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ZHH with new jet clustering (from TIPP11 slides)

ZHH with new jet clustering (from TIPP11 slides). Taikan Suehara, Tomohiko Tanabe, Satoru Yamashita (The Univ. of Tokyo). ZHH in ILC. HHH coupling: a key to prove Higgs mechanism. m H =120 GeV. Double Higgs-strahlung: largest xsec around 500 GeV.

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ZHH with new jet clustering (from TIPP11 slides)

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  1. ZHH with new jet clustering(from TIPP11 slides) Taikan Suehara, Tomohiko Tanabe, Satoru Yamashita(The Univ. of Tokyo)

  2. ZHH in ILC HHH coupling: a key to prove Higgs mechanism mH=120 GeV Double Higgs-strahlung: largest xsec around 500 GeV Extremely small cross section of 0.2fbBackground (esp. top-pair) must bevery strongly suppressed Excellent b-tag in 6-jet environment

  3. ‘# of b jets’ in ZHH Jet clustering(Durham 6-jets) Number of jetscontainingMC b-hadrons # jets including MC b-hadron # of b-jets is reduced due to mis-jet-clustering Major problem in counting b-quarks

  4. J.Tian, ALCPG 11 s = 0.2 fb: Only 100 events in 500 fb-1

  5. qqhh (with Z-like pair)

  6. qqhh (without Z-like pair) ttbar with mis-b-tag

  7. Overall signal excess: 3.9s in 2 ab-1 -> not enough??

  8. New idea: use vertices in jet clustering Jet A(b-jet) ex. bbqq with a hard gluon with 4-jet configuration Jet B (b-jet) c c b b IP Jet C Jet E(gluon jet from D) Jet D

  9. New idea: use vertices in jet clustering Jet A(b-jet) ex. bbqq with a hard gluon with 4-jet configuration Jet B (b-jet) Standard jet clustering: A and B might be combined while E separated c c b b IP Jet C Jet E(gluon jet from D) Jet D

  10. New idea: use vertices in jet clustering Jet A(b-jet) ex. bbqq with a hard gluon with 4-jet configuration Jet B (b-jet) Standard jet clustering: A and B might be combined while E separated c c b Vertex clustering: Two b-jets can be separated with vertex information b IP Jet C Jet E(gluon jet from D) Jet D

  11. New idea: use vertices in jet clustering Jet A(b-jet) ex. bbqq with a hard gluon with 4-jet configuration Jet B (b-jet) Standard jet clustering: A and B might be combined while E separated c c b Vertex clustering: Two b-jets can be separated with vertex information b IP Jet C Jet E(gluon jet from D) Jet D

  12. Performance MC number of b-jets MC number of tracks from b-hadrons ZHH vs. top-pair b-tagging performance Effect on b-tag cut in ZHH analysis

  13. 1. MC number of b-jets Quick view of the vertex effect Procedure: • Jet clustering (Durham / Vertex) • Listing b-hadrons (MC information) Listing tracks from b-hadrons • Associate b-hadrons to reconstructed jets Jet including largest # of tracks from a b-hadron is associated to the b-hadron • Counting jets associated to b-hadrons Using ZHH -> bbbbbb events (# b-jets should be 6)

  14. 1. MC number of b-jets Durham Vertex # jets including MC b-hadron All jets including b – 52% -> 66% Significant improvement!

  15. 2. MC number of tracks from b-hadrons Effect on b-tagging at MC level UsingZHH -> qqHH (H->bb: 68%, Z decays to every flavor) tt -> bbcssc (each W decays to c and s quarks) Procedure: • Listing b-hadron tracks with MC information • Counting b-hadron tracks in each jet • Sort jets by number of b-hadron tracks • See 3rd and 4th jets: • qqHH: #b=4; # b-hadron tracks should be > 0 • tt: #b=2; # b-hadron tracks should be 0

  16. 2. MC number of tracks from b-hadrons qqhh (should be non-zero) 4th jet Durham Vertex 3rd jet tt (should be zero) 4th jet 3rd jet qqHH acceptance improved tt rejection improved

  17. 3. ZHH vs. top-pair b-tagging performance Study with realistic b-tagging Procedure: • Jet clustering (Durham / Vertex) • Flavor tagging by LCFIVertex • obtain b-likeness value (0 to 1) for each jet • Check qqHH vs bbcssc acceptance with varying b-likeness threshold • Both 3rd and 4th jets and sum b-likeness over all jets are examined Using ZHH -> qqHH & tt -> bbcssc (same as 2.)

  18. 3. ZHH vs. top-pair b-tagging performance Durham JC Vertex JC worse better Cut on 4th jet Cut on 3rd jet Cut on sum b-likeness • Improvements seen in all criteria • Improvements are particularly significant for high-purity region (signal eff. < 60%)

  19. 4. Effect on b-tag cut in ZHH analysis Practical impact on the physics study • Jet clustering & flavor tagging • Determine cut value of b-likenessat signal efficiency = 50% • High purity is neededto suppress enormous tt background • Count the remaining number of eventsand scale to 1 ab-1 luminosity Using ZHH -> qqHH & tt -> bbcssc (same as 2. & 3.)

  20. 4. Effect on b-tag cut in ZHH analysis Numbers in parentheses are at 1 ab-1 Vertex jet clustering Durham jet clustering 30% improvement!

  21. Summary & Next steps Vertex clustering can improve jet clustering performance for counting b-jets Simple analysis with ZHH shows 30% improvement in reducing tt background Next steps Flavor tagging optimization for multi-jet Realistic ZHH analysis with new algorithms

  22. 昨日の主張と議論 • 注力する物理、優先順位と力の入れ方 • Higgs (ZH, ZHH, ttH) • BSM? • 1TeVor 500 GeV or lower • DBDbenchmarkは1 TeVばかり • 物理解析どうやって検証する？ • Minimum detectorのoptimizationどうする？ • Minimumな物理成果とは？

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