New Results for ICHEP2008 from DØ

New Results for ICHEP2008from DØ

Fermilab Joint Experimental-Theoretical SeminarFermilab, July 25, 2008

Aurelio JusteFermi National Accelerator Laboratory

For the DØ Collaboration

OverviewOverview

• 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

http://www-d0.fnal.gov/Run2Physics/WWW/results.htm

Many thanks to my DØ colleagues

for their hard work!!!

2

Many thanks to the Accelerator Division

for such outstanding performance!!!

Results presented in this talk: ~0.7 - 3.0 fb-13

QCD Physics: New ResultsQCD 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• (W+charm)/(W+jet) cross section ratio• +jets differential cross sections• +heavy-flavor jets differential cross sections• …

arXiv:0802.2400 [hep-ex]

4

Dijet Angular DistributionsDijet 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):

Compositeness (=+1): >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!

*

*

21 cos1

cos1)exp(

yydijet

yi = jet rapidity

0.7 fb-1

5

g2 Measurementg2 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

6







7






• Electron and muon channels (2 fb-1):


Precision competitive with world average!

2.0 fb-1

8

)(04.0(exp)02.063.02 PDFg

PDF uncertainties not included

Photon+Heavy Flavor JetPhoton+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

ud

c (radiative)c (radiative+intrinsic)

Two different models

9

Photon+Heavy Flavor JetPhoton+Heavy Flavor Jet

• Use +b-tagged jet events:

• Photon purity: ~60-90% depending on pT

• Discriminate between b, c and light jets using information on track impact parameter.

b

bb

b

1.0 fb-1

+b

+b

+b in agreement with NLO QCD (CTEQ6.6)

10

_

Photon+Heavy Flavor JetPhoton+Heavy Flavor Jet 1.0 fb-1

• Use +b-tagged jet events:

Region probed: 0.1<x<0.3, 0.9x103<Q2<2x104 GeV2

c

cc

c

+c

+c

Large discrepancy for +c at high pT

Significant intrinsic charm contribution?11

_

CP Violation in the BS System: New ResultsCP Violation in the BS System: New Results

Weak eigenstates:

Mass eigenstates:

Bs meson allows to probe the entire matrix:

• Time-dependent angular analysis in flavor-tagged Bs J/ decays

• B(Bs Ds(*)Ds

(*))

• CP-violating asymmetry in semileptonic Bs decays


mixing 00ss BB

Sensitive to New Physics

Not sensitive to New Physics

VERY sensitive to New Physics

12

Asymmetry in Semileptonic Bs DecaysAsymmetry 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)

1 fb-1, PRD 74, 092001 (2006)


Prediction

13

Asymmetry in Semileptonic Bs DecaysAsymmetry in Semileptonic Bs Decays

•

• Flavor tagging and time-dependent analysis used for Bs-mixing measurement.

• Exploits regular reversal of solenoid/toroid polarities to control systematics.

XDB ss 0

XDBd 0

2.8 fb-1

NEW

Statistics-limited!


Prediction

Significant constraints on CPV phase

expected from combination of

measurements 14

EW Physics: New ResultsEW Physics: New Results

Precision Measurements

• AFB in Z/*ee and sin2Weff

• W charge asymmetry• (ppZ/*+X)B(Z/*)• …

Diboson• Radiation amplitude zero and

anomalous couplings in W• Search for narrow resonances

decaying to Z• ZZ production• …



15

ZZ ProductionZZ Production

• The smallest SM diboson cross section:

(ZZ)=1.6 ± 0.1 pb

reality check for New Phenomena searches.• Sensitive to New Physics:

• ZZ 4 leptons• Very small backgrounds, but small BR (~0.4%)

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

l=e,

16

ZZllZZll

• 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(*l-)

• (l1,ll)

2.7 fb-1

17

18

ZZllZZll

• 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(*l-)

• (l1,ll)

2.7 fb-1

pb )(4.0)(0.19.1)( syststatZZ

Expected Observed

P-value: 1.92x10-2 1.00x10-2

Significance: 2.1 2.3

ZZ4lZZ4l

• Careful optimization of lepton identification criteria and kinematic selections.

• Seven orthogonal channels:• 4e (3 categories)• 4• 2e+2 (3 categories)

• M(Z1)>70 GeV, M(Z2)>50 GeV

1.7 fb-1

Channel 4e 4 2e+2 All channels

Signal 0.45 0.60 1.08 2.13

Total background

0.05 0.0003 0.095 0.14

Observed events 2 1 0 3

19

4-lepton invariant mass (GeV)

Run IIb

ZZ4lZZ4l

• Careful optimization of lepton identification criteria and kinematic selections.

• Seven orthogonal channels:• 4e (3 categories)• 4• 2e+2 (3 categories)

• M(Z1)>70 GeV, M(Z2)>50 GeV

1.7 fb-1

Channel 4e 4 2e+2 All channels

Signal 0.45 0.60 1.08 2.13

Total background

0.05 0.0003 0.095 0.14

Observed events 2 1 0 3

Expected Observed

P-value: 1.32x10-4 2.94x10-8

Significance: 3.65 5.42

pb )(13.0)(75.1)( 27.186.0 syststatZZ

First observation of ZZ production!!!20

4-lepton invariant mass (GeV)

Run IIb

Top Physics: New ResultsTop 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

• …

p

p t

b

W

q

q’

t b

W+

l

X

Production cross-section

Resonant production

Production kinematics

Top Spin Polarization

Top MassW helicity

|Vtb|

Branching Ratios

Rare/ non SM Decays

Anomalous Couplings

CP violation

Top Spin

Top Charge

Top Width

_ _

_

_

21

Top Pair Cross Section and New PhysicsTop Pair Cross Section and New Physics 1.0 fb-1

22

B(H+)=1

• 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.

• tH+b: channels affected differently depending on H+ decay modes.

Tauonic: B(H+)=1• disappearance of l+jets, dilepton• appearance of l+

Leptophobic: B(H+cs)=1• disappearance of l+jets, dilepton

and l+

Tauonic

Leptophobic

23

Top Pair Cross Section and New PhysicsTop Pair Cross Section and New Physics 1.0 fb-1






and l+

Using top as a tool to look for New Physics

Top Quark MassTop 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).

GeV (syst) 3.2(stat) 6.39.172 topm

Lepton+jets (2.1 fb-1):

e+ (2.8 fb-1):

GeV (syst) 4.1(stat) 0.12.172 topm

Matrix Element Method:

2.8 fb-1

24

Top Quark MassTop 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.

GeV 5.56.169 topm

2.8 fb-1

Different systematic uncertainties25

• Top couplings to the W boson very interesting!

• Single top production directly sensitive to the tbW interaction: rate and kinematics.

SM: ~ 2.9 pb (SM)

SM:

SM

tbW Interaction: Single ToptbW Interaction: Single Top 0.9 fb-1

26



SM (f1L=1, rest=0): ~ 2.9 pb

f2L(R)=1, rest=0 : ~ 10.4 pb

SM

f2L(R)=1, rest=0


27



SM (f1L=1, rest=0): ~ 2.9 pb

f2L(R)=1, rest=0 : ~ 10.4 pb

• Use same multivariate analysis technique as for the single top production evidence.


First direct constraints on tbW tensor couplings


28

• W helicity polarizations in top quark decays:

• Lepton+jets and dilepton final states.• Reconstruct lepton helicity angle:

t

b

W

t

W

b

t

W

b

t

b

W

Left-handed W(W=-1 )

Longitudinal W(W=0 )

Right-handed W(W=+1 )

SM:PRL 100, 062004 (2008)

SM

tbW Interaction: W HelicitytbW Interaction: W Helicity

29

1W+

b

l+

• W helicity polarizations in top quark decays:

• Lepton+jets and dilepton final states.• Reconstruct lepton helicity angle.

• Model independent measurement:

t

b

W

t

W

b

t

W

b

t

b

W

Left-handed W(W=-1 )

Longitudinal W(W=0 )

Right-handed W(W=+1 )

SM:

lepton+jets

tbW Interaction: W HelicitytbW Interaction: W Helicity 2.7 fb-1

SM

Most precise measurement!Further constraints on tbW couplings to follow 30

NEW

1

New Phenomena Searches: New ResultsNew 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, • Charged massive stable particles

•

31

Scalar Leptoquarks (3rd Generation)Scalar Leptoquarks (3rd Generation)

• 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+b

• 1 isolated , pT>15 GeV• 1 candidate, pT>15-20 GeV• 2 jet, pT>25(20) GeV; 1 and 2 b-tags

1+2 tags

~ B(LQl+q)

l,

q

l,

q

_

_

_


1.0 fb-1

Most restrictive limits in this decay channel!32

Acoplanar Jets+METAcoplanar Jets+MET

2 jets, pT>15 GeV

(jet1,jet2) >165o

MET>75 GeV

Optimized cuts on MET and HT

jets

jetTT pH

1st Generation Leptoquarks (=0)

1- = B(LQq)

qqLQLQ

Precision EW

measurements

LEP

Littlest Higgs model (T-parity)HH AqAqQQ

~~~~

2.5 fb-1

Most restrictive direct limits!33

DØ Run II Preliminary


• Gravity diluted in large compactified extra spatial dimensions.

• Tower of Kaluza-Klein gravitons GKK (massive, stable, non-interacting).

• qq + GKK monophoton signature

• pT()>90 GeV, MET>70 GeV

• Backgrounds:• Z(),..• Non-collision

(cosmics, beam-halo)• Exploit fine granularity of the

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

Large Extra-Dimensions: mono-photonLarge Extra-Dimensions: mono-photon 2.7 fb-1

34



Large Extra-Dimensions: mono-photonLarge Extra-Dimensions: mono-photon 2.7 fb-1

35Improve upon LEP limits for nd>4

• qq + GKK monophoton signature

• pT()>90 GeV, MET>70 GeV

• Backgrounds:• Z(),..• Non-collision

(cosmics, beam-halo)• Exploit fine granularity of the

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



• Di-EM (ee,) final state signature.• Exploit di-EM mass and cos(*) distributions.

Large Extra-Dimensions: ee, Large Extra-Dimensions: ee, 1.0 fb-1

Virtual GKK exchange

36


Interference!


Most restrictive limits at the Tevatron!

Charged Massive Stable ParticlesCharged 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)

Gaugino-like

chargino 185 GeV

1.1 fb-1

Most restrictive limits at the Tevatron37



Higgs Searches Beyond the SMHiggs 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, enhanced (tan)

• b(b)+0bbb(b)• b(b)+0hadb(b)• 0

Significant increase in production rate: +X 2 x tan2BR(0bb)~90%, BR(0+-)~10%

38

NEW

NEW

NEW

b(b)+0bbb(b)b(b)+0bbb(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.

bb

2.6 fb-1

39Most restrictive limits at the Tevatron!

2

T

vis pppM

• Lower BR but also lower backgrounds.

• Typical experimental signature (had):• 1 isolated , pT>10 GeV• 1 candidate, pT>15(20) GeV

• Main background: Z+- • Visible mass:

• Combination of four channels:• Run IIa (1.0 fb-1): had, ehad, e

• Run IIb (1.2 fb-1) : had

00 2.2 fb-1

40Work ongoing to combine the three analyses

SM Higgs Searches: New ResultsSM 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!

• WHlbb• WHbb• ZHllbb• ttHlbjjbbb• H• HWW•

Added for the first time

41

…and more!

WHlbbWHlbb

42

• One of the most sensitive channels in the ~110-130 GeV mass range.

• Consider 8 independent channels:• e+jets, +jets• 2, 3 jets• 1, 2 b-tags (NN-based)

• Main background: W+HF jets, tt• Dijet mass multivariate discriminants

WHlbbWHlbb

• One of the most sensitive channels in the ~110-130 GeV mass range.

• Consider 8 independent channels:• e+jets, +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)

1.1 fb-1

43

HH

• 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 (~60%)• +j and dijet (jet )

• Use diphoton mass spectrum:

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)

2.7 fb-1

44

1.3 signal events

HWWHWW

• Highest sensitivity channel for mH>130 GeV.

• Main backgrounds:• mH~160 GeV: WW• mH~130 GeV: W+jets

• Low (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 SMObserved limit: 2.1 x SM

ee,, e

45

As of Moriond’08…

Moriond’08 Tevatron CombinationMoriond’08 Tevatron Combination

At mH = 160 GeV:

Expected limit: 1.6 x SMObserved limit: 1.1 x SM

Exciting prospects to start excluding in 2008!

46

47

HWWHWW 3.0 fb-1

• First 3.0 fb-1 result at DØ! • Significant improvements since Moriond:

• Lepton ID • Neural Networks• 30% more luminosity

• And the answer is….

48

HWWHWW 3.0 fb-1

Watch for updated Tevatron combination at ICHEP!

• 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

ConclusionsConclusions

• 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!

49

Backup

50

ttH Associated ProductionttH Associated Production

• (ttH)B(Hbb): ~4 fb at mH=115 GeV

• Main background: tt+jets

• Split in 12 independent channels:• e+jets, +jets• 4, ≥5 jets• 1, 2, ≥3 b-tags (NN-based)

and use HT distribution.

SM: t ~ 1

bb

Exp. Signal: ~0.12

Exp. Bckg: ~3.7

Observed: 5

2.1 fb-1

51

• Tiny cross section: ~X fb at mH=115 GeV

• Main background: tt+jets

• Split in 12 independent channels:• e+jets, +jets• 4, ≥5 jets• 1, 2, ≥3 b-tags (NN-based)

and use HT distribution.

Exp. Signal: ~0.12

Exp. Bckg: ~3.7

Observed: 5

SM: t ~ 1

bb

At mH = 115 GeV:

Expected limit: 46.1 x SM (=187 fb)Observed limit: 64.4 x SM (=271 fb)

ttH Associated ProductionttH Associated Production

Still much room for optimization!

jets

jetTT pH

2.1 fb-1

52

53

Top Pair Cross Section and New PhysicsTop Pair Cross Section and New Physics






and l+

1.0 fb-1

For mt=170 GeV:

Good agreement with the SM prediction

New Results for ICHEP2008 from DØ

Documents

new physics

low z pt region

new experimental technique

subset of new results

photon heavy flavor

heavyquark b

important information

theoretical uncertainties