Samples generated with
  • Sherpa 1.1.3 pp → jjj (ie. 3 partons, quark or gluons)
  • parton pT≥20 GeV/c, |η|<2.5
  • Sherpa's default JetFinder sqr(QCUT/E_CMS) D with different values of QCUT and D. This is a kT algorithm (Sherpa 1.2.0 allows other algorithms, including anti-kT)
  • Did not include ΔR cut for these tests, but this can be done using
          (sqr(DEta(p[1],p[2]))+sqr(DPhi(p[1],p[2]))>=0.36))" 93,93,93 2,3
    (spacing, included here for clarity, is not allowed in Sherpa's Run.dat) which requires at least two of the three ΔR between partons to be ≥0.6, ie. ΔR≥0.6 between one parton and both the other two.
Plots made for 1000 events for various samples (Sherpa examples use Qcut=20, D=1):


  • The PDG id is of the 3 partons per event. Do we really expect ~80% of the partons to be gluons, rather than quarks? Bill says yes
  • Jet plots are for jets with pT≥20 GeV/c and |η|<2.5 and at least three such jets.
  • I plot the smallest, middle, and largest ΔR and Δp in the event. The smallest shows the cut-off due to generator parameters. The middle shows what we would cut on with a ΔR cut. Note the different jet ΔR/Δp samples don't have the same normalisation (especially for Qcut=40,D=1), due to the 3-jet cut.
  • The effect of varying Qcut and D shows in the parton separations, but not much in the reconstructed jets. Is the effect really so washed out?
  • After hours of LXR/dOxygen searching, I finally found how to run a jet finder on generator output. You need to set a flag to specify the input type: this is done automatically for other input types, but not for generator input. For the record, here's the magic incantation:
    from JetRec.JetRecFlags import jobproperties as jetFlags
    jetFlags.JetRecFlags.inputFileType = "GEN"
    from JetRec.JetGetters import make_StandardJetGetter
    collname = make_StandardJetGetter('AntiKt', 0.4, 'Truth').jetAlgorithmHandle().JetCollectionName

  • jjj
    Qcut D nb
    5 1 71857
    10 1 36939
    20 1 19829
    40 1 997
    20 0.3 70470
    20 0.5 41697
    20 1.5 7386
  • Gbb (no Z)
    Qcut D nb
    10 1 558
    20 1 278
    40 1 12
    20 0.5 652
    20 1.5 91

-- TimAdye - 16-Dec-2009

Topic attachments
I Attachment History Action Size Date Who Comment
PDFpdf jetd.pdf r1 manage 42.9 K 2009-12-16 - 13:44 TimAdye varying D
PDFpdf jetq.pdf r1 manage 43.4 K 2009-12-16 - 13:43 TimAdye varying Q<sub>cut</sub>
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Topic revision: r4 - 2009-12-17 - TimAdye
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