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Little Higgs with T parity at ILC

Little Higgs with T parity at ILC. General meeting 2010/3/13 Tohoku Univ. Eriko Kato. Out line. Introduction of Little Higgs model(LHT) Motivation Selection criteria Mass extraction result Problem with result Summary. little hierarchy problem. : Higgs mass

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Little Higgs with T parity at ILC

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  1. Little Higgs with T parity at ILC General meeting 2010/3/13 Tohoku Univ. Eriko Kato

  2. Out line • Introduction of Little Higgs model(LHT) • Motivation • Selection criteria • Mass extraction result • Problem with result • Summary

  3. little hierarchy problem • : Higgs mass • :Bare Higgs mass • :Higgs mass quadrically divergent corrections • Λ:Cutoff scale • Fine tuning Λ<1 TeV • Electroweak precision measurements Λ>10TeV • Conflict between these two scales

  4. Little Higgs with T parity model Solution to little hierarchy problem • Higgs boson is regarded as pseudo Nambu-Goldstone boson of a symmetry at some higher scale. • T-parity predicts AH as a dark matter candidate

  5. Motivation Little Higgs with T-parity(LHT) predicts new heavy gauge bosons :AH,ZH,WH • By measurements of heavy gauge bosons we can find f:vacuum expectation value • Analyze e+e-→ ZH ZH and see how precise ILC can measure f at 1TeV

  6. Simulation environment Signal • e+e- -> ZH ZH (99.52fb) Background • e+e- ->WW (3069fb) • e+e- ->tt (192.9fb) • e+e- ->WWZ (5.922fb) • e+e- -> ννWW (6.682fb) Set up √s = 1 TeV Luminosity=500 fb-1 No beam polarization Higgs mass=134GeV

  7. Higgs event reconstruction • Used χ2 to assign each jet to reconstruct a higgs with a mass close to 134GeV • select jet pair with minimum χ2 as the true solution There are 4C2 /2 =3 ways to reconstruct the jets into higgs

  8. Higgs mass distribution • Success in Higgs reconstruction • Signal is buried in background • Selection cut was studied Higgs mass distribution Signal + Background Signal Buried signal GeV GeV

  9. χ2 distribution Calculated χ2 • χ2 shows mass difference from higgs. • We can cut WW background by selecting events χ2 <80 χ2 distribution Background Signal

  10. # of b-tagged jet distribution # of b-tagged jets • Br(H→bb) =42.35% Br(H→WW)=39.57% We can cut WW background by selecting #b-tagged jets>0 # of b-tagged jets Signal Background

  11. Acoplanarity distribution Acoplanarity cut • We can cut tt background by selecting acop>25° Acoplanarity Background Background Signal degree degree degree

  12. Significance 48.60 108.60 results

  13. Performing mass extraction ~ Determining ZH AH mass ~

  14. Determining ZH AHmasses from edge of Higgs energy distribution Higgs energy distribution Subtract background and fit signal Fit function SG+BG Higgs energy distribution SG assuming SM information GeV GeV Rising edge Falling edge Height correction

  15. SG&BG error result We determined ZH AH mass by fitting Higgs energy distribution Mass after fluctuating signal with gauss function. ZH mass distribution AH mass distribution 369GeV 83 GeV 79 GeV 368GeV 90 GeV (GeV) (GeV) AHmass = 87.53± 3.77GeV true value:81.9GeV ZHmass = 365.4 ±3.87GeV true value:369GeV Mass distribution doesn’t include true value!

  16. Higgs branching ratio Standard model information Pythia information When higgs mass =134GeV Br(h→bb) =42.35% Br(h→WW)=39.57% Br(h→ZZ) =5.50% Br(h→ττ)= 5.21% etc 134GeV

  17. Problem with analyzing H->WW H->WW H->bb Missing effect from Lepton Higgs energy distribution H→WW missing component Might be causing a shift in Emin edge Higgs mass distribution Edge starts at 60 GeV Edge starts over 80GeV (GeV) (GeV) (GeV) (GeV)

  18. Relation between #of b-tag jets and rising edge • see the relation to rising edge and #of b-tag jets • All events are under the condition χ2<80 • Fitting improved when selected #of b-tag jets increased. (when H->WW events were excluded) #b-tag jets≧1 Higgs Energy distribution #b-tag jets≧2 #b-tag jets≧3 (GeV) (GeV) (GeV)

  19. New selection criteria • H→WW missing component causes a shift in Emin edge • Possible solution: cut H->WW events within the signal by b-tag cuts • Chose a cut that minimizes H->WW events. • Χ2<80 #of b-tagged jets≧3 acop>25 # of b-tag jets ZHZH(H->WW) ZHZH(H->bb) ZHZH (H-> non of the above ->bW etc)

  20. Results(Maximizing H->bb) Higgs Energy distribution True value: AH mass 81.9GeV ZH mass 369GeV • Next: investigate what causes mZH peak around 350GeV ZH mass distribution AH mass distribution 352 GeV 86 GeV 372GeV (GeV) (GeV)

  21. fitting causing mZH=352GeV peak Higgs Energy distribution &fitting when mZH~352GeV • fitting causing mZH=352GeV peak • Possible cause : tt background contribution dominant at EHiggs≧400GeV ∴fluctuation by gauss becomes large. Edge 415 GeV SG SG+BG

  22. summary • LHT is as a beyond standard model that solves little hierarchy problem . • Our motive is to investigate how precise ILC can measure LHT parameters . • When chosen selection criteria that maximizes significance, mass distribution didn’t include true value. • H->WW missing events might be causing this problem. However when chosen new selection criteria to minimize H->WW fitting still failed.

  23. plan • Continue studying on evaluating background contamination. • Continue on determining the cause of failed fitting and find a solution.

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