Bin Yan Peking University

Transcription

1 Determining V tb at e + e Colliders Bin Yan Peking University Aug. 08, TeV Physics Workshop In collaboration with Qing-Hong Cao, arxiv:

2 V tb measurements V tb 1 R V tb 2 Vtq 2 q=d,s,b = V tb 2 1.Three generation of quarks 2.Unitarity of CKM matrix V tq V tb = ± PDG2015 gv tb 2 Universality of the weak gauge coupling g V tb = ± 0.038(exp) ± 0.016(theo) V. Khachatryan et al. JHEP 1406,090 (2014) 2

3 V tb & New Physics New Physics models Fourth-generation of quarks Three generation of quarks un-unified and top-flavor models.. Universality of the weak gauge coupling g R =? V tb 2 q=d,s,b V tq 2 =? 1 V tb 2 =? σ t g W 2 V tb How to determine? 3

4 V tb & New Physics The deviation of V tb New heavy quark (SU(2) quantum number) Vector-like quark Determining V tb The heavy quark decouple limit? Higgs Physics Modify the H-g-g effective coupling 4

5 How to determine V tb? 5

6 V tb & top gauge couplings t b L W + Wt L b L Z V tb V tb Zb L b L Zt L t L SM g ZbL b L g ZbL b L LEP-II Correlation Wt L b L coupling Zt L t L coupling V tb 6

7 Top gauge couplings & EFT Z t V W + b tb L Wt L b L V tb Zt L t L How can we measure top quark gauge couplings with a model-independent method? Effective field theory: 4 L = L SM + W. Buchmuller and D. Wyler, Nucl. Phys. B268, 621(1986) i C i Λ 2 O i 7

8 EFT (Tree-level dim-6 operators) (1) O φq = i φ + D μ φ qγ μ (3) q O φq = i φ + τ I D μ φ qγ μ τ I q O φt = i φ + D μ φ trγ μ t R O φb = i φ + D μ φ b R γ μ b R O φφ = i φ + D μ φ t Rγ μ b R q = t b L φ = iτ 2 φ E. L. Berger, Qing-Hong Cao, Ian Low, Phys.Rev.D80:074020(2009) 8

9 O Wtb = c (3) φq v 2 Λ 2 Effective Wtb, Ztt and Zbb g 2 W μ + tlγ μ b L + c φφv 2 2Λ 2 g couplings c φφv 2 2 W μ + trγ μ b R + h. c. 2Λ O Ztt = O Zbb = c (3) (1) φq cφq Λ 2 v 2 c (3) (1) φq + cφq Λ 2 g Z 2c μ tlγ μ t L c φtv 2 W 2Λ 2 v 2 g 2c W Z μ trγ μ t R g Z 2c μ b L γ μ b L c φbv 2 g W 2Λ 2 Z 2c μ b R γ μ b R W Q.-H. Cao, B. Yan, J.-H. Yu, and C. Zhang, arxiv: LEP-II (3) (1) c φq + cφq 0

10 Effective Wtb and Ztt couplings The deviations of the Wtb and Ztt couplings: g NP Wtb = ΔV tb + F L g2 W μ + tlγ μ b L + h. c. g NP Ztt = 2F L g Z 2c μ tlγ μ g t L + F R Z W 2c μ trγ μ t R W The coefficients of the left-handed neutral and charged currents are related as gnp Ztt L = 2F L = 2 gnp Wtb L ΔV tb F L = c φq 3 v 2 Λ 2 Ztt Wtb 10

11 How can we measure top quark gauge couplings? 11

12 V LHC 0.06 ΔV tb + F L 95% C.L. 8 TeV LHC Q.-H. Cao, B. Yan, J.-H. Yu, C. Zhang, arxiv: F L 95 % C.L. 13 TeV LHC with 300 fb 1 R. Rontsch and M. Schulze, JHEP 1407 (2014) 091 gnp Ztt L = 2F L = 2 gnp Wtb L ΔV tb 12

13 V unpolarized e + e collider A FB σ tt Γ t g Wtb gnp Ztt L = 2F L = 2 gnp Wtb L ΔV tb 13

14 Top quark width Top quark width in SM at NNLO in QCD and NLO EW: Γ t 0 Γ t NNLO = Γ t LO Γ t LO = G Fm t 3 8 2π V tb 2 Br t Wb 1 m W 2 m t m W 2 m t 2 J. Gao, C. S. Li and H. X. Zhu, PRL. 119, (2013) Deviations of g, m t and V tb from the SM values modify the top quark width: ΔΓ t Γ t 0 = 3 Δm t m t + 2ΔV tb + 2F L ΔX = X X 0 14

15 Top quark mass and ILC/TLEP ΔΓ t 0 Γ = 3 Δm t t m t 1% 0.006% + 2ΔV tb + 2F L ΔV tb ΔΓ t 2Γ t 0 F L Bicer, M. et al. JHEP 1401(2014) 164 Parameter Top quark mass Top quark width TLEP 10 MeV 11 MeV ILC 31 MeV 34 MeV 15

16 Top quark pair unpolarized e + e collider 16

17 Top quark pair unpolarized e + e collider σ tt = σ 0 tt 1+a L F L + a R F 0 R A FB = A FB 1+b L F L + b R F R F L 0.97 Δσ tt σ tt 0 a R ΔA FB b 0 F R 1.21 Δσ tt R A FB σ tt 0 a L ΔA FB b 0 L A FB 17

18 V unpolarized e + e collider ΔV tb ΔΓ t 2Γ t 0 F L Cross section would be NP 18

19 Error analysis Systematic error of σ tt : H. Baer, T. Barklow, et al. (2013), M. Amjad, M. Boronat, et al. (2013), δσ tt σ tt 0 sys. = 0.01 δγ t Γ t 0 = 0.01 δv tb = 1 4 δγ t Γ t δf L 2 19

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21 1.Three generation of quarks 2.Unitarity of CKM matrix Universality of the weak gauge coupling g Y Model independent method to determine V tb V tb? 1 N New heavy quark (SU(2) quantum number) Higgs Physics Vector-like quark 21

22 Wt L b L V tb LEP-II Zt L t e + e collider Model-independent method to measure V tb ΔV tb ΔΓ t 2Γ t 0 F L

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24 Back up 24

25 R b and Ab FB O Zbb = c (3) (1) φq + cφq Λ 2 v 2 g Z 2c μ b L γ μ b L c φbv 2 g W 2Λ 2 Z 2c μ b R γ μ b R W R b = σ e+ e bb q σ e + e qq L g zbb A b FB LSM ±0.992g zbb = σ F b σ B b σ F b + σ B b Z-peak R g zbb RSM ±1.26g zbb L, R (3) (1) c φq + cφq 0 D. Choudhury, T. M. P. Tait and C. E. M. Wagner, PRD 65(2002)

26 R b and Ab FB O Zbb = c (3) (1) φq + cφq Λ 2 v 2 g Z 2c μ b L γ μ b L c φbv 2 g W 2Λ 2 Z 2c μ b R γ μ b R W R b = σ e+ e bb σ e + e qq A b FB = σ F b σ B b σ F b + σ B b R b obs = ± b A FB obs = ± R b SM = b A FB SM = D. Choudhury, T. M. P. Tait and C. E. M. Wagner, PRD 65(2002) (3) (1) c φq + cφq 0 26

27 F L and F e + e collider F L 0.97 Δσ tt σ tt 0 a R ΔA FB b 0 F R 1.21 Δσ tt R A FB σ tt 0 a L ΔA FB b 0 L A FB 27

28 F L and F e + e collider 28

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30 A. 4 th generation of quarks V 4 4 = R 34 θ 34 R 24 θ 24 R 14 θ 14 V 3 3 V tb 0 1 V 0 0 cb, V ub V tb = V tb 0 + ΔV tb cosθ 34 V tb 0 cosθ 34 S. Bose and E. A. Paschos, Nucl. Phys. B169,384 (1980) 21

31 g NP Ztt = 2F L B. Ztt and New Physics g Z 2c μ tlγ μ g t L + F R Z W 2c μ trγ μ t R W Extra dimensional models Composite models s = 500 GeV Lum = 500fb 1 Richard, Francois, arxiv:

32 B. Ztt and New Physics Δσ tt σ tt 0 = a LF L + a R F R ΔA FB 0 = b L F L + b R F R A FB Extra dimensional models Composite models s = 500 GeV Lum = 500fb 1 Richard, Francois, arxiv:

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34 Composite models 34

35 A. top quark compositeness Partial compositeness mechanism Elementary sector Composite sector A. Pomarol and J. Serra arxiv: Mass-mixing terms Low-energy effective lagrangian for a composite top quark (Left-handed): (F) i c L 1 f 2 H+ D μ Hq L γ μ q L i c L 3 2f 2 H+ σ i D μ Hq L γ μ σ i q L L δg Zbb L = c L 3 + c 1 L ξ s W ξ = v2, f O TeV f2 L = c L 3 c 1 L ξ s W g Zbb L δg Ztt g Ztt 35

36 B.Littlest Higgs Model (E) SU(5) Gauge the subgroup [SU(2) U(1)] ) [SU(2) U(1)] Global symmetry breaking Σ New Gauge boson Σ Gauge symmetry breaking SO(5) ±1 2 3 ±1 [SU(2) U(1)] SM Nambu-Goldstone bosons(ngbs) arise when a continuous global symmetry spontaneously broken The number of NGBs: N 2 N N = 14 Higgs as a pseudo- Goldstone New Complex triplet Scalar [U(1)] EM Electroweak symmetry breaking, Coleman-Weinberg potential N.Arkani-Hamed et al. JHEP 0207:034,