Higgs couplings. beyond the Standard Model. Giacomo Cacciapaglia (IPN Lyon, France) IHEP Beijing

Transcription

1 Higgs couplings beyond the Standard Model Giacomo Cacciapaglia (IPN Lyon, France) In collaboration with: A.Deandrea, J.Llodra-Perez, A.Deandrea, G.Direu La Rochelle, J.B. Flament, IHEP Beijing

2 The Higgs has been discovered... h -> γγ Invariant mass of the 2 photons. Smooth background data! BR(h γγ) h -> ZZ* -> l+l- l+l- Invariant mass of the 4 leptons. Low background data! BR(h l + l l + l ) 10 4

3 The Higgs has been discovered... P-value = probability that the data is a statistical fluctuation of the Background. 4 σ evidence in γγ and ZZ 7 σ evidence combined Note that combination uses SM correlations between various channels!

4 The Higgs has been discovered......has it?

5 The Higgs has been discovered......has it? Data look SM-like in all channels, but there is still room for New Physics!

6 ATLAS and CMS fits SM SM The wrong sign region is preferred by di-photon enhancement! Note: it s not the sign of the Yukawa couplings!!!

7 ATLAS and CMS fits ATLAS seen enhancement in WW and ZZ CMS sees deficit in WW and ZZ

8 Higgs physics 101: the couplings The Higgs boson is a quantum fluctuation around the Vacuum solution of the Higgs field! v v + h(x µ ) v = 246 GeV m 2 W W µ W µ g2 (v + h(x)) 2 W µ W µ = g2 v W µ W µ + g2 v 2 hw µ W µ + g2 4 h2 W µ W µ The couplings are always proportional to the masses!!! g hw W =2 m2 W v The same is true for fermions: g hf f = m f v

9 Higgs physics 101: the couplings The Higgs couples to massless particles at loop level, g g hγγ e2 16π 2 v 2 ( A W (τ W )+3 ( ) 2 ( ) ) A f (τ t )+3 A f (τ b )+A f (τ τ ) , g g hgg g2 s 16π 2 v 2 (A f (τ t )+A f (τ b )+... ) A f (τ f ) τ f = 4m2 f m 2 h for m h m f (τ f 1) A f (τ f ) 4 3 for m h m f (τ f 1) Non-decoupling limit!

10 Higgs physics 101: the couplings The Higgs couples to massless particles at loop level, g g hγγ e2 16π 2 v 2 ( A W (τ W )+3 ( ) 2 ( ) ) A f (τ t )+3 A f (τ b )+A f (τ τ ) , g g hgg g2 s 16π 2 v 2 (A f (τ t )+A f (τ b )+... ) Result independent on top Yukawa coupling! A f (τ f ) τ f = 4m2 f m 2 h for m h m f (τ f 1) A f (τ f ) 4 3 for m h m f (τ f 1) Non-decoupling limit!

11 Higgs physics 101: production and decays

12 Higgs physics 101: production and decays Lucky mass region! Many decay modes can be potentially observed! h -> bb h -> WW h -> ZZ h -> ττ h -> γγ...

13 Where can New Physics appear? Loops: Loop induced couplings are very sensitive to new states that couple to the Higgs! t t

14 Where can New Physics appear? Loops: t t Model of fermionic top partner Generically, cancellations may lure: L Y ukawa = y Qφ H t R λ Qφ H T R M T L T R + h.c. M = ( yv 2 λv 2 0 M ) m t,m t Mass eigenstates: both depend on M and v. m_t = top mass

15 Where can New Physics appear? Loops: t t Model of fermionic top partner Generically, cancellations may lure: L Y ukawa = y Qφ H t R λ Qφ H T R M T L T R + h.c. M = ( yv 2 λv 2 0 M ) m t,m t v m t m t v + v m t m t v =1 g hgg v m t m t v A f (τ t )+ v m t m t v A f (τ t ) A f Cancellation between change in top loop and t loop.

16 Where can New Physics appear? Loops: M = t Generically, cancellations may lure: ( yv 2 L Y ukawa = y Qφ H t R λ Qφ H T R M T L T R + h.c. λv 2 0 M ) t Ignoring the mass, the Higgs couples to a single fermion! m t,m t Model of fermionic top partner v m t m t v v mt + m t v =1 L Y ukawa = Qφ H (yt R + λt R )= ỹ Qφ H t R g hgg v m t m t v A f (τ t )+ v m t m t v A f (τ t ) A f Cancellation between change in top loop and t loop.

17 Where can New Physics appear? An impostor: Dilatons couple to the breaking of scaling invariance: masses of SM particles! L dilaton = e ϕ/f m 2 W W µ W µ m2 W f ϕw µ W µ +... g ϕpp v f g hpp <g hpp Generic reduction of couplings to massive SM particles g ϕγγ, g ϕgg Loop induced couplings receive extra contributions from New Physics 3 parameters enough to characterise a dilaton!

18 Where can New Physics appear? An impostor: Dilatons couple to the breaking of scaling invariance: masses of SM particles! L dilaton = e ϕ/f m 2 W W µ W µ m2 W f Can a dilaton ϕw µ W µ +... g ϕpp v f g hpp <g hpp g ϕγγ, g ϕgg fit the Higgs data? Generic reduction of couplings to massive SM particles (Technicolour, Higgsless...) Loop induced couplings receive extra contributions from New Physics 3 parameters enough to characterise a dilaton!

19 Higgs couplings: general analysis Two possible strategies: Operator analysis: chiral lagrangian! Theoretically consistent. Model independent? Parameterisation: effective couplings! Experimentally driven. Truly model independent.

20 Chiral lagrangian Assumptions: SU(2)xU(1) gauge symmetry at high energies The Higgs h is a CP even scalar field Approximate custodial symmetry in the EWSB sector Power counting: Derivative -> 1/Λ Higgs -> g*/λ = 1/f probes New Physics scale probes Higgs couplings

21 Chiral lagrangian

22 Chiral lagrangian Forbidden by custodial symmetry Probe Higgs couplings Probe NPh scale

23 Chiral lagrangian Forbidden by custodial symmetry Probe Higgs couplings These operators modify the tree level couplings of the Higgs boson: g hv V g SM hv V = κ V =1 c H 2 g hf f g SM hf f = κ f =1 c H 2 c f g hhh g SM hhh =1 3 c H 2 + c 6

24 Chiral lagrangian These operators modify the couplings to gauge bosons: c i m 2 W 1 Λ 2 g2 16π π 2 f 2 Operators of this sort can only be generated at loop level in minimal models

25 Chiral lagrangian Theoretically consistent framework! Pros: Constraints on the parameters can be imposed. New state scan be easily added. Cons: Predictions can change in the presence of light new states! Theoretical considerations (bias) necessary to reduce number of parameters.

26 Effective couplings Cross sections and partial decay widths can be rescaled: σ Wh = κ 2 W σ SM Wh σ Zh = κ 2 Zσ SM Zh σ t th = κ 2 t σ SM t th σ V BF = κ 2 W σ SM WWh + κ 2 Zσ SM ZZh Γ b b = κ 2 bγ SM b b Γ WW = κ 2 W Γ SM WW Γ ZZ = κ 2 ZΓ SM ZZ Γ τ + τ = κ2 τ Γ SM τ + τ... Similarly, for the loop induced couplings: σ ggh = κ 2 gσ SM ggh Γ gg = κ 2 gγ SM gg Γ γγ = κ 2 γγ SM γγ Problem: correlations!

27 Effective couplings σ ggh = κ 2 gσ SM ggh Γ gg = κ 2 gγ SM gg Γ γγ = κ 2 γγ SM γγ These quantities depend on tree level couplings: Γ γγ = G F α 2 m 2 H 128 2π 3 Γ gg = G F αsm 2 2 H 16 2π 3 ( ) 2 κ W A W + C γ 2 t 3 κ t A t Cg t 2 κ t A t σ gg Γ gg A W = 8.32 A t =1.37 C γ t,c g t are QCD corrections. Problem: correlations!

28 Effective couplings Our proposal: parameterise the NPh loop contributions independently from the tree level couplings! Γ γγ = G F α 2 m 2 H 128 2π 3 Γ gg = G F αsm 2 2 H 16 2π 3 σ gg Γ gg κ W A W + C γ t 3 Cg t ( (κ t + κ gg ) A t +... ) 2 (κ t + κ γγ) A t All parameters are truly independent! Flexible and easy to compute!

29 Effective couplings Γ γγ = G F α 2 m 2 H 128 2π 3 Γ gg = G F αsm 2 2 H 16 2π 3 κ W A W + C γ t 3 Cg t ( (κ t + κ gg ) A t +... ) 2 (κ t + κ γγ) A t σ gg Γ gg Easily computable in models of New Physics: for instance, in the Simplest Little Higgs κ W =1 1 3 κ γγ = m2 t m t 16 m 2 W m 2 W, κ t = 1 + m2 t m 2 t 4 3 m 2 W m 2 W, m 2 W m 2 W, κ gg = m2 t m 2 t. Deviations scale like 1/M^2!!

30 Effective couplings Γ γγ = G F α 2 m 2 H 128 2π 3 Γ gg = G F αsm 2 2 H 16 2π 3 κ W A W + C γ t 3 Cg t ( (κ t + κ gg ) A t +... ) 2 (κ t + κ γγ) A t σ gg Γ gg Flexible: un-measurable parameters can be reabsorbed. For instance, the top couplings: κ γγ = κ γγ + κ t 1= m 2 W m 2 W, κ gg = κ gg + κ t 1= 4 3 m 2 W m 2 W. Parameters only depend on W mass!

31 Effective couplings Γ γγ = G F α 2 m 2 H 128 2π 3 Γ gg = G F αsm 2 2 H 16 2π 3 κ W A W + C γ t 3 Cg t ( (κ t + κ gg ) A t +... ) 2 (κ t + κ γγ) A t σ gg Γ gg In specific models, correlations can be easily explored: In models with a single new state in the loop: κ γγ = 3N c,np Q 2 NP κ gg C(r NP ) =1 For a top partner!

32 Our fits We define signal strengths in various channels: The signal strengths are functions of the fit parameters: Experimental data allows to define a chi square function:

33 Our fits We computed the parameters in various models of New Physics:

34 2 parameter fits CMS data B A kgg kγγ

35 2 parameter fits CMS data top partner B A kgg favoured by data kγγ

36 2 vs. 3 parameter fits 2 parameters 3 parameters k_w = 0.89 CMS data CMS data B A kgg kgg kγγ kγγ Very similar: at this stage, 2 parameters enough!

37 Dilaton fits Rescale all tree level couplings: 2 CMS data κ W = κ Z = κ f = κ d 1 We marginalise in k_d, allowed regions: kgg kγγ

38 Conclusions Measuring the couplings of the new resonance crucial to determine if it is the Higgs! Simple and flexible parameterisations of the couplings can help extract information and connect to models of New Physics! Complementary approach to a Chiral Lagrangian/operator expansion!