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Studies of W’  tb  Wbb  lvbb. Why W' important?. Many beyond-the-standard model theories have predicted W' Extra-dimension model Theories that have an extra SU(2) gauge group Right-handed W boson Technicolor theory Little higgs theory Main decay channels: W' -> e/mu + neutrino

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Studies of W’tbWbblvbb


Why W' important?

  • Many beyond-the-standard model theories have predicted W'

    • Extra-dimension model

    • Theories that have an extra SU(2) gauge group

    • Right-handed W boson

    • Technicolor theory

    • Little higgs theory

  • Main decay channels:

    • W' -> e/mu + neutrino

    • W' -> tb


Current limits of W'

  • Standard model couplings assumed

  • W' -> lnu

    • CDF: 1.12TeV

    • ATLAS: 1.49TeV (a soon-published result pushes the limit to 2.15TeV)

    • CMS: 1.58TeV

  • W' -> tb

    • CDF (right-handed coupling)

      • mass(W') > mass(right-handed neutrino): 800GeV

      • mass(W') < mass(right-handed neutrino): 825GeV

    • D0

      • mass(W') > mass(right-handed neutrino)

        • left-handed coupling: 863GeV

        • right-handed coupling: 885GeV

        • both couplings: 916GeV

      • mass(W') < mass(right-handed neutrino)

        • right-handed coupling: 890GeV

    • LHC experiments: no results yet


Why W' -> tb important?

  • Mass limit of W'->lnu greater than 1.5TeV, but standard model coupling is assumed

  • In reality, W' may weakly coupled to leptonic channel

  • There are models that W' is leptophobic

  • It is possible that we find something in hadronic channel for W' < 1.5TeV

  • W'->tb channel provides information about the chirality of W' but not the leptonic channel

  • Question:

  • Given that the current limit of W'->tb is at least 800GeV

  • Should we optimize cuts for W' mass ~800GeV?


Matrix method:finding QCD in muon channel for W’tbWbblvbb


Introduction to matrix method

  • Measuring QCD with the help of two control regions

  • Region 1 gives the probability of loose real muons being tight real muons

  • Region 2 gives the probability of loose fake muons being tight loose muons

  • N(loose) = N(loose,real) + N(loose, fake)

  • N(tight) = N(tight,real) + N(tight, fake)

  • N(tight) = r*N(loose,real) + f*N(loose, fake)

  • Where:

    • N(loose): number of events that have a loose muon, selected MET, at least two jets, and a b-tag

    • N(loose,real/fake): number of events that have a loose real/fake muon, selected MET, at least two jets, and a b-tag

    • N(tight): number of events that have a tight muon, selected MET, at least two jets, and a b-tag

    • N(tight,real/fake): number of events that have a tight real/fake muon, selected MET, at least two jets, and a b-tag

    • r: efficiency of loose real muons being tight = N(tight,real)/N(loose,real)

    • f: efficiency of loose fake muons being tight = N(tight,fake)/N(tight,fake)


Introduction to matrix method

  • Loose muons: pass through all cuts except isolation cut

  • Tight muons: pass through all cuts (including isolation cut)

  • Region 1:

  • Tag-and-probe events:

    • 80GeV < mass of Zmumu < 100GeV

    • muons with opposite charges

    • Tag muon is tight, probe muon satisfies the loose requirement

  • Probe muons give N(loose,real) and N(tight,real)

  • Give r (with assumptions)

  • Region 2:

  • QCD region:

    • transverse mass of W < 20 GeV

    • transverse mass of W + MET < 60 GeV

  • Give N(loose,fake) and N(tight,fake)

  • Give f (with assumptions)


N(loose) = N(loose,real) + N(loose, fake)

N(tight) = r*N(loose,real) + f*N(loose, fake)

full selection (b-tag included)

QCD shape obtained from matrix method

QCD scale factor found by template fit


Cross-check that “real muon region” really gives real muons

Z->mumu mass distributionexactly two same charge muons

no constraint on number of jets

Z->mumu mass distributionexactly two opposite charge muons

no constraint on number of jets


80GeV < Zmass < 100GeV muonsexactly two opposite charge muons

number of jets = 0

80GeV < Zmass < 100GeVexactly two opposite charge muons

no constraint on number of jets

efficiency of probe muon passing through isolation cut

80GeV < Zmass < 100GeVexactly two opposite charge muons

at least 2 jets

80GeV < Zmass < 100GeVexactly two opposite charge muons

number of jets = 1


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