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A charged Z' to explain the apparent disagreement in top-antitop asymmetries between Tevatron and LHC. Estefanía Coluccio Leskow (In collaboration with E. Álvarez) Buenos Aires University (UBA) ICHEP 2012 7/6/12. Outline. 1- Brief Introduction : Top quark asymmetries at LHC and Tevatron.
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A charged Z' to explain the apparent disagreement in top-antitop asymmetries between Tevatron and LHC Estefanía Coluccio Leskow (In collaboration with E. Álvarez) Buenos Aires University (UBA) ICHEP 2012 7/6/12
Outline 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
1- Introduction Top Quark Asymmetries at Tevatron and LHC Forward-Backward Asymmetry Invariant under boosts Charge Asymmetry LHC: symmetric initial state
At Tevatron: 1- Introduction (p-value=0.006) At LHC: Is there anything wrong? OR Could both be explained simultaneously!?
2- New Physics 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 • 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: 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'Nand Mz' > m t • constraints at the LHC relaxed by making larger • Asymmetry cancellation at LHC COULD EXPLAIN not present at TevatronRESULTS!! (arxiv: 1203.1320) (DM?, Invisible?) (arxiv: 1203.4489, ATLAS-CONF-2011-100., ATLAS-CONF-2011-121, ATLAS-CONF-2011-142, CMS PAS TOP-11-005, )
3- Z' Model Feynmann 's Diagrams involving a Z'C boson So.... there is a cancellation at LHC! t- channel: Ac > 0 Needs antiquarks! So Dominates At Tevatron Needs gluons and Phase space so “ switched on “ At LHC! s- channel: Ac < 0
3- Z' Model How do we search for the cancellation? • Using MADGRAPH we simulate: Tevatron: LHC: SM + NP • We make a 2 test with the last measurements at: Region of parameter space:
4- Results Results: t – channel contribution Positive Ac • Ac (NP) > 0 • Ac (NP) < 0 • Numbers: Difference (in ) to measured values.
4- Results s – channel contribution Negative Ac • Ac (NP) > 0 • Ac (NP) < 0 • Numbers: Difference (in ) to measured values.
4- Results 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) . Remember? constraints at the LHC can be relaxed by making larger...
4- Results '' 3*' '' 3*' Larger allowed region! Only s-channel controlled by the width Tevatron's results are safe! But still....
4- Results '' 3*' '' 5*' '' 7*' Limit by LHC with 0.7 fb-1 - - - - Expected Limit with 5 fb-1 Reference Point: fR=0.7, MZ' =225 GeV
4- Results Distinctive features of the Model ZC' Model Low pT Channel-s OFF Channel-t ON AC > 0 High pT Channel-sON Channel-t OFF AC
4- Results Other differential observables of the Model ZC' Model Z' Model ZC' Model
And what about the AFB at Tevatron ? ZC' Model
Conclusions • 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...)
