New Results for ICHEP2008 from DØ

Fermilab Joint Experimental-Theoretical Seminar Fermilab, July 25, 2008 New Results for ICHEP2008 from DØ Aurelio Juste Fermi National Accelerator Laboratory For the DØ Collaboration

Overview • By ICHEP2008 we will have released in calendar year 2008: • 37 preliminary results, • 30 publications (~1/week). • [34 submitted in CY 2007] • 81 abstracts submitted to ICHEP. • This talk will only cover a subset of new results since Moriond 2008 spanning: • 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

Many thanks to the Accelerator Division for such outstanding performance!!! Results presented in this talk: ~0.7 - 3.0 fb-1

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 • … arXiv:0802.2400 [hep-ex]

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!

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

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

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!

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)

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

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?

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

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)

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!

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]

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 llvv • Manageable backgrounds, larger BR (~2.6%)

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)

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: 1.92x10-2 1.00x10-2 Significance: 2.1s2.3s

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)

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: 1.32x10-4 2.94x10-8 Significance: 3.65s5.42s 4-lepton invariant mass (GeV) First observation of ZZ production!!!

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 • …

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

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

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):

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

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

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

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

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

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

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 • ...

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!

2.5 fb-1 AcoplanarJets+MET 2 jets, pT>15 GeV Df(jet1,jet2) >165o MET>75 GeV Optimized cuts on MET and HT 1st Generation Leptoquarks (b=0) Littlest Higgs model (T-parity) DØ Run II Preliminary 1-b = B(LQnq) LEP Precision EW measurements DØ Run II Preliminary Most restrictive direct limits!

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 DØ EM calorimeter and central preshower detector to do “photon pointing”.

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

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!

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

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

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!

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

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

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

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)

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)

HWW As of Moriond’08… ee, mm, em • Highest sensitivity channel for mH>130 GeV. • Main backgrounds: • mH~160 GeV: WW • mH~130 GeV: W+jets • Low f(l,l) because of spin-0 Higgs. • Capitalize on improvements in lepton identification and multivariate techniques. At mH = 160 GeV: Expected limit: 2.4 x SM Observed limit: 2.1 x SM

Moriond’08 Tevatron Combination At mH = 160 GeV: Expected limit: 1.6 x SM Observed limit: 1.1 x SM Exciting prospects to start excluding in 2008!

3.0 fb-1 HWW • First 3.0 fb-1 result at DØ! • Significant improvements since Moriond: • Lepton ID • Neural Networks • 30% more luminosity • And the answer is….

3.0 fb-1 HWW • First 3.0 fb-1 result at DØ! • Significant improvements since Moriond: • Lepton ID • Neural Networks • 30% more luminosity • And the answer is…. • will finalize review in ~2 days Watch for updated Tevatron combination at ICHEP!

Conclusions • 21 new results from DØ discussed here covering a wide range of physics topics. • These represent a fraction of the results from DØ that will be discussed at ICHEP. • With ~4 fb-1 of data recorded, more to come, and getting smarter by the day on how to most effectively extract the physics information, Tevatron results will continue to resonate for years to come. • See you in Philadelphia next week!

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New Results for ICHEP2008 from DØ