1. Studies of Diboson Production and Triple Gauge Boson Couplings
7/27/2006
Studies of Diboson Production and Triple Gauge Boson Couplings
Zhengguo Zhao
University of Michigan, Ann Arbor, USA
9th ACFA Physics and Detector Workshop& ILC GDE Meeting
Feb. 4-7, 2007, Beijing
1/5/2007
Beijing, Zhengguo Zhao

2. Outline Introduction Recent Tevatron results Effort from ATLAS/CMS
7/27/2006
Outline
Introduction
Recent Tevatron results
Effort from ATLAS/CMS
Summary
1/5/2007
Beijing, Zhengguo Zhao

3. Introduction
1/5/2007
Beijing, Zhengguo Zhao

4. Diboson Production at Hadron ColliderV3 V1 V2 q q’
LO Feynman diagram, V1, V2, V3 = Z, W, g WW, ZW, ZZ, Wg.
Production cross section predictable
Only s channel has three boson vertex, which manifest the
gauge boson coupling
SM:
Pure neutral vertexes ZZZ, ZZ g are forbidden
(Z/g carry no charge and weak isospin that needed for
gauge bosons couple)
Only charged couplings WWg, WWZ are allowed
1/5/2007
Beijing, Zhengguo Zhao

5. Triple Gauge Boson Couplings
Characterized by an effective
Lagrangian, parameterized in
terms of coupling parameters
for new physics
C, P and CP symmetry conservation, 5 free parameters:
- lg ,lZ: grow with s, big advantage for LHC
- kg = kg-1, g1Z = g1Z-1, kZ = kZ-1: grow with s
Tree level SM: lg = lZ = kg = g1Z = kZ = 0
1/5/2007
Beijing, Zhengguo Zhao

6. Production of WZ, WW q q’ W Z l+ l- l n  l s-channel dominates,
Sensitive only to WWZ coupling
Clean signal eee, eem, mme, mmm
3 isolated high pT leptons with large ET(miss)
s-channel  l
Sensitive to WWZ and WWg
Clean signal ee, mm, em
2 isolated high pT leptons with opposite
charge and large missing ET
s-channel
t-channel
1/5/2007
Beijing, Zhengguo Zhao

7. Production of Wg, ZZ Isolated high pT lepton (e, m) large missing ET
Isolated g
Main bkg: W+jet, Z+ g
s channel suppressed by O(10-4)
Only t-channel at tree level,
4 isolated high pT leptons from
the Z pair decays
Clean signal eeee, eemm, mmmm,
almost bkg free z l+ l-
l’+
l’- q
qbar q’ z
1/5/2007
Beijing, Zhengguo Zhao

8. Diboson as background for searchesZZ H
1/5/2007
Beijing, Zhengguo Zhao

9. Motivations • Measure diboson production  and TGCs
• Explore none-Abelian SU(2)U(1) gauge structure of SM
• Probe new physics if production cross section, or
TGCs deviate from SM prediction  complementary
to direct search for new physics
• Understand the backgrounds of many important
physics analyses
Search for Higgs, SUSY, graviton and study of ttbar
1/5/2007
Beijing, Zhengguo Zhao

10. Recent Results from Tevatron
1/5/2007
Beijing, Zhengguo Zhao

11. WW Production at Tevatron
L(pb-1)
Nobs/Nb
(pb) D0
25/9.8
CDF
825
95/43.4
13.6±2.3(stat) ±1.6(sys) ±0.9(lum)
NLO
12±0.8
1/5/2007
Beijing, Zhengguo Zhao

12. WW+WZlnjj 1 lepton with pT>25GeV, ET>25 GeV
≥2 jets with pT > 15 GeV
(WW+WZ) < 36 95% CL
1/5/2007
Beijing, Zhengguo Zhao

13. WW+WZlnjj anomalous coupling from CDF
Select 56 < mjj < 112 peak region
Minimize likelihood for pT of W(l,ET)
-0.51 <  < 0.44, < l < 0.28
1/5/2007
Beijing, Zhengguo Zhao

14. WZ  lnll q q’ W Z l+ l- l n
3 leptons (e, m)
- CDF: pT(leading) >20 GeV, pT(others) > 10 GeV
- D0: pT(all) > 15 GeV
m(l+l-) within mZ window
ET is used to suppress the bkg of Z+jet/g
1/5/2007
Beijing, Zhengguo Zhao

15. WZ  lnll results L(pb-1) Nobs (pb) D0 760-860 12 7.5 ± 1.2 3.6 ± 0.2
CDF
825 2
3.7 ± 0.3
0.9 ± 0.2
< 6.3 (95% CL)
NLO
3.7 ± 0.1
1/5/2007
Beijing, Zhengguo Zhao

16. WWZ Anomalous Coupling
For L = 300 pb-1 data, expect 2
signal and 1 background events.
Observed 3 events. TGCs are
determined to be
1/5/2007
Beijing, Zhengguo Zhao

17. (Wglng) from D0 Channel L(pb-1) (pb) Wgeng 933 3.12 ± 0.49 ± 0.19
Wgmng
878
3.21 ± 0.49 ± 0.2 SM
3.21±0.08
1/5/2007
Beijing, Zhengguo Zhao

18. Tevatron Results on Dibson Studies
Tevatron results consistent with SM prediction
1/5/2007
Beijing, Zhengguo Zhao

19. Diboson Studies from ATLAS and CMS
1/5/2007
Beijing, Zhengguo Zhao

20. LHC Expectations for the TGCs
High CM energy  larger s
High luminosity  high statistics
High sensitivity
Expected to be ~10 improvement on LEP/Tevatron
Predictions for TGCs at 95% C.L. for L=30 fb-1 (inc syst)
< lg <
< lZ <
< Dkg <
-0.11 < DkZ < +0.12
< Dg1Z <
1/5/2007
Beijing, Zhengguo Zhao

21. MC Data for Diboson Studies(ATLAS)
7/27/2006
MC Data for Diboson Studies(ATLAS)
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) 4 l (e,m)
4.66104
Z+jet ee/mm/tt
5.80106
Zbb4 l
4.99104
DY Z/g  l+ l- (e, m, t)
1.67107
Zg ll (e,m)
2.50104
Data produced in ATLAS GRID, and Michigan ATLAS
computer cluster
Background (pythia 6.2), 106 ~ 107 for Z+jet, W+jet,
DY, W+jet and Wlepton
Signal events produced by (v2.3)–Jimmy, W/Z
width effect is not included (v3.1 has included width)
1/5/2007
Beijing, Zhengguo Zhao

22. ZW Signal and Backgrounds(ATLAS) (for 1 fb-1 data)
Neee
Neem
Nmme
Nmmm
Ntotal(1fb-1)
Nsignal
16.9
17.1
21.9
19.8
75.7
Nbkg
1.71
0.88
1.73
2.00
6.32
S/B
9.84
19.4
12.7
9.92
12.0
47.4%
42.9%
7.7%
2.1%
1/5/2007
Beijing, Zhengguo Zhao

23. WW Signal and Background (ATLAS) (for 1 fb-1 data)
Process
Nee
Nmm
Nem
Ntotal
WWl+X (l=e,m)
36.7
37.6
284.4
358.7
Total background
188.6
112.1
59.4
360.1
S/B
0.19
0.34
4.79
1.0
47.3%
38.4%
8.3%
3.4%
2.6%
1/5/2007
Beijing, Zhengguo Zhao

24. Invariant Mass and Pt Distributions for ZZ
For 1 fb-1 data at ATLAS
M(e+e-)
M(m+m-)
Pt(e+e-)
Pt(m+m-)
13 events candidates
Background free with current statistics
1/5/2007
Beijing, Zhengguo Zhao

25. Comparison of the efficiencies of BDT/ANN
Background efficiency
Signal efficiency
1/5/2007
Beijing, Zhengguo Zhao

26. Signal and Background Samples (CMS)
×Br
k-factor
ZZ(4e)
18.7 fb
1.3
WZ(3l, l=e,m,t)
1.6 pb
1.92
ttbar(2l)
62.3 pb
1.6
Z(ee)bb
60.3 pb
2.4
Z(mm)bb
ttbar(4e)
194 fb
ZZ(2e2m)
32.3 fb
1.35
Signal
Main bkg
tt(2l) generated with TopReX, Zbb with CompHEP, all others with Pythia
1/5/2007
Beijing, Zhengguo Zhao

27. WZ→3l Expected Signal & Background
M(l+l-) after all cuts 4 channels
combined (3e,2e1m,2m1e,3m)
Presence of peaking backgrounds
- Zbb
- ZZ (irreducible)
High significance in the first 1 fb-1
L = 1 fb-1
Expected signal and background yields for 1 fb-1
1/5/2007
Beijing, Zhengguo Zhao

28. ZZ→4e Expected Signal & Background
L = 10 fb-1
M(e+e-) after all cuts
(2 entries per event)
Nearly background free!
Expected signal and background yields for 1 and 10 fb-1
1/5/2007
Beijing, Zhengguo Zhao

29. WZ and ZZ Discovery Potential (CMS)
ZZ→4e signal significance
WZ →3l signal significance
Ideal simulation
miscalibration
Systematic effects
Ideal simulation
miscalibration
Systematic effects
5 s discovery
ZZ: ~1 fb-1
WZ: ~150 pb-1
1/5/2007
Beijing, Zhengguo Zhao

30. Summary
D0 and CDF have been actively studies diboson production and the corresponding TGCs. The results so far are consistent with SM predictions.
WZ, WW and ZZ signals are expected to be established at CMS and ATLAS with 100pb-1~1fb-1
Anonymous gauge boson coupling can be probed with a few fb-1 data
Advanced techniques (BDT, ANN) can significantly improve the S/B.
To improve the TGCs with LHC data, it’s crucial to correctly build the TGCs into event generators
1/5/2007
Beijing, Zhengguo Zhao

31. Experiments at Tevatron
1/5/2007
Beijing, Zhengguo Zhao

32. CDF & D0 Detectors CDF Run II Upgrades:
New Silicon Vertex Detector (SVX) and
faster tracking drift chamber (COT)
New scinitllating-tile end-plug
calorimeters
Increased ηφ coverage for muon
detectors
New Scintillator Time-Of-Flight system
D0 Run II Upgrades:
New silicon (SMT) and Fiber (CFT)
trackers, placed in new 2T Solenoid
Calorimeters supplemented with
Preshower detectors
Significantly improved Muon System
1/5/2007
Beijing, Zhengguo Zhao

33. 1/5/2007
Beijing, Zhengguo Zhao

34. The LHC Experiments
4.5 km
1/5/2007
Beijing, Zhengguo Zhao

35. Collisions at the LHC 2804 bunch/beam 7 + 7 TeV
Particle
Parton
(quark, gluon)
Proton l
jet
Bunch
SUSY.....
Higgs Z o e + -
2804 bunch/beam
7 + 7 TeV
separation: 7.5 m (25 ns)
40 MHz crossing rate
1011 proton / bunch
109 pp collision/s
(superposition of 23 pp interactions
per bunch crossing: pile-up)
N = L × (pp) = 109
Mostly low pt events (soft) events
Interesting high pt events are rare
New physics rate ~ Hz
 event selection:
1 in 10,000,000,000,000
1/5/2007
Beijing, Zhengguo Zhao

36. Length: ~ 46 m Radius : ~ 12 m Weight : ~ 7000 tons Channels: ~ 108
7/27/2006
Muon spectrometer
air-core toroids,
MDT+RPC+TGC
s/pT ~ 2-7 %
|h| < 2.7, |h|<2.5 ( precision
phys.)
Length: ~ 46 m
Radius : ~ 12 m
Weight : ~ 7000 tons
Channels: ~ 108
Lcable: ~ 3000 km
EM Calorimetry
Pb-LAr
s/E ~ 10%/√E(GeV)1%
|h|<3.2, |h| < 2.5 (fine granularity) a
Inner detector
Si pixels and strips
Transition Radiation Detector
(e/ separation)
s/pT ~ 0.05% pT(GeV)0.1%;
|h| < 2.5, B=2 T(central solenoid)
Hadron Calorimeter
Fe/scintillator (central), Cu/W-LAr (fwd)
s/E ~ 50%/√E(GeV)3%
||<3
1/5/2007
Beijing, Zhengguo Zhao

37. Silicon pixels and strips
EM calorimeter:
Lead tungstate
s/E = 5% / √E (GeV)  2%
Muon spectrometer
DT+CSA+RPC
Magnet solenoid
4 T
Hadron Calorimeters
Barrel & Endcap:
Cu/Scintillating sheets
s/E = 65% /√E (GeV)5%
Inner Detector:
Silicon pixels and strips
1/5/2007
Beijing, Zhengguo Zhao

38. Anomalous Coupling and Form Factor
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
TGCs manifest in
- cross section enhancement
- high pT(V=Z,W,)
- production angle
1/5/2007
Beijing, Zhengguo Zhao

39. Diboson Production Cross Section
Tevatron
LHC
1/5/2007
Beijing, Zhengguo Zhao

40. Boosted Decision Trees (BDT) and Artificial Neural Network (ANN)
ATLAS
e-boost
ANN
1/5/2007
Beijing, Zhengguo Zhao

41. WZ tt MZ(ee) Vector∑Et(jet) MZ(mm)-MW(en) cut Pt(l+l-) WW ZZ Zjet Zg
Pt(l+l-) cut
to reject
fate events
Vector∑Et(jet) tt
to reject jet
MZ(ee)
MZ(mm)-MW(en) WZ
1/5/2007
Beijing, Zhengguo Zhao