Estefanía Coluccio Leskow (In collaboration with E. Álvarez) Buenos Aires University (UBA)
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Transcript of Estefanía Coluccio Leskow (In collaboration with E. Álvarez) Buenos Aires University (UBA)
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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
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Estefanía Coluccio Leskow - Top Quark Physics - ICHEP2012
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
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Estefanía Coluccio Leskow - Top Quark Physics - ICHEP2012
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
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Estefanía Coluccio Leskow - Top Quark Physics - ICHEP2012
At TevatronAt Tevatron:
At LHC:At LHC:
Is there anything wrong?
1- Introduction
OR OR Could both be explained simultaneously!?
(p-value=0.006)
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Estefanía Coluccio Leskow - Top Quark Physics - ICHEP2012
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)
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Estefanía Coluccio Leskow - Top Quark Physics - ICHEP2012
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?)
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Estefanía Coluccio Leskow - Top Quark Physics - ICHEP2012
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!
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Estefanía Coluccio Leskow - Top Quark Physics - ICHEP2012
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:
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Estefanía Coluccio Leskow - Top Quark Physics - ICHEP2012
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
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Estefanía Coluccio Leskow - Top Quark Physics - ICHEP2012
s – channel contribution s – channel contribution Negative AcNegative Ac
Ac (NP) > 0 Ac (NP) < 0
Numbers: Difference (in ) to measured values.
4- Results
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Estefanía Coluccio Leskow - Top Quark Physics - ICHEP2012
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...
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Estefanía Coluccio Leskow - Top Quark Physics - ICHEP2012
4- Results
Larger allowed region!
Only s-channel controlledby the width Tevatron'sresults are safe!
But still....
'' 3*'
'' 3*'
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Estefanía Coluccio Leskow - Top Quark Physics - ICHEP2012
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
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Estefanía Coluccio Leskow - Top Quark Physics - ICHEP2012
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
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Estefanía Coluccio Leskow - Top Quark Physics - ICHEP2012
Z' Model
4- Results
Other differential observables of the ModelOther differential observables of the Model
ZC' Model
ZC' Model
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Estefanía Coluccio Leskow - Top Quark Physics - ICHEP2012
ZC' Model
And what about the AAnd what about the AFBFB at at Tevatron ? Tevatron ?
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Estefanía Coluccio Leskow - Top Quark Physics - ICHEP2012
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...)
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Estefanía Coluccio Leskow - Top Quark Physics - ICHEP2012
Thank you!Thank you!
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Estefanía Coluccio Leskow - Top Quark Physics - ICHEP2012
Back - Up SlidesBack - Up Slides
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Estefanía Coluccio Leskow - Top Quark Physics - ICHEP2012
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Estefanía Coluccio Leskow - Top Quark Physics - ICHEP2012
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Estefanía Coluccio Leskow - Top Quark Physics - ICHEP2012
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Estefanía Coluccio Leskow - Top Quark Physics - ICHEP2012