Results from the Dzero Experiment at the Tevatron · Meenakshi Narain, ICHEP2002, 7/29/2002 DØ. in . RunII • Center of Mass Energy = 1.96 TeV • Expect 2 fb-1. by end of 2004

Meenakshi Narain, ICHEP2002, 7/29/2002

Results from the Results from the DzeroDzero Experiment at the Experiment at the TevatronTevatron

Meenakshi NarainBoston University

Representing the Dzero Collaboration

XXXI International Conference on High Energy Physics (ICHEP2002), Amsterdam, The Netherlands


DDØØ in in RunIIRunII

• Center of Mass Energy = 1.96 TeV• Expect 2 fb-1 by end of 2004 (RunIIa),

15 fb-1 by 2008 (RunIIb)• Goals

– Comprehensive study of top quark properties– Precise measurements of mtop, mW, AFB

– Search for new phenomena (SUSY, technicolor,…)– Search for the Higgs boson– QCD (proton structure, quark compositeness)– B-physics (Bs mixing)

• DØ’s strength is high-pT physics• Requires

– Measurement of leptons (e, µ), jets, missing pT

– Flavor tagging of jets


Main Injector& Recycler

Tevatron

Chicago↓

p source

Booster

p

p CDF

DØDØ

DØ

• pp collisions• Ecom = 1.96 TeV• 396 ns bunch spacing• Run II peak luminosity

now: 2.1×1031 cm-2s-1

goal: 8.6×1031 cm-2s-1

• pp collisions• Ecom = 1.96 TeV• 396 ns bunch spacing• Run II peak luminosity

now: 2.1×1031 cm-2s-1

goal: 8.6×1031 cm-2s-1

FermilabFermilab


D0 D0 RunIIRunII DetectorDetector


Tracking SystemTracking System

SuperconductingSolenoid

Scintillating Fiber Tracker

Silicon Microstrip Tracker


CalorimeterCalorimeter

DØ

D0 LIQUID ARGON CALORIMETER

1m

CENTRAL CALORIMETER

END CALORIMETER

Outer Hadronic(Coarse)

Middle Hadronic(Fine & Coarse)

Inner Hadronic(Fine & Coarse)

Electromagnetic

Coarse Hadronic

Fine Hadronic

ElectromagneticNew preamps, signal shaping


Muon SystemMuon System

Muon Trigger Counters

DØ Detector in Collision Hall, January 2001


Detector PerformanceDetector Performance

• Silicon Tracker

p-side pulse-height (ADC)n-

side

pul

se-h

eigh

t (AD

C)

p-side pulse-height (ADC)

Silicon cluster charge

noise < 2 ADC counts1 mip ~25 ADC counts⇒ S/N ~ 12

Charge correlation between p and n-side of a silicon detector

Hit efficiencies >97%


pT GeV

track

x

width = 36 µmσ(beam) = 30 µm

σ = 20 µm

width = 36 µmσ(beam) = 30 µm

σ = 20 µm

Impact parameter

Detector PerformanceDetector Performance y

• Impact Parameter Resolution

Survey-only alignment constants

significant improvement expected from alignment with data in near future



• Fiber Tracker

light yield vs pseudorapidity η

Hit efficiency ¼ 98%

Ks0! π+π-

All tracking detectors working as expected

Z→ee candidateMass 89.9GeV/c2



0 10 20 30 40 50 60 70 80 90 100

10-1

1

10

Missing Transverse Energy, GeV

J/ψ and ψ’• Muons

• Electrons

E/P0 0.5 1 1.5 2 2.5 3

Eve

nts

/ 0.

05

0

50

100

150

200

250Chi2 / ndf = 0.5317 / 4

156.4 ±p0 = 105.6

490.4 ±p1 = -411.3

459.2 ±p2 = 530.6

141.7 ±p3 = -192.2

26.31 ±N = 147.6

0.01741 ±Mean = 1.031

0.02659 ±Sigma = 0.165

DØ Run 2 Preliminary

candidate eventsν e→W

>20 GeVmissT>20 GeV, Eel

TP

E/P Chi2 / ndf = 0.5317 / 4

156.4 ±p0 = 105.6

490.4 ±p1 = -411.3

459.2 ±p2 = 530.6

141.7 ±p3 = -192.2

26.31 ±N = 147.6

0.01741 ±Mean = 1.031

0.02659 ±Sigma = 0.165

W! eν

Z→µµ


• Missing ET

Detector performanceconsistent with expectations!

Di-photon Data

Multijet data


IdentyfyingIdentyfying bb--quarksquarks• Signed impact parameter

jet

trackImpact parameter > 0(secondary decay vertex)

IP

jet

trackImpact parameter < 0(resolution)

IP

Reconstruct secondary vertexAlso use semileptonic decays

-15 -10 -5 0 5 10 151

10

102

103

104

Significance = dca/σ

~Resolution

-15 -10 -5 0 5 10 15

1

10

102

10

Significance = dca/σ

µ+jet sampleenhanced b-jet content

dijet sample


RunIIRunII Data and First Physics ResultsData and First Physics Results

• Delivered luminosity about 50 pb-1

• Mostly used to commission detector– Now complete

• First results from about 10 pb-1 of physics quality data– New center of mass energy → measure cross sections

– Exploit our High pT Physics capabilities at the energy frontier

• See also talks in parallel sessions – include results from both RunI and RunII


DzeroDzero talks during the parallel sessionstalks during the parallel sessions

• Jet measurement with the KT method (Ursula Bassler) • Minireview on Low Scale Gravity and ED at HERA/LEP/Tevatron

(Gregorio Bernardi )• Photon and Jet Physics at DØ (Marek Zielinski)• Search for SUSY at the Tevatron (Vishnu Zutshi)• W boson mass and width measurements (Sarah Eno)• Top physics at the Tevatron (Ia Iasvilli)• The DØ tracking system for Run II (George Ginther) • The DØ detector for Run II (Levan Babukhadia)

• +… a few more talks by CDF speakers which include DzeroRunII results.


BB--Mesons Mesons

) [GeV]+,K-µ,+µM(5 5.1 5.2 5.3 5.4 5.5 5.6 5.7

0

2

4

6

8

10

0.021 GeV±Mean = 5.277 0.014 GeV±Sigma = 0.057

D0 Run 2 PreliminaryB+(-)! J/ψ K+(-)

20 30 40 50 60 70 80 90 1010-4

10-3

10-2

10-1

1

Run 2 Preliminary D

MC

R = 0.5 Cone Jets

| < 0.6jetη|

> 4 GeV/cµTp

| < 0.8µη|

) < 0.7µR(jet, δ

EJet [GeV]T

d[n

b/10

GeV

]d/

σE

T

DØ Run 2 Preliminaryµ+jet Production Cross SectionDataMC Pythia

Proper decay length (cm)-0.1 -0.05 0 0.05 0.1 0.15 0.2 0.25 0.3

mµE

ven

ts/5

0

1

10

102

103


mµE

ven

ts/5

0

1

10

102

103

Data

Background from sidebands

ψBackground + prompt J/

B lifetime signal

Signal+background

D0 Run II Preliminary

+ X)ψ J/→Average B lifetime (B

DataBackground from sidebandsBackgrounds from prompt J/ψB-lifetime signalSignal + background

Average B Lifetime (B! J/ψ+X)

details

Rapid

ityJ/

00.2

0.40.6

0.81

1.21.4

1.61.8

2

Cross Section, arbitrary scale

1

Cross

Sectio

n per

unit o

f rapid

ity

Dzero

Run2

PREL

IMINA

RY

)>5Ge

V/cψ

pT(J/

)>8Ge

V/cψ

pT(J/

Cross

Sectio

n per

unit o

f rapid

ity

J/ψ production cross section asa function of pseudo rapidity

pT >

5 GeV

8 GeV

10102ψJ/η: 0.2 1.6ψJ/


eta

3.7

0.0

-3.7

-1.2

1.2

phi

0.0

2PI

ET Ge

55

Bins: 1097Mean: 0.405Rms: 2.88Min: 0.00188Max: 52.4

E_t: 0.0062phi_t: 160deg

Run 131957 Event 4781549 Wed Nov 14 17:33:47 2001Jets Physics Jets Physics • At √s=1.96 TeV, cross section 2x

larger compared to 1.8 TeV (Run I) for jets with pT > 400 GeV

2-jet event• ET

jet1~230 GeV

• ETjet2~190 GeV

[GeV]Tp50 100 150 200 250 300 350 400

[nb/

GeV

]ηd

Tpa

rtial

ly c

orre

cted

dN

/Ldp

10-4

10-3

10-2

10-1

1

10

Cone algorithm, R = 0.7

| < 0.4η |

| < 0.7η 0.4 < |

DØ preliminary

Inclusive jet pT spectrum

[GeV]jjM200 300 400 500 600 700

[nb/

GeV

]2η

d1η

d jjpa

rtia

lly c

orre

cted

dN

/LdM

10-4

10-3

10-2

10-1

Cone algorithm, R = 0.7

| < 0.41,2η |

| < 0.71,2η 0.4 < |

DØ preliminary

Dijet mass spectrum

• Only statistical errors• Preliminary jet energy scale• Not fully corrected

(for unsmearing, efficiencies)• In the works:

– expanded η range, Improved energy scale…

Luminosity5.8 pb-1


W and Z boson productionW and Z boson production

Di-Electron Mass (GeV)0 20 40 60 80 100 120

Eve

nts

/ 2

GeV

0

20

40

60

80

100

Number of Entries: 604

Peak Mass: 90.8 +- 0.2 GeV

Width: 3.6 +- 0.2 GeV


W(! eν) event characteristics

25 30 35 40 45 50 55 60 65 70 75

0

100

200

300

400

500

600

0 10 20 30 40 50 60

0

100

200

300

400

500

600

700

800

25 30 35 40 45 50 55 60 65 70 75

0

100

200

300

400

500

600

30 40 50 60 70 80 90 100 110 120

0

100

200

300

400

500

ET

/GeV

T/GeVM

DO Run2 Preliminary

ET

/GeV

pT/GeV

a)

c)

b)

d)

Red dots: DataYellow filled histogram: MC

missing ET

electron ET

MTW pT

Z!ee

Distributions modeled well by MC

Invariant mass (GeV)


W and Z Boson production cross sectionW and Z Boson production cross section

• Data Sample:– Luminosity ¼ 7.5 pb-1

– 9205 W candidates– 328 Z candidates

• Cross section measurements:

10 2

10 3

1Center of Mass Energy (TeV)

σ W, Z

× B

(pb)

DØ Run2 Preliminary

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

pp_ → W+X → lν+X

pp_ → Z+X → ll+X

DØ(e) Run2DØ(e)CDF(e) CDF(µ)UA1 UA2

DØ(µ)


theory

theory


W and Z Boson production cross sectionW and Z Boson production cross section

• Ratio of cross sections

• W boson width

– Using σ(W)/σ(Z) from theory and B(Z! ee) from LEP

– In good agreement with world averageΓW = 2.135§0.069 GeV

First results at 1.96 TeV


W/Z boson + W/Z boson + multijetmultijet eventsevents

2GeV/c20 40 60 80 100 120

0

2

4

6

8

10

12

14e+jets data

multijet background

DØ Run 2 PreliminaryW + >= 2 jets njets≥0 1 2 3 4 5

Eve

nts

10-1

1

10

102

103

|<2jetη |

>15 GeVjetTE

>20 GeVjetTE

>25 GeVjetTE


stat. errors. only

W! eν+jets

JetsN0 2 4 6

Eve

nts

1

10

102

Events with

Jets N≥no. of Jets

candidates-µ +µ →0Z

DØ Run II Preliminary• Jet multiplicity distributions

W+≥ 2jetsTransverse massspectrum

•Top Physics:W+≥3jets, Z+≥2jets

•Higgs Physics: W/Z +≥ 2jets

•Need excellent b-jet identification•Secondary vertex recons.•Soft leptons in jets

Z!µ+µ-


H H !! WW WW • Why H ! WW at low luminosities?

– 4th fermion family enhances SM Higgs cross sections by a factor of ¼ 8.5 for Higgs mass between 100-200 GeV

– Fermiophobic Higgs: B(H! WW) >98% for mH ≥ 100 GeV

• Search for ee+ET events• Understand Backgrounds for SM Higgs Search

Require good e+e-

luminosity8.8 pb-1Azimuthal opening angle

between the leptons

Observed events in our data and estimated backgrounds are in good agreement.

Develop tools necessary for analysisOf larger data sets.


eta

4.7

0

-4.7

1 2

3

-1 -2

-3

phi180

0

360

ET(GeV)

10

Run 152415 Event 603157 Wed Jun 19 07:23:52 2002

An eeµ candidate

XGG

ZWgauginospp

++→

+→→~~

,, 01

01

γγ

χχγ

Search for Phenomena beyond the SMSearch for Phenomena beyond the SM• Many Analyses in progress:

– Likesign dielectrons– Jets+Missing Et

– Tri-lepton signatures• One of cleanest signatures of SUSY

chargino+neutralino production via W*• GMSB SUSY

⇒inclusive search for γγET + X– Limit:

– Sensitivity is still too low to exclude SUSY pointsCLpb %[email protected]<σ


LeptoquarksLeptoquarks• particles with properties of both quarks and

leptons; restore symmetry between the two• Signature: eejj events

Data : 18 eventsBackground : 15.3 ± 5.3 eventsLQ (m = 100 GeV) : 15.4 ± 2.0 eventsLQ (m = 140 GeV) : 3.1 ± 0.3 events

MLQ > 113 GeV/c2

at 95% CL, for β=1

β2×C

ross

Sec

tion

[pb]

Consistent with our Run I result6 candidates after removing Z

8.8 pb-1


Extra DimensionsExtra Dimensions

• Search for large extra spatial dimensions via virtual graviton effects

• e+e-, γγ and µ+µ- events

• Run2 Preliminary Limit:– Ms(GRW) > 0.92 TeV (ee,γγ)

• DØ Run I limits:– Ms(GRW) > 1.2 TeV


Future ProspectsFuture Prospects

• Continue to Search for New Physics– SUSY, strong dynamics, others…

• Rich program of B-physics • Measure W/Z Properties (AFB, W mass to 30 MeV)• Comprehensive study of Top quark Properties (2fb-1)

– Cross section(7%), Mass (2 GeV) – spin correlations, charge, top-gauge boson couplings

• Precision measurements of Top quark and W Boson mass ⇒ constrain the Higgs Boson

• Direct Searches for the Higgs Boson – Run IIa: MH & 115 GeV– Run IIb: MH & 180 GeV or see signal

• With 15 fb-1

– δmt ¼ 1 GeV, δmW ¼ 15 MeV, δAFB ¼ 2 £ 10-4


• current central values• δ∆α(5)

had(MZ2) = 10-4, δMW = 20 MeV, δmt = 1 GeV

• could lead to inconsistency within SM framework

¼ 2008summer 2002Grünewald, Heintz, Narain, Schmitt, hep-ph/0111217

0

2

4

6

10020 400

mH GeV

∆χ2

Excluded Preliminary

∆αhad =∆α(5)

0.02761+÷∠ 0.00036

0.02747+÷∠ 0.00012

Without NuTeV

theory uncertainty

?

Can we exclude the SM?Can we exclude the SM?


Thanks to my collaborators…Thanks to my collaborators…

33 US, 40 non USInstitutions:

Collaborators:334 from US 312 from non US institutions


ConclusionConclusion• First physics results at 1.96 TeV

– W and Z production cross sections– First generation LQ limits, Limit on Large Extra Dimensions– Lay foundation towards measurement of:

• B lifetime, b-quark cross sections, jet cross sections• Many High pT analyses in progress awaiting more luminosity

• Enormous progress made over the last year – detector performance optimization– developing analysis tools

• Improvements in store:– optimization of event reconstructionand selection procedures – Triggers and DAQ performance,– calibration, and alignment of the detectors

• Looking forward to collecting large integrated luminosity !


OutlookOutlook

• We are curious to see where it leads…

H?Prof. Peter Higgs


Status detailsStatus detailsAll subdetectors operational & reading out

All electronics, fronts ends, trigger & DAQ hardware installedRemaining: tuning up of the trigger/DAQ system2.5 106 int./sec396 nsec 5-10kHz 1000Hz 50HzDesign:

Level 2Level 1 Level 3 tapeNow: ~200Hz

2.5 106 int./sec396 nsec 50Hz~100Hz

Changed to new modern L3/DAQ system this year (done)

Commissioning and tuning up this systemVERY COMPLEX and high bandwidth systemExpect full rate by middle of fall of 2002

Large effort

Data taking continuesNo loss of physics at current luminosities


Backup SlidesBackup Slides

• Insert backup slides after this page


The Most Massive Candidate eventThe Most Massive Candidate event

M(diEM) = 377 GeV; cosθ* = 0.77; MET = 12.6 GeV;

EM2EM1

ET = 106.2 GeVη = -2.10ϕ = 2.19No track match

ET = 120.3 GeVη = 0.10ϕ = 5.27No track match


LuminosityLuminosity

Total Run 2 luminosity delivered & used A snapshot: July 1 to July

6, 2002


BB--Mesons Mesons

) [GeV]+,K-µ,+µM(5 5.1 5.2 5.3 5.4 5.5 5.6 5.7

0

2

4

6

8

10



20 30 40 50 60 70 80 90 10010-4

10-3

10-2

10-1

1

Run 2 Preliminary Data

MC

R = 0.5 Cone Jets

| < 0.6jetη|

> 4 GeV/cµTp

| < 0.8µη|

) < 0.7µR(jet, δ

EJet [GeV]T

d[n

b/10

GeV

]d/

σE

T

DØ Run 2 Preliminaryb-quark Production Cross SectionDataMC Pythia


mµE

ven

ts/5

0

1

10

102

103


mµE

ven

ts/5

0

1

10

102

103

Data



B lifetime signal

Signal+background





Also have measured J/ψ cross sections out to pseudorapitidy of 1.6


BB--quark Production Cross Section quark Production Cross Section

0 0.5 1 1.5 2 32.5 30

100

200

300

400

500

600

700

800

900

TRelP of (GeV)

Mu

on

s/0.

1 G

eV

µ


µ→Pythia b

Fit

Run 2 data,20 < E < 25 GeV T

jet

Pythia

µ→Pythia c

µ→/Kπ

20 30 40 50 60 70 80 90 1010-4

10-3

10-2

10-1

1

Run 2 Preliminary D

MC

R = 0.5 Cone Jets

| < 0.6jetη|

> 4 GeV/cµTp

| < 0.8µη|

) < 0.7µR(jet, δ

EJet [GeV]T

d[n

b/1

0 G

eV

]d/

σE

T

yDataMC

PythiaP jet

p trel

Pµ

back

fit b component

µ+jet Cross Section


BB--Mesons Mesons

) [GeV]+,K-µ,+µM(5 5.1 5.2 5.3 5.4 5.5 5.6 5.7

0

2

4

6

8

10




mµE

ven

ts/5

0

1

10

102

103


mµE

ven

ts/5

0

1

10

102

103

Data



B lifetime signal

Signal+background





20 30 40 50 60 70 80 90 1010-4

10-3

10-2

10-1

1

Run 2 Preliminary D

MC

R = 0.5 Cone Jets

| < 0.6jetη|

> 4 GeV/cµTp

| < 0.8µη|

) < 0.7µR(jet, δ

EJet [GeV]T

d[n

b/10

GeV

]d/

σE

T

DØ Run 2 Preliminaryb-quark Production Cross SectionDataMC Pythia


IdentyfyingIdentyfying bb--quarksquarks• Signed impact parameter µ+jet data sample

muon pTrel > 1.5 GeV wrt jet

enhanced b-jet contentjet

jet

track

track

Impact parameter < 0(resolution)

Impact parameter > 0(secondary decay vertex)

IP

IP

Reconstruct secondary vertexAlso use semileptonic decays


W/Z boson + W/Z boson + multijetmultijet eventsevents

2GeV/c20 40 60 80 100 120

0

2

4

6

8

10

12

14e+jets data

multijet background

DØ Run 2 PreliminaryW + >= 2 jetsJetsN

0 2 4 6e+jets inclusive jet multiplicity

0.5 1 1.5 2 2.5 3 3.5 4 4.5

W+≥ 2jetsTransverse massspectrum

•Top Physics: W+≥3jets, Z+≥2jets•Higgs Physics: W/Z +≥ 2jets

•Need excellent b-jet identification•Secondary vertex recons.•Soft leptons in jets

Eve

nts

1

10

102

Events with

Jets N≥no. of Jets

candidates-µ +µ →0Z

DØ Run II Preliminary

Nu

mb

er o

f ev

ents

10

102

e+jets data

multijet background

DØ Run 2 Preliminary• Jet multiplicity distributions

DataBackground

W! eν+jets

Z!µ+µ-

Documents

Results from the Dzero Experiment at the Tevatron · Meenakshi Narain, ICHEP2002, 7/29/2002 DØ. in . RunII • Center of Mass Energy = 1.96 TeV • Expect 2 fb-1. by end of 2004