Estefanía Coluccio Leskow (In collaboration with E. Álvarez) Buenos Aires University (UBA)

Estefanía Coluccio Leskow - Top Quark Physics - ICHEP2012

A charged Z' to explain the apparent A charged Z' to explain the apparent disagreement in top-antitop disagreement in top-antitop

asymmetries between Tevatron and asymmetries between Tevatron and LHC LHC

Estefanía Coluccio Leskow(In collaboration with E. Álvarez)

Buenos Aires University (UBA)

ICHEP 2012

7/6/12


OutlineOutline

1- Brief Introduction: Top quark asymmetries at LHC and Tevatron.

2- New Physics: New Models try to explain the discrepancies.

3- Z' Model: Model studied to explain the apparent disagreement between the asymmetries.

4- Results

5- Conclusions


Forward-Backward Asymmetry

Charge Asymmetry LHCLHC: symmetric initial state

Invariant under boosts

Top Quark Asymmetries at Tevatron and LHCTop Quark Asymmetries at Tevatron and LHC 1- Introduction


At TevatronAt Tevatron:

At LHC:At LHC:

Is there anything wrong?

1- Introduction

OR OR Could both be explained simultaneously!?

(p-value=0.006)


New Physics Models arise to explain the discrepancies. New Physics Models arise to explain the discrepancies.

Extra light gluon G ' with a broad width

Extra Scalars Extra W ' with d-t-W ' interaction Extra Z' boson with flavor - conserving interaction Extra Z' Neutral boson with flavor - violating interaction …. etc

Excluded by LHC Not Excluded by LHC

2- New Physics

Extra Z' charged (not electrically) boson with flavour- violating u-t-Z ' interaction given by:

Blue Region: Same sign-tops constraint!Model EXCLUDED

(CMS PAS SUS-11-020)


3- Z' Model

The New Phenomenological term of the Lagrangean is given by:The New Phenomenological term of the Lagrangean is given by:

Some remarks:

Left handed coupling constrained by b physics

Mz' > m

t (avoids Flavour Change Top Decay)

No same sign tops production no constraint!

Atomic parity violation relaxed because Z'N

and Mz' > m

t

constraints at the LHC relaxed by making larger

Asymmetry cancellation at LHC Asymmetry cancellation at LHC COULD EXPLAINCOULD EXPLAIN not present at Tevatronnot present at Tevatron RESULTS!!RESULTS!!

(arxiv: 1203.4489, ATLAS-CONF-2011-100., ATLAS-CONF-2011-121, ATLAS-CONF-2011-142, CMS PAS TOP-11-005, )

(arxiv: 1203.1320)

(DM?, Invisible?)


3- Z' Model

Feynmann 's Diagrams involving a Z'Feynmann 's Diagrams involving a Z'CC boson boson

t- channel:Ac > 0

s- channel:Ac < 0

Needs antiquarks! So Dominates

At Tevatron

Needs gluons andPhase space so“ switched on “

At LHC!

So.... there isSo.... there isa cancellation a cancellation

at LHC!at LHC!


Using MADGRAPH we simulate:

Tevatron: LHC:

How do we search for the cancellation?How do we search for the cancellation?

Region of parameter space:Region of parameter space:

3- Z' Model

SM + NP

We make a 2 test with the last measurements at:


Results:Results:

t – channel contribution t – channel contribution Positive Ac Positive Ac

Ac (NP) > 0 Ac (NP) < 0

Numbers: Difference (in ) to measured values.

4- Results


s – channel contribution s – channel contribution Negative AcNegative Ac

Ac (NP) > 0 Ac (NP) < 0

Numbers: Difference (in ) to measured values.

4- Results


All : Expected Cancellation!!All : Expected Cancellation!!

Ac (NP) > 0 Ac (NP) < 0

Upper Number: Difference (in ) to measured values of Ac.

Lower Number: Difference (in ) to measured values of (1 = %13) .

4- Results

Remember?Remember?

constraints at the LHC

can be relaxed by making

larger...


4- Results

Larger allowed region!

Only s-channel controlledby the width Tevatron'sresults are safe!

But still....

'' 3*'

'' 3*'


4- Results

Reference Point: fR=0.7, M

Z' =225 GeV

'' 3*'

'' 5*'

'' 7*'

Limit by LHC with 0.7 fb-1

- - - - Expected Limit with 5 fb-1


Distinctive features of the ModelDistinctive features of the Model

ZC' Model

Low pT

Channel-s OFF

Channel-t ON

AC

> 0

4- Results

High pT

Channel-s ON

Channel-t OFF

AC


Z' Model

4- Results

Other differential observables of the ModelOther differential observables of the Model

ZC' Model

ZC' Model


ZC' Model

And what about the AAnd what about the AFBFB at at Tevatron ? Tevatron ?


ConclusionsConclusions Charged FC”N”C Z': All Tevatron

All LHC

Increase in Z' width:

Atomic Parity Violation:

Prediction: Ac vs. pT

tj resonance search see talk by Merlin Davies for Atlas.

Increase in Z' width Increase Single Top Production (~ %20, new search strategy required...)


Thank you!Thank you!


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Estefanía Coluccio Leskow (In collaboration with E. Álvarez) Buenos Aires University (UBA)