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Chuan- Ren Chen IPMU, Univ. of Tokyo

Top Quarks as A Probe of Heavy Resonances at the LHC. Chuan- Ren Chen IPMU, Univ. of Tokyo. 2 nd Workshop of LHC Topic Program @ NCTS, Dec. 8~10, 2010. In collaboration with Ed. Berger, Q-H Cao, G. Shaughnessy , H. Zhang. Outline. why s -channel heavy resonances why top quark

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Chuan- Ren Chen IPMU, Univ. of Tokyo

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  1. Top Quarks as A Probe of Heavy Resonances at the LHC Chuan-Ren Chen IPMU, Univ. of Tokyo 2nd Workshop of LHC Topic Program @ NCTS, Dec. 8~10, 2010 In collaboration with Ed. Berger, Q-H Cao, G. Shaughnessy, H. Zhang

  2. Outline • why s-channel heavy resonances • why top quark • color sextet scalar, W’, Z’ • Conclusion

  3. Heavy s-channel Resonances generic in models beyond the SM e.g. Extra SU(2) W’ and Z’ Extra U(1) Z’ CDF, dijet search, 0812.4036 G Simple topology and large discovery potential SU(2)LXU(1)Y q f W’/Z’ can serve as model discriminators (W’/Z’) q’ f’ e.g. Carena, Daleo, Dobrescu, Tait, hep-ph/0408098 (Z’); Rizzo, 0704.0235 (W’); Petriello and Quackenbush, 0801.4389 (Z’); Diener, Godfrey, Martin, 1006.2845 (Z’); Gopalakrishna, Han, Lewis, Si, Zhou, 1008.3508 (W’); Godbole, Rao, Rindani, Singh, 1010.1458(Z’)  talk this afternoon 400 600 800 1000 1200 1400 (GeV)

  4. 1008.2461 1010.0203 Z’ → e+e- (CMS NOTE 2006-083) Tevaton limits on W’/Z’ are stronger

  5. Top quark • The heaviest particle ~173 GeV, (PDG 2010) • ~100% decay into W, b • Bare quark decay quickly before hadronization (~10-25 sec) V-A coupling (PDG 2010) Spin information is kept • main production at hadron colliders – QCD (top pair,~800 pb), • EW(single-top, ~300 pb)

  6. top quark reconstruction in (1) Barger, Han, Walker, hep-ph/0612016 Semileptonic decay mode (1) Two-fold solution Z’ if < 0 (2) break the 2-fold ambiguity by selection break the 2-fold ambiguity by selection

  7. top quark reconstruction in (2) purely leptonic decay • two missing neutrinos • two neutrinos and two charged leptons are from two Ws • two neutrinos, two charged leptons and two (b) jets are from • two quarks • two top quarks are from a heavy resonance • using on-shell conditions, momentum of 2 neutrinos can be solved Z’ Sonnenshein, hep-ph/0603011 MT2 HOWEVER, correct paring is crucial!

  8. MT2 method C. G. Lester and D. J. Summers, hep-ph/9906349 knowing the correct mx, mT2 is correct mass mother particle

  9. MT2 method Cho, Choi, Kim, Park, 0804.2185; CDF, 0911.2956 visible missing Z’ 10 20 30 40 50 60 70 80 90 100 0 50 100 150 200 250 300 350 400 450 500

  10. Reconstructions choose the pair whose MT2 is smller

  11. Top polarization Tait, Yuan, hep-ph/0007298 (transverse W) (longitudinal W) (longitudinal W) (transverse W) charged lepton from top (anti-top) decay prefers to move along (against) the direction of top (anti-top) polarization

  12. Probing Heavy Resonances

  13. Color sextet Mohapatra, Okada, Yu, 0709.1486; CRC, Klemm, Vikram, Wang, 0811.2105; Han, Lewis, McElmurry, 0909.2666; Arnold, Pospelov, Trott, Wise, 0911.2225 Gogoladze, Mimura, Okada, Shafi, 1001.5260 same-sign right-handed top-quark pair

  14. collider signature Berger, Cao, CRC, Shaughnessy and Zhang, 1005.2622 background

  15. cuts b-tagging mis-tagging signal >> background

  16. distributions after all cuts MΦ = 600 GeV clearly, it is right-handed!

  17. W’ and Z’ Z’ Z’

  18. W’ and Z’ here, for simplicity, only couple to quarks Z’ Z’ in Mt 0 limit, Br(W’ tb) = 1/3, Br(Z’ ttbar) = 1/6 narrow width approximation still holds

  19. W’ and Z’ cross section is not small! main background: W’ single-top, Wjj Z’ top pair

  20. HT Mtrans 0 200 400 600 800 1000 1200 1400 1600 1800 2000 0 200 400 600 800 1000 1200 1400 1600 1800 2000 (GeV) (GeV) Cuts:

  21. after cuts gv’ = 0.4 discovery potential: ~9σ (10 fb-1) for 1 TeV mass window ~3σ (10 fb-1) for 1.5 TeV mass window

  22. cos distributions after reconstructions, all cuts

  23. W’ Gopalakrishna, Han, Lewis, Si, Zhou, 1008.3508 W’ signal: ~ 0.1 pb >> background (~ 10-3pb) in analysis, only need to consider signal!!

  24. cos distributions after reconstructions, all cuts

  25. Can we extract the information of couplings?? fitting with left-handed and right-handed Z’ distributions (statistical only) true: 30 % 0 10 20 30 40 50 0 10 20 30 40 50 xL (%) xL (%) due to Th error

  26. Berger, Cao, CRC and Zhang, 1012.**** combine W’ and Z’ expectW’⊕Z’ in SSM, LH models in progress true: (70, 70) true: (30, 30) expectW’⊕Z’ in R-L symm. models

  27. Conclusion Heavy resonances produced in S-channel will be soon discovered/strongly constrained at LHC. top quark final state is complementary to dijet and and leptonic state searches. Z’ (1 TeV) -> ttbar can be discovered with > 5σ statistical significance, W’ -> tb >> background. top quark momentum can be reconstructed, spin information study through charged lepton can be done. W’/Z’ couplings to top quark serve as a model discriminator. (in progress) 5% th error, stat. in 10 fb-1 data -> both cause ±10% in xL

  28. Top polarization

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