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Search for New Physics in tt Final State in Boosted Regime at CMS

Search for New Physics in tt Final State in Boosted Regime at CMS. Motivation Analysis method Jet topologies Background estimation Results Summary. Sam Meehan o n behalf of the Group E Collaboration. Example Boosted Top Event Display from CMS. Motivation.

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Search for New Physics in tt Final State in Boosted Regime at CMS

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  1. Search for New Physics in tt Final State in Boosted Regimeat CMS • Motivation • Analysis method • Jet topologies • Background estimation • Results • Summary Sam Meehan on behalf of the Group E Collaboration Example Boosted Top Event Display from CMS Group E - tt Resonances Search

  2. Motivation • What are they searching for and why? • CERN has a top factory in the LHC • New physics will likely couple to the top (oddly heavy) • Benchmark models : RS-KK gluons , Z’ resonances • How are they doing this? • Using 5 fb-1 of 7 TeVpp data collected by CMS during 2011 • Reconstruct fully hadronic final state  gain in BR for top decay • Examine tt invariant mass spectrum for excess in data p t Z’, KK-gluon, Spaghetti monster … ???? p t Group E - tt Resonances Search

  3. Analysis Overview • Massive resonances (>1 TeV)  boosted tops • ΔR ~ 2M/pT  R = 0.8 jets contain boosted top with few 100 GeV of pT • Derive data-driven estimate of dominant QCD background • Examine invariant mass of tt system for excesses • Set CLs limits on σ✕BR 1+2 – Trijet Channel : Type I top-tag jet + Type II top-tag from W-tag plus jet 1+1 – Dijet Channel : Require both jets to be type I top-tagged jets b W W (W-tagged) b Type-1 top candidate Type-2 top candidate Group E - tt Resonances Search

  4. Top-tagging • Decompose C/A jet building algorithm from the final recombination to find subjets and then ask about their kinematics C/A Jets : R=0.8 dij = ΔR(i,j)/R diBeam= 1 Group E - tt Resonances Search

  5. Top-tagging • Decompose C/A jet building algorithm from the final recombination to find subjets and then ask about their kinematics C/A Jets : R=0.8 dij = ΔR(i,j)/R diBeam= 1 Group E - tt Resonances Search

  6. Top-tagging • Decompose C/A jet building algorithm from the final recombination to find subjets and then ask about their kinematics C/A Jets : R=0.8 dij = ΔR(i,j)/R diBeam= 1 This is just out working hypothesis to get a picture of how a boosted top may be formed t Group E - tt Resonances Search

  7. Top-tagging • Decompose C/A jet building algorithm from the final recombination to find subjets and then ask about their kinematics C/A Jets : R=0.8 dij = ΔR(i,j)/R diBeam= 1 SubjetDecomposition : CheckpTi/pTjet > δP=0.05 and separation splitting Both pass Consider both as “subjets” Try to split both One Pass Softer protojet from radiation Discard softer Both Fail Irreducible Final subjet identified t Fails Passes t Group E - tt Resonances Search

  8. Top-tagging • Decompose C/A jet building algorithm from the final recombination to find subjets and then ask about their kinematics C/A Jets : R=0.8 dij = ΔR(i,j)/R diBeam= 1 SubjetDecomposition : CheckpTi/pTjet > δP=0.05 and separation splitting Both pass Consider both as “subjets” Try to split both One Pass Softer protojet from radiation Discard softer Both Fail Irreducible Final subjet identified Both pass  subjets W b t t Group E - tt Resonances Search

  9. Top-tagging • Decompose C/A jet building algorithm from the final recombination to find subjets and then ask about their kinematics C/A Jets : R=0.8 dij = ΔR(i,j)/R diBeam= 1 Both fail irreducible SubjetDecomposition : CheckpTi/pTjet > δP=0.05 and separation splitting Both pass Consider both as “subjets” Try to split both One Pass Softer protojet from radiation Discard softer Both Fail Irreducible Final subjet identified W b t t Group E - tt Resonances Search

  10. Top-tagging • Decompose C/A jet building algorithm from the final recombination to find subjets and then ask about their kinematics C/A Jets : R=0.8 dij = ΔR(i,j)/R diBeam= 1 SubjetDecomposition : CheckpTi/pTjet > δP=0.05 and separation splitting Both pass  subjets Both pass Consider both as “subjets” Try to split both One Pass Softer protojet from radiation Discard softer Both Fail Irreducible Final subjet identified q’ q W b t t Group E - tt Resonances Search

  11. Top-tagging • Decompose C/A jet building algorithm from the final recombination to find subjets and then ask about their kinematics C/A Jets : R=0.8 dij = ΔR(i,j)/R diBeam= 1 Both fail  irreducible SubjetDecomposition : CheckpTi/pTjet > δP=0.05 and separation splitting Both pass Consider both as “subjets” Try to split both One Pass Softer protojet from radiation Discard softer Both Fail Irreducible Final subjet identified q’ q W b t Kinematic Top-Tagging: M(subjets) ε [100 GeV, 250 GeV] min[M(i,j)] > 50 GeV t If subjets satisfy  Yay! Top-Tag! Group E - tt Resonances Search

  12. W-tagging • Prune jets to increase mass resolution and tag them using mass drop technique Pruning Mass Drop W Tagging • Goal : better define M(jet) by removing “bad” constituents • Discard soft and large angle radiation by checking if • Z = min(pT1,pT2)/pT(1+2) < Zcut • D = ΔR12 > Dcut • Decompose into subjets • For 2 subjet jets, require: • mj-heavy/Mjet-total < 0.4 (mass drop μ) • 60 GeV < Mjet< 100 GeV W- tag ! C/A R=0.8 Jet Subjet 2 Subjet 1 μ>0.4 μ < 0.4 Mass Drop Group E - tt Resonances Search

  13. Background Estimation (I) • Main Backgrounds • Standard Model tt taken from MC • Non-Top MultiJet (NTMJ)  data-driven technique using control region and estimated mistag rate for normalization • Mistag Probability • Using 1+2 topology  invert mass drop requirement on type 2 top μ>0.4 to obtain QCD fake sample with “same” kinematics • As function of type 1 top pT calculate top-tag mistag rate 50-60% efficiency plateau Pm(pT) = Probability of mistagging at jet pT 4-5% mistag probability plateau Group E - tt Resonances Search

  14. Background Estimation (II) • Dominant NTMJ background taken from loosened selection in each channel • Event-by-event weight calculated as mistag probability for pT of probe jet • Background shape extraction • Probe jet mass distribution kinematically biased • Replace mprobe-jet in probe-jet four vector by random value drawn from NTMJ MC in [140,250] GeV • Closure of procedure tested on MC 1+2 – Trijet Channel : Tag type 2 candidate using two jets in single event hemisphere Third jet is “probe jet” 1+1 – Dijet Channel : Tag type I candidate Second jet is “probe jet” Group E - tt Resonances Search

  15. Results 1+2 Channel 1+1 Channel • Combined SM tt(red) and MultiJet(yellow) backgrounds compared to data • Dominant systematics shown in grayed bands: • Trigger, JES, Luminosity, reconstruction efficiency • No significant excess observed Group E - tt Resonances Search

  16. Interpretation of Results • Resonance search: • Limits set on σ✕BR as a function of resonance mass using CLs method with likelihood ratio as test statistic • tt Continuum Enhancement • Limits set on σ(tt) enhancement rom new physics using CLs method SM + New physics SM only Excluded M(Z’)>1.6 TeV Group E - tt Resonances Search

  17. Conclusions • First search constraining mtt > 1 TeV and using developing jet substructure techniques • No indication of new physics (Z’, KKG, ???) coupling to top pairs • Limits on σ✕BR set for benchmark models and general broad excesses • Substructure is interesting and will allow us to probe high pT regime in hadronic final states • Many thanks to all organizers of ESHEP, and especially Maurizio for many wonderful discussion sessions these past two weeks!!! Group E - tt Resonances Search

  18. Group E Collaboration • Boris Bulanek • Alexander Gramolin • Claudio Heller • Brett Jackson • HouryKeoshkerian • Olga Kochebina • Lukas Marti • Sam Meehan • Nicola Orlando • Maurizio Pierini • Leonid Serkin • Rosa Simoniello • Jared Sturdy • Dmitry Tsirkov • Xiaoxiao Wang • ChristophWasicki • Adam Webber • Jonas Weichert Group E - tt Resonances Search

  19. Backup Group E - tt Resonances Search

  20. Systematics • Determination of efficiency: Trigger, jet energy scale • Mistag probability: statistics (high-mass region), systematic associated to mass spectrum correction (low-mass) • Shape of the tt_bar invariant mass: Renormalisation and factorisation scales. Group E - tt Resonances Search

  21. Topcolor: width = 10% Group E - tt Resonances Search

  22. Randall–SundrumKaluza–Klein gluon production Group E - tt Resonances Search

  23. CMS Detector Group E - tt Resonances Search

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