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Stilianos Kesisoglou

Search for exotic resonances decaying into V + Z using di-jet and di-lepton final states in CMS/LHC. Stilianos Kesisoglou. 2 nd Annual INP Meeting Institute of Nuclear Physics National Center for Scientific Research “Demokritos” May 28, 2011 - Athens, Greece. Theoretical Motivation.

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Stilianos Kesisoglou

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  1. Search for exotic resonances decayinginto V + Z using di-jet and di-leptonfinal states in CMS/LHC Stilianos Kesisoglou 2nd Annual INP Meeting Institute of Nuclear Physics National Center for Scientific Research “Demokritos” May 28, 2011 - Athens, Greece

  2. Theoretical Motivation Standard Model predicts that gauge boson self-coupling is possible,for example W W scattering ( W W → W W ) In the absence of Higgs or for a very heavy Higgs > 1TeVW W interactions become so strong that violate perturbativeunitarity at: s ~ 16πv2 ~ (1.2 TeV)2 To restore perturbative unitarity there must be some additional fields (resonances or new physics) not been detected experimentally to date Higgs (or any similar resonance) restores perturbative unitarityin di-vector boson scattering (V=W,Z) and postpones the problem. Several models predict particles that couple to vector bosons Sequential Standard Model W’ coupling to WZ Randall-Sundrum (RS) gravitons GRS coupling to ZZ and WW Techni-mesons coupling to WZ terms ~ s2/M4W sum ~ s/M2W + + + termswithsum ~ – s/M2W

  3. Experimental Signature • Analysis based on the assumption that resonance is heavy • Resonance decays to a Z and a vector boson V • Z decays leptonically: Z → l l (with l = e,μ) • V decays hadronically: V → 2 jets • Decay chains considered: • W’ → WZ → l l j j (Sequential Standard Model) • GRS → ZZ → ll j j (Randall-Sundrum gravitons) • Two fermion system produced in the Z decay is boosted • Fermions emitted within a small opening angle • Special care in the leptonic isolation of each leg • Two jet system produced in the V decay are overlapping • Clustered during reconstruction with a large cone producingone jet (“fat jet”)

  4. Collision and Monte Carlo Datasets MC Signal MC Backgrounds • Collision Dataset • 2011 collected dataset at s = (7 Tev)2 • 2012 collected dataset at s = (8 Tev)2 - ongoing • Monte Carlo Dataset • Signal generation and parton showering with PYTHIA • NNLO corrections from FEWZ (mass-dependent k factor) • Background generation with MADGRAPH,parton showering with PYTHIA

  5. Candidate, Background and Pileup Events • Candidate Events • At least two good quality reconstructed leptons • | η | < 2.5 (electrons) , | η | < 2.4 (muons) • pT > 45 GeV/c • Trigger Selection • Single Muon or Double Electron trigger • Reconstruction & electron ID cuts • Calorimetric isolation (electromagnetic) • Hadronic/Electromagnetic component ratio cut • Cluster shower shape cut • Reconstruction & muon ID cuts • Global muons (tracker muon matched with outer muon system) • Reconstruction & jet ID cuts • At least one R = 0.7 reconstructed with the “anti-kt” algorithm • | η | < 2.4 , pT > 30 GeV/c (particle-flow jets)

  6. Candidate, Background and Pileup Events • Candidate Events • Z → ll Candidates • 70 < mZ < 110 GeV/c2 , pZT > 150 GeV/c • V → j j Candidates • Reconstructed as single “fat jet” • ΔR(jet, l) > 1.0 • 65 < mj < 120 GeV/c2 , pVT > 250 GeV/c • Background Events • Z + jets (dominant), t tbar + jets, WZ, ZZ • Data-driven extraction from mj sideband • Pileup Events • Superimposed min-bias events weightedto reproduce the luminosity profile

  7. Systematic Uncertainties • Standard Model background • Data-driven method used for the background determination • Several systematic effects are eliminated • Pileup (negligible) • Jet Energy Scale ~3.0% • From max difference between pT ± σJES(pT,η) • Expected yield of signal events • Luminosity ~ 2.2% • Jet Energy Scale ~ 3.0% (same as for the bkgr.) • Parton Density Function • From max difference between CTEQ6.6, MRSTW2008, NNPDF2.0 • Trigger and Reconstruction efficiencies • “Tag + Probe” method using Z → l l (with l = e,μ) • 0.960 ± 0.004 (electrons), 0.974 ± 0.001 (muons)

  8. Limits

  9. Conclusions • No significant excess is observed in the mass distribution of theVZ candidates compared to the background expectation fromStandard Model processes. • Low bounds at 95% CL are set on the mass of hypotheticalresonances decaying to the VZ final state • 700 – 929 GeV/c2 (Sequential Standard Model) • 700 – 924 GeV/c2 (Randall-Sundrum gravitons for k/mPL = 0.05) • Analysis to be repeated with 2012 data (at 8TeV)

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