1 / 37

New Vector Resonance as an Alternative to Higgs Boson (Strong EWSB)

Fyzika za Štandardným modelom klope na dvere Svit, 9.-16.9. 2007. New Vector Resonance as an Alternative to Higgs Boson (Strong EWSB). Ivan Melo University of Zilina. EWSB - one of Great Mysteries of Particle Physics. SM ………………………. 1 Higgs Strong EWSB …….. no Higgs

adriano
Télécharger la présentation

New Vector Resonance as an Alternative to Higgs Boson (Strong EWSB)

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Fyzika za Štandardným modelom klope na dvere Svit, 9.-16.9. 2007 New Vector Resonance as an Alternative to Higgs Boson(Strong EWSB) Ivan Melo University of Zilina

  2. EWSB - one of Great Mysteries of Particle Physics • SM ………………………. 1 Higgs • Strong EWSB …….. no Higgs • SUSY (MSSM) ..... 5 Higgs • Large Extra Dimensions • Little Higgs Problem ! Monotheists Atheists Polytheists Classical New

  3. Naturalness problem (Fine-tuning, Gauge Hierarchy problem) ≈ - (200 GeV)2 for Λ = 103 GeV ≈ - (200 GeV)2 . 1032for Λ = 1019 GeV mH≈ 100 – 200 GeV ≈ - (200 GeV)2 . 1032 ≈ + (200 GeV)2 . 1032

  4. SM Strong EWSB SUSY (MSSM) Large Extra Dimensions Little Higgs = 0 → mH = 319 GeV H not elementary, it melts into techniquarks at ΛTC ≈ 1-3 TeV ~ t1(2) Λ is not 1019 GeV, Λ is as low as 103 GeV

  5. Fundamental energy scales Greg Anderson, Northwestern University

  6. Every fundamental energy scale should have a dynamical origin K. Lane

  7. Linear sigma model (model of nuclear forces) U(σ,π) σ v= μ/√λ ≈ 90 MeV σ = v + σ (spontaneous chiral symmetry breaking) SU(2)L x SU(2)R→ SU(2)V

  8. Standard model Higgs Lagrangian U(σ,π) σ SU(2)L x SU(2)R→ SU(2)V v= μ/√λ ≈ 246 GeV Higgs Lagrangian ≡ Linear sigma model

  9. Where are EW pions ??? mσ = μ2 mπ = 0 SU(2)L x SU(2)R→ SU(2)V (global) massless GB Higgs mechanism: W,Z become massive by eating GB SU(2)L x U(1)Y→ U(1)Q (local) EW pions Φ1,Φ2,χ become WL, ZL

  10. Where is σ ? … the (linear) σ model, although it has some agreeable features, is quite artificial. A new particle is postulated, for which there is no experimental evidence … M. Gell-Mann, M. Levy, Nuovo Cimento 16 p.705 (1960) … and they decided to get rid of σ particle …

  11. Nonlinear σ model (QCD) v = 90 MeV Effective Lagrangian valid until a few hundred MeV

  12. Where is Higgs boson ? … Higgs Lagrangian, although it has some agreeable features, is quite artificial. A new particle is postulated, for which there is no experimental evidence … … so we get rid of the Higgs boson Higgs boson is not necessary, Higgs mechanism works even without Higgs !

  13. Nonlinear σ model (SM Higgs sector) v = 246 GeV Effective Lagrangian valid until 1-3 TeV

  14. Chiral SB in QCD SU(2)L x SU(2)R → SU(2)V , vev ~ 90 MeV EWSB SU(2)L x SU(2)R → SU(2)V , vev ~ 246 GeV

  15. Technicolor Technicolor of massless U and D techniquarks: SU(2)L x SU(2)R invariant As a result of dynamics, interactions of massless techniquarks, we get - SU(2)L x SU(2)R→ SU(2)V - v = 246 GeV - EW pions = WL, ZL made of U,D techniquarks Best explanation of Naturalness & Hierarchy problems

  16. Extended Technicolor (ETC) ETC was introduced to give masses to fermions … but introduced also large FCNC and conflict with precision EW measurements U D ETC Walking technicolor f f ETC has alsoproblem to explain large top mass (mt = 174 GeV) Topcolor assisted technicolor

  17. WL WL→ WL WLWLWL → t tt t → t t t t t (Equivalence theorem) π = WL L = i gπMρ/v (π- ∂μπ+ - π+ ∂μπ-)ρ0μ + gt t γμ t ρ0μ+ gt t γμ γ5 t ρ0μ

  18. International Linear Collider: e+e- at 1 TeV ee ―› ρtt ―›WW tt ee ―› ρtt ―›tt tt ee ―› WW ee ―› tt ee ―› ννWW ee ―›ννtt Large Hadron Collider: pp at 14 TeV pp ―› ρtt ―›WW tt pp ―› ρtt ―›tt tt pp ―› WW pp ―› tt pp ―› jj WW pp ―› jj tt

  19. Chiral effective Lagrangian SU(2)L x SU(2)R global, SU(2)L x U(1)Y local L = Lkin + Lnon.lin. σ model -a v2 /4 Tr[(ωμ + i gvρμ . τ/2 )2] + Lmass+ LSM(W,Z) +b1ψL i γμ (u+∂μ – u+i gvρμ . τ/2+ u+ i g’/6 Yμ) u ψL + b2ψRPb i γμ (u ∂μ – u i gvρμ . τ/2 + u i g’/6 Yμ) u+PbψR + λ1ψL i γμ u+ Aμγ5 u ψL +λ2ψR Pλ i γμ u Aμγ5 u+PλψR BESS Our model Standard Model with Higgs replaced with ρ ωμ = [u+(∂μ + i g’/2 Yμτ3)u + u(∂μ+ i g Wμ . τ/2)u+]/2 Aμ = [u+(∂μ + i g’/2 Yμτ3)u - u(∂μ+ i g Wμ . τ/2)u+]/2 u = exp(i π . τ/2v) ψL = (tL,bL) Pb = diag(p1,p2) gπ= Mρ /(2 v gv) gt=gv b2/4+ … Mρ≈ √a v gv/2 t

  20. Low energy constraints Unitarity constraints WLWL → WLWL , WLWL → t t,t t → t t gv≥ 10 → gπ ≤ 0.2 Mρ(TeV) |b2 – λ2| ≤ 0.04 → gt≈ gv b2 / 4 |b1 – λ1| ≤ 0.01 → b1 = 0 gπ ≤ 1.75 (Mρ= 700 GeV) gt ≤ 1.7 (Mρ= 700 GeV)

  21. Partial (Γ―›WW) andtotal width Γtot of ρ

  22. Subset of fusion diagrams + approximations (Pythia) Full calculation of 66 diagrams at tree level (CompHEP)

  23. Pythia vs CompHEP ρ (M = 700 GeV, Γ = 12.5 GeV, gv = 20, b2 = 0.08) Before cuts √s (GeV) 800 1000 1500 Pythia (fb) 0.35 0.95 3.27 CompHEP (fb) 0.66 1.16 3.33

  24. Backgrounds (Pythia) e+e- → tt γ e+e- → e+e- tt σ(0.8 TeV) = 300.3 + 1.3 fb → 0.13 fb(0.20 fb) σ(1.0 TeV) = 204.9 + 2.4 fb → 0.035 fb (0.16 fb)

  25. |N(ρ) – N(no res.)| √N(ttγ+eett)+(N(no res.)) R = ≈ S/√B > 5 = gv = gv

  26. e- e+→ t t ρ different from Higgs ! x+y=560 nm z=0.40 mm n=2x1010 ρ (M= 700 GeV, b2=0.08, gv=20)

  27. 39/8 diagrams in the dominant gg channel ρ No-resonance background ρ ρ

  28. CompHEP results: pp → W W t t + X ρ: Mρ=700 GeV, Γρ=4 GeV, b2=0.08, gv=10 39 diagrams 8 diagrams MWW(GeV) gπ=Mρ/2vgv gt1,2= gv b2/4 σ(gg) = 10.2 fb ―› 1.0 fb Cuts: 700-3Γρ < mWW < 700 +3Γρ (GeV) pT (t) > 100 GeV, |y(t)| < 2 No resonance background: σ(gg) = 0.037 fb

  29. l jjbjjbjj reconstruction (CompHEP, Pythia, Atlfast, Root) Athena 9.0.3 One charged lepton channel: 40% of events electron > 30 GeV muon > 20 GeV of Cuts: GeV mass of the W: jets > 25 GeV 50% b-tagging efficiency Reconstruction criterion

  30. 8 diagrams 39 diagrams Lum=100/fb Lum=100/fb 12.2 events 2.4 events number of events/17 GeV Distribution in invariant mass of WW pair (ρ →WW) ρ: Mρ=700 GeV, Γρ=4 GeV, b2=0.08, gv=10 Pz(ν) chosen correctly in 61.5 % of events number of events/17 GeV

  31. 39 diagrams 8 diagrams Mass of the W boson Lum=100/fb Lum=100/fb 12.2 events 2.4 events number of events/0.6 GeV number of events/0.6 GeV Mass of the top quark Lum=100/fb Lum=100/fb 12.2 events 2.4 events number of events/2.5 GeV number of events/2.5 GeV

  32. ρ: Mρ=1000 GeV Γρ=26 GeV Lum = 100 fb-1 12.8 events number of events/32 GeV

  33. 1. Can we improve WWtt reconstruction ? L = 100/fb 2.4 events 8 diagrams versus 2. 8 diagrams

  34. Conclusions • New vector resonance as an alternative to Higgs Boson • Modified BESS model motivated by technicolor • Rich e+e- and pp phenomenology

More Related