Transcript Top Physics At DØ DØ Freya Blekman

Top Physics
Higgs
At DØ
top
Freya Blekman
b
NIKHEF / Universiteit van Amsterdam
Leptons
tracks
DØ
Outline
1. Introduction
2. Triggers
3. Analyses:
tt  all hadrons
tt  electron + jets
4. Conclusion, Prospects
NIKHEF Annual Scientific Meeting
Amsterdam, December 19th, 2002
Freya Blekman
NIKHEF/ Universiteit van Amsterdam
2
Physics motivation
•
X-sec:
QCD HQ production
•
Mass:
DØ Run 1 Mtop
DØ Run 2 Mtop
Mtop provides
restriction on Mhiggs
•
Top physics
•
•
spin correlations
Vtb
NIKHEF Annual Scientific Meeting
Amsterdam, December 19th, 2002
Freya Blekman
NIKHEF/ Universiteit van Amsterdam
3
Tevatron Top Physics
•
(s)=1.96 TeV
•
Top pair
production
•
Single top
•
tW+b
BR > 99%
tt analyses
classified by W
decay channels
σ(pptt)≈ 7 pb
•
21%
44%
15%
tau+X
mu+jets
e+jets
e+e
e+mu
mu+mu
all hadronic
1% 3% 1%
NIKHEF Annual Scientific Meeting
Amsterdam, December 19th, 2002
15%
(this talk)
•
Freya Blekman
NIKHEF/ Universiteit van Amsterdam
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Event topology
•
•
•
•
Background
reduction most
important factor
Lepton + jets:
jet
e+jets:
b-jet
jet
Background mainly
QCD and W + jets
b-jet
Hadronic channel: e
Background
mainly QCD
All tt channels:
2 b-jets!
 B-tagging of
vital importance
4 jets +
e + νe

jet
jet
b-jet
Hadronic:
6 jets
jet
jet
NIKHEF Annual Scientific Meeting
Amsterdam, December 19th, 2002
Freya Blekman
NIKHEF/ Universiteit van Amsterdam
b-jet
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Triggers
•
•
Hadronic channel:
focus on jet multiplicity, high total transverse
energy (= HT)
Electron + jets channel:
focus on electron identification + jet multiplicity
tt  e+jets
Signal
Efficiency
L1 99 %
tt hadronic
Background
Trigger Rate
Signal
Efficiency
Background
Trigger Rate
Simulated BG
Trigger Rate
88 Hz
100 %
36 Hz
47.8 Hz
(only pT > 20 QCD MC)
L2 95 %
52 Hz
99.0 %
8 Hz
4.1 Hz
L3 75 %
6 Hz
97.8 %
1.4 Hz
1.4 Hz
NIKHEF Annual Scientific Meeting
Amsterdam, December 19th, 2002
Freya Blekman
NIKHEF/ Universiteit van Amsterdam
6
tt  e + jets
•
(L. Phaf, I. Iashvili et al.)
Finding electrons:
EM ID efficiency
• High pT
electrons:
Count Z  e+ewith and
without ID cuts
ID cuts: isolation, EM
fraction, pT > 20 GeV,
shower shape.
NIKHEF Annual Scientific Meeting
Amsterdam, December 19th, 2002
Freya Blekman
NIKHEF/ Universiteit van Amsterdam
7
tt  e + jets candidate
• passes Run I cuts
• Isolated electron
• 4 reconstructed jets above
15 GeV
• HT = 191 GeV
• Aplanarity = 0.11
φ
η
NIKHEF Annual Scientific Meeting
Amsterdam, December 19th, 2002
Freya Blekman
NIKHEF/ Universiteit van Amsterdam
8
Offline event selection
•
event-shape variables
NIKHEF Annual Scientific Meeting
Amsterdam, December 19th, 2002
Freya Blekman
NIKHEF/ Universiteit van Amsterdam
9
tt  e + jets candidate
• passes Run I cuts
• Isolated electron
• 4 reconstructed jets above
15 GeV
• HT = 191 GeV
• Aplanarity = 0.11
• Mtop (χ2 fit) = 165 GeV
φ
η
NIKHEF Annual Scientific Meeting
Amsterdam, December 19th, 2002
Freya Blekman
NIKHEF/ Universiteit van Amsterdam
10
tt  e + jets candidate
NIKHEF Annual Scientific Meeting
Amsterdam, December 19th, 2002
Freya Blekman
NIKHEF/ Universiteit van Amsterdam
11
tt  hadrons
•
•
•
•
N jets > 5
Centrality > 0.6
(F.Blekman,M.Vreeswijk,G.Massaro)
HT > 225 GeV
Aplanarity > 0.05
After selection signal/bg ~1/30 (MC signal eff ~ 44 %)
Jet multiplicity
HT = total hadronic sum
Centrality = HT/H
Aplanarity
Data
Lum: 2 pb-1
QCD MC
Pythia, pT > 80
tt MC
Pythia,hadronic tt
Mtop = 174 GeV
NIKHEF Annual Scientific Meeting
Amsterdam, December 19th, 2002
Freya Blekman
NIKHEF/ Universiteit van Amsterdam
12
tt  hadrons candidate event
ET scale: 59 GeV
y
E scale: 51 GeV
x
+z
-2
•
•
•
•
180
6 jets
Passes selection cuts
Secondary vertices
tagged
Mtop (χ2 fit) = 168 GeV
2
40
0
NIKHEF Annual Scientific Meeting
Amsterdam, December 19th, 2002
ET GeV
2PI
-3.7
-1.2
phi
φ
0.0 3.7
Freya Blekman
NIKHEF/ Universiteit van Amsterdam
1.2
0.0
eta
η
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Results Hadronic Channel
•
Efficiencies and
Purities
Secondary vertex probability
DØ Run 2 Preliminary
DØ Run 2 Data
tt 
hadrons
efficiency
S/B
ratio
Selection
44 %
1/30
2 vertex
tags + non-
25 %
1/2
Cuts
(this study)
tt hadronic MC
QCD MC
leading jet cut
Results for preliminary study on 2 pb-1
Further study still to be done, but
promising for larger dataset….
NIKHEF Annual Scientific Meeting
Amsterdam, December 19th, 2002
ANN output
Freya Blekman
NIKHEF/ Universiteit van Amsterdam
14
Prospects
Expect to have 50 pb-1 reconstructed data by February 2003
•
Lepton + jet , di-lepton:
•
All hadronic:
•
For now: Use Analysis similar
to Run 1
(based on event topology)
•
Make use of improved
b-tagging
tt decay channel
Signal events
DØ Run 1
‘Expected’ signal by
spring 2003
Lepton+lepton
6
1-5
Lepton+jet
20
5 - 27
Hadronic
13
7 - 40
110 pb-1 @ 1.8 TeV
50 pb-1 @ 1.96 TeV, σ = 6 pb
(expected eff 5 - 30 %)
NIKHEF Annual Scientific Meeting
Amsterdam, December 19th, 2002
Freya Blekman
NIKHEF/ Universiteit van Amsterdam
15
Conclusion
•
•
•
•
We see top events being
produced at Tevatron
Improved b-tagging starting
to make a difference
Potential measurement for
the winter conferences
More interesting high pT
physics to come:
Stay Tuned…
NIKHEF Annual Scientific Meeting
Amsterdam, December 19th, 2002
Freya Blekman
NIKHEF/ Universiteit van Amsterdam
16
Event Selection
•
event-shape variables ( hadronic channel)
Sphericity
Sphericity
ttbar
QCD
data
Thrust
NIKHEF Annual Scientific Meeting
Amsterdam, December 19th, 2002
Aplanarity
Oblateness
Freya Blekman
NIKHEF/ Universiteit van Amsterdam
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