Higgs Physics, after July 2012

Transcription

1 Higgs Physics, after July 2012 C.-P. Yuan Michigan State University, USA July 10, IHEP

2 July 4, 2012 Scientists at CERN say they've found a new particle consistent with the Standard Model Higgs boson with 5-sigma certainty a false positive probability of about 1 in 9 trillion. This is hardly the end of the road for Higgs study, though. It s only the beginning. So a Higgs-like boson has been discovered. What s next?

3 What do we know about this New Boson Its mass is between 124 GeV and126 GeV Its production rates in various decay channels have been found to be in good agreement with the Standard Model (SM) predictions. The Higgs boson couplings to any SM particles are found to generally agree with SM predictions within 20%.

4 A New Boson

5 ATLAS Moriond EW 2013 ATLAS-CONF ,012,013

6 CMS Moriond EW 2013 CMS-PAS-HIG ,2 CMS-PAS-HIG

7 Data and Theory The observed Higgs event number is proportional to the product of Higgs Production cross section and Higgs decay branching ratio into a specific decay channel (i.e. detection mode). arxiv:

8 SM 14 TeV LHC

9 Higgs decay branching ratios For 125 GeV Higgs, Total decay width is 4.03 MeV. Br bb = 0.58 Br WW = 0.22 Br gg = Br ττ = 0.06 Br cc = Br ZZ = Br γγ = Br Zγ =

10 What do we know about these couplings? Assuming No BSM Decays Test Consistency of SM

11 Post Moriond 2013 Fits: Falkowski, et. al., arxiv: Giardino, et. al., arxiv: Ellis, et. al., arxiv: (ATLAS and CMS)

12 Properties of the Higgs Boson All masses proportional to H =v, hence L SM and M 2 W 1+ H v 2 W +µ W µ Important loop effects gluon L SM X f m f 1+ H v + M 2 Z 2 1+ H v 2 Z µ Z µ Lf Rf + h.c. gluon (pp! H) (H! ) non-decoupling!

13 Allow Couplings to Float within SM g htt g HWW

14 Allow Couplings to Float within SM t g hxx = m v Z b W g hxx = M 2 v 2 τ Scott Thomas Ellis and You

15 The Future? t b W Z H? τ μ Scott Thomas

16 What accounts for Vector Boson Mass Generation? Higgs Mechanism Electroweak Symmetry Breaking (EWSB) The Standard Model Higgs Boson Make the Higgs Composite: Little Higgs Make the (Multiple) Higgs Natural: Supersymmetry

17 The Higgs Mechanism (EWSB) W + W

18 The Higgs Mechanism (EWSB) W + W

19 Trial answer: the SM with a Higgs

20 Matrix Notation

21 Non-linear Representation

22 Custodial Symmetry: SU(2)V

23 Custodial Symmetry is an important part of any theory of EWSB! SU(2)V

24 Violations of Custodial Symmetry (i.e. mass differences)

25 Problems with the Higgs Model Problems with the Higgs Model No (other?) fundamental scalars observed in nature No explanation of dynamics responsible for Electroweak Symmetry Breaking Hierarchy or Naturalness Problem ( ) ( ) Triviality and Vacuum Stability Problems... m 2 ( ) References

26 Triviality and Vacuum Stability Triviality For 125 GeV Higgs, Λ GeV with m t = 173 GeV Vacuum Stability

27 Updated Or: other particles (e.g. superpartners) could stablize the potential... Elias-Miro, et. al., arxiv:

28 Further tests in the TeV region are absolutely needed Must study the longitudinally polarized vector boson scatterings in the TeV region to check the unitarity property. If the scattering amplitudes are shown to be unitary, then the discovered Higgs boson is responsible for the electroweak symmetry breaking. Otherwise, New Physics must exist to unitarize the longitudinal vector boson scatterings in the TeV region.

29 Electroweak Symmetry Breaking Loss of Unitarity in

30 Sum 0 SU(2) x E 4

31 SU(2) x E 2 & The Higgs ghww including (d+e) Lee, Quigg, Thacker

32 Weak Boson Scatterings in the TeV region Consider an Effective Chiral Lagrangian, with custodial symmetry (as g 0): Hep-ph/

33 Dimension-6 Operators hep-ph/ B Zhang, Y.-P. Kuang, H.-J. He, CPY

34 SU(2) x E & The Higgs t+ - t+ Z WL + WL - + t+ - t+ b WL + m te v 2 WL - t+ WL + Bad high-energy H behavior cancelled by: - t+ ghtt ghww WL - Chanowitz, Furman, Hinchliffe

35 Symmetry Magazine, Oct 30, 2012

36 Composite Higgs

37 Composite Higgs

38 Fundamental or Composite Higgs Boson Fundamental and Composite are in the eye of the calculator... more important: strong or weak interacting particle at electroweak symmetry breaking scale.

39 Composite Higgs Higgs as (Pseudo-)Goldstone Boson: Hard to do! V (h) = Cg2 16π 2 g 1 ( η 2 f 2 h 2 h 4 ) + η Decay Constant Yields: h 2 η 2 η 4 f 2 ( But, EWPT: f>few TeV ) Must suppress η 2 without suppressing η 4 Georgi & Kaplan; Banks Chacko et. al., hep-ph/

40 Little Higgs Theories Collective Symmetry Breaking: m 0 m 1 m 2 m N m N+1 k 1 k 2 k 3 k N k N+1 For weak springs, masses at end very weakly coupled! η 2 g2 In practice: m 2 h g2 16π 2 f 2 η 4 16π 2 Arkani-Hamed, Cohen, Georgi Meade, hep-ph/

41 Little Higgs: The Hierarchy Cancellation of divergences by particles of same spin! T-Parity: minimize Z-pole effects & DM Schmaltz hep-ph/

42 Cancellation of Λ 2 in top sector: Little Higgs Models ( λt λt λ T ) ( ) ~ 0 Λ + =Λ (approximate) global symmetry relates T with t (Little Higgs mechanism) To ensure ρ=1 at tree level, T-parity was introduced. SM particles (t) T-partners (T P ) a) Lightest T-odd particle A H, dark matter candidate b) Need mass term for T P Induce new Higgs coupling (non-decoupling effects!!!)

43 Little Higgs Models σ(gg h) Large suppression in σ(gg h) ( ) LH σ( gg h) SM = σ( gg h) SM σ gg h Higgs couplings v 2 f 2 v 2 f 2 (from T) (from T p ) v= h = 246 GeV Λ f 4π for f t ~ v 2 f 2 h tot ~ h ( LH ) ( SM ) Γ <Γ tot v 2 f 2

44 Discriminate New Physics Models using σ(gg h) Little Higgs models: σ(gg h) < σ(gg h) SM (destructive contributions from the partners of top quark to cancel quadratic divergence) Universal Extra-Dimension Models: σ(gg h) > σ(gg h) SM (additive contributions from KK states of top quark)

45 Little Higgs Models For m h ~ 100 GeV, Br(h γγ) LH up by ~ 20% Br(h bb) LH about the same down by ~ a factor of 2 for f = 700 GeV close to SM prediction could dramatically modify Higgs discovery potential at LHC for m h ~ 100 GeV becomes dominant discovery channel

46 Constraints On Composite Higgs D 4 interactions same as standard model! Higher dimension operators: ( D µ ) 2 f 2 ΔT 0, f > few TeV ( )D µ D µ s 4 Y 4 f 2 X f 2 q f 2 f 2 m q q q G aµ G a µ B µ B µ } g H = O v 2 f 2 = O(10%) Ignored on next page

47 Flavor-Universal Deviations Coupling to fermions Negative c region disfavored Coupling to vectors Ellis and You

48 Multiple Higgs, SUSY & Decoupling

49 Two-Higgs Model

50 Two-Higgs Model

51 Two-Higgs Model

52 Couplings to Fermions X ij Most general quark couplings: h u1ij q i L 1u j + u 2ij q i L 2u j + d 1ij q i L 1d j + d 2ij q i L 2d j i Fermion masses and Higgs couplings not diagonalized at same time! + h.c. Model-building solutions: Type-I : λ2u,d=0 One Higgs gives mass only to W and Z Type-II : λ2u=0 & λ1d=0 Each Higgs gives mass to only ups or downs md 1/sinβ, could have λt=λb Glashow and Weinberg, 1977

53 Limits on Two-Higgs Models Giardino, et. al.

54 SuperSymmetry Make the Higgs Boson natural! Higgs mass protected by chiral symmetry of partner Δm 2 H log(m 2 SUSY) λ g 2,g 2, mh bounded by ~130 GeV Why is μ of order a TeV?

55

56 SUSY Higgs Sector Limits Giardino, et. al.

57 Theory Summary Theory Fundamental Higgs Hierarchy Problem Precision EW ΛUV δgh/gh LHC YES! < 10 9 GeV 0% SUSY No MGUT? <10% Composite Higgs No f > few TeV 50 TeV O(10%) Dilaton No? 1-10 TeV O(100%) Higgsless/ TC No Ideal fermions 1-10 TeV no narrow scalar? What is the Higgs trying to tell us?

58 Precision Tests are needed New Physics effects (from heavy particles) could contribute in loops. Hence, precision tests of Higgs production cross sections and decay branching ratios are needed.

59 CTEQ-TEA PDF Global Analyses CTEQ-Tung et al (TEA) Collaboration: S. Dulat, J. Gao, M. Guzzi, T.J. Hou, J. Huston, H.-L. Lai, Z. Li, P. Nadolsky, J. Pumplin, D. Stump, C.-P. Yuan CT10NNLO (without including LHC data) is available via LHAPDF. Working on next generation CT PDFs with LHC W/Z and jet data included.

60 CT10NNLO and CT1X NNLO PDFs CT10 Website:

61 CT10NNLO Hessian error PDFs Q=2 GeV Q=85 GeV

62

63 CT10NNLO central PDFs, as ratios to CT10W NLO, at Q=85 GeV

64

65

66

67 PDF induced Correlations of gg H and t t cross sections

68 CTEQ-TEA NNLO PDF analysis Need to know well Higgs production cross sections, with the combined PDF and α s uncertainties.

69 LHC collider energy dependence GF VBF

70 Correlations of Higgs cross sections to PDFs GF strongly correlates to g(x) around 125 GeV s VBF g GF u g s

71 Discriminate Higgs Production Mechanisms Using Jet Energy Profiles Important to measure the couplings of Higgs boson to other SM particles. Need to separate vector boson fusion (VBF) from gluon fusion (GF) production mechanisms for the Higgs boson. Various kinematical distributions look alike after imposing relevant kinematic cuts. Propose to study the final state jet energy profiles to discriminate VBF from GF processes. Hep-ph/ V. Rentala, N. Vignaroli, H.-N. Li, Z. Li, CPY

72 Higgs production mechanisms

73 SM 14 TeV LHC

74 Higgs decay branching ratios For 125 GeV Higgs, Total decay width is 4.03 MeV. Br bb = 0.58 Br WW = 0.22 Br gg = Br ττ = 0.06 Br cc = Br ZZ = Br γγ = Br Zγ =

75 Higgs + 2 jets, in di-photon channel Following CMS analysis: Longer tail in GF, due to large M jj cut. P T Peaks around M W In VBF, 2 due to weak boson propagators.

76 Jet Energy Profiles

77 pqcd Resummation calculations The perturbative QCD resummation technique is applied to improve prediction on jet energy profile to describe CDF and CMS data. Final state quark jets can be statistically separated from gluon jets by studying their corresponding jet energy profiles. Hep-ph/ ; H.-N. Li, Z. Li, CPY

78 Separating Quark from Gluon Jets

79 For 125 GeV SM Higgs Boson Simulate H+1,2,3 jets events with MadGraph v5 Pass them to Pythia v6.4 for showering and hadronization, and use MLM prescription for matching. Jets are reconstructed using SpartyJet, a wrapper for FastJet, using the anti-k t jet algorithm with R = 0.7

80 Compare Jet Energy Profiles from Pythia and pqcd The central jet is chosen, for its jet energy profile (JEP) could be better measured than a forward jet.

81 Our Analyses Pythia predictions depend on the specific tune considered (Pythia tune-a). pqcd resummation predictions, without including power suppressed contribution, do not depend on any non-perturbative physics. Hence, we use pqcd prediction to determine the central value of the JEP, and use Pythia results to estimate the error on the JEP.

82 Compare various model predictions in JEP Compare SM prediction with two hypothetical cases of a Higgs produced via pure VBF or LHC The statistical errors are derived from Madgraph+Pythia simulation.

83 Event rates and f V at 14 TeV LHC (with 100 1/fb)

84 Background contamination Assume the (γγjj) background JEP, ψ B r, can be measured from (side-band) data, so that the signal JEP, ψ s r, can be obtained from the observed JEP, ψ obs r. The errors scale by the factor

85 Background cross sections

86 Summary on JEP We use (quark vs. gluon) Jet Energy Profile to discriminate the production mechanism of Higgs boson, VBF vs. GF. Similar techniques can be applied to probe New Physics.