search for exotic production of top quarks with same -sign
TRANSCRIPT
Search for exotic production of top quarks with same-sign leptons
Simon Berlendis
17.05.2016 Simon Berlendis - Same-sign leptons 1
Introduction β’ Search for exotic top quark production is theoretically motivated
β Top mass, radiative Higgs correction, Higgs stability β¦
β’ Same-sign leptons can be the signature of many exotic top production: β Same-sign tops π‘π‘ or οΏ½Μ οΏ½οΏ½Μ οΏ½ , β₯3π‘, π‘οΏ½Μ οΏ½+extra bosons β Leading to πΒ±πΒ±(π) + ππππ‘π + πππ‘π + πΈπ‘ππππ β Low background from the standard model
β’ Today, I will present 4 analyses from ATLAS and CMS: β Search for top quark partners with charge 5/3 at 13TeV (CMS T5/3): Link β Search for new physics in same-sign dilepton events at 13TeV (CMS Susy): link β Search for supersymmetry at 13TeV with jets and
two same-sign leptons or three leptons (ATLAS Susy) : link β Analysis of events with b-jets and a pair of leptons of the
same charge at 8TeV (ATLAS VLQ) : link β’ Will soon be published with 13TeV data
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BSM Models (1): VLQ and SUSY β’ Vector Like Quark (VLQ) signatures: π‘π‘Μ + π
β Double production: ππ, π΅π΅ or π5/3π5/3 β’ Limit in mQ and Br(QβqV)
β TβZt, Ht or Wb β BβZb, Hb or Wt β π5/3βWt
β Single production: β’ Limit in mQ and coupling C
β Large jet activities (HT)
β’ Supersymmetric signature: π‘π‘Μ + π + πΈπππππ
β Light gluino and 3rd generation squark motivated by naturalness β’ Large production of ποΏ½ποΏ½, οΏ½ΜοΏ½οΏ½ΜοΏ½ and ποΏ½ποΏ½ β’ And large Br(ποΏ½ β οΏ½ΜοΏ½π‘)
β Two signals producing top quarks: β Large MET from neutralino
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BSM Models (2): RPV and 4tops β’ Baryonic number violation search: same-sign tops
β Low energy constraint (proton stability) implies βB=2 processes involving top quarks
β Possible realization with R-parity violation SUSY: β No neutralino (low MET)
but high jet activities
β’ Four tops signature: π‘π‘Μ π‘π‘Μ
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β’ Effective theory: β’ Extra-dimension β Universal Extra Dimension
β’ 2HDM type-II
Selections: β’ All analyses require same-sign leptons or 3 leptons
β + additional cuts on jet activities, Number of jets/b-jets, METβ¦
β’ General feature: β CMS T5/3 and ATLAS VLQ cuts optimized for the search of energetic tops
β’ High jet activities cut and high lepton Pt (25-30GeV)
β CMS Susy and ATLAS Susy cuts optimized for massive neutralinos (compressed scenario): β’ High MET cut and low lepton Pt (10GeV)
β Additional cuts are also required on Nbjets, Njets , MTmin, Meff, Nconstuents β¦
β’ Signal region: β CMS T5/3 and ATLAS Susy analysis use inclusive signal regions β CMS Susy and ATLAS VLQ analysis use several signal regions
split in different kinematic cut requirements
β’ More detailed signal region description in backup 17.05.2016 Simon Berlendis - Same-sign leptons 5
Nlep HT MeT Nlep+jet
β₯2 >900 GeV > 0 GeV β₯5
ATLAS Susy CMS T5/3
Background composition 1) True same-sign/three leptons
β From Standard Model β Dominant: π‘οΏ½Μ οΏ½ + π and ππ β Simulated by Monte-Carlo method
2) Fake/non-prompt lepton β Light jet reconstructed as lepton β Lepton coming from heavy-flavor jet β Estimated by data-driven method
3) Charge mis-identification β Detector effect β Negligible for muon β Two sources:
β’ Tracker charge reconstruction efficiency β’ Electron from photon conversion
β Estimated by data-driven method
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Photon conversion:
Fake/non-prompt lepton estimation method β’ Lepton definition:
β The fake estimation methods rely on the definition of lepton criteria: loose and tight criteria
β’ For electrons, the identification and isolation are used β’ For muons, the isolation criteria is used
β’ Matrix method:
ππ‘ππ‘οΏ½
= π ππππππππππ
π =ππ ππ
(1β ππ) (1 β ππ)
β πππππ is estimated by weighting ππ‘ and ποΏ½Μ οΏ½ with the elements of M-1
β Generalized for 2 and 3 leptons
β’ Tight-to-loose method: β πππ : probability that a fake loose lepton is tagged as tight (~ππ)
β πππππ estimated by β’ selecting events with β₯1 loose but not tight lepton β’ Weight them by πππ/(1β πππ)
β Equivalent to Matrix Method by considering that ππ β 1
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π‘=tight οΏ½Μ οΏ½=loose but not tight
Real and fake efficiency measurement and systematic β’ Efficiency estimation:
β ππ estimated on enriched real lepton region β’ Single lepton region: High MET and MT (W+jets) β’ Dilepton region: Z mass window (Z->ll)
β ππ estimated on enriched fake lepton region β’ Single lepton region: Low MET and MT (multijet background) β’ SS Dilepton region: Tight muon + 1 loose lepton (V+jets and ttbar) β’ Real lepton contribution are subtracted from fake region
β Usually parameterized in Pt and |Ξ·| of the leptons β’ And sometimes other parameters like triggers, Nbjets β¦ etc
β’ Systematic uncertainties: around 35-60% β Fake composition (light jet, c-jets, b-jets) can be different in other regions
β’ Alternative control region or truth matching studies
β Other kinematic dependences β Statistical uncertainty from fake/real lepton control regions β Real lepton bkg removal in fake region β Closure tests or comparison with other methods
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Charge mis-identification background β’ Based on the charge flip rates π
β Defined as the probability of one electron to have its charge mis-identified β Parameterized on Pt and|Ξ·|
β’ Charge mis-identification bkg estimated by weighting opposite-sign dielectron events by:
β’ Charge flip rate estimation on enriched ppβZβee data events: β πππ β [ππ§ βπ,ππ§ + π] β Count the number of π+πβ and same-sign πΒ±πΒ± β Charge flip rates estimated by Likelihood minimization β π|π,πππ
β’ Systematic uncertainties: around 20-30% β Statistical uncertainty from likelihood minimization β Kinematic dependences β Closure tests on MC V+jets samples β Invariant mass cuts variations
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Ο΅1 charge flip rate of 1st electron Ο΅2 charge flip rate of 2nd electron
Validation plots
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β’ Validation plots at pre-selection level:
β’ Control regions ATLAS Susy :
Deviation of 1.5Ο
CMS T5/3 CMS Susy ATLAS Susy CMS PAS B2G-15-006
arxiv:1605.03171v1 arxiv:1602.09058
arxiv:1602.09058
arxiv:1602.09058
Results: SUSY β’ ATLAS Susy
β’ CMS Susy
β Better sensitivity for CMS because of the exclusives SRs
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arxiv:1605.03171v1
arxiv:1602.09058
Results: T5/3
β’ CMS T5/3
β 100-200GeV of improvement compared to 8TeV β Results combined with 1 lepton analysis
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CMS PAS B2G-15-006
Conclusion β’ Same-sign lepton is a well-motivated signature for the search of
new physics involving top quarks β Supersymmetry, vector-like quarks β¦
β’ Different selection strategy for each analysis β’ Imply to use sophisticated data-driven technique to estimate
fake and charge mis-identification background β Handled in a different way for each analysis
β’ No deviation found at 13TeV β Exclusion limits set for supersymmetric and T5/3 models
β’ New results will be published soon: β ATLAS VLQ search on going β And future 2016 data !
β’ I hope we will find surprising excess 17.05.2016 Simon Berlendis - Same-sign leptons 13
Backup
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Selection: Susy
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ATLAS Susy
CMS Susy
Selection VLQ
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CMS T5/3
ATLAS VLQ
Fake/non-prompt lepton: method
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ATLAS Susy ATLAS VLQ CMS Susy CMS T5/3
Method Matrix Method Matrix Method Tight-to-loose Matrix Method
Fake lepton region Dilepton: 1ΞΌ+1lepton
Single lepton: Low MT, ETmiss
Single lepton: Low MT, ETmiss
Single lepton: Low MT, ETmiss
Real lepton region Dilepton: Z mass window
Single lepton: High MT, ETmiss
Dilepton: Z mass window
Parametrization Pt /|Ξ·| Pt /|Ξ·|/Nbjet/trigger Pt /|Ξ·|/trigger No param
Validation Alternative fake estimate
Closure tests Alternative rate measurement
Closure tests
Charge mis-identification: Method β’ Based on the Charge flip rates π
β Defined as the probability of one electron to have its charge mis-identified β Parameterized on Pt and|Ξ·|
β’ Then, assuming a true number of opposite-sign dielectron events, we have:
β’ NSSreco can be estimated by weighting NOS
reco by:
β’ Charge flip rate estimation on enriched ppβZβee data events: β πππ β [ππ§ βπ,ππ§ + π]
β’ ex: X=10GeV in CMS T5/3 β Count the number of π+πβ and same-sign πΒ±πΒ± β Charge flip rates estimated by Likelihood minimization
β π|π,πππ = πππππππ(πππ|π, π)
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Ο΅1 charge flip rate of 1st electron Ο΅2 charge flip rate of 2nd electron
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