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Preliminary Study on Kinematic Edge for ttH Reconstruction

A study focusing on M(b,l) variable for ttH reconstruction, exploring potential impact on reducing combinatorial backgrounds. Analysis based on ttHbl.bjj.bb and ttjj events. Investigates correlations with other variables and discusses experimental limitations and potential usefulness.

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Preliminary Study on Kinematic Edge for ttH Reconstruction

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  1. Study for ttH reconstruction Work in progress… Ricardo Gonçalo, Pedro Teixeira-Dias, RHUL

  2. Introduction • This is a preliminary study intended for the CSC ttH, Hbb meeting (shown here due to colliding meetings, please bear with me) • ttH, Hbb (and ttH in general) plagued by too many combinations of b/light jets and leptons; trying to find ways of reducing this number • Concentrating on getting the right tbl combination but also looked at tbjj • Already know that what I’ll show won’t help in the likelihood analysis (see Georges Aad’s talk yesterday) but perhaps useful to someone else ATLAS Higgs WG

  3. b l W t  M(b,l) Kinematic edge • Invariant mass of the b quark and the lepton in the semileptonic top decay has a kinematic edge (thanks for D.Tovey for pointing this out) • Can this be used to improve the combinatorial background in ttH reconstruction? • Data: • ttHbl bjj bb (5341, Pythia) • ttjj (5212, MC@NLO + Herwig) • Reconstructed with 11.0.41 • EventView-based Ntuples produced by Lorenzo Feligioni and CPPM group (thanks!) t ATLAS Higgs WG

  4. M(b,l) Kinematic edge Detector effects smear distribution, but may still be useful  ATLAS Higgs WG

  5. Summary • M(b,l) variable under study for ttH reconstruction • Use limited by experimental resolution but doesn’t look too bad for tblcase • Tried M(b,j) for tbjj but resolution there is worse • May be useful in other ttH channels since these are usually plagued by large number of combinations • A few questions (and answers after discussion with CPPM group): • Correlations with other discriminant variables? • Yes, with M(bl) • Useful in multivariate methods? • Unfortunately no! (  !!!!) After combination likelihood (see G.Aad’s talk) bad combinations all have M(bl) < 160 GeV ATLAS Higgs WG

  6. Backup slides ATLAS Higgs WG

  7. M(b,j) for t bWbjj ttHbl bjj bb ttjjbl bjj jj ATLAS Higgs WG

  8. ttjjbl bjj jj ttHbl bjj bb • Positive weight selects mostly b-initiatied jets • Matching done between b quark from tbl/ tbjj and closest jet ATLAS Higgs WG

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