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Update on the hadronic top squark search: Top reconstruction @ 100 TeV

Update on the hadronic top squark search: Top reconstruction @ 100 TeV. Loukas Gouskos , Allan Sung, Joe Incandela. Physics motivation. SUSY: one of the most extensively studied BSM theories An excellent answer to: hierarchy problem, Dark Matter, unification of couplings

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Update on the hadronic top squark search: Top reconstruction @ 100 TeV

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  1. Update on the hadronic top squark search: Top reconstruction @ 100 TeV Loukas Gouskos, Allan Sung, Joe Incandela FCC-hh analysis meeting

  2. Physics motivation • SUSY: one of the most extensively studied BSM theories • An excellent answer to: hierarchy problem, Dark Matter, unification of couplings • Top squark searches @ 100 TeV: • Understand naturalness of the EWK state • Viability of SUSY [top squarks should be < ~10 TeV] Current status Papucci et al. hep-ph 1110.6926 Recent articles relax these conditions: Mstop<~3 TeV[e.g. Baer et. al. 1602.0769, 1611.08511Ross et. al. 1110.6926] ̴TeV FCC-hh analysis meeting

  3. Physics motivation • SUSY: one of the most extensively studied BSM theories • An excellent answer to: hierarchy problem, Dark Matter, unification of couplings • Top squark searches @ 100 TeV: • Understand naturalness of the EWK state • Viability of SUSY [top squarks should be < ~10 TeV] Current status Papucci et al. hep-ph 1110.6926 Recent articles relax these conditions: Mstop<~3 TeV[e.g. Baer et. al. 1602.0769, 1611.08511Ross et. al. 1110.6926] GOAL: Probe the ~10 TeV regime with FCC-hh ̴TeV FCC-hh analysis meeting

  4. Signal characteristics • Top squark decays: very distinct signature in the all hadronic channel • Key player of top squark searches: top tagging • Top quarks are typically boosted decay products merge into a single jet • Identification of boosted top quarks provides a powerful handle to suppress many of the SM backgrounds • Multiple jets • 2 b-jets • On-shell top quarks • Large MET [from the two LSPs] Mj~Mt b W q1 t q2 FCC-hh analysis meeting

  5. Object reconstruction & event selection FCC-hh analysis meeting

  6. Objects & Baseline selection • Baseline selection: • Veto events with electrons & muons • Nj (high-pT)>=2 & Nb >= 1 • MET> 2 TeV • Δφ (j1,2 ; MET) > 0.5 ; Δφ (j3 ; MET) > 0.3 • low-pT jets: • PF Jets, R=0.4 • pT> 20 GeV • high-pT jets: • PF Jets, R=0.4 • pT> 1000 GeV • b jets: • PF Jets, R=0.4 • pT> 20 GeV • Electrons / Muons: • pT> 30 GeV • Iso/pT < 0.4 FCC-hh analysis meeting

  7. Background composition • Relevant backgrounds after the baseline sections: • QCD multijet • Huge cross-section • Rejected with large met and top-tagging selection • EWK backgrounds: Z/W+jets, VV, VVV • Leptonic decays where leptons escape lepton vetoes -> large MET • Highly suppressed after applying top-tagging and requiring multiple b-jets • Top (+X) backgrounds: ttV, ttVV, tttt, single-t • similar characteristics as signal • Multiple tops, multiple bs and MET from invisible particles • main challenge: tt & ttZ(->nunu) : needs dedicated analysis techniques [next slides] Prod xsec @ 100 TeV [M Mangano et. al] σ(mstop~7 TeV) ~10-4 [NLO] FCC-hh analysis meeting FCC-hh analysis meeting

  8. Top reconstruction: Multi-R tagger • The choice of the jet distance parameter (R) is important: • Large enough to contain the topdecay products • But not larger… need to suppress contamination from the underlying event, pile-up and ISR • This leads to large contributions to the jet mass. • Procedure: • Start from an anti-kT SoftDrop PF jetwith R=0.8 • Recluster with smaller R (=0.2 and 0.4) • Calculate jet mass and substructure variables for each case • Expect a very distinct behaviour betweenSignal and Background 0 < pT(gen-top) < 2 TeV 2 < pT(gen-top) < 4 TeV 4 < pT(gen-top) More details in: https://indico.cern.ch/event/697489/contributions/2873783/attachments/1590416/2516620/fcc-hh-susystop-20180126-lg.pdf FCC-hh analysis meeting meeting

  9. Multi-R tagger: performance • Modest gain in efficiency [5-10%] wrt the cut-based approach for the same mistagging rate • As expected in this pT regime • BDT Multi-R inputs: • Softdrop mass, pT, τ32, τ31, τ21 • R = 0.2, 0.4, 0.8 • CC [LHC-based]: • Cut based selection on M(SD) & τ32 • CC-L : 110 < M(SD) < 220 GeV, τ32<0.67 • CC-T : 110 < M(SD) < 220 GeV, τ32<0.57 pT(AK8) < 1 TeV BDT: Multi-R * = CC-T * = CC-L better FCC-hh analysis meeting meeting

  10. Multi-R tagger: performance (2) • Significant improvement in performance for boosted jets • ~ and order of magnitude pT(AK8) > 5 TeV pT(AK8) < 1 TeV Improvement BDT: Multi-R * = CC-T * = CC-L BDT: Multi-R * = CC-T * = CC-L better better However, performance degrades in the case of very boosted tops FCC-hh analysis meeting meeting

  11. Multi-R tagger + tracks • Calorimeter granularity not sufficient for efficient identification of boosted tops [i.e. pT >~4-5 TeV] • ΔR (ECAL) ~ 0.02 , ΔR (HCAL) ~ 0.1 vs. ΔRmax (qi,qj) ~ 0.05 • Exploit tracking – an order of magnitude finer granularity • Procedure [a’la arxiv: 1503.03347 Michele et al.]: • Start from an anti-kT SoftDrop PF jet with R=0.8 • Recluster pfJets with smaller R (=0.2 and 0.4) • Cluster TrkJets with R (=0.2, 0.4, 0.8) • Calculate jet mass and substructure variables for each case CALO-BASED TRK-based FCC-hh analysis meeting meeting

  12. Multi-R + tracks tagger: performance • No improvement from the BDT Multi-R + Tracks tagger ; • Neither from the translated Track – based CC tagger • As expected in this pT regime • BDT Multi-R + tracks inputs: • PFJets and TrkJets with: • Softdrop mass, pT, τ32, τ31, τ21 • R = 0.2, 0.4, 0.8 • CC [LHC-based]: • Cut based selection on M(SD) & τ32 • CC-L : 110 < M(SD) < 220 GeV, τ32<0.67 • CC-T : 110 < M(SD) < 220 GeV, τ32<0.57 • CC-Trk [TrkJets] : • As for CC but selecting on the translatedtrack-based mass and on the track-based subjetiness ratio pT(AK8) < 1 TeV BDT: Multi-R BDT: Multi-R + Trk * = CC-T * = CC-L = CC-Trk-T = CC-Trk-T better FCC-hh analysis meeting meeting

  13. Multi-R + tracks tagger: performance • BDT Multi-R + Tracks tagger: 5-10% gain in efficiency wrt BDT Multi-R • The translated Track – based CC tagger shows significant improvement wrt to the other CC approaches pT(AK8) < 1 TeV pT(AK8) > 5 TeV BDT: Multi-R BDT: Multi-R + Trk * = CC-T * = CC-L = CC-Trk-T = CC-Trk-T BDT: Multi-R BDT: Multi-R + Trk * = CC-T * = CC-L = CC-Trk-T = CC-Trk-T better better FCC-hh analysis meeting meeting

  14. Highlights from search design • Dominant SM processes after baseline selection + top tagging: • ttbar [1Lep] and ttZ (Z->vv) • MET in Z->vv (and ttbar through the “lost” lepton) is aligned with one of the 2 tops • MET in top squarks: more democratically distributed between the 2 tops ttZ(->vv) Top squark FCC-hh analysis meeting

  15. Highlights from search design (2) • Things look as expected :) ttZ(->vv) Top squarks FCC-hh analysis meeting

  16. Highlights from search design (3) • Define an extra handle for stop searches: min Δφ(top1,2;MET) • Powerful variable to suppress ttZ [and ttbar]: • min Δφ(top1,2;MET)> 0.5 : reject ~60% of BKG for ~10% signal ttZ(->nunu) SUSY FCC-hh analysis meeting

  17. Event categorization • On top of the baseline, categorize events based on Nt and Nb: • Fit MET shape: • [for now 7 bins] Nt = 1 Nt >= 2 Nb >= 2 Nb = 1 Nb >= 2 Nb = 1 Top-tagging WP: ~10% mistagging Nt=1, Nb>=2 FCC-hh analysis meeting

  18. Background estimation FCC-hh analysis meeting

  19. Background estimation • Main SM backgrounds after baseline selection: • ttbar [1L] and ttV • Estimation of the main backgrounds: • Measurement of each process in dedicated control samples in “data” • Use MC to translate the measurement into a prediction in the search sample • Rare processes [e.g. ttVV, V, multi-V] from simulation with generous uncertainties FCC-hh analysis meeting

  20. Estimation of the ttbar BKG • Stems from events with leptonically decaying W boson(s) where the lepton is not identified by the vetoes or is out of acceptance : aka “Lost Lepton” (LL) Background • Utilize a 1L control sample [CS] by inverting e/μ veto • “+” : similar kinematics to the search sample [0L] • “-” : limited statistics of the CS • Prediction of LLB : where: • Important: the relative differences [trends] between 0l & 1l need to be similar between data and MC [not the shapes themselves] 1L Selection: - NL = 1 with pT[L] ≥ 30 GeV- MT(L,MET)<100 GeV: suppress potential signal contamination [ TFLL & N(1L) :calculated for each search region] FCC-hh analysis meeting

  21. Estimation of ttV and “Rare” BKGs • The ttZ background is estimated using a multiLepton region: • 3 leptons; OSSF pair consistent with a Z, (pT[Z]>2000 GeV) • Nj>=2, Nb>=2 • Off-Z region used to constrain ttbar background [currently not implemented] • Extract a SF vs pT(Z) • Rare backgrounds [e.g. ttVV, Dibosons,..] are estimated from simulation with 50% uncertainty FCC-hh analysis meeting

  22. Systematic uncertainties • In the ttbar and ttV estimation[particularly in high MET regions] the statistics of the control regions is the dominant uncertainty [~% - 100%]. • 1L and 3L control regions fit simultaneously with the search regions for the signal extraction • Define two scenarios to account for additional sources of systematic uncertainties: • Nominal: 10% [uncertainty uncorrelated across all regions / processes] • Conservative: 20% FCC-hh analysis meeting

  23. Results FCC-hh analysis meeting

  24. Setting the scene • SMS: used in SUSY searches (design & result interpretation) • Minimal set of free parameters to describe a particular set of decay chains • More generic description -> results applicable to other scenarios • But.. there are some simplifications: • eg. full SUSY spectrum not provided; particle properties, (usually) BR=100% for the sparticle decays Set Upper Limitsin cross-section LSP Region kinematically forbidden m[prod. sparticle] < m[LSP] Observed & Expected mass limits based on the nominal production cross-section Excluded parameterspace Produced sparticle Searches for 3rd Generation SUSY

  25. Results @ 3 ab-1 Expected limit Systematics:Nominal scenario [ k-factors applied on both BKG and Signal ] FCC-hh analysis meeting

  26. Results @ 30 ab-1 Expected limit Significance Systematics:Nominal scenario Systematics:Nominal scenario NB: Work on going [smoothing, finer signal scan] FCC-hh analysis meeting

  27. Summary and next steps FCC-hh analysis meeting

  28. Summary • A search for top squarks @ 100 TeV is in place • Focus on all hadronic channel -> largest BR • Tagging ultra-boosted top quarks @ 100 TeV needs detector granularity and improved methods • Multi-R top/W taggers • Track-based substructure variables • Improvements also in the search design • Ttbar & ttV significantly suppressed • For signal models with large mass difference between the top squark and the LSP: • We can reach the mstop~9-10 TeV barrier with 3 ab-1 • We can discover top squarks with mstop~10 TeV with 30 ab-1 5-10x improved background rejectionwrt to cut based approaches FCC-hh analysis meeting

  29. Next steps • For FCC Week: • Small tweaks in top-tagging and search design • Expect ~0.5TeV gain in sensitivity • Exclusion / discovery plots using a scan with higher granularity • Top tagging performance in FullSimulation [?] • Documentation • Longer term plans: • Dedicated search for compressed models • Further improve top-tagging algorithm FCC-hh analysis meeting

  30. Multi-R tagger + tracks + calo (?) • Add also calojets: • … does not improve things .. BDT: Multi-R BDT: Multi-R + Trk BDT: Multi-R + Trk + Calo * = CC-T * = CC-L = CC-Trk-T = CC-Trk-T better FCC-hh analysis meeting meeting

  31. Alternative methods • Similar efficiency with the μ-tagger; a bit better than CC track based • We could include it as input in the BDT to tag the b through non-iso muons • NB. the μ-tagger has very small signal efficiency – by construction Muonic-top tagging Track-based tagging FCC-hh analysis meeting meeting

  32. Top reconstruction: Multi-R tagger (2) • The Signal pT(AK8)<1 TeV Background pT(AK8)<1 TeV ΔR = 0.2 ΔR = 0.4 ΔR = 0.8 ΔR = 0.2 ΔR = 0.4 ΔR = 0.8 Background pT(AK8)>5 TeV Signal pT(AK8)>5 TeV ΔR = 0.2 ΔR = 0.4 ΔR = 0.8 ΔR = 0.2 ΔR = 0.4 ΔR = 0.8 FCC-hh analysis meeting meeting

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