Chuan-Ren Chen IPMU, Univ. of Tokyo 2 nd Workshop of LHC Topic 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

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

e.g. Carena, Daleo, Dobrescu, Tait, hep-ph/ (Z’); Rizzo, (W’); Petriello and Quackenbush, (Z’); Diener, Godfrey, Martin, (Z’); Gopalakrishna, Han, Lewis, Si, Zhou, (W’); Godbole, Rao, Rindani, Singh, (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’) (GeV) CDF, dijet search, e.g.

Z’ → e + e - (CMS NOTE ) Tevaton limits on W’/Z’ are stronger

Top quark  The heaviest particle  Bare quark ~173 GeV, decay quickly before hadronization (~ 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

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/ if < 0

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/ HOWEVER, correct paring is crucial!

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

MT2 method Cho, Choi, Kim, Park, ; CDF, Z’ missing visible

Reconstructions choose the pair whose MT2 is smller

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

Probing Heavy Resonances

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

background collider signature Berger, Cao, CRC, Shaughnessy and Zhang,

cuts mis-tagging b-tagging signal >> background

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

W’ and Z’ Z’

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

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

HTHT M trans (GeV) Cuts:

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

cos distributions after reconstructions, all cuts

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

cos distributions after reconstructions, all cuts

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)

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.****

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

Top polarization