Kenneth Wraight. semileptonic ttbar + jet events. pt spectra of extra jets. Motivations. Study top quark properties: charge, spin, etc.
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semileptonic ttbar + jet events
pt spectra of extra jets
Study top quark properties: charge, spin, etc.
Background to associated Higgs production and multi-jet SUSY decays (10s of ttbar events per second for σ=833pb at L=1034cm-2s-1): must be controlled.
Ultimate test of generation and simulation software: multiscale QCD calculations
4/9 fully hadronic, 4/9 semileptonic, 1/9 fully leptonic
Looking for 4 jets from the hard process: 2 b quarks and 2 hadronic W daughters
(↑Tevatron’s favourite (~85%))
LHC: ~90% gluon-gluon production.
expect over 1million events per year @ 1034cm-2s-1
* electron or muon with Ptlep>20GeV within |η|<2.5 fulfilling isolation requirement Et,ΔR=0.2<6GeV (not yet implemented). Also ignore electrons in crack region 1.37<|η|<1.52.
** jets with Ptlep>20GeV within |η|<2.5. Also remove jets with good electron nearby i.e. ΔRj-el<0.2.
What’s ‘The best’ method of matching?
=no. of events ‘correctly’ reconstructed / number of sample matched
2798 electronic events selected and 3277 muonic.
Com matched events: 5952, alt matched: 1417, overlap:1366
*additional requirement matched b-jet must have suitable ‘TruthLabel’
ξsel= 16.37, for 37066 event sample (less than a day @ 1034cm-2s-1)
top left: Nikhef matched and recon.
above: Glasgow matched and recon.
left: all reconstructed tops
black: standard, red: W constraint,
blue: closest b-tagged jet, pink: both
MLM for Alpgen and CKKW for Sherpa.
MLM avoids double counting by splitting generation sample into exclusive multiplicities for 0->N-1 then recombine sample along with an inclusive N-jet sample.
CKKW uses Sudakov form factors to control jet production by reweighting the matrix element.
Jets from “well-reconstructed top” events: b-vetoed and not part of top tri-jet
Extra jet pt spectra generator comparisons
[email protected] ~25k 5200 sample
Fastsim AFjets (blue)
Alpgen Fastsim (pink)