HIGGS BOSONS AT THE LHC

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1 IGGS BOSONS AT TE LC Dieter Zeppenfeld Universität Karlsruhe, Germany SUSY06 UC Irvine, June 12-17, 2006 Goals of iggs Physics SM Channels MSSM: /A and ± Coupling measurements QCD Corrections VV vertex structure Conclusions

2 Goals of iggs Physics iggs Search = search for dynamics of SU(2) U(1) breaking Discover the iggs boson Measure its couplings and probe mass generation for gauge bosons and fermions Fermion masses arise from Yukawa couplings via Φ (0, v+ 2 ) L Yukawa = Γ i j d = f Q L i Φd j R Γ i j d m f f f ( 1 + v d R i Φ Q j ) L +... = Γ i j d v + 2 d i L d j R +... Test SM prediction: f f iggs coupling strength = m f /v Observation of f f Yukawa coupling is no proof that v.e.v exists Dieter Zeppenfeld iggs Bosons at the LC 1

3 iggs coupling to gauge bosons Kinetic energy term of iggs doublet field: [ (D µ Φ) (D µ Φ) = 1 ( gv ) 2W 2 µ µ + µ+ W µ W, Z mass generation: m 2 W = ( gv 2 WW and ZZ couplings are generated ) 2, m 2 Z = ( g 2 +g 2 )v 2 4 ( g 2 + g 2) ] ( v 2 Z µ Z µ v ) 2 iggs couples propotional to mass: coupling strength = 2 mv 2 /v within SM Measurement of WW and ZZ couplings is essential for identification of as agent of symmetry breaking: Without a v.e.v. such a trilinear coupling is impossible at tree level Dieter Zeppenfeld iggs Bosons at the LC 2

4 Feynman rules f f i m f v W ν - ig m W g µν W µ + Z ν i g 1 cos θ W m Z g µν Z µ Verify tensor structure of VV couplings. Loop induced couplings lead to V µν V µν effective coupling and different tensor structure: g µν q 1 q 2 g µν q 1ν q 2µ Dieter Zeppenfeld iggs Bosons at the LC 3

5 The MSSM iggs sector The SM uses the conjugate field Φ c = iσ 2 Φ to generate down quark and lepton masses. In supersymmetric models this must be an independent field L Yukawa = Γ d Q L Φ 1 d R Γ e L L Φ 1 e R + h.c. Γ u Q L Φ 2 u R + h.c. Two complex iggs doublet fields Φ 1 and Φ 2 receive mass and v.e.v.s v 1, v 2 from generalized iggs potential. Mass eigenstates constructed out of these 8 real fields are Neutral sector: 2 CP even iggs bosons: h and 1 CP odd iggs boson: A 1 Goldstone boson: χ 0 Charged sector: charged iggs bosons: ± charged Goldstone boson: χ ± Goldstone bosons absorbed as longitudinal degrees of freedom of Z, W ± Dieter Zeppenfeld iggs Bosons at the LC 4

6 Couplings of the MSSM iggses Fermions Two doublet fields mix, two v.e.v s v 1 = v cos β, v 2 = v sin β: L Yuk. = Γ b bl Φ 0 1 b R Γ t t L Φ 0 2 u R + h.c. v = Γ 1 + cosα h sinα + ia sin β v b bl b R Γ t t 2 + sinα + h cosα + ia cos β L t R Expressed in terms of masses the Yukawa Lagrangian is L Yuk. = m ( b v b v + cosα cos β h sinα ) cos β iγ 5A tan β b m ( t v t v + sinα sin β + h cosα ) sin β iγ 5A cot β t = coupling factors compared to SM h f f coupling i m f /v Gauge Bosons extra coupling factors for hvv and VV couplings as compared to SM hvv sin(β α) VV cos(β α) Dieter Zeppenfeld iggs Bosons at the LC 5

7 SM iggs mass fit to EW precision data m = GeV Including theory uncertainty m < 186 GeV Does not include Direct search limit from LEP m > 114 GeV Renormalize probability for m > 114 GeV to 100%: m < 219 GeV (95% CL) (95% CL) (95% CL) χ Theory uncertainty α had = α (5) ± ± incl. low Q 2 data Excluded m [GeV]

8 iggs boson channels at LC Two steps Production of the iggs boson Detection of the decay products of the iggs boson and identification of the events

9 Production Modes X q p p g t p p V V X Gluon fusion Weak-Boson Fusion q p q V p t p _ q p _ t iggs Strahlung t t Dieter Zeppenfeld iggs Bosons at the LC 8

10 Total cross sections at the LC gg (NNLO) σ(pp + X) [pb] s = 14 TeV NLO / NNLO t t t qq _ ' W qq qq gg/qq _ tt _ (NLO) qq _ Z MRST [Krämer ( 02)] M [GeV] q q q _ q q _ q V V W, Z _ t t

11 Decay of the SM iggs iggs decay width and branching fractions within the SM 10 2 Γ() [GeV] W + W Z 0 Z Branching Ratio cc γ γ Z γ ss + µ µ gg bb + τ τ t t [hep-ex/ ] M [GeV] iggs Mass (GeV) Dieter Zeppenfeld iggs Bosons at the LC 10

12 γγ g g t W/t γ γ BR( γγ) 10 3 large backgrounds from q q γγ and gg γγ but CMS and ATLAS will have excellent photon-energy resolution (order of 1%) Look for a narrow γγ invariant mass peak extrapolate background into the signal region from sidebands. Dieter Zeppenfeld iggs Bosons at the LC 11

13 ZZ l + l l + l Events for 100 fb -1 / 2 GeV/c ZZ* 4e CMS, 100 fb -1 2 m = 130 GeV/c m = 150 GeV/c 2 m = 170 GeV/c 2 ZZ* + tt + Zbb invariant mass of the charged leptons fully reconstructed m 4e (GeV/c 2 ) 200 For m TeV, use the silver-plated mode ZZ ν νl + l BR( ν νl + l ) = 6 BR( l + l l + l ) the large missing E T allows a measurement of the transverse mass Dieter Zeppenfeld iggs Bosons at the LC 12

14 WW l + νl ν ν ATLAS TDR g g W - W + l - ν l + Events / 5 GeV Exploit l + l angular correlations measure the transverse mass with a Jacobian peak at m m T = 2 p ll T /E T (1 cos ( Φ)) background and signal have similar shape = must know the background normalization precisely m T (GeV) m = 170 GeV integrated luminosity = 20 fb 1

15 Weak Boson Fusion W q W τ m > 120 GeV p p V V q W τ + γ γ m < 140 GeV m < 150 GeV b _ b m < 140 GeV [Eboli, agiwara, Kauer, Plehn, Rainwater, D.Z.... ] [Mangano, Moretti, Piccinini, Pittau, Polosa ( 03)] Most measurements can be performed at the LC with statistical accuracies on the measured cross sections times decay branching ratios, σ BR, of order 10% (sometimes even better).

16 WBF signature p + µ J 2 J 1 ϕ θ 2 J 1 θ 1 p µ + ϕ ϕ jj e - J 2 e - η Characteristics: η = 1 2 log 1 + cosθ 1 cosθ energetic jets in the forward and backward directions (p T > 20 GeV) iggs decay products between tagging jets Little gluon radiation in the central-rapidity region, due to colorless W/Z exchange (central jet veto: no extra jets with p T > 20 GeV and η < 2.5) Dieter Zeppenfeld iggs Bosons at the LC 15

17 iggs discovery potential Signal significance 10 2 L dt = 30 fb -1 (no K-factors) ATLAS γ γ tt ( bb) ZZ (*) 4 l WW (*) lνlν qq qq WW (*) qq qq ττ Total significance S B m (GeV/c 2 )

18 Reach for /A discovery within MSSM ATLAS TDR Enhancement of bb and Abb coupling by factor tan β compared to SM iggs = large production cross section for pp bb/a = decay dominated by /A bb, τ + τ 5σ discovery contours Dieter Zeppenfeld iggs Bosons at the LC 17

19 Reach for ± discovery within MSSM ATLAS TDR For m ± > m t + m b expect ± tb decay Dominant production process gg ± tb b-quark has low p T : gb ± t is dominant subprocess Main background from tt(+jets) production 5σ discovery contours Dieter Zeppenfeld iggs Bosons at the LC 18

20 Statistical and systematic errors at LC Assumed errors in fits to couplings: QCD/PDF uncertainties - ±5% for WBF - ±20% for gluon fusion luminosity/acceptance uncertainties - ±5%

21 Measuring iggs couplings at LC LC rates for partonic process pp xx given by σ(pp ) BR( xx) σ() BR( xx) = σ()sm Γ SM p ΓpΓ x Γ, Measure products Γ p Γ x /Γ for combination of processes (Γ p = Γ( pp)) Problem: rescaling fit results by common factor f Γ i f Γ i, Γ f 2 Γ = obs f Γ i + Γ rest leaves observable rate invariant = no model independent results at LC Loose bounds on scaling factor: f 2 Γ > obs. f Γ x = f > obs. Γ x Γ = BR( xx)(= O(1)) obs. Total width below experimental resolution of iggs mass peak ( m = GeV) f 2 Γ < m = f < m Γ < O(10 40)

22 Fit LC data within constrained models g ττ g bb = SM value g WW g ZZ = SM value no exotic channels With 200 fb 1 measure partial width with 10 30% errors, couplings with 5 15% errors

23 Distinguishing the MSSM iggs sector from the SM Alternative: compare data to predictions of specific models Example: m max Consider modest m A : scenario of LEP analyses decoupling almost complete for hww and hγγ (effective) vertices enhanced hbb and hττ couplings compared to SM increases total width of h = tan β σ-effects or more at small m A 2 * 30 fb -1 2 * * 100 fb -1 2 * 300 fb -1 m h max scenario 3σ m h = 130 GeV 125 GeV SM rates for h ττ in WBF suppressed h γγ and h WW rates in WBF M A (GeV) Dieter Zeppenfeld iggs Bosons at the LC 22

24 QCD corrections for iggs production Measurement of partial widths at 10 20% level or couplings at 5 10% level requires predictions of SM production cross sections at 10% level or better = need QCD corrections to production cross sections Much work in recent years gg (all but NLO in m t limit) NLO for finite m t : Graudenz, Spira, Zerwas (1993) NNLO: arlander, Kilgore (2001); Anastasiou, Melnikov (2002); Ravindran, Smith, van Neerven (2003) NNLL: Catani, de Florian, Grazzini, Nason (2003) N 3 LO in soft approximation: Moch, Vogt (2005) weak boson fusion total cross section at NLO: an, Willenbrock (1991) distributions at NLO: Figy, Oleari, D.Z (2003); Campbell, Ellis, Berger (2004) tt associated production at NLO: Beenakker et al.; Dawson, Orr, Reina, Wackeroth (2002) bb associated production at NLO: Dittmaier, Krämer, Spira; Dawson et al. (2003)

25 QCD corrections to gg σ(pp +X) [pb] M = 120 GeV NLO N 3 LO SV LO N 2 LO µ r / M Moch & Vogt, hep-ph/ σ(pp +X) [pb] M = 240 GeV NLO N 3 LO SV LO N 2 LO µ r / M uge improvement in recent years Remaining scale uncertainty below 10% Uncertainty from gluon pdf 4 7% What is K-factor for cross section with cuts? Most problematic: central jet veto against tt background for WW search Dieter Zeppenfeld iggs Bosons at the LC 24

26 NLO QCD corrections to WBF Small QCD corrections of order 10% Tiny scale dependence of NLO result - ±5% for distributions - < 2% for σ total K-factor is phase space dependent QCD corrections under excellent control Need electroweak corrections for 5% uncertainty m = 120 GeV, typical WBF cuts Dieter Zeppenfeld iggs Bosons at the LC 25

27 NLO QCD corrrections to b b production Dittmaier, Krämer, Spira hep-ph/ tot σ(pp bb _ + X) [fb] s = 14 TeV M = 120 GeV µ 0 = m b + M /2 NLO 200 LO Discovery channel for /A in the MSSM at sizeable tan β NLO corrections known for bb final state b-quarks at low p T : effective process is bb : cross section known at NNLO arlander, Kilgore (2003) _ p Tb and p Tb > 20 GeV NLO 20 LO µ/µ 0 scale dependence of inclusive vs. double b-tagged cross section Dieter Zeppenfeld iggs Bosons at the LC 26

28 Tensor structure of the VV coupling Most general VV vertex T µν (q 1, q 2 ) g µ µ q q q q q V q 1 1 q 2 V q 2 Q Q Q Q ν ν (a) (b) Physical interpretation of terms: SM iggs L I V µ V µ a 1 loop induced couplings for neutral scalar CP even L e f f V µν V µν a 2 T µν = a 1 g µν + a 2 ( q1 q 2 g µν q ν 1 qµ 2 ) + a 3 ε µνρσ q 1ρ q 2σ CP odd L e f f V µν Ṽ µν a 3 Must distinguish a 1, a 2, a 3 experimentally The a i = a i (q 1, q 2 ) are scalar form factors Dieter Zeppenfeld iggs Bosons at the LC 27

29 Azimuthal angle correlations Tell-tale signal for non-sm coupling is azimuthal angle between tagging jets Dip structure at 90 (CP even) or 0/180 (CP odd) only depends on tensor structure of VV vertex. Very little dependence on form factor, LO vs. NLO, iggs mass etc.

30 Azimuthal angle correlations in gluon fusion Effective gg vertex is induced via top-quark loop CP even : CP odd : i m t G a v µνg µν,a coupling m t v γ 5 G a µν G µν,a coupling Consider j j production via gluon fusion, e.g. events GF EW WWjj ttj QCD WWjj Φ jj (a) Parton level analysis with relevant backgrounds (ankele, Klämke, DZ, hep-ph/ ) = Difference visible in j j, WW l + l p/ T events at m 160 GeV with 30 fb 1 at 6σ level Method can be generalized for any iggs mass. Problem is lower signal rate for h ττ or h γγ events GF EW WWjj ttj QCD WWjj Φ jj

31 Summary LC will observe a SM-like iggs boson in multiple channels, with % statistical errors = great source of information on iggs couplings Extraction of couplings at the LC requires knowledge of NLO QCD corrections for signal and important backgrounds Absence of VV and AVV couplings for the heavy /A of supersymmetry make their observation more challenging = Need sizable tan β rate enhancement for discovery iggs boson CP properties from jet-angular correlations in WBF and gluon fusion Dieter Zeppenfeld iggs Bosons at the LC 30

32 t t t tb b events / 10 GeV/c CMS L int = 30 fb -1 k = 1.5 gen. m : 115 GeV/c 2 const. : ± 3.76 mean : ± 4.14 sigma : ± m inv (j,j) [GeV/c 2 ] h t = t t Yukawa coupling = measure h 2 t BR( b b) must know the background normalization precisely Dieter Zeppenfeld iggs Bosons at the LC 31