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Nuclear Seminar, FMFI UK Bratislava May 21, 200 8. Signatures of a new vector resonance from strongly interacting electroweak symmetry breaking at LHC. M. Gintner, I. Melo, B. Trpi šová University of Žilina. Outline Strong Electroweak Symmetry Breaking - PowerPoint PPT Presentation
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Signatures of a new vector resonance from strongly interacting electroweak
symmetry breaking at LHC
M. Gintner, I. Melo, B. TrpišováUniversity of Žilina
Nuclear Seminar, FMFI UK Bratislava May 21, 2008
Outline
• Strong Electroweak Symmetry Breaking
• BESS Model Vector Resonance ρ
• LHC processes sensitive to ρ, cross sections (CompHEP calculation)
• Reconstruction of pp → W+ W- t t + X; pp → b b t t + X
(CompHEP, Pythia, Atlfast, Root)
EWSB - one of Great Mysteries of Particle Physics
• SM ………………………. 1 Higgs
• Strong EWSB …….. no Higgs
• SUSY (MSSM) ..... 5 Higgs
Monotheists
Atheists
Polytheists
Problem !
Classical
Naturalness problem (Fine-tuning problem)
≈ - (200 GeV)2 . 1032 for Λ = 1019 GeV
mH ≈ 100 – 200 GeV - (200 GeV)2 . 1032 + (200 GeV)2 . 1032
SM
SUSY (MSSM)
= 0 → mH = 319 GeV
t1(2)
~
H not elementary, melts into techniquarks above ΛTC ≈ 1-3 TeV
Strong EWSB
Chiral SB in QCD SU(2)L x SU(2)R → SU(2)V , vev ~ 90 MeV
EWSBSU(2)L x SU(2)R → SU(2)V , vev ~ 246 GeV
052
01
0)(v
ttgttg
MigL tt
t t t
π = WL
v is EW scale (v = vev ~ 246 GeV)
1,2 1,2 1,2
R.Casalbuoni et al. Phys.Lett. B155 (1985) 95; M.Gintner, I.Melo, B.Trpisova, Acta Phys. Slovaca, 56(2006)1
,b
,b ,b
,b
mt = 171 GeV ≈ v/√2
(Equivalence theorem)
Large Hadron Collider: pp at 14 TeV
pp ―› jj WW pp ―› jj ttpp ―› ρtt ―› WW tt +Xpp ―› ρbb ―› WWbbpp ―› ρtt ―› tt ttpp ―› ρtt ―› bb ttpp ―› ρbb ―› bb ttpp ―› ρ+tb ―› tb tbpp ―› ρ+tb ―› W+Z tb
pp ―› WW+Xpp ―› tt+X
Mρ = 1 000 GeVΓρ = 42.3 GeV
Vg
Mg
v2
BESS (Breaking EW Symmetry Strongly) Model 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 gv ρμ . τ/2 )2] + Lmass + LSM(W,Z)
+ b1 ψL i γμ (u+∂μ – u+ i gv ρμ . τ/2 + u+ i g’/6 Yμ) u ψL
+ b2 ψR Pb i γμ (u ∂μ – u i gv ρμ . τ/2 + u i g’/6 Yμ) u+ Pb ψR + λ1 ψL i γμ u+ Aμ γ5 u ψL
+ λ2 ψR Pb i γμ u Aμ γ5 u+ Pb ψR
Standard Model with Higgs replaced with ρ
Our model
ωμ = [u+(∂μ + i g’/2 Yμτ3)u + u(∂μ+ i g Wμ . τ/2)u+]/2Aμ = [u+(∂μ + i g’/2 Yμτ3)u - u(∂μ+ i g Wμ . τ/2)u+]/2u = exp(i π . τ /2v)ψL = (tL,bL)
Pb = diag(1,p)Mρ ≈ √a v gv /2 v ≈ 246 GeV
R.Casalbuoni et al. Phys.Lett. B155 (1985) 95; M.Gintner, I.Melo, B.Trpisova, Acta Phys. Slovaca, 56(2006)1
2
21
21 4 V
Vtt
g
gO
bgggt
1,2
(2)
Unitarity constraints
WL WL → WL WL , WL WL → t t, t t → t t unitary up to 3 TeV
Low energy constraints
gπ ≤ 1.4 (Mρ= 1 000 GeV)gt ≤ 2.0 (Mρ= 1 000 GeV)
gv ≥ 10 gπ = Mρ /(2v gv) ≤ 0.2 Mρ (TeV)
|b2 – λ2 | ≤ 0.04 gt ≈ gv b1(2) / 4
|b1 – λ1 | ≤ 0.01
if
Partial (Γ―›WW) andtotal width Γtot of ρ0
Mρ = 1 000 GeVΓρ = 42.3 GeV
gv = 20b1 = 0.08
CompHEP: pp → bb → tt + X
σS = 121 fb Background G G → tt 3 diagrams
σB = 26 617 fb
Signal bb → tt 6 diagrams
Cuts: Mρ-3Γρ < mtt < Mρ +3Γρ (GeV)
pT(t), pT(t) > 350 GeV
σB = 6 353 fb
σS = 47 fb
M±3Γ
CompHEP: pp → bb → W+W- + X
uu → W+W-
dd → W+W-
4 diagrams
Signal 4 diagramsσS = 15.4 fb
σB = 450 fb
σS → 14.0 fb
σB → 100 fb
mWW
pTW
Background
M±3Γ
CompHEP: pp → ttρ0 + X → bb t t + X
Signal 8 diagrams
σS = 3.7 fb
σB = 17 fb
QCD background 35 diagrams
QCD
Signal
mbb
pTb
QCD bottom
Signal bottom
M±3Γ
CompHEP: pp → bbρ0 + X → bb t t + X
Signal 8 diagramsσS = 134 fb
σB = 833 fb
QCD background 35 diagrams
QCD
Signal
mtt
pTt
QCD top
Signal top
Γρ=127 GeV σ = 337 fb
CompHEP: pp → tbρ+ + X → bb t t + X
Signal 8 diagrams
σS = 86 fb
σB = 332 fb
QCD background 35 diagrams
mtb
Signal top
QCD top
QCD
Signal
pTq
bottom
bottom
39/8 diagrams in the dominant gg channel
ttWW -
jjbjjbjjl l
No-resonancebackground
ρ
ρ
ρ
CompHEP: pp → (W+ W-) t t + X pp → (W+ W-) b b + X
signal
Signal + Background: 39 diagrams
CompHEP: pp → (W+ W-) t t + X (continued) pp → (W+ W-) b b + X
Signal: 8 diagrams
b,
b,
,bσS+B = 4 400 fb
σS = 9.4 fb σS+B = 9.4 fb
σS = 6.7 fb
Cuts: Mρ-3Γρ < mWW < Mρ +3Γρ (GeV)
mW+b, mW-b > 200 GeV
Signal + Background: 46 diagrams
CompHEP: pp → (W+ Z) t b + X
Signal: 8 diagramsσS+B = 12.7 fb
σS = 2.9 fb σS+B = 2.9 fb
σS = 2.5 fb
Cuts: Mρ-3Γρ < mWZ < Mρ +3Γρ (GeV)
mW+b > 200 GeV
W+
Z
Signal + Background: 54 diagrams
CompHEP: pp → (tt) tt + X
Signal: 8 diagrams
σS+B = 3.7 fb
σS = 1.3 fb
Cuts: Mρ-3Γρ < mtt < Mρ +3Γρ (GeV)
t
t
1. pp → bb → tt + X
2. pp → bb → W+W- + X
3. pp → (bb) tt + X
4. pp → bb (tt) + X
5. pp → b(bt) t + X
6. pp → (W+W-) t t + X
7. pp → (W+W-) b b + X
8. pp → (W+Z) t b + X
9. pp → (tt) tt + X
σS = 47
σS = 14
σS = 3.7
σS = 134
σS = 86
σS = 0.23
σS = 6.7
σS = 2.5
σS = 1.3
Cross sections in fb + statistical significance (peak region)
S = NS/ √(NB) statistical significance
NS = L σS , NB = L σB , with L = 100 fb-1 integrated luminosity
S = 5.9 *
S = 14.0 *
S = 9.0
S = 46.4
S = 47.2
S = 4.6
S = 40.8 *
S = 39.5 *
S = 8.4
σB = 6 353
σB = 100
σB = 17
σB = 833
σB = 332
σB = 0.25
σB = 2.7
σB = 0.4
σB = 2.4
signal background significance
* More than 1 cut applied
pp → W W t t + X l jjbjjbjj reconstruction (in collaboration with Jonathan Ferland, University of Montreal)
One charged lepton channel:
jjbjjbjjlWbbWWWttWW l
Cuts: Tpelectron > 30 GeV
muon > 20 GeVjets > 25 GeV
Reconstruction criterion
22
2222
)()(
)()()(
2211
654321
tbWtbW
WjjWjjWjj
mmmm
mmmmmm
l
40% of events
mass of the W: 25Wm GeV
b-tagging efficiency 50%
of
(CompHEP, Pythia, Atlfast, Root)
nu
mb
er o
f ev
ents
/17
GeV
GeV]mWW[
nu
mb
er o
f ev
ents
/17
GeV
GeV]mWW[
39 diagrams 8 diagrams
Lum=100/fb
12.2 events
Lum=100/fb
2.4 events
Distribution in invariant mass of WW pair (ρ →WW)
GeV]mWW[ GeV]mWW[
ρ: Mρ=700 GeV, Γρ=4 GeV, b2=0.08, gv=10
Pz(ν) chosen correctly in 61.5 % of events
8 diagrams 39 diagramsn
um
ber
of
even
ts/0
.6 G
eV
nu
mb
er o
f ev
ents
/0.6
GeV
nu
mb
er o
f ev
ents
/2.5
GeV
nu
mb
er o
f ev
ents
/2.5
GeV
GeV]m jj[ GeV]m jj[
GeV]mWb[ GeV]mWb[
Mass of the W boson
Mass of the top quark
Lum=100/fbLum=100/fb
Lum=100/fbLum=100/fb
2.4 events
2.4 events 12.2 events
12.2 events
GeV]mWW[
GeV]mWW[
nu
mb
er o
f ev
ents
/32
GeV
Lum = 100 fb-1
12.8 events
ρ: Mρ=1000 GeV Γρ=26 GeV
CompHEP
Reconstruction
pp → ρ0 tt → bb t t + X → bb lνlb jjb (43.5%) reconstruction
(in collaboration with J. Ferland)
NS=0.8
NB=8
L = 100 fb-1Cuts: Tp
25Wm
of
e > 30 GeV
j > 25 GeV
μ > 20 GeV
L = 100 fb-1
GeV
2222 )()()(221121 tbWtbWWjj mmmmmm
Conclusions
• Strong EWSB: an alternative to SUSY
• ρ is a general prediction of Strong EWSB
• (Modified) BESS model preferentially couples ρ with t,b
• Several processes promising at CompHEP level
Backup
EWSB: SU(2)L x U(1)Y → U(1)Q
Weakly interacting models: - SUSY - SM (light) Higgs
Strongly interacting models: - Technicolor
A new strong vector resonance ρ as an isospin triplet ( ) → BESS0,