Topics in Electroweak and Top quarkPhysics

Laura Reina

Aspen Winter Conference, February 2006

Outline

• Electroweak (EW) physics. EW precision physics: tensions and predictions.

. Hadron colliders: W/Z production, W/Z rapidity distributions,

W/Z + jj and W/Z + bb production.

• Top quark physics. mt: crucial to EW precision fits.

. tt cross section: matching Monte Carlos to NLO QCD

calculations.

. top quark couplings: single top production, tth production.

with emphasis on the status of theoretical predictions

Precision EW Physics . . .

LEP, SLD, and Run I+II of the Tevatron have and are thoroughly testing

the Standard Model (SM) of EW interactions (see LEP EWWG web page)

Measurement Fit |Omeas−Ofit|/σmeas

0 1 2 3

0 1 2 3

∆αhad(mZ)∆α(5) 0.02758 ± 0.00035 0.02767

mZ [GeV]mZ [GeV] 91.1875 ± 0.0021 91.1874

ΓZ [GeV]ΓZ [GeV] 2.4952 ± 0.0023 2.4959

σhad [nb]σ0 41.540 ± 0.037 41.478

RlRl 20.767 ± 0.025 20.742

AfbA0,l 0.01714 ± 0.00095 0.01643

Al(Pτ)Al(Pτ) 0.1465 ± 0.0032 0.1480

RbRb 0.21629 ± 0.00066 0.21579

RcRc 0.1721 ± 0.0030 0.1723

AfbA0,b 0.0992 ± 0.0016 0.1038

AfbA0,c 0.0707 ± 0.0035 0.0742

AbAb 0.923 ± 0.020 0.935

AcAc 0.670 ± 0.027 0.668

Al(SLD)Al(SLD) 0.1513 ± 0.0021 0.1480

sin2θeffsin2θlept(Qfb) 0.2324 ± 0.0012 0.2314

mW [GeV]mW [GeV] 80.410 ± 0.032 80.377

ΓW [GeV]ΓW [GeV] 2.123 ± 0.067 2.092

mt [GeV]mt [GeV] 172.7 ± 2.9 173.3

−→ only high Q2 data included

plus

direct measurements (Tevatron):

mt = 172.7 ± 2.9 GeV

and

MW = 80.452 ± 0.059 GeV

ΓW = 2.102 ± 0.106 GeV

. . . tests the consistency of the SM and constrains MH

80.3

80.4

80.5

150 175 200

mH [GeV]114 300 1000

mt [GeV]

mW

[G

eV]

68% CL

∆α

LEP1 and SLD

LEP2 and Tevatron (prel.)

old “old”: early Summer 2005

mt = 178.0 ± 4.3 GeV

“new”: late Summer 2005

mt = 172.7 ± 2.9 GeV

strong correlation between MW (sin θeffW ), mt and MH

160

180

200

10 102

103

mH [GeV]

mt

[GeV

]

Excluded

High Q2 except mt

68% CL

mt (Tevatron)

80.3

80.4

80.5

10 102

103

mH [GeV]

mW

[G

eV]

Excluded

High Q2 except mW/ΓW

68% CL

mW (LEP2 prel., pp−)

MW /(GeV) = 80.409− 0.507

(

∆α(5)h

0.02767− 1

)

+ 0.542

[

(

mt

178GeV

)2

− 1

]

− 0.05719 ln(

MH

100GeV

)

− 0.00898 ln2(

MH

100GeV

)

A. Ferroglia, G. Ossola, M. Passera, A. Sirlin, PRD 65 (2002) 113002

W. Marciano, hep-ph/0411179

10 2

10 3

0.23 0.232 0.234

sin2θlept

eff

mH [

GeV

]

χ2/d.o.f.: 11.8 / 5

A0,l

fb 0.23099 ± 0.00053

Al(Pτ) 0.23159 ± 0.00041

Al(SLD) 0.23098 ± 0.00026

A0,b

fb 0.23221 ± 0.00029

A0,c

fb 0.23220 ± 0.00081

Qhad

fb 0.2324 ± 0.0012

Average 0.23153 ± 0.00016

∆αhad= 0.02758 ± 0.00035∆α(5)

mt= 172.7 ± 2.9 GeV

- 1

1659

000

10 1

0× µ

a

150

160

170

180

190

200

210

220

230

+µ

-µ

Avg.

]-e+

[e

]τ[

Experiment Theory

The muon g − 2 collaboration

PRL 92 (2004) 161802

sin2 θW (MZ)MS

= 0.23101 + 0.00969

(

∆α(5)h

0.02767− 1

)

− 0.00277

[

(

mt

178GeV

)2

− 1

]

+ 0.0004908 ln(

MH

100GeV

)

+ 0.0000343 ln2(

MH

100GeV

)

(

sin θeff

W = sin θW (MZ)MS

+ 0.00028)

Low energy measurements of sin2 θW

0.001 0.01 0.1 1 10 100 1000Q [GeV]

0.225

0.23

0.235

0.24

0.245

0.25

sin2 θ W

APV E 158(Run I)

Qweak eD-DIS

DIS

Z-pole

(JLAB) (?)

SMMSSM

Weak Mixing Anglescale dependence in MS-bar scheme

J. Erler, M. J. Ramsey-Musolf

Prog.Part.Nucl.Phys. 54 (2005) 351

−→ Running of sin2 θW not unsatisfactory;

−→ NuTeV (DIS) almost 3σ deviation still a puzzle.

Precision crucial to disentangle new physics

160 165 170 175 180 185 190mt [GeV]

80.20

80.30

80.40

80.50

80.60

80.70

MW

[GeV

]

SM

MSSM

MH = 113 GeV

MH = 400 GeV

light SUSY

heavy SUSY

SMMSSM

both models

Heinemeyer, Weiglein ’05

experimental errors 68% CL:

LEP2/Tevatron (today)

Tevatron/LHC

80.20 80.25 80.30 80.35 80.40 80.45 80.50MW [GeV]

0.2305

0.2310

0.2315

0.2320

0.2325

sin2 θ ef

f

SM (mH = 113 ... 400 GeV)

mt = 170 ... 180 GeV

MSSM

Heinemeyer, Weiglein ’03

experimental errors:

LEP2/SLD/Tevatron

LHC/LC

GigaZ

−→ SM main uncertainty: Higgs boson mass.

−→ MSSM main uncertainty: unknown masses of SUSY particles.

Experimental uncertainties, estimate

Present Tevatron LHC LC GigaZ

δ sin2 θeffW (×10−5) 14 63 14-20 6 1.3

δ(MW )(MeV) 34 27 10-15 7-10 7

δ(mt) (GeV) 5.1 2.7 1.0 0.2 0.13

δ(MH)/MH (indirect) 60% 35% 20% 15% 8%

U. Baur, LoopFest IV, August 2005

Intrinsic theoretical uncertainties

−→ δMW ≈ 4 MeV: full O(α2) corrections computed.

M. Awramik, M. Czakon, A. Freitas, G. Weiglein

−→ δ sin2 θeffW ≈ 5 × 10−5: full fermionic O(α2) corrections computed,

bosonic O(α2) in progress.

M. Awramik, M. Czakon, A. Freitas, G. Weiglein

Summary at a glance

0

1

2

3

4

5

6

10030 500

mH [GeV]

∆χ2

Excluded

∆αhad =∆α(5)

0.02761±0.00036

0.02749±0.00012

incl. low Q2 data

Theory uncertainty

0

1

2

3

4

5

6

10030 300

mH [GeV]∆χ

2

Excluded

∆αhad =∆α(5)

0.02758±0.00035

0.02749±0.00012

incl. low Q2 data

Theory uncertainty

Before Summer 2005{

MH = 117+67−45 GeV

MH < 251 GeV (95% CL)

Since Summer 2005{

MH = 91+45−32 GeV

MH < 186− 219 GeV (95% CL)

Combined theoretical constraints

100

200

300

400

500

600

1 10 102

Hig

gs m

ass

(GeV

)

Λ (TeV)

Vacuum Stability

Triviality

Electroweak

10%

1%

Λ→ scale of new physics

amount of fine tuning =

2Λ2

M2H

∣

∣

∣

∣

∣

nmax∑

n=0

cn(λi) logn(Λ/MH)

∣

∣

∣

∣

∣

←− nmax = 1

C. Kolda and H. Murayama, JHEP 0007:035,2000

Light Higgs consistent with low Λ: new physics at the TeV scale.

Discovering a Higgs boson more crucial then ever

Tevatron

LHC

1

10

10 2

100 120 140 160 180 200

mH (GeV/c2)

Sig

nal s

igni

fica

nce

H → γ γ ttH (H → bb) H → ZZ(*) → 4 l H → WW(*) → lνlν qqH → qq WW(*)

qqH → qq ττ

Total significance

5 σ

∫ L dt = 30 fb-1

(no K-factors)

ATLAS

−→ WH and ZH associated production

−→ Hbb in MSSM-like models (yb =

tanβySMb )

In low mass region:

−→ weak boson fusion

−→ ttH associated production

−→ inclusive with H → γγ

Theoretical predictions: overview

QCD predictions for total cross sections to Higgs production processes are

under good theoretical control:

�� � � � �� � �� � �

�� � � � �� �

� � � � �� ��� � �

�� � �� ��� � � �

�� � �� � � � � �

� �� � � � � � �

� ! � " # $ %&' ( ) *,+ - .0/ 1 2 1 / + -

+ 3 �54 ( ) �

6 7 78 9 78 : 78 ; 78 < 78 = 78> 78 ? 78 6 7

8 7 7 78 7 7

8 78

7@ 8

A AB C DEF GH I IJK D L EMN O E M P QSR T

EF GH I IJK D L EMU ON QVW

U F X GH I IJK D L E M Y OU Q VW

N F GH I IJK D L EMU ON QVW

Z Z[ \ ]_^a` ^ b c

d ef f b c gh ijk l m

Z[ \ ] n nop p b ^ ^ c

[ q r ] s t u vwx y z o {| u } ~ g� � �0�

� � j5� y z m

�| |� �|� �|� �|� �|� �|�� |� �|� �|�|

�|� �

|� | �

Caution:

. uncertainties only include µR/µF dependence

. uncertainties from PDF’s are not included (but should improve)

Of direct interest to the Tevatron

. WH and ZH: QCD corrections at NNLO

O. Brien, A. Djouadi, R. Harlander, PLB 579 (2004) 149

. Hbb: QCD corrections at NLO in both 4FNS (qq, gg → Hbb) and

5FNS (bg → bH and bb → H): very good agreement.

J. Campbell, K. Ellis, F. Maltoni, S. Willenbrock,PRD 67 (2003) 095002

S. Dawson, C. Jackson, L.R., D. Wackeroth,PRD 69 (2004) 074027, PRL 94 (2005) 031802

S. Dittmaier, M. Kramer, M. Spira,PRD 70 (2004) 074010

First measurements already

constrain MSSM parameter space

(GeV) Am80 100 120 140

βta

n

20

40

60

80

100 DØMSSM Higgs bosons = h, H, Aφ), b b→(φbb

Exc

lud

ed a

t L

EP

No mixingMax. mixing

(GeV) Am80 100 120 140

βta

n

20

40

60

80

100

Tevatron/LHC : single W/Z boson production

• QCD corrections to W/Z boson total cross sections known at NNLO

R. Hamberg, W. L. van Nerveen, T. Matsuura, NPB 359 (1991) 343,

W. L. van Neerven and E. B. Zijlstra, NPB 382 (1992) 11

• W/Z pT distributions include resummed QCD corrections

C. Balazs, J. W. Qiu, C. P. Yuan, PLB 355 (1995) 548

• Rapidity distributions of the Z boson calculated at NNLO

C. Anastasiou, L. Dixon, K. Melnikov, F. Petriello, PRL 91 (2003) 182002

Testing NNLO PDF’s =⇒ “parton-parton luminosity” monitors

• At the percent level (≈ 1%) EW corrections become important.In particular if:

. QCD corrections are small (ex.: W/Z cross section ratio);

. enhanced by large logs:

−→ ln(s/m2f ) (collinear logs, near W/Z resonance),

−→ ln(s/M2

W/Z) (Sudakov logs, when l+l− or lν have large

invariant mass);

. precision measurement (MW , MZ , . . .).

O(α) corrections to W/Z production fully calculated.

S. Dittmaier and M. Kramer, PRD 70 (2002) 073007

U. Baur, D. Wackeroth, PRD 70 (2004) 073015

MRSTQED2004 −→ contain QED corrections.

• Tev4LHC EW working group: “tuned comparison” of existing

calculations: HORACE,WGRAD/ZGRAD, WINHAC/ZINHAC,

RESBOS, PYTHIA+PHOBOS, . . .

W/Z production with jets: W/Z + jj and W/Z + bb

• W/Z + jj and W/Z + bb important background to W/Z + H and

single top production.

• NLO QCD corrections to W/Z + jj and W/Z + bb (in the mb → 0

limit) known and coded in MCFM (now version 4.2)

J. Campbell, R. K. Ellis, S. Veseli, see mcfm.fnal.gov

• NLO QCD corrections to Wbb including full mb effects soon available

0 50 100 150 200Mbbb (GeV)

0

0.01

0.02

0.03

0.04

0.05

0.06

dσ/d

Mbb

b (pb/

GeV

)

LONLO

LO and NLO Mbbb distributionb-jets cuts: pt > 15 GeV & η < 2 & R > 0.7 (20 GeV < Mbbb < 200 GeV))

F. Febres-Cordero, L.R, D. Wackeroth

Preliminary

Zbb: in preparation

tt production: very refined prediction

M. Cacciari, S. Frixione, M. Mangano, P. Nason,

JHEP 04 (2004) 68

−→ NLO QCD corrections to heavy quark production well established

P. Nason, R. K. Ellis, S. Dawson, NPB 303 (1988) 607

W. Beenakker, H. Kujif, W. L. van Nerveen, J. Smith, PRD 40 (1989) 54

−→ Resummed soft QCD corrections at NNLO and NLL or NNLL:

R. Bonciani, S. Catani, M. Mangano, P. Nason, NPB 529 (1998) 424

N. Kidonakis and R. Vogt, PRD 68 (2003) 1140014

Single top production: measuring Vtb

ud

Wt

b Vtb

(a)

q

q

Wt

bVtb

(b)

b

g

W

t

Vtb

(c)

. Direct measurement of Vtb

. s-channel and t-channel have distinct signatures

. NLO QCD corrections calculated for total cross section and

distributions

B. W. Harris, E. Laenen, L. Phaf, Z. Sullivan, S. Weinzierl, PRD 66 (2002) 054024

Z. Sullivan, PRD 70 (2004) 114012

J. Campbell, R. K. Ellis, F. Tramontano, PRD 70 (2004) 094012

Q.-H. Cao, R. Schwienhorst, C.-P. Yuan, PRD 71 (2005) 054023

Theory CDF D∅

s-channel (0.88 ± 0.14) pb < 13.6 pb < 6.4 pb

t-channel (1.98 ± 0.30) pb < 10.1 pb < 5.0 pb

ttH production: measuring the top Yukawa coupling

[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(H,Z)2g

(H,W)2g

)τ(H,2g

(H,b)2g

(H,t)2g

HΓ

without Syst. uncertainty

2 Experiments-1

L dt=2*300 fb∫-1WBF: 2*100 fb

At the LHC : qq, gg → ttH with

• MH ≤ 130 GeV: H → bb, ττ

• MH ≥ 130 GeV: H →WW

M. Duhrssen et al., PRD 70 (2004) 113009,

hep-ph/0407190;

A. Belyaev, L.R., JHEP 0208 (2002) 041

D. Zeppenfeld et al., PRD 62 (2000) 013009

δyt/yt ≈ 10-20%

m

At a LC : δyt/yt ≈ 5% (√

s = 800 GeV)

NLO QCD corrections fully calculated: th. uncertainty reduced to 15-20%

W. Beenakker, S. Dittmaier, Plumper, M. Spira, P. Zerwas

S. Dawson, C. Jackson, L. Orr, L.R., D. Wackeroth

Summary

• EW precision fits still not conclusive: need prove/disprove the

existence of a Higgs boson.

• EW physics (as well as top physics) now played at hadroncolliders:−→ QCD corrections well under control;

−→ Many interesting new measurements (Z-rapidity, single top, ...);

−→ matching of higher order calculations with event generators under

construction/testing;

−→ huge statistics coming with the LHC;

−→ EW corrections may become important soon.

Great potential!

• Next stage: the ILC (see Snowmass working group reports).