precision top measurements from DØ Ulrich Heintz Boston University (for the D0 collaboration) Joint Experimental & Theoretical Physics Seminar, Fermilab, April 18, 2008

4/18/2008Ulrich Heintz - Joint Experimental & Theoretical Physics Seminar2 outline top quark physics at DØ lepton+jets channel cross section measurement –b-tag analysis –likelihood analysis –combination –comparison to theory/mass determination top quark mass measurement summary and outlook

4/18/2008Ulrich Heintz - Joint Experimental & Theoretical Physics Seminar3 outline top quark physics at DØ lepton+jets channel cross section measurement –b-tag analysis –likelihood analysis –combination –comparison to theory/mass determination top quark mass measurement summary and outlook

4/18/2008Ulrich Heintz - Joint Experimental & Theoretical Physics Seminar4 the top quark in the standard model fermion –spin = 1/2 color triplet –coupling to gluons –production cross section only unknown –mass weak isospin partner of b- quark with –weak isospin T 3 = +1/2 –charge Q = +2/3 –coupling to W,Z,  –branching fractions

4/18/2008Ulrich Heintz - Joint Experimental & Theoretical Physics Seminar5 it is by far the most massive quark e   volume of spheres  mass no measurable extend (< m) leptons quarks e 0.5 MeV d ≈ 7 MeV  MeV s ≈ 110 MeV u ≈ 3 MeV  MeV b ≈ 4300 MeV c ≈ 1300 MeV t ≈ 172,000 MeV

4/18/2008Ulrich Heintz - Joint Experimental & Theoretical Physics Seminar6 top quark properties strong production –cross section –kinematics –resonances –spin correlations properties –mass –charge –width/lifetime –spin decay –branching fractions –non-sm decays –rare decays –Wtb coupling weak production –cross section –|V tb | –Wtb coupling new at La Thuile accepted by PRL new at Moriond QCD

4/18/2008Ulrich Heintz - Joint Experimental & Theoretical Physics Seminar7 top quark properties strong production –M tt > 760 GeV –stop searches –FB asymmetry properties –Q = +2/3 decay –B(Wb) > 79% –B(H + b) < 35% –f 0 = 0.43 ±0.19 –f + = 0.12 ±0.10 weak production –σ = 4.7 ± 1.3 pb –|V tb | > 0.68 –M W’ > 739 GeV –FCNC searches

4/18/2008Ulrich Heintz - Joint Experimental & Theoretical Physics Seminar8 top quark production top-antitop pair production sm m top =175 GeV –σ = 6.7±0.7 pb Cacciari et al, JHEP04(2004)068 –σ = 6.8±0.6 pb Kidonakis & Vogt, PRD 68, (2003) –assumes sm coupling to gluons and no non- standard processes –depends on pdfs and top quark mass 85% 15%

4/18/2008Ulrich Heintz - Joint Experimental & Theoretical Physics Seminar9 top quark decay decay –t  Wb with B ≈ 100% –W  qq with B ≈ 67 % –W  ℓ with B ≈ 11%   e  with B ≈ 17 % final state signatures for top-antitop pairs e/μ+jets 38% dilepton 6% all jets 56%

4/18/2008Ulrich Heintz - Joint Experimental & Theoretical Physics Seminar10 cross section –basic understanding of data sample –consistency across channels –is there does new physics? mass –dominant contributor to radiative corrections WW t b WW H0H0  m top 2  log(m H ) B(t  H + b) = 0B(t  H + b) = 0.1B(t  H + b) = 0.2B(t  H + b) = 0.3B(t  H + b) = 0.4B(t  H + b) = 0.5B(t  H + b) = 0.6 why is this important? all jets dileptons lepton+jets

4/18/2008Ulrich Heintz - Joint Experimental & Theoretical Physics Seminar11 Run IIa Run IIb layer 0 silicon trigger upgrade

4/18/2008Ulrich Heintz - Joint Experimental & Theoretical Physics Seminar12 Tevatron

4/18/2008Ulrich Heintz - Joint Experimental & Theoretical Physics Seminar13 D0 detector

4/18/2008Ulrich Heintz - Joint Experimental & Theoretical Physics Seminar14 outline top quark physics at DØ lepton+jets channel cross section measurement –b-tag analysis –likelihood analysis –combination –comparison to theory/mass determination top quark mass measurement summary and outlook

4/18/2008Ulrich Heintz - Joint Experimental & Theoretical Physics Seminar15 event selection e+jets –exactly 1 electron from primary vertex isolated p T > 20 GeV |η| < 1.1 –missing p T > 20 GeV –Δφ(e,p T ) > 0.7π – p T both channels –veto events with a second lepton –at least 3 jets with p T > 20 GeV and |η| < 2.5 –leading jet p T > 40 GeV μ+jets –exactly 1 muon from primary vertex isolated p T > 20 GeV |η| < 2 –missing p T > 25 GeV –Δφ(e,p T ) > 2.1 – p T

4/18/2008Ulrich Heintz - Joint Experimental & Theoretical Physics Seminar16 backgrounds w/o W  lν decays model with “loose” data samples –relax lepton id cuts cut on p T and Δφ(e,p T ) residual contamination N loose = N W + N b N data = ε W N W + ε b N b N b = –determine ε b from low p T region 20±2 % for e+jets 27±5 % for μ+jets ε W from MC 84±2 % ε W N W - N b ε W - ε b D0 Run II “matrix method” missing p T (GeV) Δφ(e,missing p T )

4/18/2008Ulrich Heintz - Joint Experimental & Theoretical Physics Seminar17 sample composition non-W backgrounds –matrix method contributions with W  lν decays –single top: CompHEP+PYTHIA –dibosons: PYTHIA –Z+jets: ALPGEN+PYTHIA fix to NLO cross section –tt: PYTHIA m top = 175 GeV start with predicted cross section iterate with measured cross section –W+jets: ALPGEN+PYTHIA scale W+heavy flavor fraction by data driven factor scale so that MC prediction = number of events observed

4/18/2008Ulrich Heintz - Joint Experimental & Theoretical Physics Seminar18 sample composition Run IIa data sample: –  Ldt = 913 pb -1 (for e+jets) –  Ldt = 871 pb -1 (for μ+jets) N tt based on measured tt cross section e+3 jetse+4 jetsμ+3 jetsμ+4 jets N data N loose ε s (%)84.8± ± ± ±2.2 ε b (%)19.5± ±5.4 N tt 154±17132±14115±13109±12 N W+jet s 746±41 93±18824±24151±14 N other 132±15 35±4139±15 36±4 N non-W 268±34 60±10 42±14 10±6 using events with 3 jets reduces statistical uncertainty systematics due to migration between between multiplicity bins

4/18/2008Ulrich Heintz - Joint Experimental & Theoretical Physics Seminar19 data – MC comparison e+1 jet e+≥4 jets e+3 jets e+2 jets

4/18/2008Ulrich Heintz - Joint Experimental & Theoretical Physics Seminar20 data – MC comparison μ+1 jet μ+≥4 jets μ+3 jets μ+2 jets

4/18/2008Ulrich Heintz - Joint Experimental & Theoretical Physics Seminar21 outline top quark physics at DØ lepton+jets channel cross section measurement –b-tag analysis –likelihood analysis –combination –comparison to theory/mass determination top quark mass measurement summary and outlook dominant uncertainty: b-tagging dominant uncertainty: statistical fluctuations in kinematic distributions

4/18/2008Ulrich Heintz - Joint Experimental & Theoretical Physics Seminar22 b-tag analysis every tt decay produces two b-jets b-jet tagging –b-hadron lifetime ≈ 1.6 ps travels a few mm before decaying reduce backgrounds by requiring ≥1 b-tagged jet secondary vertex large impact parameter primary vertex

4/18/2008Ulrich Heintz - Joint Experimental & Theoretical Physics Seminar23 neural network b-tag algorithm combines parameters from several tagging algorithms –combined impact parameter significance of tracks –probability jet originates from primary vertex –number of secondary vertices in jet –secondary vertices decay length significance χ 2 /dof of fit number of tracks mass efficiency for tagging b-jets ≈ 54% rate for tagging light quark jets ≈ 1.2%

4/18/2008Ulrich Heintz - Joint Experimental & Theoretical Physics Seminar24 b-tag analysis determine non-W backgrounds using matrix method scale all other backgrounds from the pretagged sample using tagging probabilities maximize likelihood for observed number of events wrt tt cross section in 8 channels 3 jets/1tag3 jets/≥2 tags≥4 jets/1 tag≥4 jets/≥2 tags N tt 147±12 57±6130±10 66±7 N W+jet s 105±5 10±1 16±2 2±1 N other 27±2 5±1 8±1 2±1 N non-W 27±6 3±2 6±3 0±2 total306±14 74±6159±11 69±7 N data

4/18/2008Ulrich Heintz - Joint Experimental & Theoretical Physics Seminar25 b-tag analysis e+jets: σ tt = 7.3 ± 0.7(stat) ± 0.7(syst) ± 0.4 (lum) pb μ+jets: σ tt = 9.0 ± 0.9(stat) ± 0.8(syst) ± 0.6 (lum) pb σ tt = 8.05 ± 0.54 (stat) ± 0.69 (syst) ± 0.49 (lum) pb = 8.05 ± 1.00 pb (12%) σ tt = 8.05 ± 0.54 (stat) ± 0.69 (syst) ± 0.49 (lum) pb = 8.05 ± 1.00 pb (12%) 1 tag: σ tt = 8.5 ± 0.7(stat) ± 0.6(syst) ± 0.5 (lum) pb ≥2 tags: σ tt = 7.3 ± 0.8(stat) ± 1.0(syst) ± 0.5 (lum) pb for m top = 175 GeV

4/18/2008Ulrich Heintz - Joint Experimental & Theoretical Physics Seminar26 systematic uncertainties sourceuncertainty vertex0.15 pb e id0.11 pb μ id0.08 pb jet id0.12 pb non-W bkg0.06 pb jet response0.30 pb MC model0.29 pb b-tagging efficiency0.48 pb total0.69 pb W+hf scale factor b fragmentation factorization scale cross sections

4/18/2008Ulrich Heintz - Joint Experimental & Theoretical Physics Seminar27 outline top quark physics at DØ lepton+jets channel cross section measurement –b-tag analysis –likelihood analysis –combination –comparison to theory/mass determination top quark mass measurement summary and outlook

4/18/2008Ulrich Heintz - Joint Experimental & Theoretical Physics Seminar28 likelihood analysis use kinematic distributions to separate signal and background 4 channels –e+3 jets (require H T >120 GeV) –e+≥4 jets –μ+3 jets (require H T >120 GeV) –μ+≥4 jets use five or six variables for each channel –well modeled by our simulation –good signal/background discrimination –insensitive to jet energy calibration

4/18/2008Ulrich Heintz - Joint Experimental & Theoretical Physics Seminar29 likelihood input variables e+≥4 jets events (arbitrary units) sphericity ΔR(j 1,j 2 )ΔR(e,j) p T (j 3 )+p T (j 4 ) (GeV)Σp T (j)/Σp z (j) aplanarity

4/18/2008Ulrich Heintz - Joint Experimental & Theoretical Physics Seminar30 e+2 jets e+3 jets e+≥4 jets aplanarity sphericity Σp T (j)/Σp z (j) likelihood input variables

4/18/2008Ulrich Heintz - Joint Experimental & Theoretical Physics Seminar31 likelihood discriminant constrain non-W backgrounds using matrix method fit contributions from tt + all other backgrounds maximize likelihood for observed discriminant spectra wrt the tt cross section in 4 channels L s/b = Πp s/b D =L s /(L s +L b ) DDD

4/18/2008Ulrich Heintz - Joint Experimental & Theoretical Physics Seminar32 likelihood analysis e+jets: σ tt = 6.3 ± 1.0(stat) ± 0.4(syst) ± 0.4 (lum) pb μ+jets: σ tt = 7.1 ± 1.2(stat) ± 0.6(syst) ± 0.4 (lum) pb σ tt = 6.62 ± 0.78 (stat) ± 0.36 (syst) ± 0.40 (lum) pb = 6.62 ± 0.95 pb (14%) σ tt = 6.62 ± 0.78 (stat) ± 0.36 (syst) ± 0.40 (lum) pb = 6.62 ± 0.95 pb (14%) for m top = 175 GeV

4/18/2008Ulrich Heintz - Joint Experimental & Theoretical Physics Seminar33 systematic uncertainties sourceselectionfittotal vertex0.13 pb e id0.10 pb μ id0.06 pb jet id0.10 pb0.02 pb0.12 pb non-W bkg0.10 pb jet response0.35 pb0.26 pb0.11 pb MC model0.13 pb0.09 pb0.11 pb template stats0.15 pb total0.36 pb b fragmentation factorization scale cross sections

4/18/2008Ulrich Heintz - Joint Experimental & Theoretical Physics Seminar34 outline top quark physics at DØ lepton+jets channel cross section measurement –b-tag analysis –likelihood analysis –combination –comparison to theory/mass determination top quark mass measurement summary and outlook

4/18/2008Ulrich Heintz - Joint Experimental & Theoretical Physics Seminar35 combination use Best Linear Unbiased Method* –determine statistical correlation factor using toy Monte Carlo simulation –throw random numbers for independent subsamples such that mean event numbers agree with observation –assume σ tt = 7.4 pb –feed counts into b-tagging analysis –draw discriminant spectra from templates and fit for likelihood analysis –assume all systematic uncertainties are completely correlated for every source *L. Lyons, D Gibaut, P. Clifford, Nucl. Inst. Meth., A270, 110 (1988). r = 0.31

4/18/2008Ulrich Heintz - Joint Experimental & Theoretical Physics Seminar36 combination  most precise measurement of the tt cross section systematic uncetaintyb-taglikelihoodcombined selection efficiency0.26 pb0.25 pb jet energy scale calibration0.30 pb0.11 pb0.20 pb b-tagging0.48 pb0.24 pb MC model0.29 pb0.11 pb0.19 pb non-W background0.06 pb0.10 pb0.07 pb likelihood fit0.15 pb0.08 pb σ tt = 7.42 ± 0.53 (stat) ± 0.46 (syst) ± 0.45 (lum) pb = 7.42 ± 0.83 pb (11%) σ tt = 7.42 ± 0.53 (stat) ± 0.46 (syst) ± 0.45 (lum) pb = 7.42 ± 0.83 pb (11%) for m top = 175 GeV

4/18/2008Ulrich Heintz - Joint Experimental & Theoretical Physics Seminar37 tt cross section

4/18/2008Ulrich Heintz - Joint Experimental & Theoretical Physics Seminar38 top quark mass dependence repeat assuming different values of m top

4/18/2008Ulrich Heintz - Joint Experimental & Theoretical Physics Seminar39 outline top quark physics at DØ lepton+jets channel cross section measurement –b-tag analysis –likelihood analysis –combination –comparison to theory/mass determination top quark mass measurement summary and outlook

4/18/2008Ulrich Heintz - Joint Experimental & Theoretical Physics Seminar40 mass from cross section compare measured cross section to prediction

4/18/2008Ulrich Heintz - Joint Experimental & Theoretical Physics Seminar41 joint likelihood m top = 170 ± 7 GeV different systematics than direct measurement

4/18/2008Ulrich Heintz - Joint Experimental & Theoretical Physics Seminar42 outline top quark physics at DØ lepton+jets channel cross section measurement –b-tag analysis –likelihood analysis –combination –comparison to theory/mass determination top quark mass measurement summary and outlook

4/18/2008Ulrich Heintz - Joint Experimental & Theoretical Physics Seminar43 data sample Run IIb (1.2 fb -1 ) selection –same as for cross section analysis plus –exactly 4 jets –at least one jet is b-tagged number of events –e+jets: 150 –μ+jets: 121

4/18/2008Ulrich Heintz - Joint Experimental & Theoretical Physics Seminar44 lepton+jets event kinematics jet energy calibration –external γ + jet events dijet events uncertainty ≈ 1.7% limited by systematics uniform response in E,η –in situ W  qq from top decay out overall scale α jes statistically limited tt  Wb Wb  e qq MWMW

4/18/2008Ulrich Heintz - Joint Experimental & Theoretical Physics Seminar45 matrix element method probability density for event o if top quark mass is m t signal probability combine all events in a joint likelihood and maximize wrt m t  jes f top top fraction jet scale parameter normalization (acceptance, efficiencies) pdf |M| 2 dLIPS transfer function

4/18/2008Ulrich Heintz - Joint Experimental & Theoretical Physics Seminar46 ensemble tests randomly draw –N sig signal events –N bkg background events from MC samples so that –N obs = N sig +N bkg –signal fraction matches observation on average f top ≈ 40% without b-tag requirement f top ≈ 78% with ≥1 b-tag

4/18/2008Ulrich Heintz - Joint Experimental & Theoretical Physics Seminar47 ensemble tests from each ensemble determine –measured top quark mass m –statistical uncertainty Δm –pull = (m-m top )/Δm m (GeV) Δm (GeV) pull

4/18/2008Ulrich Heintz - Joint Experimental & Theoretical Physics Seminar48 calibration curve for top quark mass correct measured mass according to this calibration curve correct uncertainties for difference of pull width from 1

4/18/2008Ulrich Heintz - Joint Experimental & Theoretical Physics Seminar49 MC bias 2-dimensional fit external jet calibration

4/18/2008Ulrich Heintz - Joint Experimental & Theoretical Physics Seminar50 result m top = ± 1.9(stat  jes) ± 1.0 (syst) GeV

4/18/2008Ulrich Heintz - Joint Experimental & Theoretical Physics Seminar51 systematic uncertainties sourceuncertainty signal model0.40 GeV background model0.08 GeV W+heavy flavor0.07 GeV b fragmentation function0.10 GeV pdfs0.24 GeV residual jet calibration0.03 GeV relative b/q jet response0.82 GeV b-tagging efficiency0.16 GeV trigger efficiency0.09 GeV jet energy resolution0.30 GeV non-W background0.20 GeV MC calibration0.14 GeV total1.00 GeV

4/18/2008Ulrich Heintz - Joint Experimental & Theoretical Physics Seminar52 systematic uncertainties study using ensemble tests b/q jet energy calibration –MC derived transfer functions correct b and q-jets to the parton level –estimate difference in b/q response between data and MC using parametrized single particle response tuned to data and tuned to MC –difference = 1.8% –correct all jets matched to b-hadrons in MC by this amount signal modeling –modeling of additional jet from ISR or FSR –reweight MC tt events so that 4/≥5 jet ratio agrees with data jet energy resolution –vary jet energy resolution by uncertainty

4/18/2008Ulrich Heintz - Joint Experimental & Theoretical Physics Seminar53 combination with Run IIa Run IIb (1.2 fb -1 ) ± 1.9(stat  jes) ± 1.0 (syst) GeV Run IIa (0.9 fb -1 ) ± 2.5(stat  jes) ± 1.4 (syst) GeV combined (2.1 fb -1 ) –BLUE method (some procedure as world average)  most precise single measurement of m top m top = ± 1.1 (stat) ± 1.6 (syst  jes) GeV = ± 1.9 GeV (1.1%) m top = ± 1.1 (stat) ± 1.6 (syst  jes) GeV = ± 1.9 GeV (1.1%)

4/18/2008Ulrich Heintz - Joint Experimental & Theoretical Physics Seminar54 world average combination Run II Measurement CDF di-l D0 di-l CDF l+j D0 l+j CDF all-j CDF lxy world average ∫Ldt (fb -1 ) Result Jet Energy Scale Signal Background Fit MC Systematic Statistical Total Uncertainty statistical: uncorrelated jet energy scale: several subcategories with different correlations signal: ISR, FSR, pdf, b-id – correlated for all background: correlated within channels fit: MC stats – uncorrelated MC: Monte Carlo generator – correlated for all

4/18/2008Ulrich Heintz - Joint Experimental & Theoretical Physics Seminar55 top quark mass TeV-EWWG

4/18/2008Ulrich Heintz - Joint Experimental & Theoretical Physics Seminar56 winter 2008 global electroweak fit LEP EWWG procedure results for winter 2008 (summer 2007) –  had = ± –  s = ± –M Z = ± GeV –m top = 172.8±1.4 GeV (171.3±1.7 GeV) –M H = GeV( GeV)  2 /dof = 17.2/13 (18.2/13) –p-value = 19%

4/18/2008Ulrich Heintz - Joint Experimental & Theoretical Physics Seminar57 winter 2008 global electroweak fit m H < % C.L. (<190 GeV incl. LEP-2 limit) LEP-EWWG procedure

4/18/2008Ulrich Heintz - Joint Experimental & Theoretical Physics Seminar58 outline top quark physics at DØ lepton+jets channel cross section measurement –b-tag analysis –likelihood analysis –combination –comparison to theory/mass determination top quark mass measurement summary and outlook

4/18/2008Ulrich Heintz - Joint Experimental & Theoretical Physics Seminar59 summary most precise single measurements –top quark mass with 2 fb -1 m top = ± 1.9 GeV  m/m = 1.1% –tt cross section σ tt = 7.62 ± 0.85 m top = GeV  σ/σ = 11% –compare with theory m top = 170 ± 7 GeV

4/18/2008Ulrich Heintz - Joint Experimental & Theoretical Physics Seminar60 outlook September 2005 July 2005 how do we stack up to our predictions?  continue to beat on systematic uncertainties

4/18/2008Ulrich Heintz - Joint Experimental & Theoretical Physics Seminar61 ➔ 19 countries ➔ 80 institutions ➔ 700 physicists DØ Collaboration