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Recent Results from DØ

CPPM High Energy Physics Seminar, September 11, 2008. Recent Results from DØ. Aurelio Juste Fermi National Accelerator Laboratory. Today’s Program. Since the beginning of calendar year 2008: 37 preliminary results 39 publications (~1/week) [34 submitted in CY 2007]

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Recent Results from DØ

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  1. CPPM High Energy Physics Seminar, September 11, 2008 Recent Results from DØ Aurelio Juste Fermi National Accelerator Laboratory

  2. Today’s Program • Since the beginning of calendar year 2008: • 37 preliminary results • 39 publications (~1/week) • [34 submitted in CY 2007] • 81 abstracts submitted to ICHEP 2008. • 3 press releases in the last 2 months. • This talk will only cover a subset of recent results spanning the whole physics program: • QCD physics • B physics • EW physics • Top physics • Higgs searches • New phenomena searches Many thanks to my DØ colleagues for their hard work!!! http://www-d0.fnal.gov/Run2Physics/WWW/results.htm

  3. Run I Run IIa Run IIb Bunches in Turn 6  6 36  36 36  36 s (TeV) 1.8 1.96 1.96 Typical L (cm-2s-1) 1.6 1030 1x1032 2.5 1032  Ldt (pb-1/week) 3 20 50 Bunch crossing (ns) 3500 396 396 Interactions/ crossing 2.5 2.5 6.7 Tevatron Accelerator • Current performance: • Instantaneous luminosity: ~2.8x1032 cm-2s-1 • Integrated luminosity: • ~4.8 fb-1 • Project ~7.3-8.8 fb-1 by end of FY10

  4. DØ Detector Central Tracking System • Features: • Central tracking system in a 2 T solenoidal field: • Silicon Tracker (||<3) • Scintillating Fiber Tracker (||<1.5) • Central and forward preshowers • LAr/U calorimetry (||<4.2) • Muon system (3 layers, (||<2.0) • Run IIb upgrades for further improved performance: • L1 trigger: CAL, Track and CAL+Track • Additional silicon layer (LØ) at R=1.6 cm. • Multipurpose detector: • Lepton (e, , t) identification • Jets and MET reconstruction • Jet flavor ID via displaced tracks and soft-leptons • Data taking efficiency: 85-90% • Recorded luminosity to date: ~4.2 fb-1 Results presented in this talk: ~0.7 - 3.0 fb-1

  5. QCD Physics: New Results • Jet Physics • Inclusive jet cross section • Dijet angular distributions • … • Vector Boson(+jets) Physics • Z pT spectrum • Measurement of g2 parameter • Z+jets total/differential cross sections • s(W+charm)/s(W+jet) cross section ratio • g+jets differential cross sections • g+heavy-flavor jets differential cross sections • … PRL 101, 062001 (2008) arXiv:0808.1296 [hep-ex]

  6. 0.7 fb-1 Dijet Angular Distributions • Dijet angular distributions in bins of dijet mass: • First differential cross section measurement at partonic energies >1 TeV! • Small experimental and theoretical uncertainties. • Sensitive to New Physics (95% CL limits): yi = jet rapidity Compositeness (l=+1): L>2.6 TeV ADD extra-dimensions (n=4): Ms>1.6 TeV TeV-1 extra-dimensions: Mc>1.4 TeV Most restrictive limits at the Tevatron!

  7. g2 Measurement • Z boson differential distributions provide important information on production mechanism. • Low Z pT region dominated by multiple soft-gluon emissions  resummation • g2 traditionally extracted from Z pT spectrum. • New experimental technique almost insensitive to dominant systematic uncertainties in previous measurements (lepton energy resolution/efficiency). BNLY non-perturbative form factor ResBos

  8. g2 Measurement • Z boson differential distributions provide important information on production mechanism. • Low Z pT region dominated by multiple soft-gluon emissions  resummation • g2 traditionally extracted from Z pT spectrum. • New experimental technique almost insensitive to dominant systematic uncertainties in previous measurements (lepton energy resolution/efficiency). BNLY non-perturbative form factor

  9. 2.0 fb-1 g2 Measurement • Z boson differential distributions provide important information on production mechanism. • Low Z pT region dominated by multiple soft-gluon emissions  resummation • g2 traditionally extracted from Z pT spectrum. • New experimental technique almost insensitive to dominant systematic uncertainties in previous measurements (lepton energy resolution/efficiency). • Electron and muon channels (2 fb-1): BNLY non-perturbative form factor PDF uncertainties not included Precision competitive with world average!

  10. Photon+Heavy Flavor Jet • Limited knowledge on heavy-quark (b,c) PDFs. • Is there an “intrinsic charm” (non-perturbative) component of the proton? arXiv:hep-ph/0701220 u d c (radiative+intrinsic) Two different models c (radiative)

  11. 1.0 fb-1 Photon+Heavy Flavor Jet • Use g+b-tagged jet events: • Photon purity: ~60-90% depending on pTg • Discriminate between b, c and light jets using information on track impact parameter. g+b _ b g+b in agreement with NLO QCD (CTEQ6.6) b b b g+b

  12. 1.0 fb-1 Photon+Heavy Flavor Jet • Use g+b-tagged jet events: • Region probed: 0.1<x<0.3, 0.9x103<Q2<2x104 GeV2 g+c _ c g+c c c c Large discrepancy for g+c at high pTg Significant intrinsic charm contribution?

  13. CP Violation in the BS System: New Results • Time-dependent angular analysis in flavor-tagged Bs J/ decays • B(Bs Ds(*)Ds(*)) • CP-violating asymmetry in semileptonic Bs decays Weak eigenstates: arXiv:0802.2255 [hep-ex] Mass eigenstates: Bs meson allows to probe the entire matrix: Sensitive to New Physics Not sensitive to New Physics VERY sensitive to New Physics

  14. Asymmetry in Semileptonic Bs Decays • Previous DØ measurements: • vs. •  time-integrated, no flavor tagging • vs. •  depends on b-fragmentation and Bd asymmetries from B factories • Combination of both measurements: 1.3 fb-1, PRL 98, 151801 (2007) arXiv:hep-ph/0612167 Prediction 1 fb-1, PRD 74, 092001 (2006)

  15. 2.8 fb-1 Asymmetry in Semileptonic Bs Decays NEW • Flavor tagging and time-dependent analysis used for Bs-mixing measurement. • Exploits regular reversal of solenoid/toroid polarities to control systematics. arXiv:hep-ph/0612167 Prediction Significant constraints on CPV phase expected from combination of measurements Statistics-limited!

  16. B-Baryon Spectroscopy • Heavy quark hadrons are the “hydrogen atom” of QCD and b hadrons offer the heavier quarks in bound systems. • Very sensitive tests of potential models, HQET, lattice gauge calculations… • Unique to Tevatron (not produced in B factories). • Before Tevatron, only Lb observed. • Recent observations at the Tevatron: b ±, b*±, b-.

  17. Search for the b- • Similar experimental strategy to that used for b- observation. • Challenges: soft particles, large impact parameter •  reprocessing with special version of tracking. • Optimization of analysis based in intermediate resonances with blinded signal region. ~5 cm ~3 cm

  18. 1.3 fb-1 Search for the b- arXiv:0808.4142 [hep-ex] 17.8 ± 4.9 (stat) ± 0.8 (syst) events Mass: 6.165 ± 0.010(stat) ± 0.013(syst) GeV Significance: 5.4 First observation of the b- !!! • Relative production rate:

  19. EW Physics: New Results arXiv:0804.3220 [hep-ex] • Precision Measurements • AFB in Z/g*ee and sin2qWeff • W charge asymmetry • s(ppZ/g*+X)B(Z/g*tt) • … • Diboson • Radiation amplitude zero and anomalous couplings in Wg • Search for narrow resonances decaying to Zg • ZZ production • … arXiv:0807.3367 [hep-ex]

  20. ZZ Production • The smallest SM diboson cross section: • s(ZZ)=1.6 ± 0.1 pb •  reality check for New Phenomena searches. • Sensitive to New Physics: l=e,m • ZZ 4 leptons • Very small backgrounds, but small BR (~0.4%) • ZZ llnn • Manageable backgrounds, larger BR (~2.6%)

  21. 2.7 fb-1 ZZllnn • Large background from fake MET reduced by constructing an optimized MET variable. • Build likelihood discriminant against WW background: • Mee or P(2Z) • pT(l1) • Cos(q*l-) • Df(l1,ll)

  22. 2.7 fb-1 ZZllnn • Large background from fake MET reduced by constructing an optimized MET variable. • Build likelihood discriminant against WW background: • Mee or P(2Z) • pT(l1) • Cos(q*l-) • Df(l1,ll) Expected Observed P-value: 0.0244 0.0042 Significance: 2.0s2.6s

  23. 1.7 fb-1 ZZ4l Run IIb • Careful optimization of lepton identification criteria and kinematic selections. • Seven orthogonal channels: • 4e (3 categories) • 4m • 2e+2m (3 categories) • M(Z1)>70 GeV, M(Z2)>50 GeV 4-lepton invariant mass (GeV)

  24. 1.7 fb-1 ZZ4l Run IIb • Careful optimization of lepton identification criteria and kinematic selections. • Seven orthogonal channels: • 4e (3 categories) • 4m • 2e+2m (3 categories) • M(Z1)>70 GeV, M(Z2)>50 GeV Expected Observed P-value: 4.3x10-8 Significance: 3.7s5.3s 4-lepton invariant mass (GeV) First observation of ZZ production!!!

  25. 1.7 fb-1 ZZ4l Run IIb • Careful optimization of lepton identification criteria and kinematic selections. • Seven orthogonal channels: • 4e (3 categories) • 4m • 2e+2m (3 categories) • M(Z1)>70 GeV, M(Z2)>50 GeV • Combination with Run IIa analysis (1.1 fb-1; no candidates observed) and ZZ llnn analysis: Expected Observed P-value: 6.2x10-9 Significance: 4.8s5.7s 4-lepton invariant mass (GeV) First observation of ZZ production!!!

  26. W helicity Top Mass l+ Top Width Anomalous Couplings Production cross-section Top Spin W+ CP violation Top Charge Resonant production p n t b Production kinematics _ b X _ Top Spin Polarization _ q’ t q Rare/ non SM Decays W- _ p Branching Ratios |Vtb| Top Physics: New Results • Multiple cross section measurements including their combination • Precise top quark mass measurement in lepton+jets and dilepton channels. • Top mass extraction from cross section • Limits on anomalous tbW couplings from single top production • Model-independent measurement of the W helicity fraction in top quark decays • Search for W’tb • Search for H±tb • Limits on H± in top quark decays • …

  27. 1.0 fb-1 Top Pair Cross Section and New Physics • Combine tt cross section measurements in lepton+jets, dilepton and lepton+tau (14 independent channels). • Precise measurements in different channels allows to place constraints on New Physics. • tH+b: channels affected differently depending on H+ decay modes. • Tauonic: B(H+tn)=1 • disappearance of l+jets, dilepton • appearance of l+t • Leptophobic: B(H+cs)=1 • disappearance of l+jets, dilepton and l+t For mt=170 GeV: Good agreement with the SM prediction

  28. 1.0 fb-1 Top Pair Cross Section and New Physics • Combine tt cross section measurements in lepton+jets, dilepton and lepton+tau (14 independent channels). • Precise measurements in different channels allows to place constraints on New Physics. • tH+b: channels affected differently depending on H+ decay modes. • Tauonic: B(H+tn)=1 • disappearance of l+jets, dilepton • appearance of l+t • Leptophobic: B(H+cs)=1 • disappearance of l+jets, dilepton and l+t B(H+tn)=1

  29. 1.0 fb-1 Top Pair Cross Section and New Physics • Combine tt cross section measurements in lepton+jets, dilepton and lepton+tau (14 independent channels). • Precise measurements in different channels allows to place constraints on New Physics. • tH+b: channels affected differently depending on H+ decay modes. • Tauonic: B(H+tn)=1 • disappearance of l+jets, dilepton • appearance of l+t • Leptophobic: B(H+cs)=1 • disappearance of l+jets, dilepton and l+t Tauonic Leptophobic Using top as a tool to look for New Physics

  30. 2.8 fb-1 Top Quark Mass • Important parameter in precision electroweak analyses. • Challenges: • Jet energy scale (JES) • Signal modeling • Combinatorics • Sophisticated techniques to minimize statistical and dominant systematic uncertainties (JES via in-situ calibration in lepton+jets). Matrix Element Method: Lepton+jets (2.1 fb-1): e+m (2.8 fb-1):

  31. 2.8 fb-1 Top Quark Mass • Important parameter in precision electroweak analyses. • Sophisticated techniques to minimize statistical and dominant systematic uncertainties. • Good agreement between mass from direct reconstruction and cross section measurement. Different systematic uncertainties

  32. 0.9 fb-1 tbW Interaction: Single Top • Top couplings to the W boson very interesting! • Single top production directly sensitive to the tbW interaction: rate and kinematics. • SM: s ~ 2.9 pb (SM) SM: SM

  33. 0.9 fb-1 tbW Interaction: Single Top • Top couplings to the W boson very interesting! • Single top production directly sensitive to the tbW interaction: rate and kinematics. • SM (f1L=1, rest=0): s ~ 2.9 pb • f2L(R)=1, rest=0 : s ~ 10.4 pb f2L(R)=1, rest=0 SM

  34. 0.9 fb-1 tbW Interaction: Single Top • Top couplings to the W boson very interesting! • Single top production directly sensitive to the tbW interaction: rate and kinematics. • SM (f1L=1, rest=0): s ~ 2.9 pb • f2L(R)=1, rest=0 : s ~ 10.4 pb • Use same multivariate analysis technique as for the single top production evidence. arXiv:0807.1692 [hep-ex] First direct constraints on tbW tensor couplings

  35. Left-handed W (lW=-1 ) Longitudinal W (lW=0 ) Right-handed W (lW=+1 ) b b W W t t t t W W b b tbW Interaction: W Helicity • W helicity polarizations in top quark decays: • Lepton+jets and dilepton final states. • Reconstruct lepton helicity angle: n W+ b q* SM: PRL 100, 062004 (2008) l+ SM 1s 2s

  36. Left-handed W (lW=-1 ) Longitudinal W (lW=0 ) Right-handed W (lW=+1 ) b b W W t t t t W W b b 2.7 fb-1 tbW Interaction: W Helicity • W helicity polarizations in top quark decays: • Lepton+jets and dilepton final states. • Reconstruct lepton helicity angle. • Model independent measurement: lepton+jets SM: SM NEW 1s 2s Most precise measurement! Further constraints on tbW couplings to follow

  37. New Phenomena Searches: New Results • Scalar top pair production • Leptoquarks (1st, 2nd, 3rd generation) • T-odd quarks in Little Higgs models • Large extra-dimensions in mono-photon • Large extra-dimensions in di-EM • Long-lived particles decaying into ee, gg • Charged massive stable particles • ...

  38. 1.0 fb-1 Scalar Leptoquarks (3rd Generation) 1+2 tags • Predicted by a variety of New Physics models (GUTs, Compositeness, etc). • Couple directly to a quark and a lepton: • Consider 3rd gen scalar LQ with charge 2/3 or 4/3: LQt+b l,n q _ b ~ B(LQl+q) _ l, n _ q arXiv:0806.3527 [hep-ex] • 1 isolated m, pT>15 GeV • 1  candidate, pT>15-20 GeV • 2 jet, pT>25(20) GeV; 1 and 2 b-tags Most restrictive limits in this decay channel!

  39. 2.5 fb-1 AcoplanarJets+MET 2 jets, pT>15 GeV Df(jet1,jet2) >165o MET>75 GeV Optimized cuts on MET and HT arXiv:0808.0446 [hep-ex] 1st Generation Leptoquarks (b=0) Littlest Higgs model (T-parity) 1-b = B(LQnq) LEP Precision EW measurements Most restrictive direct limits!

  40. 2.7 fb-1 Large Extra-Dimensions: mono-photon • Gravity diluted in large compactified extra spatial dimensions. • Tower of Kaluza-Klein gravitons GKK (massive, stable, non-interacting). • qq  g + GKK monophoton signature • pT(g)>90 GeV, MET>70 GeV • Backgrounds: • Z(nn)g,.. • Non-collision (cosmics, beam-halo) • Exploit fine granularity of the EM calorimeter and central preshower detector to do “photon pointing”.

  41. 2.7 fb-1 Large Extra-Dimensions: mono-photon • Gravity diluted in large compactified extra spatial dimensions. • Tower of Kaluza-Klein gravitons GKK (massive, stable, non-interacting). • qq  g + GKK monophoton signature • pT(g)>90 GeV, MET>70 GeV • Backgrounds: • Z(nn)g,.. • Non-collision (cosmics, beam-halo) • Exploit fine granularity of the EM calorimeter and central preshower detector to do “photon pointing”. Improve upon LEP limits for nd>4

  42. 1.0 fb-1 Large Extra-Dimensions: ee, gg • Gravity diluted in large compactified extra spatial dimensions. • Tower of Kaluza-Klein gravitons GKK (massive, stable, non-interacting). Interference! Virtual GKK exchange • Di-EM (ee,gg) final state signature. • Exploit di-EM mass and cos(q*) distributions. DØ Run II Preliminary DØ Run II Preliminary Most restrictive limits at the Tevatron!

  43. 1.1 fb-1 Charged Massive Stable Particles • Charged: leaves track in detector • Massive: long time-of-flight, heavily ionizing • “Stable” = long-lived  signal in muon system • Search for dimuon-like signature with long time-of-flight. Exploit timing information from muon scintillator system (resolution: ~2.5 ns) DØ Run II Preliminary DØ Run II Preliminary Gaugino-like chargino 185 GeV Most restrictive limits at the Tevatron

  44. Higgs Searches Beyond the SM • Within a generic (Type II) 2HDM: • u and d couple respectively to up- and down-type fermions; tan=vu/vd. • After EWSB: four massive scalars (h0,H0,H±) and one pseudo-scalar (A0) • MSSM at large tan: • 0={h0/H0,A0} nearly degenerated in mass • Coupling to b, t enhanced (tan) • b(b)+0bbb(b) • b(b)+0tmthadb(b) • 0t+t- • Significant increase in production rate: +X  2 x tan2 • BR(0bb)~90%, BR(0t+t-)~10% NEW NEW NEW

  45. 2.6 fb-1 b(b)+0bbb(b) b b • Experimental signature: • 3, 4 or 5 jets; 3 b-tags • Select on likelihood discriminant (mass information not used). • Invariant mass of leading two jets peaks at M • Backgrounds dominated by heavy flavor-enriched QCD multijets: • Shape extracted from 2-tag sample • Rate normalized outside the “signal region” • Run IIb preliminary result combined with Run IIa (1 fb-1) publication. Most restrictive limits at the Tevatron!

  46. 2.2 fb-1 0t+t- t+ t- • Lower BR but also lower backgrounds. • Typical experimental signature (tmthad): • 1 isolated m, pT>10 GeV • 1  candidate, pT>15(20) GeV • Main background: Zt+t- • Visible mass: • Combination of four channels: • Run IIa (1.0 fb-1): tmthad, tethad, tetm • Run IIb (1.2 fb-1) : tmthad Work ongoing to combine the three analyses

  47. SM Higgs Searches: New Results • Major effort underway to continue to improve sensitivity: • Adding channels, • Optimized object identification/resolution • Optimized selections and signal-to-bckg discrimination, and of course, • Adding more luminosity! • WHlnbb • WHtnbb • ZHllbb • ttHlnbjjbbb • Hgg • HWW • ... …and more! Added for the first time

  48. WHlnbb • One of the most sensitive channels in the ~110-130 GeV mass range. • Consider 8 independent channels: • e+jets, m+jets • 2, 3 jets • 1, 2 b-tags (NN-based) • Main background: W+HF jets, tt • Dijet mass  multivariate discriminants

  49. 1.1 fb-1 WHlnbb • One of the most sensitive channels in the ~110-130 GeV mass range. • Consider 8 independent channels: • e+jets, m+jets • 2, 3 jets • 1, 2 b-tags (NN-based) • Main background: W+HF jets, tt • Dijet mass  multivariate discriminants • ~20% improvement in limit re-analyzing same dataset (1.1 fb-1) for publication. • Input to Tevatron combination w/ 1.7 fb-1: • expected limit: 8.5 x SM. At mH = 115 GeV: Expected limit: 10.1 x SM (=1.29 pb) Observed limit: 10.7 x SM (=1.37 pb)

  50. 2.7 fb-1 Hgg • Small BR in SM (~0.2%) but one of the most promising channels at the LHC. • It also contributes at the Tevatron! • Event selection: • 2 photons with pT>25 GeV and ||<1.1 • [NN-based photon ID] • Main backgrounds estimated from data: • Direct QCD gg (~60%) • g+j and dijet (jet g) • Use diphoton mass spectrum: 1.3 signal events At mH = 115 GeV: Expected limit: 23.2 x SM (=65.1 fb) Observed limit: 30.8 x SM (=86.5 fb) Limits improved by x2 since Moriond’08 (2.3 fb-1)

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