o Motivation o Analysis method o Jet topologies o Background estimation o Results o Summary 17 June 2012Group E - tt Resonances Search1 Search for New Physics in tt Final State in Boosted Regime at CMS Example Boosted Top Event Display from CMS Sam Meehan on behalf of the Group E Collaboration

Motivation What are they searching for and why? o CERN has a top factory in the LHC o New physics will likely couple to the top (oddly heavy) o Benchmark models : RS-KK gluons, Z’ resonances How are they doing this? o Using 5 fb -1 of 7 TeV pp data collected by CMS during 2011 o Reconstruct fully hadronic final state  gain in BR for top decay o Examine tt invariant mass spectrum for excess in data 17 June 2012Group E - tt Resonances Search2 Z’, KK-gluon, Spaghetti monster … ???? t t p p

Massive resonances (>1 TeV)  boosted tops o ΔR ~ 2M/p T  R = 0.8 jets contain boosted top with few 100 GeV of p T Derive data-driven estimate of dominant QCD background Examine invariant mass of tt system for excesses Set CL s limits on σ ✕ BR Analysis Overview 17 June 2012Group E - tt Resonances Search3 1+1 – Dijet Channel : Require both jets to be type I top-tagged jets 1+2 – Trijet Channel : Type I top-tag jet + Type II top-tag from W-tag plus jet Type-1 top candidate Type-2 top candidate W b W (W-tagged) b

17 June 2012Group E - tt Resonances Search4 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 d ij = ΔR(i,j)/R d iBeam = 1

17 June 2012Group E - tt Resonances Search5 C/A Jets : R=0.8 d ij = ΔR(i,j)/R d iBeam = 1 Top-tagging Decompose C/A jet building algorithm from the final recombination to find subjets and then ask about their kinematics

t This is just out working hypothesis to get a picture of how a boosted top may be formed 17 June 2012Group E - tt Resonances Search6 C/A Jets : R=0.8 d ij = ΔR(i,j)/R d iBeam = 1 Top-tagging Decompose C/A jet building algorithm from the final recombination to find subjets and then ask about their kinematics

t t Fails Passes 17 June 2012Group E - tt Resonances Search7 Subjet Decomposition : Check p Ti /p Tjet > δ P =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 C/A Jets : R=0.8 d ij = ΔR(i,j)/R d iBeam = 1 Top-tagging Decompose C/A jet building algorithm from the final recombination to find subjets and then ask about their kinematics

t t Both pass  subjets 17 June 2012Group E - tt Resonances Search8 W b Subjet Decomposition : Check p Ti /p Tjet > δ P =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 C/A Jets : R=0.8 d ij = ΔR(i,j)/R d iBeam = 1 Top-tagging Decompose C/A jet building algorithm from the final recombination to find subjets and then ask about their kinematics

t t Both fail  irreducible 17 June 2012Group E - tt Resonances Search9 W b Subjet Decomposition : Check p Ti /p Tjet > δ P =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 C/A Jets : R=0.8 d ij = ΔR(i,j)/R d iBeam = 1 Top-tagging Decompose C/A jet building algorithm from the final recombination to find subjets and then ask about their kinematics

t t Both pass  subjets 17 June 2012Group E - tt Resonances Search10 W b q q’ Subjet Decomposition : Check p Ti /p Tjet > δ P =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 C/A Jets : R=0.8 d ij = ΔR(i,j)/R d iBeam = 1 Top-tagging Decompose C/A jet building algorithm from the final recombination to find subjets and then ask about their kinematics

t t Both fail  irreducible 17 June 2012Group E - tt Resonances Search11 W b q q’ Subjet Decomposition : Check p Ti /p Tjet > δ P =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 C/A Jets : R=0.8 d ij = ΔR(i,j)/R d iBeam = 1 Kinematic Top-Tagging: If subjets satisfy  Yay! Top-Tag! M(subjets) ε [100 GeV, 250 GeV] min[M(i,j)] > 50 GeV Top-tagging Decompose C/A jet building algorithm from the final recombination to find subjets and then ask about their kinematics

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(p T1,p T2 )/p T(1+2) < Z cut –D = ΔR 12 > D cut Decompose into subjets For 2 subjet jets, require: – m j-heavy /M jet-total < 0.4 (mass drop μ ) –60 GeV < M jet < 100 GeV C/A R=0.8 Jet Subjet 1 Subjet 2 μ>0.4 μ < 0.4 Mass Drop 17 June 2012 Group E - tt Resonances Search 12 W-tagging Prune jets to increase mass resolution and tag them using mass drop technique W- tag !

Background Estimation (I) Main Backgrounds o Standard Model tt  taken from MC o Non-Top MultiJet (NTMJ)  data-driven technique using control region and estimated mistag rate for normalization Mistag Probability o Using 1+2 topology  invert mass drop requirement on type 2 top μ>0.4 to obtain QCD fake sample with “same” kinematics o As function of type 1 top p T calculate top-tag mistag rate 17 June 2012Group E - tt Resonances Search % efficiency plateau 4-5% mistag probability plateau

Background Estimation (II) Dominant NTMJ background taken from loosened selection in each channel Event-by-event weight calculated as mistag probability for p T of probe jet Background shape extraction o Probe jet mass distribution kinematically biased o Replace m probe-jet in probe-jet four vector by random value drawn from NTMJ MC in [140,250] GeV o Closure of procedure tested on MC 17 June 2012Group E - tt Resonances Search – Dijet Channel : Tag type I candidate Second jet is “probe jet” 1+2 – Trijet Channel : Tag type 2 candidate using two jets in single event hemisphere Third jet is “probe jet”

17 June 2012Group E - tt Resonances Search15 Combined SM tt (red) and MultiJet (yellow) backgrounds compared to data Dominant systematics shown in grayed bands: o Trigger, JES, Luminosity, reconstruction efficiency No significant excess observed Results 1+1 Channel 1+2 Channel

SM + New physics SM only ModelExclusion Limit Z’ (1% width) TeV/c 2 Z’ (3.0% width)~1.0 TeV/c TeV/c 2 Z’ (10% width) TeV/c 2 Kaluza–Klein gluon production With σ g ∙Br(g’ ➝ tt ̅ ) < 1 pb ~1 TeV/c TeV/c 2 tt ̅ enhancement S < June 2012Group E - tt Resonances Search16 Resonance search: o Limits set on σ ✕ BR as a function of resonance mass using CLs method with likelihood ratio as test statistic tt Continuum Enhancement o Limits set on σ(tt) enhancement rom new physics using CLs method Interpretation of Results Excluded M(Z’)>1.6 TeV

Conclusions First search constraining m tt > 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 p T regime in hadronic final states Many thanks to all organizers of ESHEP, and especially Maurizio for many wonderful discussion sessions these past two weeks!!! 17 June 2012Group E - tt Resonances Search17

Group E Collaboration Boris Bulanek Alexander Gramolin Claudio Heller Brett Jackson Houry Keoshkerian Olga Kochebina Lukas Marti Sam Meehan Nicola Orlando 17 June 2012Group E - tt Resonances Search18 Maurizio Pierini Leonid Serkin Rosa Simoniello Jared Sturdy Dmitry Tsirkov Xiaoxiao Wang Christoph Wasicki Adam Webber Jonas Weichert

Backup 17 June 2012Group E - tt Resonances Search19

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. 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. 17 June 2012Group E - tt Resonances Search20

Topcolor: width = 10% 17 June 2012Group E - tt Resonances Search21

Randall–Sundrum Kaluza– Klein gluon production 17 June 2012Group E - tt Resonances Search22

CMS Detector 17 June 2012Group E - tt Resonances Search23