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Issues in verification of ALPGEN heavy flavor production

Issues in verification of ALPGEN heavy flavor production. Regina Demina University of Rochester with M. Begel, T.Ferbel, M. Zielinski. Outline. Mechanisms of heavy flavor production In association with W-boson In multijets Run 1 approach to MC verification Problems

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Issues in verification of ALPGEN heavy flavor production

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  1. Issues in verification of ALPGEN heavy flavor production Regina Demina University of Rochester with M. Begel, T.Ferbel, M. Zielinski

  2. Outline • Mechanisms of heavy flavor production • In association with W-boson • In multijets • Run 1 approach to MC verification • Problems • Fractions of heavy flavor and Angular correlations • Summary: What can and what cannot be measured MC4Run2 Workshop, FNAL

  3. SM W+heavy flavor production. Initial state gluon splitting Final state gluon splitting Flavor excitation. These processes can only be separated at the ME level. For x-section calculation, interference must be accounted for. MC4Run2 Workshop, FNAL

  4. Heavy flavor production in multijets • Run 1 approach: • Use high statistics QCD samples to calibrated MC prediction for gluon splitting component on data. • Tag jets using different methods – lifetime or lepton. • Df or DR are typically used • to distinguish different mechanisms of h.f. production. MC4Run2 Workshop, FNAL

  5. CDF Run 1 tt x-section Herwig (parton shower) prediction for angular correlations Wbb scaled up by this factor T. Affolder et al., The CDF Collaboration, Phys. Rev. D64, 032002 (2001). MC4Run2 Workshop, FNAL

  6. Problems with this approach • Assume in Wbb (bb) comes • predominantly from gbb production • shower evolution • Neglect interference terms in multijet production • Use parton shower approximation in multijet production • Combine LO with NLO • bb with bbj • Advantage • Tunable parameter – f(gbb) MC4Run2 Workshop, FNAL

  7. ALPGEN: bbj and Wbb Parton Level E(Q)>50GeV Dr(QQ)>0.4 • ME level calculation • Deals with exclusive final states • bbj, Wbb, not • bb+>=0j • No artificial separation between production mechanisms • ME gbb does not look like parton shower gbb bbj Wbb MC4Run2 Workshop, FNAL

  8. ALPGEN verification • Still work under the assumption that by comparing data and MC in multijets we verify WQQ production • But no tunable parameter (cannot separate gbb) • Difficult to quantify the level of agreement • Need to work with exclusive final states, e.g. bbj • Loss in statistics • How to relate observed 3j to 3 partons MC4Run2 Workshop, FNAL

  9. bbj observables • Fraction of bbj in jjj • Compare distribution in Dr(bb), or • Ratio of away/toward jet (R. Field’s terminology): • DR(bb)<1.5 – toward jet • DR(bb)>1.5 – away jet Toward Away 28% 72% MC4Run2 Workshop, FNAL

  10. DØ Statistics • b-tagging e~40%, double tagging ~16% • Wbb: • Wbb/Wjj = 1.17% • #observed events(Wjj)=~2300/100 pb-1 =>4 double tagged events/100pb-1 • bbj: • bbj/jjj=1.41% • #observed events(jjj)=1 million/100pb-1 (in trigger JT65) => ~2000 double tagged events/100pb-1 MC4Run2 Workshop, FNAL

  11. Summary: What can and what cannot be measured • ME level Monte Carlo • Correct handling of parton multiplicity • Interference included • ME instead of parton shower (very different angular correlation) • No obvious tunable parameter in the model (too predictive) => no f(gbb) • Use 3jet final state to compare data and MC • bbj/jjj ratio • Toward/away ratio • Problem: parton vs jet counting MC4Run2 Workshop, FNAL

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