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Hidden U (1) at the Electroweak Scale B. N. Grossmann Oklahoma - PowerPoint PPT Presentation

Hidden U (1) at the Electroweak Scale B. N. Grossmann Oklahoma State University 2010 May 11 PHENO 2010 in collaboration with R. McElrath, S. Nandi, and S. K. Rai Outline Introduction Model Phenomenology Summary 2 / 18 Introduction Why


  1. Hidden U (1) at the Electroweak Scale B. N. Grossmann Oklahoma State University 2010 May 11 PHENO 2010 in collaboration with R. McElrath, S. Nandi, and S. K. Rai

  2. Outline Introduction Model Phenomenology Summary 2 / 18

  3. Introduction Why consider an extra U (1)? Many models have an extra U (1) Left-Right Leptophobic U (1) SO (10) GUT Hadrophobic U (1) 3 rd generation U (1) Supersting E 6 Topflavor ...etc... Common feature: SM fermions couple to the U (1) LHC can explore an extra U (1) beyond the EW scale 3 / 18

  4. Introduction What are some features of this extra U (1)? SM particles don’t couple to this symmetry (Unlike most extra U (1) symmetries) Broken at the EW scale Exotic quarks and singlet Higgs Messengers between SM sector and extra U (1) sector × U (1) ′ SU (3) C × SU (2) L × U (1) Y � �� � Standard Model Gauge Group 4 / 18

  5. Model Particle content Fermions SM fermions: New Weak singlet quarks: q i L , l i L , u i R , d i R , e i D = D L + D R R Scalar bosons SM EW doublet Higgs: H New EW singlet Higgs: S Gauge bosons SM gluons and EW bosons: New gauge boson: Z ′ G µ , W µ , B µ µ 5 / 18

  6. Model Quantum numbers Quantum numbers U (1) ′ SU (3) C SU (2) L U (1) Y − 1 b R 3 1 0 3 − 1 D L , D R 3 1 − 1 3 S 1 1 0 1 SM particles are neutral under U (1) ′ 6 / 18

  7. Model Higgs sector Higgs potential V ( H, S ) = − µ 2 H ( H † H ) − µ 2 S ( S † S ) + λ H ( H † H ) 2 + λ HS ( H † H )( S † S ) + λ S ( S † S ) 2 Vacuum expectation values and mass matrix � � 1 1 0 2( v S + S 0 ) √ √ S → H → v H + H 0 2 � 2 λ H v 2 � λ HS v H v S M 2 = H 2 λ S v 2 λ HS v H v S S The mass eigenstates are φ H and φ S with a mixing angle β 7 / 18

  8. Model Yukawa interactions, mass terms, and mixing Mixing between the SM and the U (1) ′ sector occurs through the Yukawa and mass terms Not relevant for D mixing � �� � j L ( Yuk H ) = y d jk q j L d k y u jk q j L u k R � H + y e L e k R H + jk l R H + h.c. L ( Yuk S ) = y Dd k D L d k R S + h.c. L ( mass ) = M D D L D R + h.c. L ( Yuk H ) is the SM Yukawa couplings L ( Yuk S ) only has down-type couplings L ( mass ) allowed D L and D R have same quantum numbers 8 / 18

  9. Model Yukawa interactions, mass terms, and mixing Let y Dd , y Ds ≈ 0 Mass matrix in gauge basis of ( b, D ) is not symmetric √ � y b v H / � 2 0 √ M = y Db v S / 2 M D Diagonalize with a bi-unitary transformation: R L MR † R � cos θ i � sin θ i R i = i = L, R − sin θ i cos θ i ( b L , D L ) mixing is different from ( b R , D R ) 9 / 18

  10. Model Fermion-gauge interactions Kinetic Lagrangian terms contain a new interaction for the D L ∋ Diγ µ D µ D The covariant derivative (ignoring color interactions) D µ = ∂ µ − ig ′ Y B µ − ig ′′ Y q Z ′ µ Mixings of b and D creates new effective gauge couplings 10 / 18

  11. Model Effective couplings from mixing Effective couplings with gauge bosons: ψ i ∈ { D, b, t } and V µ ∈ { Z µ , Z ′ µ , W ± µ } ψ i Kγ µ ( c V − c A γ 5 ) V µ ψ j Effective couplings with Higgs bosons: ψ i ∈ { D, b } and φ ∈ { φ H , φ S } ψ i K ( c S − c P γ 5 ) φψ j K , c V , c A , c S , c P are in terms of mixing angles, Yukawa couplings, and gauge couplings 11 / 18

  12. Phenomenology Production of D 1000 Pair production: pp → DD E CM � 7 TeV Large production cross section 100 E CM � 14 TeV 10 Production cross sections (pb) Σ � pb � 1 √ s m D 0.1 (GeV) 7 TeV 14 TeV 300 4 . 265 34 . 368 0.01 500 0 . 194 2 . 270 0.001 200 400 600 800 1000 m D � GeV � 12 / 18

  13. Phenomenology Decays of D Two parameter points chosen for examining decays Parameters Point I Point II ( λ H , λ S , λ HS ) (0 . 11 , 0 . 16 , 0 . 005) (0 . 2 , 0 . 05 , 0 . 1) v S 1000 GeV 800 GeV y Db 0 . 15 0 . 05 m φ H 115 GeV 127 GeV m φ S 566 GeV 268 GeV m Z ′ 1000 GeV 800 GeV sin β 0 . 004 0 . 380 13 / 18

  14. Phenomenology Branching ratios of D Point I Point II 1.00 1.00 0.50 0.50 0.20 0.20 Branching Ratio Branching Ratio 0.10 0.10 D � tW D � tW D � bZ D � bZ 0.05 0.05 D � b Φ H D � b Φ H 0.02 0.02 D � b Φ S D � b Φ S 100 200 300 400 500 600 700 800 100 200 300 400 500 600 700 800 m D � GeV � m D � GeV � 14 / 18

  15. Phenomenology Signals and detection Interesting final states   6 b + X     4 b + 2 l + X DD →  2 b + 2 l + X     nb + l + X ( n ≥ 3) Kinematic selection cuts p b | η b | < 3 . 0 T > 20 GeV ∆ R bb > 0 . 7 p l | η l | < 2 . 5 T > 20 GeV ∆ R lb > 0 . 4 ∆ R ll > 0 . 2 15 / 18

  16. Phenomenology Signals and detection Final state cross sections (fb) SM m D = 300 GeV m D = 500 GeV background I II I II √ s = 14 TeV 6 b + X ∼ 70 1394 5521 531 115 4 b + 2 l + X < 10 384 184 20 22 √ s = 7 TeV 6 b + X < 10 182 719 5 115 4 b + 2 l + X < 1 51 24 1 . 8 2 . 1 Some final states have large signal, small SM background 6 b + X really stands out 16 / 18

  17. Phenomenology What about Z − Z ′ mixing? Kinetic mixing assumed to be zero θ -mixing will occur at the one-loop level D Z Z � g Z g Z � D θ Z − Z ′ < 10 − 3 LEP bound m Z ′ > 1 TeV does not apply 17 / 18

  18. Summary Extra gauge symmetry: U (1) ′ Exotic quarks D L , D R and Higgs singlet S Charged under U (1) ′ Communicate U (1 ′ ) to the SM sector SM particles neutral under U (1) ′ Large production of DD at LHC Decay signals above the SM background 6 b + X stands out 18 / 18

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