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Y. Sumino (Tohoku Univ.)

Boost-invariant Leptonic Observables and Reconstruction of Parent Particle Mass. Y. Sumino (Tohoku Univ.). Collab. S.Kawabata, Y.Shimizu, H.Yokoya. ☆ Plan of Talk. Motivations Construction of Boost-inv. Leptonic Observables Higgs Mass Reconstr . in VBF Mode (demonstration)

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Y. Sumino (Tohoku Univ.)

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  1. Boost-invariant Leptonic Observables and Reconstruction of Parent Particle Mass Y. Sumino(Tohoku Univ.) Collab. S.Kawabata, Y.Shimizu, H.Yokoya

  2. ☆ Plan of Talk • Motivations • Construction of Boost-inv. Leptonic Observables • Higgs Mass Reconstr. in VBF Mode (demonstration) • Summary and Future Applications

  3. Challenges for precise measurements of properties of (new) particles in LHC experiments: • In reconstructing kinematics of events, difficult to reconstruct jet energy scales accurately. • cf. electron and muon energy-momenta • Often interesting events include missing momenta. • Parton-level c.m. frame unknown from initial-state. • Limited accuracy of PDF. e.g. Reconstruction of energy-momenta of (new) particles is non-trivial.

  4. We propose a class of observables for measurements of properties of a particle (scalar or unpolarized), which decays as Virtues of the new observables • At Leading Order (no cuts, no bkg.): • Use only lepton energy distribution. (indep. of jet obs., missing mom.) • Independent of parent particle velocity, i.e. free from PDF, ISR, etc. • Including cuts and bkg: • A large d.o.f. of the observables allows to reduce/control effects of cuts and backgrounds. • Effects of cuts and bkgcan be kept small and under control.

  5. Lepton energy distributionin lab. frame Construction of the observables 2-body decay: : velocity of in lab. frame : energy of in rest frame : energy of in lab. frame ( : rapidity) Heuristic argument: contributions cancel By appropriately choosing , , …, one can eliminate dependence to arbitrary order.

  6. ….. Answer Maximal set of observables indep. of of . (1) (2) If , Usage:For example, if , we adjust the value of , such that to determine the true value of .

  7. Many-body decay: Observable energy in lab. frame energy distr. in rest frame • Dependent on and the parameters of . • Same as in the two-body decay case.

  8. mH reconstruction using Higgs bosons in VBF and decay q W H W q W Strategy of our analysis follows, to a large extent, that of Asai et al., EPJ C32S2, 19 (2004). S/N of order 2-4 is expected for . H W

  9. q • Two Criteria need to be satisfied to ensure use of the observable . • The lepton energy distribution in the Higgs rest frame agrees with the • theoretical prediction . • (2) The lepton angular distribution in the Higgs rest frame is isotropic. W H W q Effects of cuts should not violate these criteria significantly. • Cuts involving only jets would not affect the above criteria but only affect the b distribution of the Higgs boson. • Cuts involving leptons can affect the above criteria significantly. Slight modification of the leptonic cuts from Asai et al. In particular, lepton angular cuts are replaced by a Lorentz inv. cut GeV. By including this cut in the theoretical prediction , it does not affect the above criteria (1)(2).

  10. Data Analysis based on MC simulations (MadEvent+PYTHIA+PGS) mH=150GeV, mmmode

  11. Check two criteria MC signal events after all cuts Theory prediction GeV, GeV cosqdistribution Lepton energy distr. in the Higgs rest frame l Second criterion is satisfied only by events with small boost factors. We can adjust to suppress contributions from events with large . First criterion OK. q Boost vec. H rest frame

  12. G(ey)=1/cosh(ny) with n=4 mH reconstruction using Systematic effect DmH Only signal events Signal Effect of cuts +2.6 GeV (+1.7%) Bkg tt+tW -2 GeV (-1%) WWjj(EW) 0 GeV (0%) Statistical error: using Nl leptons. Signal+bkg events Signal tt+tW WWjj

  13. Summary and Future Applications • We proposed a class of observables: • constructed from lepton energy distribution, • independent of parent particle’s velocity, • a large deg. of freedom. • mH reconstruction using VBF and decay • Stat. error likely to dominate over sys. errors. • Possible applications • Slepton decay • Top mass measurement • Measurements of various couplings ~

  14. ２体崩壊（　　　　　　）の場合 ローレンツ不変性 このオブザーバブルはなぜローレンツ不変か？ テンソル解析により、各項はローレンツ不変でないことが分かる →　無限項の足し合わせで　　依存性が消える これは従来のローレンツ群の表現論の枠組におさまらない 新しいオブザーバブルのローレンツ不変性が明白な形で表せるような テンソル解析の拡大が望まれる →　より一般的な物理過程に適用できる可能性

  15. Many-body decay: boost Observable • Dependent on and the parameters of . • Same G(x) as in the two-body decay case.

  16. Modification of cuts

  17. Check two criteria q W H W q Theory prediction GeV, GeV l q Boost vec. Jet1 Lab H rest frame Jet2 Effects of PT-cut, h-cut, and isolated lepton requirement cosqdistribution

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