1. Diboson Production Studies with Full Simulation Data Sets
T. Dai, A. Wilson, B. Zhou, Z. Zhao
University of Michigan, USA
Ma Hong
Brookhaven National Laboratory, USA
April 27, 2006
North America SM and Higgs ATLAS Workshop
4/16/2006
Zhengguo Zhao

2. Outline Introduction MC Data Samples Events Selection and Results
Plans and Summary
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Zhengguo Zhao

3. Diboson Production at Hadron ColliderV1 V2 V3
V1, V2, V3 = Z, W, g
Diboson can be produced so long
as the quantum numbers of the
vertex conserves
e.g. WW, ZW, ZZ, Wg, Zg
SM:
Only WWg, WWZ couplings are allowed
Pure neutral vertexes are forbidden
(Z/g carry no charge and weak isospin that needed for
gauge bosons couple)
Diboson production cross section predicable (NLO).
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Zhengguo Zhao

4. Diboson Physics-Motivations
● Explore none-Abelian
SU(2)xU(1) gauge structure of
SM and test of Triple Gauge
Couplings (TGCs)
● Backgrounds of many important
physics analyses:
Search for Higgs, SUSY,
graviton and study of ttbar
● Probe new physics if TGCs(exp)
deviate from the SM prediction
Tevatron
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5. Diboson as Background of New PhysicsZZ H
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6. Triple Gauge Boson Couplings
Characterized by an effective Lagrangian, parameterized in terms of coupling parameters for new physics
Two overall parameters
gWWg = -e, gWWZ = -cotθ
Seven parameters for
WWZ and WWg each
C, P and CP symmetry
conservation free
parameters are:
lg, kg, lZ, kZ , g1Z
Tree level SM
g1Z = kV = 1, lV =0 (V=Z, g)
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7. Anomalous Coupling
Cross section increase for coupling with non-SM values,
yielding large cross section at high energies that
violating tree level unitarity - form factor scale
s: subprocess CM energy
L: form factor scale
s (for WW)
s (for ZW)
LHC/ATLAS:
Mush higher CM energy-larger s
High luminosity - high statistics
High sensitivity
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8. MC Data for Diboson Studies
Signal: (V2.3)
Background: Pythia 6.2
Simulation-digitization: 9.0.4
Reconstruction: (2,4)
Data produced in ATLAS GRID, and Michigan ATLAS computer cluster
Process
MC data
ZW+  2e/2m + X
26033
ttbar l+x
1.96×105
ZW-  2e/2m + X
29085
 ee/mm/ tt
2.30×106
ZZ  4e, 4m, 2e2m
19933
W e/m/t + n
1.61×106
WW ln + x
32056
W+jets  ln + x
1.59×106
ZZ(pythia) 4l (e,m)
4.66×104
Z+jet ee/mm/tt
5.80×106
Zbb 4l
4.99×104
DY Z/g  l+ l- (e, m, t)
1.67×107
Zg ll (e,m)
2.50×104
Significantly increased background statistics, e.g. for Z+jet,
W+jet, DY, W+jet and Wlepton to the level of 106 or more.
Rome Di-boson signal events produced by (v2.3)
- W and Z width effect is not included.
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9. WZ q W q’ Z Sensitive to WWZ vertex (SM) = 57.7 pb at 14 TeV
– Allows study of WWZ coupling parameters with no
assumptions about WWg couplings
(SM) = 57.7 pb at 14 TeV
ZW→ l+l- lν mode is clean and unambiguous
ZW→ jj lν mode has larger branching fraction, but
difficult to distinguish ZW from W+jets, WW
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10. ZW Events Selection (eeen, eemn, emmn, mmmn)
3 leptons with high pt and
high missing Et,
2 leptons have opposite
charge and the same flavor,
invariance mass within mZ
window
Njet(Et>30 GeV)<2, Cuts to jet
Et vector/scale sum
Pre-selctction:
pt (l1) > 6 and pt(l2,3) > 20 GeV
R(l+l-) > 0.2
Etmiss > 25 GeV
Vector ∑Et(jet) < 100 GeV
Scalar ∑Et(jet) < 200 GeV
ZWselection
40 < MT(W) < 120 GeV
MET > 25 GeV
|M(+-) – MZ| < 12 GeV
|M(e+e-) – MZ| < 9 GeV q q’ W Z l+ l- l 
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11. Signal scaled
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12. 4/16/2006
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13. 4/16/2006
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14. ZW Signal and Backgrounds (for 1 fb-1 data)
Neee
Neem
Nmme
Nmmm
Ntotal(1fb-1) Ns
16.9
17.1
21.9
19.8
75.7 Nb
1.71
0.88
1.73
2.00
6.32
S/B
9.84
19.4
12.7
9.92
12.0
S/B
12.9
18.2
16.7
14.0
30.1
47.4%
42.9%
7.7%
2.1%
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15. WW Sensitive to WWZ and WWg  Clean signal een, mmn, emn, but l
low branching fraction
Two isolated high Pt leptons
with opposite charge
Large missing Et  l
Pt(l1) > 20 GeV and Pt(l2) > 25 GeV, (l1l2) < 2.8, R(l+l-) > 0.2
Et(Miss) > 30, 35, 40 GeV for een, emn and mmn
Mee & Mmm>50 GeV, (Veto Z) Mem>30 GeV
Njet(Et>30 GeV) ≤1 and
Vector∑Et(jet)<60 GeV, Scalar∑Et(jet)<45 GeV
Mtmin =min(Mtl1,Mtl2)>20 GeV, Mt(WW) < 500 GeV, Pt(l+l-)>30 GeV
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Zhengguo Zhao

16. tt WW cut ZZ Pt(l+l-) Vector∑Et(jet) Reject low Reject jet activitiesZg
Zjet
cut
Reject jet activities
Reject low
Pt fake events
Pt(l+l-)
Vector∑Et(jet)
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Zhengguo Zhao

17. WW Signal and Backgrounds (for 1 fb-1 data)
Process
Nee
Nmm
Nem
Ntotal
WWl+X (l=e,m)
36.73
37.58
284.41
358.71
ZW+2l+X (l=e, m)
0.759
1.422
5.499
7.679
ZW-  2l+X (l=e, m)
0.194
0.679
3.831
4.704
ZZ  4e, 4m, 2e2m
0.0043
0.0255
0.0298
Z+jet  2l+X(l=e, m, t)
68.67
42.90
27.46
139.04
DY  l+l-(l=e, m, t)
103.47
55.14
12.57
171.18
Z+g  2l+g (l=e, m)
1.20
0.60
3.00
W+jets  l+X(l=e,m,t)
3.03
1.28
4.31
ttbar l+X
11.32
7.54
30.17
Total background
188.6
112.1
59.41
360.1
S/B
0.19
0.34
4.79
1.00
S/B
2.67
3.55
36.90
18.90
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18. Background Contributions to WW
47.3%
38.4%
8.3%
3.4%
2.6%
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19. ZZ l1+ l1- l2+ l2- 4 high Pt isolated leptons (l=e, m)
- Pt(l1 or l2) > 25 GeV
- R(l+l-) > 0.2
2 have the same flavor and their invariant mass
satisfy |m(l+l-) – mZ| < 12 GeV
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20. Invariant Mass and Pt Distributions for ZZ
m(e+e-)
m(m+m-)
PT(Z)
MZZ
13 events for 1 fb-1
Background free with current statistics
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Zhengguo Zhao

21. Progress after Rome Meeting
Significantly increased background statistics
More background channels have been included
Optimized events selections, and significantly improved S/B
ATLAS note based on Rome data-sets and high statistic background events has been prepared
BHO MC for TGC studies interfaced to Pythia 6.205
Validate (v3.1) diboson generator for DC3.
Major improvement:
- W-width included in WW production
- Spin-correlation included.
But the Z-width has not been included for ZW and ZZ.
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22. Plans Analysis with DC3 data using MC@NLO new version(3.1).
Prepare for the measurements of the ZW, WW, ZZ production cross sections with 100 – 500 pb-1 data. Study the systematic errors
Apply advanced techniques to increase the S/B: boosted decision tree, artificial neuronal net work, matrix method.
Establish the tools to determine the TGCs. We will start from the existing techniques using BHO MC (from Matt Dobbs)
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23. How To Find SM BGK Data Sets used in this analysis?
Contact persons:
Tiesheng Dai,
Hong Ma,
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Zhengguo Zhao

24. Backup Slides
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25. Summary
Post Rome background: statistics increased 5-10 times; add more channels  tremendous effort.
ZW and WW events selection has been significantly improved  much better S/B.
Even with 100 pb-1 early ATLAS data, diboson cross section measurements and the determination of TGCs will be guaranteed early physics.
To improve the TGC’s with ATLAS data, it’s crucial to build the TGCs into event generator
 need joint effort and experts
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26. Signal and Background of All
Four Channels
Process
Neee
Neem
Nmme
Nmmm
Nobs
Nobs/NMC
Ntotal
(1fb-1)
ZW+  2e/2m+X
107
110
140
132
489
0.0188
46.4
ZW-  2e/2m+X
139
138
178
150
605
0.0208
29.3
Signal total
246
248
318
282
1094
75.7
ZZ  4e/4m/2e2m
149
186
158
209
702
0.0352
2.99
Z+jet  2e/2m/2t 2 1 3 8
1.41×10-6
3.34
DYl+l-(l=e, m, t)
7.03×10-7
0.42
Zg  2e/2m
1.50×10-5
0.74
Background total
153
187
163
211
714
7.5
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27. WW Signal and Background for MC Sample
Process
Nee
Nmm
Nem
Nobs
Nobs/NMC
WWl+X (l=e,m) 43 44
333
420
1.31×10-2
ZW+2(l)+X (l=e, m) 8 15 58 81
3.11×10-3
ZW-2(l)+X (l=e, m) 4 14 79 97
3.33×10-3
ZZ4e, 4m, 2e2m 1 6 7
3.51×10-4
Z+jet2(l)+X(l=e, m, t)
200
105 84
389
2.40×10-5
DYl+l+(l=e, m, t)
151
100 2
253
1.62×10-4
Z+g2(l)+g (l=e, m) 5
3.34×10-5
W+jetsl+X(l=e,m,t)
1.26×10-6
ttbarl+X 3
7.23×10-5
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28. Ns/Nb(ZW) Ns/Nb(WW) Ns(ZW) Nb(ZW) Ns(WW) Nb(WW) 4/16/2006
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