Jet tagging with ATLAS for discoveries in Run II Ayana Arce (Duke University) November 5th 2014 The Large Hadron Collider 2008-2013: ECM: 7.0 – 8.0 TeV mH = 125.4 +/- 0.4 (ATLAS) mH = 125.0 +/- 0.3 (CMS) 2015-2018: ECM: 13 – 14 TeV ??? Discoveries at the LHC dark matter/low EWSB scale new physics The LHC is prepared to find: top partners superpartners (squark/gluino) new gauge couplings extra dimensions Inner tracker |η|< 2.5 σ(pT)/pT = 0.05% pT/GeV + 1% EM Barrel/Endcap |η|< 3.2 σ(E)/E = 10%/√(E/GeV) Forward Calorimeter 3.0 < |η|< 4.9 σ(E)/E = 100%/√E the ATLAS detector Hadronic 0 < |η|< 1.7 1.7 < |η|< 3.2 σ(E)/E = 50%/√E Overview What’s left to discover in Run II? Why jets? Why now? Jet substructure tagging experimental challenges + solutions Run I constraints on models of new physics using substructure tags Outlook Prospects for discoveries in Run II Probing the electroweak scale in Run I Probing electroweak symmetry breaking in Run I Beyond the electroweak scale Lessons from Run I Higgs mass requires us to study a variety of decays: • large branching fraction to bb • Searches for exotic di-higgs, etc. require fermionic decay channels Next searches must probe multi-TeV mass scales • large pT for final-state particles in decay • parton luminosity requires large acceptance in searches Hadronic decays and boosted object Looking towards Run II Quigg: http://lutece.fnal.gov/PartonLum We will probe higher masses/boosts at the same luminosity… Jet substructure at ATLAS Hadronic measurements at ATLAS EM Barrel/Endcap |η|< 3.2 : δφ ~ 0.025-0.1 σ(E)/E = 10%/√(E/GeV) Hadronic 0 < |η|< 1.7: : δφ ~ 0.1 1.7 < |η|< 3.2 : δφ ~ 0.1 σ(E)/E = 50%/√E Hadronic reconstruction perturbative shower suggests iterative, pairwise merging algorithms: jet reconstruction Jet reconstruction stable hadrons Calorimeter jet Calorimeter cells Truth jet iteratively combine closest pairs of particles distance = min(pTk) (ΔR/Rmax) jets topological clusters Jet constituent observable moments: calculations jet mass average jet charge m2 = (Σ Ei )2 – (Σ p i)2 jet functions from fragmentation functions jet charge Boost2012 Report, EPJC 74 (2014) Krohn et. al. “Jet Charge at the LHC” (2012) Jet constituent observables: parton shower top jet mass Jet constituent calibration Cluster constituents calibrated to local hadron scale Substructure moments re-calibrated at jet level Substructure-based tagging Interesting particles are color singlet Color singlet Color octet Charge conservation is powerful LHC backgrounds are … gluey q/g tagger Sensitive variables Modeling Gallicchio and Schwartz, PRL107 (2011) Color factor (g=3 vs. q=9/4) in substructure moments leads to many sensitive variables High pT BG are mostly light partons Butterworth, Cox, Forshaw (2002) top/W tagging variables n-subjettiness ~ 0 typically combined in a “tag” Thaler, Van Tilburg (2011) Splitting scale ~(m/2)2 Top-tagging performance W-tagging correlations W-tagging performance Challenges in substructure tagging the LHC environment Jet grooming Modeling substructure variables Theory typically predicts moments – tagging uses distributions Parton showers may disagree, and require tuning Modeling substructure variables artist: M. Swiatlowski Data-driven efficiency: q/g tag construct width and ntrk distributions expected for pure samples • bin in jet pT, η; fix flavor ratios to MC predictions ⁃ also fix heavy flavor templates (shape and normalization) Solve to extract pure templates Data-driven efficiency: jet charge/pull Opposite to leptonic W charge Color singlet Charge bias also possible in W+jets, dijets Jet charge validation W → qq candidate charge Performance of a W+ tagger ATLAS-CONF-2013-086 Jet pull validation W-tagging validation top-tagging validation Challenging the SM with substructure tags Search for W’ tb in hadronic channel Consider new gauge interactions in models preferring quark/3rd gen couplings Top tagging variables small differences in signal distribution for WL, WR due to top polarization Limits on W’ Search for W’ WZ, G* ZZ in leptonic Z+jet channel apply three signal regions (2 jet and 1 jet) Boosted channel backgrounds Limits Outlook Confronting Run II challenges Strategy for 2015 Tagger calibrations: • W, top tags: In-situ efficiency/fake rate measurements from Run I (being completed) • better q/g purified samples Pileup: • grooming and area subtraction perform well • also: track-based pileup constraints (subjet JVT) Beyond Run II: Looking ahead No evidence of physics beyond the SM in Run I …but a great laboratory for careful validation of jet tagging observables in data! Will hadronic final states show us new physics first in Run II?
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