47. Typical d0 resolution Impact parameter resolution Wine&Cheese Seminar, Fermilab September 9th 2005

  48. B-jet cross section: Data/Herwig MC Wine&Cheese Seminar, Fermilab September 9th 2005

  49. bb jets differential cross section Comparison Data VS MC @NLO + UE tuning Differential cross section as function of dijet mass Comparison Data VS MC @NLO + UE tuning Differential cross section as function of leading jet ET Wine&Cheese Seminar, Fermilab September 9th 2005

  50. Z m+m-+ b Z m+m-channel: same-sign muons events with a reconstructed jet Specific background in muon channel Wine&Cheese Seminar, Fermilab September 9th 2005

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