Recent DØ results in B, QCD Electroweak, Top and Higgs Physics · Electroweak, Top and Higgs Physics Brad Abbott University of Oklahoma For the DØ Collaboration Wine and Cheese

Wine and Cheese March 14, 2003Brad Abbott 1

Recent DØ results in B, QCD Electroweak, Top and Higgs

PhysicsBrad Abbott

University of OklahomaFor the DØ CollaborationWine and Cheese seminar

March 14, 2003


DØ Detector


Status of the DØ detectors• Silicon detector

– Running smoothly: ~91% of channels are in readout– A few noisy HDIs are causing infrequent HV trips– Working on optimizing monitoring and L1 accept data speed transfer

• Fiber tracker and preshowers– More then 99% of channels are operating well– Concentrating on commissioning the new tracking trigger

• Calorimeter– Number of channels in operation is 99.9%– Precision readout is working stably and reliably– Concentrating on commissioning Level 1 calorimeter trigger in the eta region

between 2.4 and 3.3– Triggering on jets and electrons in physics runs

• Muon system– Total number of dead channels is < 0.5% for tracking detectors and ~0.1% for

trigger detectors– Detectors are operating stably– Triggering on muons (single, di-muon, muon+jets, etc.) during physics data taking


L1 rate 1KHz

L2 rate 0.6 KHz

L3 rate 50 Hz

Currenttrigger rates

February data taking ε:~90% per run~85% overall


Many new results from DØ

• QCD• B• Electroweak• Higgs• Top• New Phenomena (Last week’s wine and

cheese seminar by S. Protopopescu)


Dijet Mass Cross Section

• probe of– QCD– Proton structure at large x– hunting for resonances– quark compositeness

• data sample:– 34.1 pb-1

– ET / PTj1 < 0.7– primary vertex: |zvtx| < 50 cm, Ntrks > 4

• selection & sample definitions– ∆R = 0.7 cone jets– |ηjet| < 0.5– Njet > 1– calculate invariant mass of leading two jets

Mjj = 838 GeV

twice the σ at 1.96 TeV


Jet Energy Scale

• methods currently used– O: underlying event, noise

• minimum bias events– R: non-linearities, dead material

• direct photon candidate events• statistics up to 200 GeV energy

– S: particle showers• jet transverse shapes in data

• errors– large statistical errors– substantial systematic errors

• increase with energy due to extrapolation

–Ecorr = (Euncorr - O)/ R*S

– for central jets : error ~ 9%


Raw dijet mass spectrum

Jet energy scale corrected

Wine and Cheese March 14, 2003Brad Abbott 9 [GeV]JJM

200 400 600 800 1000 1200 1400

unsm

earin

g cor

recti

on

0.5

0.6

0.7

0.8

0.9

1

DØ Run II preliminary

Unsmearing correction• Measure PT resolution

using PT imbalance in dijets

• Derive dijet mass resolution using jet PTresolution

• Use ansatz function to unsmear data

• Correction is small

)/2 [GeV]T2+pT1(p0 50 100 150 200 250 300

T/p

pTσ

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.2

DØ RunII preliminary

| < 0.5jet

η|

cone R=0.7

−

−

−=s

MMN jj

jjf 1β

α

σσ

A

TPPT 2=


Dijet mass spectrum

[GeV]JJM200 400 600 800 1000 1200 1400

[nb/

GeV

]⟩

JJ/d

Mσd⟨

10-8

10-7

10-6

10-5

10-4

10-3

10-2

10-1 | < 0.5

jet1,2ηcone R=0.7, |

-1 RunII, L=34 pb

=1.3sep NLO CTEQ6, R

maxT = 0.5 ERµ = Fµ


10% luminosityerror not shown

MjjLdMjjd

CN

UNSMEAR

evt

∆=

1ε

σ


(Data-Theory)/Theory

[GeV]JJM200 400 600 800 1000 1200 1400

(dat

a -

theo

ry)/

theo

ry

-1

-0.5

0

0.5

1

1.5

2

CTEQ6

maxT = 0.5 ERµ = Fµ = 1.3, sepR


[GeV]JJM200 400 600 800 1000 1200 1400

(da

ta -

th

eo

ry)/

the

ory

-1

-0.5

0

0.5

1

1.5

2

MRST2001

maxT = 0.5 ERµ = Fµ = 1.3, sepR


Dominant error is energy scale10% luminosityerror not shown


B physics• Cross sections• Lifetimes• Flavor tagging• Prove we understand detector before moving on to

other interesting physics• Bs mixing, Sin(2β), b baryons,…• Mixing measurements

– Reconstruct B– Determine proper time– Flavor tag


B jet cross section

jetµ

µ+jet

pTRel

• Measured in Run I: 2-3 times higher than predictions

Strategy:Measure µ+jet cross-sectionExtract b-content using PT

Rel

Data selection & kinematic cuts

• pTµ >6 GeV/c, |ηµ| <0.8

(Muon PT measured in muon system only)

• |ηjet| < 0.6

• ETcorr>20 GeV

• 0.5 cone jet

δR(jet,µ)<0.7•

Data:

02/28/02-05/10/02 :

(3.4 pb-1)


(GeV/c)µ RelTP

0 0.5 1 1.5 2 2.5 3 3.5

En

trie

s/0.

1 G

eV

0

100

200

300

400

500

600

700DØ Run 2 Preliminary

Data

Background template

Signal template

Fitted templates

jetTE

20 30 40 50 60 70 80 90 100%

b-j

ets

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

b fractionUncertainty

DØ Run 2 Preliminary

Obtain B jet cross section from µ+jets cross section:Fit PT

rel templates to data in jet ET bins

PTrel for jets with

20 GeV < ET < 25 GeV B fraction as a function of Jet ET

(cannot distinguish c µX and decays in flight so only fit b, non-b)→


b jet cross section

(GeV)jetTE

20 30 40 50 60 70 80 90 100

(n

b/G

eV)

jet

Td

Eσd

10-3

10-2

10-1 Data

R<0.3δPythia, CTEQ4M,

DØ Run 2 PreliminaryData unsmearedusing ansatz function

Dominant erroris due to jetenergy scale

Uncertainty due to•b quark mass•renormalization/factorization scale•pdf’s•fragmentation functionsBased on NLO calculations and applied to Pythia Consistent with Run I result

(not fully correctedfor lepton losses andbranching ratio)

Wine and Cheese March 14, 2003Brad Abbott 162GeV/c

2.2 2.4 2.6 2.8 3 3.2 3.4 3.6 3.80

2000

4000

6000

8000

10000

Signal = 75013 eventsψJ/2 0.0003 GeV/c±Mean = 3.0719

0.0003±Sigma = 0.0713

’ Signal = 1746 eventsψ2 0.004 GeV/c±Mean = 3.669 2 0.004 GeV/c±Sigma = 0.057

Invariant Mass-µ+µ

Run 2 Preliminary∅D

Lifetimes and exclusive B decays

• For now focusing on J/Ψ µ+ µ− sample• Useful for calibration

75,000*0.17~13,000 b’s

L~ 40 pb-1

→

• Easy trigger and provides lots of B’s


Average B Hadron Lifetime

J/ψ Sources ( ) states (prompt)B → J/ψ X

Differencedecay

Prompt ~ PVJ/ψ(B) ~ SV

cc

λλB B through through λλψψ

)( ΨΨ

Ψ

=TT

xyB PFPMLλ

MCMC

ΨΨΨ =

T

BT

BT P

PMMPF )(


cm-0.2 -0.1 -0 0.1 0.2 0.3 0.4

mµE

ven

ts/8

5

1

10

102

103

104

Data

Sideband

B Signal

B Signal + background

Inclusive B Lifetime

mµ 22(syst) ± 7(stat) ± = 468 Bλ

Run II Preliminary∅D

Inclusive B lifetime

B fraction 17.3 0.5 % (sys)074.0 (stat)024.0561.1 ±±=τ psFraction of outliers = 1x10-3

14.0Fitting Bias

15.9Correction factor

Error (µm)Source

Dominant Sys Errors

014.0564.1 ±=τ ps (PDG)

±±

λb distribution


Charged B

B+- J/Psi K+-

Cuts (J/ψ): 1. Muons with opp. charge2. pT(µ) > 2.0 GeV3. SMT hits ≥ 14. χ2 on J/ψ vertex < 105. 2.8 < J/ψ mass < 3.3

Cuts (Charged B):1. χ2 for K < 102. Total χ2 < 203. Kaon hits ≥ 34. pT(K) > 2.0 GeV5. Collinearity>0.96. B decay length >

0.3mm

→


Charged B lifetime

<τ>=1.76 0.24 ps (stat)

cm-0.05 0 0.05 0.1 0.15 0.2 0.25

mµE

ven

ts/ 5

0

1

10

102

103

data∅D

Total Fit

B+ signal

Background

Run II Preliminary∅D

m (stat) µ 72 ± = 528 +Bλ

Lifetime +B

±

)()(

BBM

PL

T

xy=λ

<τ>=1.674 0.018 ps (PDG)±

Fully reconstructedB so no need for acorrection factor


Use charged B sample to measure flavor tagging performance

B+

Use Jet charge orLepton charge toDetermine b flavor

µ

∑

∑=

i

ii

pTqpT

Q*

Muon taggingMuon ∆R >2.0 from B+

Muon PT > 1.9 GeV/cMuon charge ⇒ B-tag

Jet Charge tagging•Remove B+ daughters•Only use tracks with impact parameter< 0.2 within a phi cone 1.14 opposite to direction of B

•Only events with |Q|>0.2 are usedas tags

µµ

K+


ε: efficiency for a tag =

D: Dilution=

3.3 1.8 %2.4 1.7%D=-3.7 19.2%D=2.4 4.1% ε= 8.5 1.6 %ε= 65.8 2.4%D=44.4 21.1%D=15.8 8.3 %ε= 8.3 1.9%ε= 63.0 3.6%

Tagging power :εD2 Significance of a mixing measurement proportional toεD2

Jet tag Muon tag

Signalregion

Sidebands

εD2 for signal

±

±

NNNNN

notagwrongcorrrect

wrongcorrect

+++

NNNN

wrongcorrect

wrongcorrect

+−

±±

±

±

±±

±±


-10

-5

0

5

10

-10 -5 0 5 10x (cm)

y (c

m)

X-Y vertex location of γ e+ e-

Silicon modules

→

Photon conversions

Since low PT tracks arevery important for B physics, tracking algorithm has been improved

Improved performance forlow PT tracks and tracks withlarge impact parameter(Ks,Λ)


), GeVψ) - M(J/γ ψM(J/0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

0

5

10

15

20

25

30

35

40

DØ Run II Preliminary

γ ψ J/→ cχ

12±N = 84 0.004 GeV± = 0.403 c1 M∆ 0.004 GeV± = 0.018 σ

χ C →J/ψ γ

Cuts:1. Track pT > 2.0

GeV on tracks from J/Ψ

2. pTγ > 1.0 GeV

According to CDF Run I measurement: fraction of J/Ψ from χc

27.4 1.6 5.2 %

Expect ~ 80 events

±±

Fit with fixed Mχc1-Mχc2 = 46 MeV but float relative contributions


D0 RunII Preliminary

0

50

100

1.25 1.3 1.35 1.4 1.45 1.5 1.55M(Λπ) GeV/c2

Ξ → ΛπM = 1322.2 ± 0.5 MeV/c2

σ = 5.4 ± 0.4 MeV/c2


0

10

20

30

1.6 1.65 1.7 1.75 1.8 1.85 1.9M(ΛΚ) GeV/c2

Ω → ΛKM = 1671.5 ± 1.9 MeV/c2

σ = 8.5 ± 2.3 MeV/c2


0

1000

2000

1.08 1.1 1.12 1.14 1.16 1.18M(pπ) GeV/c2

Λ → pπM = 1115.9 ± 0.2 MeV/c2

σ = 2.8 ± 0.2 MeV/c2


0

2000

4000

6000

8000

0.4 0.45 0.5 0.55 0.6M(π+π−) GeV/c2

K0s → π+π−

M = 497.4 ± 0.1 MeV/c2

σ = 7.0 ± 0.2 MeV/c2

Results with new tracking algorithm

K π π

Λ pπ

Ω ΛK

Ξ Λπ

→

→

→

→


Exclusive B decays


0

50

100

150

4.8 5 5.2 5.4 5.6 5.8 6M(J/ψ K±) GeV/c2

B± → J/ψ K±

N = 328 ± 34M = 5.270 ± 0.005 GeV/c2

σ = 0.044 ± 0.005 GeV/c2


0

25

50

75

100

4.8 5 5.2 5.4 5.6 5.8 6M(J/ψ K*0) GeV/c2

Bd → J/ψ K*0

N = 155 ± 28M = 5.280 ± 0.006 GeV/c2

σ = 0.036 ± 0.007 GeV/c2

Combine J/Ψ with track or combine J/Ψ with K* andthen require decay length significance>3.0

Β J/Ψ K→± ± Βd J/Ψ K*→


Towards Sin(2β)


0

5

10

15

20

4.8 5 5.2 5.4 5.6 5.8 6M(J/ψ K0

S) GeV/c2

Bd → J/ψ K0S

N = 45 ± 10M = 5.291 ± 0.007 GeV/c2

σ = 0.028 ± 0.005 GeV/c2

Combine J/Ψ with Ks and require decay lengthsignificance >3.0

Βd J/Ψ Ks→


Electroweak

• Search for Z in Dielectron Decays (Presented at last week’s Wine and Cheese seminar)

• Measurement of the Z → µ µ Cross Section at = 1.96 TeV

''

s


pT (GeV)10 20 30 40 50 60 70 80 90 100

Eve

nts

/ 3

GeV

0

5

10

15

20

25

30

35

40

45 D0 Run II Preliminary

No track foundTrack found

• data sample: 31.8 pb-1

• selection– |ηµ| < 1.8– pair of oppositely charged muons

• PT > 15 GeV• > 2.0• require one be isolated in calorimeter

AND tracker• timing cut to remove cosmics

– di-muon trigger• efficiency calculated from data

• 1585 events pass cuts

εL1 = 87%

εtrk = 82%

σσ*BR(Z *BR(Z µµµµ))→

φη ∆∆ + 22

µtag

µprobe

L1+L2,central track

L1 OR no L1

track OR no track

Z


• cosmics negligible

• heavy flavor ( bb )– compare dimuon events

• two isolated muons• one isolated muon

– two samples agree well• < 1% non-isolated muons• 1% +/- 1% BG

• Z ττ µµ• Drell-Yan

– Pythia plus fast detector simulation• Z and Z/γ*• muon resolution tuned to data• correction factor = NZ/NZ,γ

→→

DimuonDimuon BackgroundsBackgrounds

Z ττ→


• calculation of efficiency

effic. error– Monte Carlo (acceptance) 0.403 0.012– Level 1 muon 0.912 0.017– loose muon identification 0.909 0.01– track efficiency 0.822 0.014

σ∗Br = 263.8 ± 6.6 (stat) ± 17.3 (sys) ± 26.4 (lum) pb

Measured Measured σσ*BR(Z *BR(Z µµµµ))→

First measurement at = 1.96 TeVs

εz = εmc x εL12 x εloose

2 x εtrack2 x εfz x (2εL2-εL2

2) x εopposite_q x εisol x εcosmic


10 2

10 3

1Center of Mass Energy (TeV)

σ W, Z

× B

(pb

)

DØ and CDF Run2 Preliminary

Center of Mass Energy (TeV)Center of Mass Energy (TeV)Center of Mass Energy (TeV)

pp_ → W+X → lν+X

pp_ → Z+X → ll+X

DØ(µ) Run2DØ(e) Run2

CDF(e) Run2CDF(µ) Run2DØ(e)CDF(e) CDF(µ)UA1 UA2

DØ(µ)

This measurement


Higgs• Study of the W/Z(→lepton) + jets production

– First step towards W/Z (→leptons) +H (→ bb) measurement– The W/Z + b-jets distributions related to W/Z+ jets distributions– Try to understand major background source from W/Z + di-jets

• Search for H→WW(*) (→ eeνν/µµνν/eµνν) decays

Others• Search for H →γγ decays• WH(→ l±ν + bb)• ZH(→ l+l− or νν + bb)• φbb (→ 4 b jets) (φ = h,H,A ; SUSY Higgs)


Indirect limit from global SM fitMH< 195 GeV at 95% CL

Direct SM Higgs search of LEPMH>114.4 GeV at 95% CL

Higgs Mass Limits


• gg → H … σ(gg → H) ~ 1pb• For masses below ~140GeV,

Background hides H → bb signals• For higher masses; mH> ~120GeV,

Combination with H → WW(*) decay process can be useful

• HW, HZ … σ(HW/HZ) ~ 0.1pbLeptonic decays of W/Z help background rejection

• Hqq … σ(Hqq) ~ 0.1 pbBackgrounds too large

• Hbb … σ(Hbb) ~ 5fbSM extensions may enhance φbb (φ =h,H,A)


Tevatron Higgs Working Group Study• The Higgs discovery potential for the RunII Tevatron has been evaluated.

– hep-ph/0010338

• A joint effort of theorists and both experimental groups, CDF and DØ.• Simulation performed using a parameterized fast detector simulation.• Main conclusion :

– Discovery at 3-5 σ can be made,– Combine all channels.– Combine the data from both

experiments, CDF and DØ– Must improve understanding of signal

and background cross sections, kinematics and detector performance.

– b-tagging, resolution of Mbb

– Advanced analysis techniques are vital

LEP

excl

uded

at 9

5% C

.L.

• Results of studies with full simulations for selected signal process are consistent with SHWG expectations.


W/Z + jets production

• First step towards W/Z (→leptons) +H (→bb) measurement.• W/Z + b-jets distributions related to W/Z + jets distributions well.• Try to understand major background source from W/Z + di-jets.• Analysis utilized ~35 pb−1

• Data samples triggered by lepton– No bias for jets distribution.

• Basic Selection:– Isolated lepton with large missing ET (for W)– 2 high pT leptons and mll consistent with mz

– Look at high pT jets


• Selection– W(eν)

• Isolated e : pT > 20 GeV • |η| < 0.8• Missing ET > 25 GeV

– W(µν)• Isolated µ : pT > 25 GeV • |η| < 1.5• missing ET> 20 GeV

– Jets• pT > 20 GeV • |η| < 2.5

• Compare PYTHIA with DATA• Normalized by area• Error includes stat. error and dominant

sys. error from JES

2nd leading jets

1st leading jets

GeV

W(eν)+jets

Dot : DataBar : MC

QCD BKG

QCD BKG

Dot : DataBar : MC

W+jets production

GeV


W+jets production (2)

GeV/c2 ∆Rjj

Di-jet Mass ∆R between di-jetsW(eν)+jets W(eν)+jets

• Reconstructed di-jet mass and ∆R(= ∆φ2 + ∆η2 ) between di-jet– MC represents jet distributions well– First step towards study of Z(→leptons)H(→ bb) decay process

Dot : DataBar : MC

Dot : DataBar : MC

QCD BKGQCD BKG


Z+jets production• Selections

– 2 muons from Z(µµ) •pT > 15 GeV •|η| < 2

– 2 electrons from Z(ee)•pT > 20 GeV •|η| < 2.3

– Jets•pT > 20 GeV •|η| < 2.5

1st leading jets 2nd leading jets

• Compared PYTHIAwith DATA

• Normalized by area

Combined Z(ee)+jets and Z(µµ)+jets

• Error includes stat. error and dominant sys. error from JES


Z+jets production (2)• Number of jets in Z + jets production• Reconstructed di-jet mass and ∆R(= ∆φ2 + ∆η2 ) between di-jet

– MC represents jet distributions well– First step towards study of Z(→leptons)H(→ bb) decay process

Di-jet Mass ∆R between di-jets#jets in Z+jets

Combined Z(ee)+jets and Z(µµ)+jets


b-tagging• Next step towards study of W/Z + H(→bb) production is b-jet

reconstruction• b tagging is performed using secondary vertex reconstruction• Lepton from semileptonic decay of b is very useful

Positive IP

Negative IP

• Impact Parameter > 0 → track cross jet axis after closest point

Jet

Jet

track

track

Resolution

b enhanced

µ + jet sample

Interaction point

Interaction point

• Impact Parameter < 0 → track cross jet axis before closest point


H→WW(*) → l+l−νν• Lot of interesting physics in WW production

– SM Higgs at high mass region– 4th fermion family enhances SM Higgs cross section

(factor ~8.5 for mH=100 - 200GeV) – Fermiophobic/Topcolor Higgs

(Br(H →WW)>98% for mH > 100GeV)– Non Higgs-related … Tri-linear couplings, New Phenomena

• Look at ee/eµ/µµ plus missing ET events• Cannot directly reconstruct mass

– Transverse mass computed by the mll and missing ET• Opening angle between leptons (∆Φll) is useful discriminating variable

– Two leptons tend to move in parallel (→ ∆Φll is small) , due to spin correlation of Higgs boson decay products.

– Leptons from Z/γ* , multijets are emitted back to back, large ∆Φll• Backgrounds include Z/γ*, WW, tt, W/Z+jets, QCD


Results of H→WW(*) → e+e−νν

262264 ± 18.6 ± 4.3mee < mH/21112.3 ± 2.5 ± 0.7ET > 20 GeV/c2

13.6 ± 1.4 ± 0.2Transverse mass

27532748 ± 42 ± 245Lepton ID, pT>20 GeV/c

00.7 ± 1.4 ± 0.1∆Φee < 2.0

DATAExpected background L=44.5 pb−1

Selection optimized mH = 120 GeV

εsig = ~ 8%

43.1 ± 1.7 ± 0.1ET > 20 GeV/c2

21.4 ±1.5 ±0.1Anti W

2222 ± 2.1 ± 2.2Lepton ID, pT>20 GeV/c

10.9 ± 1.5 ± 0.1∆Φeµ < 2.0

DATAExpected background

Results of H→WW(*) → eµνν

L=34 pb−1

Selection optimized mH = 160 GeV

εsig = ~ 12%


Top

• Improved measurement of the top mass with Run I data• First measurement of tt cross section at = 1.96 TeV • Cross section at Run II ~ 30% higher than at Run I.

– Predictions between 6.7 – 7.5 pb• 6 Analysis channels

µµeµe + jetsµ + jetse + jets (soft muon tag)µ + jets (soft muon tag)

s


Status of the Top Mass Measurement in the Lepton+Jets Channels at Run I

Likelihood method using most available informationUses DØ Run I statistics (125 pb-1) & selection → 91 events

Additional cuts for this analysis:

4 Jets exclusively: 71 events

Pb: 22 events (pure sample)

[ ]

[ ]∫

∑++

+−=−=

dxxPcxPcxAN

xPcxPcL

bkgtt

N

iibkgitt

)();()(

)();(ln)(ln

21

121

α

αα

2top GeV/c (stat) 3.6179.9m ±=

(5.6 GeV from PRD 58 052001,1998)

Large improvement on the statistical uncertainty

(~2.4× stats) Details to be presented at an upcomingWine and Cheese seminar


Lepton+jets(topological)

Lepton+jets(soft muon tag)

dileptons

e+jets, µ+jets e+jets/µ, µ+jets/µ eµ and µµ

l l

lµ

l

EfficientNot very pure

PureNot very efficient

Pure and efficientLow branching

Analysis Channels


Data mid-August to mid-January Luminosity 30-50 pb-1

Jets: • 0.5 cone Improved Legacy algorithm with JES corrections

Electrons:• Central only• Selected based on simple cone, shower shape, EM fraction• Match with track (φ, η and E/p)

Muons:• Tracks in muon system• Tracks in central tracker• Minimum ionization in calorimeter (Used only to measure ε)

Missing ET• From calorimeter with JES corrections and muon correction

Data Sample


Dimuon ChannelSelection: 2 isolated muons, MET(Mµµ), HT and 2 or more jets

2Data

0.60±0.30Background

0.3±0.04Signal*

0.20±0.110.20±0.200.18±0.180.02±0.020.00±0.00

Z →µµDY →µµFakesZ →ττWW

* For σ = 7pb

Z→µµ

DY→µµ

QCD and W+jets

fromMC

Z→ττ

WW→µµ

Backgrounds:

WW (MC) Z→µµ (MC)

Signal (MC) Data

Estimated from data

L=42.6 pb-10 20 40 60 80 100 120 140 160 180 200

0

20

40

60

80

100

120

140

160

180

200

0 20 40 60 80 100 120 140 160 180 2000

20

40

60

80

100

120

140

160

180

200

0 20 40 60 80 100 120 140 160 180 2000

20

40

60

80

100

120

140

160

180

200

0 20 40 60 80 100 120 140 160 180 2000

20

40

60

80

100

120

140

160

180

200

2M

(

GeV

/c

)

Data

Z to mu mu (MC)

2

Signal (MC)

WW(MC)

µµM

(

GeV

/c

)µµ

E (GeV)

TE (GeV)

2M

(

GeV

/c

)µµ

T

T

E (GeV)T

E (GeV)

2M

(

GeV

/c

)µµ



eµ ChannelSelection criteria: Backgrounds:

1 electron, 1 isolated muon, MET, METCAL , HT (e) and 2 or more Jets

Estimated from data(Fakes)

33.0 pb-1

QCD and W+jets Z→ττ

WW→eµ

fromMC

0.5±0.01Signal*1Data

0.07±0.01Bkg

0.05±0.010.02±0.010.00±0.00

FakesZ →ττWW

Njets

Z Z →ττ

FakesFakes


* For σ = 7pb

NjetsHT(e) (GeV)


Lepton-plus-Jets Analyses• Luminosities: e+jets and µ+jets• Backgrounds: QCD multi-jets and W multi-jets

• Method:

• Preselection:• QCD background evaluation (matrix method):

49.5 pb-1 40.0 pb-1

- Preselect a sample enriched in W events- Evaluate QCD multi-jet (as a function of Njets)- Estimate W+4jets assuming Berends scaling- Apply topological selection

1 EM object or muon, MET, soft muon veto

QCD

LQCDTttW

ttW

ttW

NNN

εεε

ε−

−=

+

++~

QCDttW

TLQCDQCDQCD

NNN

εεε

ε−

−=

+

~

Separate W+tt and QCD with loose (L) and tight (T) lepton characteristics. Efficiencies (L→T) for signal εW+tt and background εQCD are measured independently:

QCDttWL NNN ~~ += +

QCDQCDttWT NNNttW

~~ εε += ++

⇒e+jets: Track match to the EM object

µ+jets: Muon isolation“Matrix method”


• Signal probabilities:

• Background nature:

• Background Probabilities:

QCD Background essentially due to Heavy Flavor semi-leptonic decays QCD Background due to leading π0 or compton QCD events and Fake track or γ

conversion

obtained from benchmark signal samples of Z→ ee or µµNon trivial dependence of εW+tt w.r.t. Njets (especially in

the µ+jets case)…

ε W+tt vs Njets

⇒ Correction taken from MC

e+jetse+jetsµµ+jets+jets

… are obtained from benchmark QCD samples with low MET

Dependence of the εQCDw.r.t. MET and Njet …

e+jets e+jets

e+jets


DØ Run II Preliminary DØ Run II Preliminary DØ Run II Preliminary


Berends scaling:

Estimation of the W background for Njets≥ 4:

Apply topological cuts:

α = 0.164±0.02 α = 0.145±0.02

=4~WN

24.2

11.9

44

Nobs

2.42.7±1.10.6±0.42.1±0.9µ+jets1.82.7±0.61.4±0.41.3±0.5e+jets

Signal*Bkg. Tot.NQCDNWAnalysis

=4~QCDN

11.9

12.5=4

obsN38 (µ+jets)

22 (e+jets)

Aplanarity and HT

)())1((

jets

jets

nWnW+

++≡

σσ

α

DØ Run II Preliminary DØ Run II Preliminary

* For σ = 7pb


Soft Muon Tag Analyses

Selection before Soft Muon Tag

- Use the same preselection as l+jets- Require at least 3 jets- Apply mild topological cuts

75/23 (µ+jets)

459/27 (e+jets)⇒

µ+jetse+jets

(Loose/Tight sample)

1/0 (µ+jets)

9/2 (e+jets)

QCD background. from matrix method

=SMTQCDN~

0.2±0.2 (µ)

0.2±0.1 (e)W bkg. from Tag rate functions:

DØ Run II Preliminary DØ Run II Preliminary


* For σ = 7pb0.40.5

Sig.*

02

Nobs

0.6±0.3µ+jets0.2±0.1e+jets

Bkg. Tot.Analysis

=SMTWN~

0.4±0.1 (µ)

0.0±0.1 (e)

When SMT applied


µ -

MTC

Jet 1

Jet 2

IP

SV

IP

SV

Jet 1

Jet 2

µ+jets Candidate Event

Double tag event


Cross Section Measurement• Combining the observation of all channels an excess of 3σ is observed

pb (lumi) 0.8 (syst) (stat) 8.4σ 5.33.5

4.53.7 ±= +

−+−

Combined cross section:


Conclusions

• Many new analyses are producing interesting physics results

• DØ is already showing exciting measurements/ more to come soon

• Tevatron program is rich and promising-We are enthusiastic about the physics through the end of the decade

Documents

Recent DØ results in B, QCD Electroweak, Top and Higgs Physics · Electroweak, Top and Higgs Physics Brad Abbott University of Oklahoma For the DØ Collaboration Wine and Cheese