Gauge Boson-Pair Production in pp Collision at 14 TeV

Gauge Boson-Pair Production in pp Collision at 14 TeV

Using ATLAS at the LHC

Erez Reinherz-Aronis

Supervisors:Prof. Gideon Alexander

Prof. Erez Etzion

Gauge Boson-Pair Production in pp Collision at 14 TeV

Gauge Boson-Pair Production in pp Collision at 14 TeV

Using ATLAS at the LHC

Outline:

LHC (reminder)

Physics background

Experimental procedure

Large Hadron ColliderLarge Hadron Collider• pp collider• Tunnel length: 26.7 Km • The beams energy, up to 7 TeV ( = 14 TeV)• Particles per bunch: ~1011

• Bunch crossing every 25 ns • Luminosity: Low and High phases

( )S pp

A reminder

0 05 0 1. .

LL

GoalsGoals

• In the gauge boson pair production we focus on the ZZ channel in their decay to lepton pair

• Measurement of the at 14 TeV• Measurement of and vs. • Z polarization with the emphasis on the longitudinal

part using the SDM method• Angular correlation between the two decay

planes

( )tot pp ZZ X

Z l l

l l

( )S ZZ( )

Z

d qq ZZ

d cos

( )tot qq ZZ

Physics backgrondPhysics backgrond

• LEP2 measured • agrees with the SM expectation

( )tot e e ZZ

• Tevatron ( at ~2 TeV) D0(CDF) reported 1(3) ZZ candidates

pp

Previous knowledgePrevious knowledge

Features of the ZZ channelFeatures of the ZZ channel

• Expected ( )tot pp ZZ X

Features of the channelFeatures of the channel

• Expected differential cross section

Zcos

( )tot uu ZZ

( )

Z

d uu ZZ

d cos

• Expected total cross section

200 GeV

250 GeV

300 GeV

Demonstrated by the uū→ZZ channel

qq ZZqq ZZ

Determination of the Z polarization Determination of the Z polarization

• Spin Density Matrix, :Angle definitions

0, ,

Spin Density MatrixSpin Density Matrix

• 3x3 matrix

• Were the Z SM coupling constants are:

2 2 20

2 2

1 3 3 3(1 ) 2 (1 ) (1 ) 2 =

8 4 8

3 3(1 ) (1 );

8 4

Z

Z

zf cos

T L f

dx Rx x x Rx

d cos

x x x cos

2 22 2 2 2

2 2

1

2R L

R w L wR L

g gg sin g sin R

g g

0 1T L

The SM expectationThe SM expectation• for light quarks

( ) [GeV]S ZZ

0 ( )qq ZZ

0 ( )L

200 GeV250 GeV

uū0.050.02

• Planes correlation

Average value for A( ) 1 (2 )F Acos

( )F

Experimental procedureExperimental procedure

• ZZ→4μ (golden channel)

• Expected number of events for ℒ=100 fb-1

ZZ→4μZZ→4l (e, μ)

Branching ratio (Br)0.0010.004

Produced No. of events14005600

Identification efficiency 25%

No. events350

Identification of the ZZ channelIdentification of the ZZ channel

Monte Carlo studyMonte Carlo study

• Pythia 6.221 with full simulation

• Identification efficiency

• ΓATLAS(Z)=4.8 GeVΓPDG(Z)=2.5 GeV

Eve

nts

Main BackgroundsMain Backgrounds

• Gluon fusion (gg→ZZ) on average 20-25%

• From MC study

Background (ZZ→4μ ) 6%8%

4tt 4Zbb

Gauge Boson-Pair Production in pp Collision at 14 TeV

Gauge Boson-Pair Production in pp Collision at 14 TeV

Using ATLAS at the LHC

Erez Reinherz-Aronis

Supervisors:Prof. Gideon Alexander

Prof. Erez Etzion

Measurement of the Z PolarizationMeasurement of the Z Polarization

• 3x3 matrix

• Were the Z SM coupling constants are:

2 2 20

2 2

1 3 3 3(1 ) 2 (1 ) (1 ) 2 =

8 4 8

3 3(1 ) (1 );

8 4

Z

Z

zf cos

T L f

dx Rx x x Rx

d cos

x x x cos

2 22 2 2 2

2 2

1

2R L

R w L wR L

g gg sin g sin R

g g

0 1T L

A reminder

Measurement of the Z PolarizationMeasurement of the Z Polarization

• Alternative method - proposed by Renard et al.*• Fit is not needed (provides results for low statistic)• No need for bins in • One can define:

2

20

5 1

2 5

T f

L f

cos

cos

1

1( ) ( )

N

i Z i f kk

cos cosN

f

• Lower Order SM diagrams for ZZ pair production in pp collision

• event in ATLASZZ e e X

From: Cern Courier - May -2007,

“The LHC: illuminating the high-energy frontier”

Taken from LEP EW WGhep-ph/0701261

hep-ph/0212396

From the PDG

Nucl. Phys. B321 (1989) 561

Phys. Rev D36 (1987) 1570

• Z boson couplings to fermions

gLgRgVgA

e, , 1/201/4-1/4

e, , - 1/2+sin2Wsin2W- 1/4+sin2W1/4

u, c, t1/2-2/3sin2W-2/3sin2W1/4-2/3sin2W- 1/4

d, s, b- 1/2+1/3sin2W1/3sin2W- 1/4+1/3sin2W

1/4