LPSC - Grenoble Julien MOREL 1 Discovery and identification of a Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion ' Z ee Discovery and identification of Discovery and identification of a new neutral gauge boson in a new neutral gauge boson in the e the e + e e - channel with the ATLAS channel with the ATLAS detector detector Julien MOREL Fabienne LEDROIT Benjamin TROCME ATLAS Exotic group LPSC - Grenoble 23 August 2006 - Laboratoire René-J.-A.-Lévesque - Montréal
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LPSC - Grenoble Julien MOREL 1Discovery and identification of a
Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion
'Z e e
Discovery and identification of a new neutral Discovery and identification of a new neutral gauge boson in the egauge boson in the e++ee-- channel with the channel with the
ATLAS detector ATLAS detector
Julien MOREL
Fabienne LEDROITBenjamin TROCME
ATLAS Exotic groupLPSC - Grenoble
23 August 2006 - Laboratoire René-J.-A.-Lévesque - Montréal
LPSC - Grenoble Julien MOREL 2Discovery and identification of a
Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion
'Z e e
PlanPlan
Introduction and motivationsIntroduction and motivations
The different theoretical Z’ modelsThe different theoretical Z’ models
The LHC and the ATLAS experimentThe LHC and the ATLAS experiment
The ATLAS Z’ discovery potentialThe ATLAS Z’ discovery potential
How can we infer the underlying theory ?How can we infer the underlying theory ?
Conclusions and outlook Conclusions and outlook
LPSC - Grenoble Julien MOREL 3Discovery and identification of a
Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion
'Z e e
The Standard model The Standard model
We need to search beyond the standard modelWe need to search beyond the standard model
It is very well verifiedIt makes very good prediction
Hypothetical particle : Higgs bosonLot of parametersDivergencesNumber of fermion famillyThe forces are not describe by the same gauge theory
LPSC - Grenoble Julien MOREL 4Discovery and identification of a
Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion
'Z e e
Z' is a signature of new physicsZ' is a signature of new physics
Many theories beyond the standard model predict new neutral gauge bosons (Z’) :
Grand Unified Theory (GUT)Z’Z’Z’from E(6) and Z’LR from SO(10), CDDT parameterization
Little Higgs theoryNew gauge bosons come from new gauge groups.
Almost all theories with extra-dimensions New gauge bosons are standard Z/ Kaluza-Klein excitations.
…
LPSC - Grenoble Julien MOREL 5Discovery and identification of a
Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion
'Z e e
For our studies
We focus on the channel
'pp Z e e
, ,u d s
, , 'Z Z
, ,u d s
l
l
To study the discovery potential and the underling Z’ theory
Z’ at hadrons colliderZ’ at hadrons collider
Backgrounds
Hadronic channel
Leptonic channel
Signal over background ratio very small
Small physic background (mainly Z/ process or rare processes)
LPSC - Grenoble Julien MOREL 6Discovery and identification of a
Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion
'Z e e
Tevatron ultimate limit
With 2 fb-1, Tevatron Run II can probe up to Mz’ ≈ 1 TeV
Experimental limits on the Z’ massExperimental limits on the Z’ mass
Mass limit with 200 pb-1
LPSC - Grenoble Julien MOREL 7Discovery and identification of a
Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion
'Z e e
Introduction and motivationsIntroduction and motivations
The different theoretical Z’ modelsThe different theoretical Z’ models
The LHC and the ATLAS experimentThe LHC and the ATLAS experiment
The ATLAS Z’ discovery potentialThe ATLAS Z’ discovery potential
How can we infer the underlying theory ?How can we infer the underlying theory ?
Conclusions and outlook Conclusions and outlook
LPSC - Grenoble Julien MOREL 8Discovery and identification of a
Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion
'Z e e
Extra-dimension theories
Different theoretical Z’ models
Original RS : [ L.Randall, R.Sundrum, Phys. Rev. Lett. 83 3370 (1999) ]
Di-lepton invariant mass in the RS model Di-lepton invariant mass in the RS model
According to the G.Azuelos and G.Polesello idea, According to the G.Azuelos and G.Polesello idea, to discover a Z’ we are looking for :to discover a Z’ we are looking for :
An excess of cross section due to a resonanceA lower cross section due to a destructive interference
LPSC - Grenoble Julien MOREL 30Discovery and identification of a
Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion
We calculate the significance S12 in two regions of the mass spectra : In the resonance region
Above M1
In the interference region Between 500 Gev and M1
Lack of eventsLack of events 12 0S
Excess of eventsExcess of events 12 0S
The parameter M1 represent the integration bounds
We chose it model-independent such as :
1
15 eventss
DY
s M
d
ds
M1 depend on the luminosity and represents the end of the DY process. We keep 15 events above M1 to allow
a S12 calculation with a non-zero background value M1
LPSC - Grenoble Julien MOREL 31Discovery and identification of a
Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion
'Z e e
1 en GeVKKm
-1
1
10 fb
1070 GeVe eM
-1
1
100 fb
1729 GeVe eM
12S
Z’Z’RS RS discovery potential - RS model : Point Adiscovery potential - RS model : Point A
1
1
Résonance : [ ; ]
Interférence : [500; ]
e ell
e ell
M M
M M
1 en GeVKKm
-1
1
300 fb
2129 GeVe eM
1 en GeVKKm
12S
12S
LPSC - Grenoble Julien MOREL 32Discovery and identification of a
Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion
'Z e e
Point A
-110 fb -1100 fb -1300 fb
1 en GeVKKm1 en GeVKKm1 en GeVKKm
≈ 3 TeV ≈ 4 TeV ≈ 6 TeV
12S12S 12S
Z’Z’RS RS discovery potential - RS model : Point Adiscovery potential - RS model : Point A
Z’Z’RSRS discovery potential discovery potential
We combined :We combined :•the two analyses (interference and resonance)the two analyses (interference and resonance)•the two channels (ethe two channels (e++ee-- and and ++--))
We can discover up to 3 TeV with 10 fb-1 (already excluded)
We can discover up to 6 TeV or 4 TeV with 300 or 100 fb-1
We can discover point B up to 10 TeV with 100 fb-1
LPSC - Grenoble Julien MOREL 33Discovery and identification of a
Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion
'Z e e
We have studied the ATLAS discovery potential
Conclusion on the Z’ discoveryConclusion on the Z’ discovery
Assuming we have 100fb-1 and a Z’ signal
How can we infer the How can we infer the underlying theory ?underlying theory ?
Useful observables :
Total decay width
Forward-Backward asymmetry
LPSC - Grenoble Julien MOREL 34Discovery and identification of a
Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion
'Z e e
Introduction and motivationsIntroduction and motivations
The different theoretical Z’ modelsThe different theoretical Z’ models
The LHC and the ATLAS experimentThe LHC and the ATLAS experiment
The ATLAS Z’ discovery potentialThe ATLAS Z’ discovery potential
How can we infer the underlying theory ?How can we infer the underlying theory ?
Conclusions and outlook Conclusions and outlook
LPSC - Grenoble Julien MOREL 35Discovery and identification of a
Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion
'Z e e
Estimated at tree level
The total decay width - CDDT parameterizationThe total decay width - CDDT parameterization
8 GeV
2
2 22
'
1
cos 48C V Aw
Z f f
gN g g M
B xL
d xu
10 5x
q xu
With the formula :
Strong dependence on model
parameter
TeV TeV
TeVTeV
LPSC - Grenoble Julien MOREL 36Discovery and identification of a
Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion
'Z e e
Detector resolution on Mll:
≈ 9 GeV at 1.5 TeV≈ 30 GeV at 4 TeV
Reconstructed total decay width Reconstructed total decay width
Fit of the Z’η invariant mass spectrumM=1500 GeV
(500 fb-1)
2 2
22 2 2 2
DY li ll lnt C MDY
BW C Ml
l
l
l
a M
M M Meef aM
Fit function for the invariant mass spectrum :
DYDY-Z’ interferenceResonance peak
LPSC - Grenoble Julien MOREL 37Discovery and identification of a
Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion
'Z e e
Result for the total decay widthResult for the total decay width
Fully simulated events for GUT models and ADDGenerated events for RS model
Total decay width
Well mesured with high accuracyThe different values provide a model discrimination
GUTGUT
X-dimX-dim
LPSC - Grenoble Julien MOREL 38Discovery and identification of a
Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion
Example for the model ( MZ’=1500 GeV, 1.48 TeV < Mll < 1.52 TeV) :
The theoretical behavior is :*
*2 *
8 cos( ,cos ) ( )
3 1 cosgen genFB ll FB llA M A M
An attractive method consisted in fitting the cos() evolution of the AFB
Diluted
LPSC - Grenoble Julien MOREL 46Discovery and identification of a
Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion
'Z e e
Result on the reconstruction of the forward-backward asymmetryResult on the reconstruction of the forward-backward asymmetry
For the model ( MZ’=1500 GeV) :
The correction method gives good results
We are able to reconstruct with good accuracy the forward-backward asymmetry
DilutedDiluted
LPSC - Grenoble Julien MOREL 47Discovery and identification of a
Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion
'Z e e
Introduction and motivationsIntroduction and motivations
The different theoretical Z’ modelsThe different theoretical Z’ models
The LHC and the ATLAS experimentThe LHC and the ATLAS experiment
The ATLAS Z’ discovery potentialThe ATLAS Z’ discovery potential
How can we infer the underlying theory ?How can we infer the underlying theory ?
Conclusions and outlook Conclusions and outlook
LPSC - Grenoble Julien MOREL 48Discovery and identification of a
Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion
'Z e e
ConclusionConclusion
We study Z’ from different kinds of modelsWe study Z’ from different kinds of models
Grand Unified Theory
Extra-Dimension Theory
Model independent parameterizationADD likeRS like
The ATLAS discovery potential is high The ATLAS discovery potential is high
We are able to reconstruct properly useful observables We are able to reconstruct properly useful observables for the model discriminationfor the model discrimination
The total decay width The forward-backward asymmetry
Computed using a model independent method to take into account the detector efficiency
LPSC - Grenoble Julien MOREL 49Discovery and identification of a
Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion
'Z e e
OutlookOutlook
For the Z’ studyFor the Z’ study
For the ATLAS discovery potential For the ATLAS discovery potential
For the model discriminationFor the model discrimination
Study other realistic points for the RS model
Improve the high energy electron identification
Study the systematic uncertainties due to :energy scale and linearityparton distribution functionsradiative corrections…
Study other observables : Z’ rapidity, BR, …
Study other particles : W’, 2nd KK excitation, …
LPSC - Grenoble Julien MOREL 50Discovery and identification of a
Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion
'Z e e
BackupBackup
BackupBackup
LPSC - Grenoble Julien MOREL 51Discovery and identification of a
Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion
'Z e e
This implies a lot of statistics
How can we infer the underlying theory ?How can we infer the underlying theory ?
If we observe a signal
We can study :The total decay widthThe forward-backward
asymmetry
Toward a model discrimination
LPSC - Grenoble Julien MOREL 52Discovery and identification of a
Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion
'Z e e
1000 GeVllM
ISR ON
1 en GeVKKm
Effect due to resonance
Effet due to destructive interference
Z’RS cross section Z’RS cross section
' (fb)
qq Z e e
LPSC - Grenoble Julien MOREL 53Discovery and identification of a
Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion
'Z e e
1
1
Interférence : [500; ]
Résonance : [ ; ]
ll
ll
M M
M M
1
1
Interférence : [500; ]
Résonance : [ ; ]
e ell
e ell
M M
M M
1 en GeVKKm
ATLAS
CMS
12S
Z’Z’RSRS discovery : Point B discovery : Point B
-1
1
1
10 fb
1070 GeV
1188 GeV
e eM
M
-1
1
1
100 fb
1729 GeV
1917 GeV
e eM
M
-1
1
1
300 fb
2129 GeV
2341 GeV
e eM
M
LPSC - Grenoble Julien MOREL 54Discovery and identification of a
Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion
'Z e e
Geometrical acceptance increases with mass (boost effect).
Opposite charge selection efficiency decreases with mass.
We have to optimize electron identification at very high pT .
2 e± with ||<2.5
2 identified e±
Opposite charges
back to back
In our simulations we take into account detector acceptance …In our simulations we take into account detector acceptance …
(GeV)e e
M
selection efficiency for fully simulated Z’e+e-
Selection criteria:Selection criteria:
LPSC - Grenoble Julien MOREL 55Discovery and identification of a
Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion
'Z e e
llM
#E
vene
men
ts
164.4
SSM
fb /
100
Z
fb
124.9 fb
153.1 fb
128.2 fb
148.6
LR
fb
GUT Z’ at realistic luminosityGUT Z’ at realistic luminosity
Reconstructed events
-110 fbLdt
LPSC - Grenoble Julien MOREL 56Discovery and identification of a
Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion
'Z e e
llM
#E
vene
men
ts
164.4
SSM
fb /
100
Z
fb
124.9 fb
153.1 fb
128.2 fb
148.6
LR
fb
Reconstructed events
GUT Z’ at realistic luminosityGUT Z’ at realistic luminosity-10.1 fbLdt
Not enough st
atistic
Need a lo
w lum
inosit
y study
LPSC - Grenoble Julien MOREL 57Discovery and identification of a
Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion
'Z e e
1880Ldt fb 10.1Ldt fb
11Ldt fb 110Ldt fb
( )
4.42 0.65
Bf x x
B
( )
4.80 0.19
Bf x x
B
( )
4.64 0.05
Bf x x
B
( )
4.611 0.005
Bf x x
B
#E
vene
men
ts
llM (GeV)
How can we use the low luminosity data in our Z’ study ?How can we use the low luminosity data in our Z’ study ?
Good fit for luminosity equal to few fb-1
A study of the fit parameters may give us informations even at low luminosity
Fit of the DY invariant mass between 150 and 600 GeV
LPSC - Grenoble Julien MOREL 58Discovery and identification of a
Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion