Recent D

1
Recent DØ results in B, QCD Electroweak, Top and
Higgs Physics

• Brad Abbott
• University of Oklahoma
• For the DØ Collaboration
• Wine and Cheese seminar
• March 14, 2003

2
DØ Detector
3
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 lt 0.5 for
  tracking detectors and 0.1 for trigger
  detectors
• Detectors are operating stably
• Triggering on muons (single, di-muon, muonjets,
  etc.) during physics data taking

4
Current trigger rates
L1 rate 1KHz L2 rate 0.6 KHz L3 rate 50 Hz
February data taking e 90 per run 85 overall
5
Many new results from DØ

• QCD
• B
• Electroweak
• Higgs
• Top
• New Phenomena (Last weeks wine and cheese
  seminar by S. Protopopescu)

6
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 lt 0.7
• primary vertex zvtx lt 50 cm, Ntrks gt 4
• selection sample definitions
• DR 0.7 cone jets
• hjet lt 0.5
• Njet gt 1
• calculate invariant mass of leading two jets

twice the s at 1.96 TeV
Mjj 838 GeV
7
Jet Energy Scale

• Ecorr (Euncorr - O)/ RS

• 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

• for central jets error 9

8
Raw dijet mass spectrum
Jet energy scale corrected
9
Unsmearing correction

• Measure PT resolution using PT imbalance in
  dijets
• Derive dijet mass resolution using jet PT
  resolution
• Use ansatz function to unsmear data
• Correction is small

10
Dijet mass spectrum
10 luminosity error not shown
11
(Data-Theory)/Theory
10 luminosity error not shown
Dominant error is energy scale
12
B physics

• Cross sections
• Lifetimes
• Flavor tagging
• Prove we understand detector before moving on to
  other interesting physics
• Bs mixing, Sin(2b), b baryons,
• Mixing measurements
• Reconstruct B
• Determine proper time
• Flavor tag

13
B jet cross section

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

Strategy Measure ?jet cross-sectionExtract
b-content using PTRel
?jet
Data selection kinematic cuts
?
pTRel
jet

• pT? gt6 GeV/c, ?? lt0.8
• (Muon PT measured in muon system only)

• hjet lt 0.6

Data 02/28/02-05/10/02 (3.4 pb-1)

• ETcorrgt20 GeV

• 0.5 cone jet

dR(jet,m)lt0.7

14
Obtain B jet cross section from mjets cross
section Fit PTrel templates to data in jet ET
bins
PTrel for jets with 20 GeV lt ET lt 25 GeV
B fraction as a function of Jet ET
(cannot distinguish c mX and decays in flight
so only fit b, non-b)
?
15
b jet cross section
Data unsmeared using ansatz function
Dominant error is due to jet energy scale

• Uncertainty due to
• b quark mass
• renormalization/
• factorization scale
• pdfs
• fragmentation functions
• Based on NLO calculations
• and applied to Pythia

(not fully corrected for lepton losses
and branching ratio)
Consistent with Run I result
16
Lifetimes and exclusive B decays
?

• For now focusing on J/Y m m- sample
• Useful for calibration

L 40 pb-1

• Easy trigger and provides lots of Bs

75,0000.17 13,000 bs
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Average B Hadron Lifetime
( ) states (prompt) B ? J/? X
J/? Sources
decay Prompt PV J/?(B)
SV
Difference
?B through ??
MC
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Inclusive B lifetime
lb distribution
Dominant Sys Errors
Error (mm)
Source
Correction factor 15.9
Fitting Bias 14.0

B fraction 17.3 0.5
ps

Fraction of outliers 1x10-3
ps

(PDG)
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Charged B

• Cuts (J/?)
• Muons with opp. charge
• pT(?) gt 2.0 GeV
• SMT hits ? 1
• ?2 on J/? vertex lt 10
• 2.8 lt J/? mass lt 3.3

B- J/Psi K-
?

• Cuts (Charged B)
• ?2 for K lt 10
• Total ?2 lt 20
• Kaon hits ? 3
• pT(K) gt 2.0 GeV
• Collinearitygt0.9
• B decay length gt 0.3mm

20
Charged B lifetime
Fully reconstructed B so no need for a correction
factor
lttgt1.76 0.24 ps (stat)
lttgt1.674 0.018 ps (PDG)
21
Use charged B sample to measure flavor tagging
performance
m
m
B
Muon tagging Muon DR gt2.0 from B Muon PT gt 1.9
GeV/c Muon charge ? B-tag
K
m

• Jet Charge tagging
• Remove B daughters
• Only use tracks with impact parameter
• lt 0.2 within a phi cone 1.14 opposite to
  direction of B
• Only events with Qgt0.2 are used
• as tags

Use Jet charge or Lepton charge to Determine b
flavor
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Tagging power eD2 Significance of a mixing

measurement proportional to eD2
e efficiency for a tag D Dilution
Jet tag
Muon tag
e 63.0 3.6 e 8.3 1.9
D15.8 8.3 D44.4 21.1
e 65.8 2.4 e 8.5 1.6
D2.4 4.1 D-3.7 19.2
2.4 1.7 3.3 1.8
Signal region
Sidebands

eD2 for signal
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Photon conversions
X-Y vertex location of g e e-
?
Since low PT tracks are very important for B
physics, tracking algorithm has been improved
Improved performance for low PT tracks and tracks
with large impact parameter(Ks,L)
Silicon modules
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? C ?J/? ?
According to CDF Run I measurement fraction of
J/Y from cc
27.4 1.6 5.2
Expect 80 events

• Cuts
• Track pT gt 2.0 GeV on tracks from J/Y
• pTg gt 1.0 GeV

Fit with fixed M?c1-Mcc2 46 MeV but float
relative contributions
25
Results with new tracking algorithm
K p p
?
W LK
?
L pp
?
X Lp
?
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Exclusive B decays
Combine J/Y with track or combine J/Y with K
and then require decay length significancegt3.0
Bd J/Y K
?
B J/Y K
?
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Towards Sin(2b)
Combine J/Y with Ks and require decay
length significance gt3.0
Bd J/Y Ks
?
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Electroweak
'

• Search for Z in Dielectron Decays (Presented at
  last weeks Wine and Cheese seminar)
• Measurement of the Z ? m m Cross Section at
  1.96 TeV

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sBR(Z mm)
?
mtag
L1L2, central track
eL1 87

• data sample 31.8 pb-1
• selection
• hm lt 1.8
• pair of oppositely charged muons
• PT gt 15 GeV
• gt 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

Z
L1 OR no L1
mprobe
track OR no track
etrk 82
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Dimuon Backgrounds

• cosmics negligible
• heavy flavor ( bb )
• compare dimuon events
• two isolated muons
• one isolated muon
• two samples agree well
• lt 1 non-isolated muons
• 1 /- 1 BG
• Z tt mm
• Drell-Yan
• Pythia plus fast detector simulation
• Z and Z/g
• muon resolution tuned to data
• correction factor NZ/NZ,g

?
?
Z tt
?
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Measured sBR(Z mm)
?

• 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

ez emc x eL12 x eloose2 x etrack2 x efz x
(2eL2-eL22) x eopposite_q x eisol x ecosmic
sBr 263.8 6.6 (stat) 17.3 (sys) 26.4
(lum) pb
First measurement at 1.96 TeV
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This measurement
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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() (? eenn/mmnn/emnn) decays
• Others
• Search for H ?gg decays
• WH(? l?n bb)
• ZH(? ll- or nn bb)
• fbb (? 4 b jets) (f h,H,A SUSY Higgs)

34
Higgs Mass Limits
Indirect limit from global SM fit MHlt 195 GeV at
95 CL
Direct SM Higgs search of LEP MHgt114.4 GeV at 95
CL
35

• gg ? H s(gg ? H) 1pb
• For masses below 140GeV,
• Background hides H ? bb signals
• For higher masses mHgt 120GeV,
• Combination with H ? WW() decay process can be
  useful
• HW, HZ s(HW/HZ) 0.1pb
• Leptonic decays of W/Z help background
  rejection
• Hqq s(Hqq) 0.1 pb
• Backgrounds too large
• Hbb s(Hbb) 5fb
• SM extensions may enhance fbb (f h,H,A)

36
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 s 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 excluded at 95 C.L.

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

37
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

38
Wjets production
1st leading jets
W(en)jets

• Selection
• W(en)
• Isolated e pT gt 20 GeV
• h lt 0.8
• Missing ET gt 25 GeV
• W(mn)
• Isolated m pT gt 25 GeV
• h lt 1.5
• missing ETgt 20 GeV
• Jets
• pT gt 20 GeV
• h lt 2.5
• Compare PYTHIA with DATA
• Normalized by area
• Error includes stat. error and dominant sys.
  error from JES

Dot Data Bar MC
QCD BKG
GeV
2nd leading jets
Dot Data Bar MC
QCD BKG
GeV
39
Wjets production (2)

• Reconstructed di-jet mass and DR( Df2 Dh2
  ) between di-jet
• MC represents jet distributions well
• First step towards study of Z(?leptons)H(? bb)
  decay process

Di-jet Mass
W(en)jets
W(en)jets
DR between di-jets
Dot Data Bar MC
Dot Data Bar MC
QCD BKG
QCD BKG
GeV/c2
DRjj
40
Zjets production

• Selections

• 2 muons from Z(mm)
• pT gt 15 GeV
• h lt 2

• 2 electrons from Z(ee)
• pT gt 20 GeV
• h lt 2.3

• Jets
• pT gt 20 GeV
• h lt 2.5

2nd leading jets
1st leading jets

• Compared PYTHIA
• with DATA

• Normalized by area

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

Combined Z(ee)jets and Z(mm)jets
41
Zjets production (2)

• Number of jets in Z jets production
• Reconstructed di-jet mass and DR( Df2 Dh2
  ) between di-jet
• MC represents jet distributions well
• First step towards study of Z(?leptons)H(? bb)
  decay process

jets in Zjets
Di-jet Mass
DR between di-jets
Combined Z(ee)jets and Z(mm)jets
42
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

• Impact Parameter gt 0
• ? track cross jet axis after closest point

m jet sample
Jet
Positive IP
Resolution
track
Interaction point
b enhanced

• Impact Parameter lt 0
• ? track cross jet axis before closest point

Jet
Interaction point
track
Negative IP
43
H?WW() ? ll-nn

• 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 mH100 - 200GeV)
• Fermiophobic/Topcolor Higgs
• (Br(H ?WW)gt98 for mH gt 100GeV)
• Non Higgs-related Tri-linear couplings, New
  Phenomena
• Look at ee/em/mm plus missing ET events
• Cannot directly reconstruct mass
• Transverse mass computed by the mll and missing
  ET
• Opening angle between leptons (DFll) is useful
  discriminating variable
• Two leptons tend to move in parallel (? DFll is
  small) ,
• due to spin correlation of Higgs boson decay
  products.
• Leptons from Z/g , multijets are emitted back to
  back, large DFll
• Backgrounds include Z/g, WW, tt, W/Zjets, QCD

44
Results of H?WW() ? ee-nn
Expected background DATA
Lepton ID, pTgt20 GeV/c 2748 ? 42 ? 245 2753
mee lt mH/2 264 ? 18.6 ? 4.3 262
ET gt 20 GeV/c2 12.3 ? 2.5 ? 0.7 11
Transverse mass 3.6 ? 1.4 ? 0.2 1
DFee lt 2.0 0.7 ? 1.4 ? 0.1 0
L44.5 pb-1 Selection optimized mH 120 GeV
esig 8
Results of H?WW() ? emnn
Expected background DATA
Lepton ID, pTgt20 GeV/c 22 ? 2.1 ? 2.2 22
ET gt 20 GeV/c2 3.1 ? 1.7 ? 0.1 4
Anti W 1.4 ?1.5 ?0.1 2
DFem lt 2.0 0.9 ? 1.5 ? 0.1 1
L34 pb-1 Selection optimized mH 160 GeV
esig 12
45
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
• mm
• em
• e jets
• m jets
• e jets (soft muon tag)
• m jets (soft muon tag)

46
Status of the Top Mass Measurement in the
LeptonJets Channels at Run I
Likelihood method using most available
information Uses 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)
(5.6 GeV from PRD 58 052001,1998)
Large improvement on the statistical uncertainty
(2.4? stats)
Details to be presented at an upcoming Wine and
Cheese seminar
47
Analysis Channels
Leptonjets (topological)
Leptonjets (soft muon tag)
dileptons
em and mm
ejets, mjets
ejets/m, mjets/m
Efficient Not very pure
Pure Not very efficient
Pure and efficient Low branching
48
Data Sample
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 (f, h and E/p)

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

• Missing ET
• From calorimeter with JES corrections and muon
  correction

49
Dimuon Channel
Selection 2 isolated muons, MET(Mmm), HT and 2
or more jets
Backgrounds
Z?mm DY?mm QCD and Wjets
Z?tt WW?mm
from MC
Estimated from data
DØ Run II Preliminary
WW (MC)
Z?mm (MC)
Z ?mm DY ?mm Fakes Z ?tt WW 0.20?0.11 0.20?0.20 0.18?0.18 0.02?0.02 0.00?0.00
Background 0.60?0.30
Signal 0.3?0.04
Data 2
L42.6 pb-1
Data
Signal (MC)
For s 7pb
50
em Channel
Selection criteria Backgrounds
1 electron, 1 isolated muon, MET, METCAL , HT (e)
and 2 or more Jets
QCD and Wjets
Z?tt WW?em
from MC
Estimated from data (Fakes)
DØ Run II Preliminary
Fakes Z ?tt WW 0.05?0.01 0.02?0.01 0.00?0.00
Bkg 0.07?0.01
Signal 0.5?0.01
Data 1
Z ?tt
Fakes
33.0 pb-1
Njets
For s 7pb
Njets
HT(e) (GeV)
51
Lepton-plus-Jets Analyses

• Luminosities ejets and
  mjets
• 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 W4jets assuming Berends scaling - Apply
topological selection
1 EM object or muon, MET, soft muon veto
Separate Wtt and QCD with loose (L) and tight
(T) lepton characteristics. Efficiencies (L?T)
for signal eWtt and background eQCD are
measured independently
ejets Track match to the EM object mjets
Muon isolation
?
Matrix method
52
e Wtt vs Njets
DØ Run II Preliminary

• Signal probabilities
• Background nature
• Background Probabilities

obtained from benchmark signal samples of Z? ee
or mm
Non trivial dependence of eWtt w.r.t. Njets
(especially in the mjets case)
? Correction taken from MC
mjets
QCD Background essentially due to Heavy Flavor
semi-leptonic decays
QCD Background due to leading p0 or compton QCD
events and Fake track or g conversion
ejets
are obtained from benchmark QCD samples with
low MET
DØ Run II Preliminary
DØ Run II Preliminary
DØ Run II Preliminary
ejets
Dependence of the eQCD w.r.t. MET and Njet
ejets
ejets
53

• Berends scaling
• Estimation of the W background for Njets? 4
• Apply topological cuts

DØ Run II Preliminary
DØ Run II Preliminary
a 0.145?0.02
a 0.164?0.02
38 (mjets)
24.2
11.9
11.9
12.5
22 (ejets)
Aplanarity and HT
Analysis NW NQCD Bkg. Tot. Signal Nobs
ejets 1.3?0.5 1.4?0.4 2.7?0.6 1.8 4
mjets 2.1?0.9 0.6?0.4 2.7?1.1 2.4 4
For s 7pb
54
Soft Muon Tag Analyses
Selection before Soft Muon Tag
- Use the same preselection as ljets - Require
at least 3 jets - Apply mild topological cuts
(Loose/Tight sample)
75/23 (mjets)
?
459/27 (ejets)
When SMT applied
DØ Run II Preliminary
DØ Run II Preliminary
1/0 (mjets)
mjets
ejets
9/2 (ejets)
0.2?0.2 (m)
0.2?0.1 (e)
QCD background. from matrix method
W bkg. from Tag rate functions
Analysis Bkg. Tot. Sig. Nobs
ejets 0.2?0.1 0.5 2
mjets 0.6?0.3 0.4 0
DØ Run II Preliminary
0.4?0.1 (m)
0.0?0.1 (e)
For s 7pb
55
mjets Candidate Event
SV
Jet 2
m -
IP
Jet 2
MTC
IP
Jet 1
Jet 1
SV
Double tag event
56
Cross Section Measurement

• Combining the observation of all channels an
  excess of 3s is observed

Combined cross section
57
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