1. 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 Top Quarks as A Probe of Heavy Resonances at the LHC

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

3. 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 SU(2) L XU(1) Y G Heavy s-channel Resonances generic in models beyond the SM Extra SU(2) Extra U(1) W’ and Z’ Simple topology and large discovery potential q q’ f f’ W’/Z’ Z’ can serve as model discriminators (W’/Z’) 400 600 800 1000 1200 1400 (GeV) CDF, dijet search, 0812.4036 e.g.

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

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

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

7. 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 MT2 top quark reconstruction in (2) Z’ Sonnenshein, hep-ph/0603011 HOWEVER, correct paring is crucial!

8. MT2 method C. G. Lester and D. J. Summers, hep-ph/9906349 knowing the correct m x, m T2 is correct mass mother particle

9. MT2 method Cho, Choi, Kim, Park, 0804.2185; CDF, 0911.2956 Z’ missing visible 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 charged lepton from top (anti-top) decay prefers to move along (against) the direction of top (anti-top) polarization (longitudinal W) (transverse W)

12. Probing Heavy Resonances

13. Color sextet same-sign right-handed top-quark pair 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

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

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

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

17. W’ and Z’ Z’

18. W’ and Z’ Z’ here, for simplicity, only couple to quarks in M t  0 limit, Br(W’  tb) = 1/3, Br(Z’  t tbar) = 1/6 narrow width approximation still holds

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

20. 0 200 400 600 800 1000 1200 1400 1600 1800 2000 HTHT M trans (GeV) Cuts:

21. g v’ = 0.4 after cuts 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. Gopalakrishna, Han, Lewis, Si, Zhou, 1008.3508 W’ W’ signal: ~ 0.1 pb >> background (~ 10 -3 pb) in analysis, only need to consider signal!!

24. cos distributions after reconstructions, all cuts

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

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

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) -> t tbar can be discovered with > 5σ statistical significance, W’ -> t b >> 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 x L

28. Top polarization