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) ]

Original ADD : [ N.Arkani-Hamed, S.Dimopoulos ,G.Dvali : Phys. Rev D59 086004 (1999) ]

Grand unified theories

Based on the existence of a large gauge group including the SU(3)×SU(2) ×U(1) SM gauge group

Provide a framework for the unification of the SM forces

4D brane + n compactified X-dim in which only the graviton can propagateProvide an explanation of the weakness of gravity

5D bulk with a warped geometry bounded with two 4D brane (Plank and TeV) Provide a reduction of the Plank scale on the TeV Brane

LPSC - Grenoble Julien MOREL 9Discovery and identification of a

Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion

'Z e e

Grand Unified Theories

[Phys. Rev. D70, 093009 (2004)]

Carena, Daleo, Dobrescu, Tait (CDDT) propose a model

independent parameterisation

Up to now, we study GUT Z’ from specific models

(E6 models : Z’, Z’, Z’SO(10) model : Z’LR)

It’s based on the existence of a additional U(1) gauge group :

'(1)(3) (2) (1)C W Y ZSU SU UU

Theoretical assumptions and experimental constraints :

Z-Z’ mixing small (LEP)Flavour changing neutral currents constraintsNo Z’ decay into new particlesAnomaly cancellations

LPSC - Grenoble Julien MOREL 10Discovery and identification of a

Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion

'Z e e

These new 4 classes contain :

The E6 models:

Some little higgs models

...

Grand Unified Theories - CDDT parameterization - CDDT parameterization

4 classes of solutions are found :

-B xL

10 5x

q xu

-d xu

Z'

Z'

Z'

ψ 10+x5 with x = -1 and g = 0.272

η 10+x5 with x = -0.5 and g = 0.344

χ 10+x5 with x = -3 and g = 0.211

Each model fully described by 3 free parameters :

Z’ mass Coupling strength normalisation gZ’

An x parameter (fermions coupling related)

LPSC - Grenoble Julien MOREL 11Discovery and identification of a

Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion

'Z e e

X-dim theory - X-dim theory - ADD model

Fermions confined on the 4-brane

Graviton propagates in 4-brane + 1 large extra dimension

Gauge fields propagate in 1 small extra dimension

Masses of the KK modes Mn2= M0

2 + (nMc)2

Z’ADD = Z / first KK mode (mass degenered)

R >>1 TeV-1

compactified on S1/Z2

R ~1 TeV-1

Mc is the only parameter

Couplings 2 SM Couplings

[T.G.Rizzo : Phys. Rev D61 055005 (2001) ]

LPSC - Grenoble Julien MOREL 12Discovery and identification of a

Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion

'Z e e

X-dim theory - Randall-Sundrum with bulk matterX-dim theory - Randall-Sundrum with bulk matter

Gauge fields are in the bulk.

Higgs field remains on the TeV brane.

Fermions are in the bulk with different localizations along the extra-dimension.

Z’ gauge coupling non universal

[ G.Moreau, J. I. Silva-Marcos, Hep-ph/0602155 ]

t

u

Planck Brane TeV Brane

3 important features :3 important features :

New interpretation of the fermion mass hierarchy.Compatible with a Grand Unified Theory [hep-th/0108115] .KK excitation provides WIMP candidate.

RS with bulk matter :

LPSC - Grenoble Julien MOREL 13Discovery and identification of a

Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion

'Z e e

Fermion mass in the RS modelFermion mass in the RS model

22 25D me c : tri k yds e dx dx dy

RS model : 1 spatial X-dim compactified over with radius Rc1

2S Z

( warp factor)TeV brane Gravity scale : ckRPl PlM e M w M w

4Fermion localization : i i id x dy Gm where RS metric determinantG

( )

0

1( , ) ( ) ( )

2n i

i i nnc

x y x f yR

i im c kFermion 5D masses :

Effective 4D masses matrix:(5)

0 0( ) ( )2

ij i jij

c

YM dy G H f y f y

R

ccii = new dimensionless = new dimensionless

parametersparameters

| |( ) ic k yinf y e

kkijij = new parameters related = new parameters related

to the yukawa couplingto the yukawa coupling

LPSC - Grenoble Julien MOREL 14Discovery and identification of a

Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion

'Z e e

Selected points for our studiesSelected points for our studies

Experimental constraints :

SM charged Fermions masses and mixing angles (5% uncertainty)

SM neutrino masses and mixing angles (4)

Flavor Changing Neutral Current

S and T parameters

We study two sets of parameters (labeled A and B) :

Point A = Realistic model

Point B = Strong coupling

LPSC - Grenoble Julien MOREL 15Discovery and identification of a

Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion

'Z e e

Z’ GeneratorsZ’ Generators

Grand Unified Theories

Extra-dimension theories

Standard Pythia : process n°141

/ / 'Z Z

Pythia with an user-defined process developed by T.Rizzo and interface with pythia by G.Azuelos and G.Polesello for the ADD model.

Pythia with an user-defined process developed by G.Moreau based on G.Azuelos and G.Polesello code for the RS model

These generators provide Z’RS calculation with full interference

Z/Z(1)/Z(2)//(1)/(2)

LPSC - Grenoble Julien MOREL 16Discovery 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 17Discovery and identification of a

Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion

'Z e e

The Large Hadron ColliderThe Large Hadron Collider

The installation of the LHC's magnets is progressing rapidly

LHC will start in 2007 with 450 GeV per beam

7 TeV per beamInstantaneous luminosity = 1033 cm-2 s-1 (low lumi)

= 1034 cm-2 s-1 (high lumi)

2008 :

The beam pipe The beam pipe closure date will be closure date will be

August 2007 August 2007

LPSC - Grenoble Julien MOREL 18Discovery and identification of a

Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion

'Z e e

The ATLAS experimentThe ATLAS experiment

Calorimeters are already installedInner detector is about to be installed (mid 2007)

288 muon Stations have been installed (47%)

LPSC - Grenoble Julien MOREL 19Discovery and identification of a

Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion

'Z e e

ATLAS simulationsATLAS simulations

MZ’ =1500 GeV MZ’ =4000 GeV

Z’GUT Z’ADD Z’RS

Generated 6M 6M 6M

Fully simulated 120k 3k -

'Z e e

Fast simulation :

Simulation using a parameterization of the detector resolutions

Full simulation :

Real simulation of the whole detector using Geant4

LPSC - Grenoble Julien MOREL 20Discovery 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 21Discovery and identification of a

Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion

'Z e e

ATLAS Discovery potential for a Z’ATLAS Discovery potential for a Z’

To compute the Z’ ATLAS Discovery potential we need :

The detector efficiency )

The cross section (Z’)

The DY cross section (DY)

A significance convention (S12)

'qq Z e e

=

Effective cross section

According to hep-ph/0204326 we use the significance S12 (realistic) :

12

'Signal + Background

Background

Z

DY

S S B B

S B Ldt

B Ldt

We ask |S12| > 5 for a discovery

LPSC - Grenoble Julien MOREL 22Discovery and identification of a

Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion

'Z e e

The detector efficiencyThe detector efficiency

We also use the channel for the Z’RS

with a CMS like detector efficiency inspired from

'Z

We use the channel with the ATLAS detector efficiency

(see next slides)

'Z e e

CMS-NOTE-2005-002

CMS efficiency (acceptance, trigger, reconstruction) lies in the range 70-75 %

'Z

LPSC - Grenoble Julien MOREL 23Discovery and identification of a

Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion

'Z e e

The efficiency of the event selection depends on :

The di-lepton mass

The angle between the electron and the beam in the lab frame

The ATLAS detector efficiency … The ATLAS detector efficiency …

2 identified e±2 e± with ||<2.5Opposite chargesback to back in the transverse plane

Selection criteria :

LPSC - Grenoble Julien MOREL 24Discovery and identification of a

Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion

'Z e e

The ATLAS detector efficiency …The ATLAS detector efficiency …

'SSMZY

Z’ rapidity: model-independent shapes 1 model-dependent combination

(different couplings)

'dd Z

'SSMZY

'ss Z'uu Z

'SSMZY 'SSMZY

The efficiency depend on the model due to the Z’ boost :dileptons coming from are more boosted than di-leptons coming from because of different pdfs.

uudd

This angular dependence is related to the Z’ boost :

LPSC - Grenoble Julien MOREL 25Discovery and identification of a

Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion

'Z e e

All models compatible for a given parton flavour

Efficiency only depends on initial parton flavour (for a given mass)

Efficiency for events lower than efficiency for

'u u Z

The ATLAS detector efficiency … The ATLAS detector efficiency …

Selection efficiency vs di-electron massFor and events separately (low masses):

(GeV)e e

M (GeV)e e

M

uu dd

uu dd

LPSC - Grenoble Julien MOREL 26Discovery and identification of a

Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion

'Z e e

A model-independent method to take into account the efficiency … A model-independent method to take into account the efficiency …

Selection efficiency vs di-electron massFor , , events separately (all masses and all models)uu dd ss

'uu Z 'dd Z

(GeV)llM

We assign the right efficiency depending on the initial parton flavour and the invariant mass, event by event.

In the effective cross section calculation

LPSC - Grenoble Julien MOREL 27Discovery and identification of a

Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion

'Z e e

Z’Z’GUT GUT discovery potential - CDDT parameterizationdiscovery potential - CDDT parameterization

3 free parameters in the CDDT parametrization : x , mZ’ and gZ’

CDF exclusion plots ATLAS discovery plots

MZ’/gZ’ as a function of x for different values of gZ’

LPSC - Grenoble Julien MOREL 28Discovery and identification of a

Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion

'Z e e

Z’Z’GUT GUT discovery potential - CDDT parameterizationdiscovery potential - CDDT parameterization-1400 pb - ATLASLdt

Good hope to discover model not yet excluded by cdf in 2008 with atlas

' ' vs parameterZ ZM g x

Discovery plots

-1433 pb - CDFLdt [hep-ex/0602045]

Exclusion plots

LPSC - Grenoble Julien MOREL 29Discovery and identification of a

Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion

'Z e e

Z’Z’X-Dim X-Dim discovery potential - RS modeldiscovery potential - RS model

(1) 3 TeVKKm

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

'Z e e

Z’Z’RS RS discovery potential - RS modeldiscovery potential - RS model

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

'Z e e

Forward-Backward asymmetryForward-Backward asymmetry

F BFB

F B

A

The forward-backward asymmetry is defined by :

forwardforwardbackwardbackward

P P

* is the angle between the quark and the electron in the Z’ rest frame

*

1

0

0

1

coscos

coscos

F

B

d

d

where

*

**

*

LPSC - Grenoble Julien MOREL 39Discovery and identification of a

Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion

'Z e e

On peak asymmetry

Forward-Backward asymmetry – CDDT parameterizationForward-Backward asymmetry – CDDT parameterization

B xL

d xu

10 5x

q xu

computed with only events in the

window [M-4;M+4]

M=1.5 TeV

0FBA

TeV TeV

TeVTeV

Strong dependence on

model parameter

LPSC - Grenoble Julien MOREL 40Discovery and identification of a

Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion

'Z e e

' ( 4 Te

Drell-Yan

V)Z M

FBA

en GeVe e

M

Forward-Backward asymmetry – Generated events - GUTForward-Backward asymmetry – Generated events - GUT

Big deformation of the forward backward asymmetry in the Big deformation of the forward backward asymmetry in the resonance regionresonance region

Huge statistic : 6M events

LPSC - Grenoble Julien MOREL 41Discovery and identification of a

Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion

'Z e e

' ( 4 TeV)

Drell-YanADD ADDZ M

FBA

en GeVe e

M

Forward-Backward asymmetry – Generated events – X-dim (ADD)Forward-Backward asymmetry – Generated events – X-dim (ADD)

Deformation of the forward backward asymmetry on the resonance Deformation of the forward backward asymmetry on the resonance

Huge statistic : 6M events

LPSC - Grenoble Julien MOREL 42Discovery and identification of a

Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion

'Z e e

Drell-Ya

Point A : ' ( 4 TeV)

nRS KKZ M

FBA

+ -e e en GeVM

Forward-Backward asymmetry – Generated events – X-dim (RS)Forward-Backward asymmetry – Generated events – X-dim (RS)

Deformation of the forward backward asymmetry down to ≈ 600 GeVAFB is a useful observable

Huge statistic : 12M events

LPSC - Grenoble Julien MOREL 43Discovery and identification of a

Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion

'Z e e

Reconstructed forward-backward AsymmetryReconstructed forward-backward Asymmetry

AFB is defined with the angle between the quark and electron directions

In a pp collider we don’t know the quark direction.

We assume that the Z’ and the quark are in the same direction

Probability to be wrong when taking the Z’ direction as the quark one

At high rapidity : The assumption is good

At low rapidity : We are wrong once out of two

The forward-backward asymmetry is diluted due to this effect

LPSC - Grenoble Julien MOREL 44Discovery and identification of a

Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion

'Z e e

Reconstructed forward-backward AsymmetryReconstructed forward-backward Asymmetry

1

1 2cor dilFB FBA A

= probability to be wrong

We can correct the diluted forward-backward asymmetry ( )corFBA

ATL-PHYS-PUB-2005-010

(1 )dil gen genF F B

dilB

N N N

N F B

F BFB

F B

A

Detector independent

We lose the angular information

Typical spin 1

particle behavior

*cos

LPSC - Grenoble Julien MOREL 45Discovery and identification of a

Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion

'Z e e

Reconstructed forward-backward AsymmetryReconstructed forward-backward Asymmetry

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

'Z e e

ATLAS Discovery potential ATLAS Discovery potential

' 3TeVZm

Signal = Z’background = Drell-Yan ( /Z MS )

LPSC - Grenoble Julien MOREL 59Discovery and identification of a

Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion

'Z e e

llM FBAZY

( )Tp Z ( )Tp e ( )e

Comparison between standard Pythia and our generatorComparison between standard Pythia and our generator

( ) 20 GeV and (e ) 2.5Tp e PythiaRatio ISR ON

Gene 'RSZ

LPSC - Grenoble Julien MOREL 60Discovery and identification of a

Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion

'Z e e

Pythia Z’RS

en mbqq Z e e

en mb

qq Z e e

Cross section comparison Cross section comparison 1000 GeV ISR ONllM

LPSC - Grenoble Julien MOREL 61Discovery and identification of a

Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion

'Z e e

Results from our testResults from our test

We have to be careful with the Z’RS pT and rapidity when the ISR is switched ON.

The two generators give compatible results for the standard model process.

We can generate Z’We can generate Z’RSRS events events

LPSC - Grenoble Julien MOREL 62Discovery and identification of a

Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion

'Z e e

Z’Z’GUT GUT discovery potential - CDDT parameterizeddiscovery potential - CDDT parameterized-1400 pb - ATLASLdt -1100 fb - ATLASLdt

ATLAS discovery potential goes beyond the LEP limits in most scenarii, already with 400 pb-1

LPSC - Grenoble Julien MOREL 63Discovery and identification of a

Introduction Theoretical framework LHC and ATLAS Z’ discovery Underlying theory conclusion

'Z e e

≈ 4.2 TeV

Point A

Point B

-110 fb-1100 fb -1300 fb

1 en GeVKKm

1 en GeVKKm

1 en GeVKKm

1 en GeVKKm

1 en GeVKKm

1 en GeVKKm

≈ 3 TeV ≈ 4 TeV ≈ 6 TeV

≈ 9.5 TeV > 10 TeV

12S

12S 12S

12S

12S

12S

Z’Z’RSRS discovery : the two channels and the two analyses are combined discovery : the two channels and the two analyses are combined