Signatures of alternative models beyond the Standard Model 이강영 (건국대학교) @ 연세대학교 2009. 10. 15.
Contents • Introduction • Z’ • W’ • H+ • H++ • t’, b’ • Q, L • Dark matter • Summary
Introduction • LHC will explore for the first time a relevant energy range, well above the Fermi scale. • LHC is the Energy frontier machine best to search for the new (heavy) particles. • We concentrate on the new particles discovery. • The detailed phenomenology depends upon the model.
LHC Thevoyage to the ultimate world • 2008년 9월 10일 공식적으로 가동. • 올 11월부터 정식가동. • 둘레 27km에 이르는 • 지구상 최대의 실험장치. 다음과 같은 세계를 탐구하는 양성자-양성자 충돌장치. ECM = 14 TeV (max) ~ v = 0.999999991c (c=빛의속도) ~ d = 0.000000000000000000014 m
Underlying Physics • Z’ : Extra neutral gauge boson • Exists when there is extra gauge symmetries. • U(1) extensions of the SM • LR model • Other gauge extended models • Other species : excited states of Z • Little Higgs model • Extra dimensional models
Examples of U(1) extensions E6 models breaking chain χ model : β=0 ψ model : β=π/2 η model : β=arctan(-√5/3)
LR model (WL3, WR3, B) basis Diagonalized to give eigenvalues
and eigenstates where Note that Unknown model parameters are MZ’ Z-Z’ mixing angle
Z’ couplings to quarks and leptons Lagrangian for a Z’ inE6 model The Z-Z’ mixing angle is given by
Phenomenology Z’ Drell-Yan process
Experimental limits PDG 2008
Identification of Z’ usingt and b e.g. S. Godfrey and T. A. W. Martin, Phys. Rev. Lett., 101, 151803 (2008) Kq depends on QCD and EW corrections.
Measuring Z’ couplings at the LHC e.g. F. Petriello and S. Quackenbush, Phys. Rev. D 77, 115004 (2008). • Z’ mass and totalwidth • Cross section to • Forward-backward asymmetry • Rapidity ratio • Off-peak asymmetry Basic Observables
Forward-backward asymmetry where y1 is introduced to exclude low Z’ rapidity events. • Rapidity ratio
Acceptance Cuts • Detector resolution effects are ignored. • Reconstruction efficiency of Z’ production is near 90% from CMS simulation. • CTEQ 6.5 NLO PDF used. • Integrated luminosity 100fb-1 unless stated otherwise. • Factorization and renormalization scale : MZ’
Calculation Differential cross section Parity symmetric couplings Parity violating couplings
Rewrite the differential cross section Absorbing We have
e.g. If we let Solving the Master equation to have
If MZ’ =1.5 TeV, 100 fb-1 luminosity and y1=0.8 can discriminate the example models with 90% C.L. and 1 ab-1 luminosity (SLHC) will provide precise determination. • If MZ’ =3 TeV, 100 fb-1 luminosity and y1=0.4 can discriminate some models. • For MZ’ =3 TeV, 1 ab-1 luminosity (SLHC) will provide reasonable determination.
Exotic Z’ • Generation-dependent couplings • Leptophobic • Hadrophobic • Flavour-violating • And more…
Underlying Physics • W’ : Extra charged gauge boson • Exists when there are extra gauge symmetries more than U(1). • LR model • Other gauge extended models • Other species : excited states of W • Little Higgs model • Extra dimensional models
LR model (e.g.) (WL+, WR+) basis Diagonalized to give where
Search for W’ W’ → l-ν • High energy single lepton final states • Single top production W’ → t b
Transverse mass • Edges of transverse mass distribution are crucially related to the mass of W’. D0 collaboration, PRL 100, 031804 (2008)
Experimental limits PDG 2008
D0 observations D0 collaboration, PRL 100, 031804 (2008)
Feasibility of W’ at the CMS e.g. C. Hof, Acta. Phys. Pol. B 38, 443 (2007) Reference models : same couplings as the SM
Exotic W’ • Left-right asymmetric : coupling constants and CKM • Leptophobic • Hadrophobic • Flavour-dependent SU(2) • Exotic gauge self-couplings : W’-W-Z, W’-W’-Z … • And more…
Underlying Physics • H+: Charged scalar • Exists when there is extra Higgs sector more than SM singlet. • 2HD model • MSSM and more extensions (NMSSM etc.) • LR model • Other GUT-based model