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News from Top/QCD
Andre H. Hoang
Max-Planck-Institute
Munich
Top/QCD @ ECFA Durham 2004 Andre Hoang – p.1
Program
Top/QCD Session
C. Schwinn: Top couling to Higgs and gaugebosons: 6 and 8 fermion final states
→ top couplings inthe continuum
S. Boogert: tt threshold simulation update→ top couplings at
the threshold
Top/QCD @ ECFA Durham 2004 Andre Hoang – p.2
Program
Top/QCD Session
C. Schwinn: Top couling to Higgs and gaugebosons: 6 and 8 fermion final states
→ top couplings inthe continuum
S. Boogert: tt threshold simulation update→ top couplings at
the threshold
M. Schumacher: Top Yukawa coupling from LC & LHC → synergy ofLHC & ILC
Top/QCD @ ECFA Durham 2004 Andre Hoang – p.2
Program
Top/QCD Session
C. Schwinn: Top couling to Higgs and gaugebosons: 6 and 8 fermion final states
→ top couplings inthe continuum
S. Boogert: tt threshold simulation update→ top couplings at
the threshold
M. Schumacher: Top Yukawa coupling from LC & LHC → synergy ofLHC & ILC
A. Signer: Effective theory for unstable particles → new conceptualand theoreticaldevelopments
M. Slusarczyk: Two-loop QCD corrections to Γt
Top/QCD @ ECFA Durham 2004 Andre Hoang – p.2
Program
Top/QCD Session
C. Schwinn: Top couling to Higgs and gaugebosons: 6 and 8 fermion final states
→ top couplings inthe continuum
S. Boogert: tt threshold simulation update→ top couplings at
the threshold
M. Schumacher: Top Yukawa coupling from LC & LHC → synergy ofLHC & ILC
A. Signer: Effective theory for unstable particles → new conceptualand theoreticaldevelopments
M. Slusarczyk: Two-loop QCD corrections to Γt
Other Sessions
T. Gehrmann: e+e− → 3 jets at NNLO → Loopverein
I. Melo: Signatures of EWSB in e+e− → ttνν → EW & Altern. Theo.
M. Spira: SUSY QCD corrections to e+e− → tth → Loopverein
M. Krämer: NLO Parton Showers → Loopverein
Top/QCD @ ECFA Durham 2004 Andre Hoang – p.2
Top Yukawa CouplingLinear Collider
threshold: σ(e+e− → tt) at√
s ≈ 350 GeV
→ V (r) = −CF αs
r− g2
tth
re−mhr
O(5 − 10%) correctionQQk
→ δgtth/gtth = 20 − 50 %
δM1S ≤ 50 MeV, δΓt ∼ 30 MeV, δαs ∼ 0.001
(L = 300 fb−1 , mh <∼ 120 GeV)
(assumed perfectly known Lumi spectrum) Martinez, Miquel
• perfect knowledge of luminsity spectrum assumed
• only for light Higgs
• depends on knowledge other parameters, QCD theory
• 1st phase
Top/QCD @ ECFA Durham 2004 Andre Hoang – p.3
Top Yukawa CouplingLinear Collider
threshold: σ(e+e− → tt) at√
s ≈ 350 GeV → difficult, 1st phase
continuum: σ(e+e− → tth) ∼ g2tth
Br(h → W+W−)Br(h → bb)
precision: 2 − 5% (e+e− → Zh)
→ δgtth/gtth = 5 − 6 % (mh = 120 GeV) Gay, Besson, Winter
δgtth/gtth = 10 % (mh = 190 GeV)
(√
s = 800 GeV , L = 1000 fb−1)
• √s > 500 GeV crucially needed � �� � � � � � �
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• 2nd phase
Top/QCD @ ECFA Durham 2004 Andre Hoang – p.3
Top Yukawa CouplingLinear Collider
threshold: σ(e+e− → tt) at√
s ≈ 350 GeV → difficult, 1st phase
continuum: σ(e+e− → tth) ∼ g2tth
→ 2nd phase
LHC gg → tth , h → W+W−
h → bb(many analyses)
• no absolute measurement of σtot or Γ(h → XX)
→ g2tth × Br
• recent analysis: ghW = gSMhW
± 2.5%
ghZ = gSMhZ
± 2.5%
SM particle content
Dührssen et al.
→ δgtth/gtth ∼ 12 − 25%
[GeV]Hm110 120 130 140 150 160 170 180 190
(H,X
)2
g(H
,X)
2 g∆
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
)τ(H,2g
(H,b)2g
(H,t)2g
HΓwithout Syst. uncertainty
2 Experiments-1
L dt=2*30 fb∫
Top/QCD @ ECFA Durham 2004 Andre Hoang – p.3
Top Yukawa CouplingLHC & Linear Collider Schuhmacher, Desch
• LC, 1st phase: Γ(h → bb) , Γ(h → W+W−)
from e+e− → Zhuse Z → l+l− recoil mass spectrum
• LHC: gg → tth
?Input
⇒ 1st phase measurement
MH (GeV)
rela
tive
err
or o
n g tt
H
LHC 30 fb-1 at 14 TeV+LC 500 fb-1 at 500 GeV
H → bb H → WWcombinedcombined (stat. error only)
0
0.1
0.2
0.3
0.4
0.5
0.6
100 120 140 160 180 200MH (GeV)
rela
tive
err
or o
n g tt
H
LHC 300 fb-1 at 14 TeV+ LC 500 fb-1 at 500 GeV
H → bb H → WWcombinedcombined (stat. error only)
0
0.1
0.2
0.3
0.4
0.5
0.6
100 120 140 160 180 200
δgtth/gtth = 16 − 27% δgtth/gtth = 13 − 17%
(incl. systematic errors)
Top/QCD @ ECFA Durham 2004 Andre Hoang – p.4
6 and 8 Fermion Final States→Γt = 1.4 GeV: study of fermionic final states in top production
Schwinn
• O‘Mega & WHIZARD updates
• single top production: e+e− → eνetb → |Vtb|
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• signal & background diagrams & cuts• inconsistencies selecting only top diagrams• gauge invariance for small electron scattering angle• background ∼ 5% effect after cuts• dependence on prescription for finite top lifetime
σ(e+e− → bbe−νeµ+νµ)(fb) with θ(e−) > 0.01◦
√s Fixed Width Complex Mass Fudge Factor Step Width
500 5.91 (1) 5.92 (2) 5.83 (1) 9.3 (1.9)
800 3.541 (8) 3.549 (8) 3.528 (8) 4.5 (3)
2000 3.62 (2) 3.64 (1) 3.62 (2) 98.0 (4)
Top/QCD @ ECFA Durham 2004 Andre Hoang – p.5
6 and 8 Fermion Final States→Γt = 1.4 GeV: study of fermionic final states in top production
Schwinn
• e+e− → tth → g2tth
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• 6-fermion final state bbbbW+W−: ∼ 3%
• 8-fermion final state < 3% (first studies)
→ plans: anomalous couplingsQCD effectspolarizations
Top/QCD @ ECFA Durham 2004 Andre Hoang – p.5
Unstable Particles• processes with (near) on-shell massive & unstable particles
• resonances (Z-pole, n-fermion final states)
• non-relativistic systems (tt threshold, W+W−)• finite-T QCD
• issues: factorizable vs. non-factorizable,on-shell vs. off-shell,gauge invariance, double counting,scheme-dependence, etc.
• traditional approaches:pole scheme Fadin, Khoze; Denner etal.,. . .
complex mass scheme Stuart; Aeppli etal; . . .
fermion loop scheme,. . . Beenakker etal
→ guiding principles: • gauge invariance• validity for all energies
Top/QCD @ ECFA Durham 2004 Andre Hoang – p.6
Unstable ParticlesAlternative Approach: Effective Field Theory Signer
• separation of effects at different length scales
non-resonating ↔ resonating
τ ∼ 1
Mτ ∼ 1
Γt
⇓ ⇓Wilson coefficients propagating fields
& operators
LEFT ∼ ∑
i ci(µ)O(φ)(µ)
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JJ
JJ
Top/QCD @ ECFA Durham 2004 Andre Hoang – p.6
Unstable ParticlesAlternative Approach: Effective Field Theory
• separation of effects at different length scales
• power counting in terms of δ = Γt
M∼ α
• unique δ-scaling for field, operators & loops• double counting avoided
Top/QCD @ ECFA Durham 2004 Andre Hoang – p.6
Unstable ParticlesAlternative Approach: Effective Field Theory
• separation of effects at different length scales
• power counting in terms of δ = Γt
M∼ α
• unique δ-scaling for field, operators & loops• double counting avoided
→ gauge invariance “automatic” (on-shell matching, operators)
→ exact form of EFT depends on system
→ no description off resonance (breakdown of δ-expansion)
→ gimmicks: • general (Feyman) rules to any order• factorization scheme & UV-divergences↔ renormalization, anomalous dimensions↔ summation of ln(Γ/M) to all orders
→ toy model Signer, Beneke, Chapovsky, Zanderighi
“real” application in progress . . . no free lunch!
Top/QCD @ ECFA Durham 2004 Andre Hoang – p.6
The Top Decay Width• SM: Br(t → bW ) ≈ 100% & rare decays
MSSM: Br(t → bH+) ≈ several % (1 � tan β < 100)
Br(t → tχ) <∼ 10%
Top/QCD @ ECFA Durham 2004 Andre Hoang – p.7
The Top Decay Width• SM: Br(t → bW ) ≈ 100% & rare decays
MSSM: Br(t → bH+) ≈ several % (1 � tan β < 100)
Br(t → tχ) <∼ 10%
• Corrections to Γ(t → bW )
O(αs): =−8.4% Jezbek, Kühn
O(α, ew): ' −2% Denner, Sack
O(α2s): −→ required for tt threshold at NNLL
→ BLM: O(α2sβ0) Voloshin, Smith
→ MW = 0, mb = 0 Czarnecki, Melnikov
→ MW 6= 0, mb = 0
Pade approximation Chetyrkin et al.
→ expansion for q2
m2
t
� 1, M2
W
q2 � 1
use q2 = m2t , M2
W = 0
impose analytic properties, cutsΠ(2)(q2) =
Top/QCD @ ECFA Durham 2004 Andre Hoang – p.7
The Top Decay Width• SM: Br(t → bW ) ≈ 100% & rare decays
MSSM: Br(t → bH+) ≈ several % (1 � tan β < 100)
Br(t → tχ) <∼ 10%
• O(α2s) corrections to Γ(t → bW ) MW 6= 0, mb = 0
Analytic computation Slusarczyk, Czarnecki
→ start with MW = 0 (M2
W
m2
t
= 0.213)
asymptotic expansion in M2
W
m2
t
use optical theorem
Π(2)(m2t ) =
integr. by parts recurrence relations master integrals- -
6
gaussion elimination
Top/QCD @ ECFA Durham 2004 Andre Hoang – p.7
The Top Decay Width• SM: Br(t → bW ) ≈ 100% & rare decays
MSSM: Br(t → bH+) ≈ several % (1 � tan β < 100)
Br(t → tχ) <∼ 10%
• O(α2s) corrections to Γ(t → bW ) MW 6= 0, mb = 0
Analytic computation Slusarczyk, Czarnecki
→ start with MW = 0 (M2
W
m2
t
= 0.213)
asymptotic expansion in M2
W
m2
t
use optical theorem
Π(2)(m2t ) =
→ expansion up to (M2
W
m2
t
)5
→ Γ(t → bW ) = Γ0[1 + αs
πX1 + (αs
π)215.5(1)
]
−2.15%?
Top/QCD @ ECFA Durham 2004 Andre Hoang – p.7
Top-Antitop Thresholdσ(e+e− → tt) at
√s ≈ 350 GeV ⇒ mt, αs, Γt, (gtth)
Influence of Luminosity spectrum Boogert
x0 0.2 0.4 0.6 0.8 1
even
ts
1
10
102
103
104
105
x0 0.2 0.4 0.6 0.8 1
even
ts
1
10
102
103
104
105
beam spread (bspr)
+ beamstrahlung (bspr+bstr)
+ ISR (isr+bspr+bstr)
x0.99 0.992 0.994 0.996 0.998 1 1.002 1.004 1.006 1.008 1.01
even
ts
1
10
102
103
104
x0.99 0.992 0.994 0.996 0.998 1 1.002 1.004 1.006 1.008 1.01
even
ts
1
10
102
103
104
[GeV]s330 335 340 345 350 355 360
[p
b]
σ
0
0.2
0.4
0.6
0.8
1default+beam spread+beamstrahlung+ISR
σ(s) =1∫
0
dx L(x) σ0(x2s)
-
Top/QCD @ ECFA Durham 2004 Andre Hoang – p.8
Top-Antitop Thresholdσ(e+e− → tt) at
√s ≈ 350 GeV ⇒ mt, αs, Γt, (gtth)
Influence of Luminosity spectrum Boogert
previous WS’s: • measurement of L(x) (excl. beam energy spread)
→ Bhabba accollinearity
→ accelerator & beam simulations
• TOPPIK interpolation
this WS: • beam energy spread included (cold & warm designs)
• L(x) parametrized (σ, a0, a2, a3)
Top/QCD @ ECFA Durham 2004 Andre Hoang – p.8
Top-Antitop Thresholdσ(e+e− → tt) at
√s ≈ 350 GeV ⇒ mt, αs, Γt, (gtth)
Influence of Luminosity spectrum Boogert
measσ0 0.001 0.002 0.003 0.004
[M
eV]
t m
∆
-200
-150
-100
-50
0
50
100
TESLA 0.05%TESLA 0.10%TESLA 0.20%TESLA 0.30%
NLC 0.05%NLC 0.10%NLC 0.20%NLC 0.30%
measσ0 0.001 0.002 0.003 0.004
sα ∆
-0.002
-0.0015
-0.001
-0.0005
0
0.0005
0.001
0.0015
0.002
3a-0.7 -0.65 -0.6
[M
eV]
t m
∆
-10
-5
0
5
10 bspr+bstr+isr (N=40000)
bspr+bstr+isr (N=120000)
3a-0.7 -0.65 -0.6
sα ∆
-0.003
-0.002
-0.001
0
0.001
0.002
0.003
Top/QCD @ ECFA Durham 2004 Andre Hoang – p.8
Top-Antitop Thresholdσ(e+e− → tt) at
√s ≈ 350 GeV ⇒ mt, αs, Γt, (gtth)
Influence of Luminosity spectrum Boogert
→ ∆mt ≈ −50 MeV (Paris numbers)
∆αs ≈ −0.0017 MeV
∆Γt ≈ −13 MeV
. . . things to think of:
• optimized scan strategy
• top event generator• AFB, distributions, cuts• electroweak corrections ↔ unstable particles
• other thresholds
Top/QCD @ ECFA Durham 2004 Andre Hoang – p.8
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