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 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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
Recommend
More recommend
