B-jet Energy Scale Determinationfrom Top Quark Pair All Hadronic Events Topic for summer student of University of Tsukuba @ CDF
B Jet Energy Scale Systematic uncertainties of Mtop measurement by top mass template group Top quark mass is important parameter in SM. Systematic uncertainties dominate Mtop error. • Recent recommendation Mtop systematic uncertainty from b-JES • Particle by particle calorimeter response is not different between light and heavy flavor • Uncertainties are in • b fragmentation model in MC • semi-leptonic branching fractions of heavy flavor • Estimate Mtop syst. uncertainties by re-weighting MC 1 for these components This is excellent prescription, but we always want confirmation from data.
SM Top Quark Production & Decay • Top quarks are mainly produced in pairs via strong interaction. • One top pair each 1010 inelastic collisions at the Tevatron ~85% @ Tevatron ~15% @ Tevatron • Top quark decays quickly (~10-25s) • before hadroniztion (QCD~10-23s). • Br(tWb) ~ 100% (|Vtb|2~1) • Final states are characterized by • the decay modes of W bosons. • dilepton (e,) : ~5% • lepton(e,)+jets : ~30% • all-hadronic : ~45% • no missing object • + X : ~20%
Event Selection from AllHad Group Pre-selection NN-selection • From 2D(Mtop vs w-jet-JES) Fit w/ 2tags • Nsig = 191 28 • Nbkg = 304 24 • @ 1.9/fb, allhad template group
Simplest Image of Balancing If there is no resolution effect, f=bJES where, • Simplest toy MC • AllHad Events by pythia • Change only b-parton energy scale y=(1/1.1-1)x y=(1/0.9-1)x
2nd Simplest Toy MC • Only fluctuate pT(bb) by Gaussian (keep bb direction, light quarks) f = 1 f=0.9 f=1.1 this variable doesn’t work. (works at previous page) this variable does work.
3rd Simplest Toy MC • Only fluctuate b and bbar energies by Gaussian independently (keep light quarks) f = 1 f=0.9 f=1.1 this variable doesn’t work (works at previous page) due to the change in bbbar direction. I’m stopping here... Need to continue.
Time Scale (Ambiguous due to my poor understanding) To do list 1. study toy MC & determine the way to go 2. event selection of all hadronic channel 3. study the effects of event selection 4. bJES only from signal MC 5. study the effects of backgrounds 6. compare the bJES from sigMC+bkg and data 7. summarize (give a talk @ top mass meeting & write cdfnote)