University of Victoria - Jefferson Lab · Electroweak Workshop: High Energy Experiments JLAB Dec...

Electroweak Workshop: High Energy Experiments JLAB Dec 2006 J.M.Roney, Victoria 1

Electroweak Physics: Results from Experiments and Interpretations, Complementarity with future LHC Results, Precisions to be reached

(Experiment)

Michael RoneyUniversity of Victoria


Outline• Reminders of the standard model

• LEP & SLC precision neutral current electroweak data

• LEP & Tevatron Electroweak Data

• Electroweak Expectations from LHC

• Summary


Z-fermion CouplingsEW Z W Higgs

f f 5Z V A

W W

...

( ) Z2sin cos f f

e g gγ

µ µµψ γ γ γ ψ

θ θ

= + + + +

−∼

L L L L L

L


standard model Parameters • 12 fermion masses; mixing matrix parameters (4

quark; 4 lepton), strong phase, and the following 5 precision parameters

Møller, APV


note on “derived parameters”• experimentalists view: choose the most

precisely determined independent parameters to ‘define’ the standard model

• derive other standard model parameters:

22

2

2

1sin 1 1 42 2

1 1

/(1 ) radiative corrections

42 2

QEDW

F Z

QEDZW

F

QED QE

Z

D

G mmm

G mr

r

παθ

π

α

α

α

= − −

= + −

→ −∆∆


2 22

2 22

(0) 1

In particular choice of renormalization scheme the form of the SM relation:

i

cos sin12

(0) 1cos preserve

s

( ) (

sin12

)

:

(

d

)

W WZ F

f

e top

feff eff f

Z F

wf f

W

rm G

rm

s s s

Gr rr r

µτα α α

παθ θ

παθ θ

αα

α

=−∆

=−∆

∆ = ∆ + ∆∆ = ∆ + ∆∆ = ∆ + ∆ + ∆ )

2

2

(5 ( )(0)( )

1 ( )...

cos ...sin

fW

W

h

w

a

W

d s

ss

r

r

ρ

θ

α

ρ

αα

θ∆ = −∆ +

∆ = − ∆ +

=−∆


Radiative corrections give sensitivity of precision measurements to the top and

Higgs mass


Z-lineshape: MZ and ΓZ


Neutral Current Asymmetry Parameters

( )( )

( )

2 2V AR

2 2R V A

V A2

V A

lept2V A eff

2 +

2 /

1 /

/ 1 4 sin

L

L

g gg gg g g g

g g

g g

A

g g θ

−= =+

=+

=• −

� ��

� � � �

� �

� �

�

� �


Z-fermion Couplings• Neutral current parity violating observables are

sensitive to sin2θW : asymmetries give gV/gA� Left-right asymmetries at SLD: ALR

� Forward-backward asymmetries at LEP: AFB

� Tau polarisation measurement at LEP

• gA is measured from cross sections: Rl

• Major focus of LEP and SLD on this sector of the standard model

• APV• Møller Scattering


SLAC Linear Collider (SLC)e+e- Collider with one experiment:

SLAC Linear Detector (SLD)Centre-of-mass at Z-pole 1992-1998

• electrons were longitudinally polarised

• 300k left-handed & 240k right-handed

• polarisation precisely measured

• 73%-77% for most of the data set

• Primary measure:

ALR= (NL-NR) / (NL+NR) x (1/<Polarisation>) = Ae = 0.1513±0.0021


LEP 27km circumference e+e-synchrotron storage ring collider

1989-95 LEP 1 Z-pole: 3.5M Z decays per exp’t1995-00 LEP 2 WW: O(1000) W-pairs


Z couples to all fermionse.g. tau-pair production

AFB= (NF-NB)/(NF+NB)

tree-level diagram:


Observables sensitive to couplings at LEP


Z ( ) (hadrons)qq g→


Z bb→0,bFB

All LEP measurements are consistent4 A(LEP only) 0.881 0.0173

(SLD) = 0.923 0.020Agree at 1.6

(LEP+SLD)=0.889 0.013 (0.935 0.001 SM)3.5

b

b

b

AA

A

Aσ

σ

= = ±

±

±±

�


Z bb→

Z bb→


Z bb→


Z →e+e-; µ+µ-; τ+τ-


+Tau Polarisation: e e Production τ τ− + −→

( )( )

( )

2 2V AR

2 2R V A

V A2

V A

lept2V A eff

2 +

2 /

1 /

an

d

/ 1 4 sin

Lepton universality:

L

L

e

g gg gg g g g

g g

g g

A

g g

A Aτ

θ•

−= =+

=+

= −

•

� ��

� � � �

� �

� �

�

� �


total

P

P P - P

Measure the Polarization τ

τ τ τ

σ σσ

σ σσ σ

− +

−+ + −

+ −

− −= =

≡

+

=

( )( ) ( )

( ) ( ) ( )

2 FBFB pol

total

2 FBFB pol

total

total

po

1 3 81 P 1 cos A A cos cos 16 3

1 3 81 P 1 cos A A cos cos 16 3

P = averaged over cos

A

dd

dd

τ τ ττ

τ τ ττ

τ τ

σ θ θσ θ

σ θ θσ θ

σ σ θσ

− −

−

− −

−

−

+

−

+ −

= + + + +

= − + + −

−

[ ] [ ] [ ] [ ]cos 0 cos 0 cos 0 cos 0FBl FB

total total

A τ τ τ τθ θ θ θ

σ σ σ σ σ σ

σ σ− − − −

+ − + −> < > <− − − −

= =


FBpol FBe e A3

4P 3

4AA A A Aτ τ τ= = − =−

( )( )

( )( )

FBpo

2 2

22

l

FB

81 cos cos 1 cos 2 cos3P (cos ) 8 1 cos 2 cos1 cos cos

P A

A3

e e

A AA A

τ τ τ ττ τ

τ ττ τ

τ θ θ θ θθ

θ θθ θ

ττ

− −− −

−

− −− −

+ + + += = −

+ ++ +

pure Z0 exchange at the pole

Lines assumeLEP average

solid: no lepton universality assumed

dashed: assumelepton universality


Compare different sin2θW Measurements

Prob=3.8%


Hadron Vacuum Polarisation [slides: Davier at Tau06’]

Define: photon vacuum polarization function Πγ(q2) ( ) ( )†4 2 2

em em0 ( ) ( ) 0 ( )iqxi d x e TJ x J x g q q q qµ ν µν µ νγ= − − ∏∫

Ward identities: only vacuum polarization modifies electron charge

(0)( )1 ( )

ss

ααα

=− ∆ ( ) 4 Re ( ) (0)s sγ γα πα ∆ = − ∏ −∏ with:

Leptonic ∆α lep(s) calculable in QED. However, quark loops are modified by long-distance hadronic physics, cannot (yet) be calculated within QCD (!)

Way out: Optical Theorem (unitarity) ...

(0)

(0)[ hadrons]12 Im ( ) ( )

[ ]e es R s

e eγσπσ µ µ

+ −

+ − + −→∏ = ≡→

( )2(0)Born: ( ) ( ) / ( )s s sσ σ α α=

Im[ ] ∝ | hadrons |2... and the subtracted dispersion relation of Πγ(q2) (analyticity)

0

Im ( )( ) (0)

( )sss ds

s s s iγ

γ γ π ε

∞ ′∏′∏ − ∏ =′ ′ − −∫ had

0

( )( ) Re3 ( )

s R ss dss s s i

ααπ ε

∞ ′′∆ = −′ ′ − −∫


Compare different sin2θW Measurements2

2

2

2

2

sin from only

leptons 0.23113 0.00021 Prob( ) 0.45 hadrons 0.23222 0.00027 Prob( ) 0.99

sin (leptonic

only LEP=0.23136 0.00032

couplings only)

sin (leptonic&hadr

lepteff

lepteff

lepteff

θ

χχ

θ

θ

± =

± =

−

±

( ) ( )

LR0,bFB

onic couplings)_______________________________________= 0.23113 0.00021 0.23222 0.00027= 0.00109 0Note: if A is ignored, still get -2.0 if A is

.00034

ignore

De

d,

3

spi

get

.2

6

te

-1.σ

σ

σ± − ±

− ± ⇒

0,bFB

tremendous effort looking for unaccounted systematic effect, particularly for A , none Remaining Possibilities: statistical fluctuation

has been

sign of

iden

new

tified

physics••

new leptonmeasurementsshould be atleast 0.00021to have a big impact(apart fromtesting running)


Standard Model Fits: Summer ‘06


Runningof sin2θθθθW


Z0 EW Precision sin2θW→ Mtop

precision Mz and asymmetry

measurements at LEP/SLD predicted

Mtop years prior to

the Tevatron discovery.

An important milestone in

EW physics: quantum field

theory can successfully

describe weak interaction physics


Predicting MHiggs


Measuring sin2θW at LHCAFB in Drell-Yan can be used to measure sin2θW

qFB e

3A 4 qA A∼( )

22 * *

0 1*

0 1

@ LHC p-p collisions q is a sea-quark q is a valence quarkAt parton level in CM:

ˆ1 cos cos

cos 4& determined by EW couplings of

d A Ad sA A

σ α θ θθ

→

= + +

2

0

1FB

2*

0

initial- and final-state fermions

ˆ~ New Physics

cosNew Physics obse

4ˆ3 "observable

rvable in amplit

s"3A

ude or interference with &

8

Z

s s

A

Z

As

dA

dσ γθ

πασ

γ

=

=

+

+


Measuring sin2θW at LHC

( )

( )1

1 2

2

/ 1

21 2

1 2 1

/ 2 / 1 /

2

2

parton distribution functions (PDFs)

(

Partons cross sec

) ( )

tions folded with

ˆ : cross section for

ˆ : inva

ˆ

ˆ

riant mass of

( ) ( )

i p j p j p i pij

f x f x f x f x

d ppd

q q

M s s

M dyσ

σ

τ

σ

→

+

→

= =

∑

� �

� �

�

�

∼

�

�

�

1 2

1 2

1 2

2

/

1

1 ln : rapidity of 2

parton momentum fraction

( ) : probability to find parton with momentum fraction in the p

s

rotonk

y

i k

Z

y

p

Z

E pyE p

x

f x i

e

x

x

e

τ

τ −

+= −

=

=

� �

�

� �


Measuring sin2θW at LHCRecall particle production is ~constant as function of

1 rapidity, y= ln2

difference in rapidity of two particles is independentof Lorentz boosts along the beam axisAt the parton level

Z

Z

E pE p

•

+ −

•

, these boosts are unknown at hadron colliders

Pseudorapidity, , is numerically close to y, but is onlydependent on the angle relative to the beam axis,

ln tan2

ηθ

θη = −



*FB

1 1* *

F B0 0

F-BFB

F+B

A defined in terms of cos , with respect to q directionIn p-p collisions at LHC, dir

( , ) cos c

ection

os

( , )A ( , )( , )

of q needs to be inferredfrom kinematics

y M d d

y My My M

σ σ θ σ θ

σσ

θ

± = ±

=

∫ ∫��

�

�

of system:antiquarks come from sea, quarks are valence or sea

boost direction preferentially along quark directirapidity is used as measure of quark direc ion

ot

n

+ −

+ −

⇒

⇒

� �

� �



4

2085.2 ( ) 97.2at least 1 electron with 2.5 :

Electron ID eff. ~70%; jet rejection >10allow 2nd electron up to 4.9 :Electron ID eff. ~50%;

cut dependent jet rejection

electronTp GeV

GeV M e e GeVη

η

η

+ −

>

< <≤

≤

−

ATLAS study by Sliwa,Riley,Baur reportedin hep-ph/0003275 using PYTHIA 5.7 & JETSET 7.2



Dependence of AFB on rapidityat LHC andηηηη

cuts on electron

note: AFB fromΖΖΖΖ−−−−>>>>

µµµµ++++µµµµ−−−− as for|η|<2.5|η|<2.5|η|<2.5|η|<2.5

for both µµµµ


Measuring sin2θW at LHC( )( )

3

3

2 2FB

( )

( )

A sin lepteff Z

O Born QED QCD

O Born QED QCD

b a M

a a a a

b b b b

α

α

θ= −

= + ∆ + ∆

= + ∆ + ∆

Connecting

to sin2θθθθW:



µµµµµµµµ


Measuring sin2θW at LHCSystematic uncertainties:

•PDFs: lepton acceptance & radiativecorrections

•Lepton acceptance & reco eff vs Y(need <0.1%, PDFs an issue)

•Higher order QCD & EW corrections•Mass Scale (AFB varies with lepton pair

mass)


Measuring sin2θW at LHCSystematic uncertainties:Biggest worry is•PDFs: lepton acceptance & radiative

correctionsStudied by PDFs (MRST, CTEQ3, CTEQ4)stat. limited study suggests agreementat ~1% on Afb [but these PDFs are correlated]. Moreover, need x~10 better error, to keep it small cf stat error.(note: this is more demanding than for AFB

0.b

since the sensitivity to sin2θθθθW, b factor, is much lower.)simultaneous fits for sin2θθθθW and PDFs?


Measuring sin2θW at LHCAssume something approachingthe statistcal error can be achieved:

this is in fact complementary to thee-e- measurement because it is sensitiveto quark and lepton couplings, not just lepton couplings: if LEP/SLD “discrepancy”is from new physics AND related to quark vs lepton NC couplings,that new physicsshould show up here as well:this LHC measurement is ~ QFB

had at LEP



But LHC will alsomeasurement theasymmetry wellabove the Zmeasuremests at several % level [M.Dittmar PRD 55 ’95]


Mw @ LEP & Tevatron• Current Mw measurements

give EW constraints on e.g. MHiggs… complementary to sin2θW


• Current Mtop measurements give EW constraints on e.g. MHiggs complementary to sin2θW

Mtop @ Tevatron


Mw@LEP and Mw&Mtop@Tevatron• Mw & Mtop give

complementary EW constraints on e.g. MHiggs

independent of

sin2θW measurements


Mw at LEP & Tevatron• Mw & Mtop give

constraints on Mhiggs…complementary to sin2θW


Mw at LHC expected• Mw & Mtop give constraints on Mhiggs…

complementary to sin2θW

• Uncertainties are expected to be significantly smaller than LEP & Tevatron values


Mw at LHC

from M. MalberiICHEP ‘06


Mw@Tevatron: reality check for LHC


Mw at LHC


Mw at LHC Uncertainty on Mass will be dominatedby systematics, many of which (suchas PDFs,energy scale and resolution)will be determined and themselves limited by statistics.The GOAL of 15MeV/c2 looks verychallenging at this point, but achieving~20MeV/c2 can likely be reached


Top production at the LHC~90%~90%

~10%~10%

1. 1. tttt is an essential process for is an essential process for commissioning detector and toolscommissioning detector and tools•• jet energy scale, bjet energy scale, b--tagging calibrationtagging calibration

Production (diff.)Production (diff.)crosscross--sectionsection

t masst mass

W, t W, t helicitieshelicities

Decay modesDecay modes

Light jet Light jet energy scaleenergy scale

bb--taggingtagging

bb--taggingtagging

2. 2. tttt is a fundamental process for is a fundamental process for electroweak (precision) measurementselectroweak (precision) measurements•• the top quark is interesting per se (mthe top quark is interesting per se (mtt~190m~190mpp!)!)•• mmtt, , σσtt, q, qtt, , VVtbtb ,, σσtttt, , BRBRtt, , tttt, , pdfspdfs•• mmtt can greatly help in the indirect constraint can greatly help in the indirect constraint

of the Standard Model (and new physics !)of the Standard Model (and new physics !)

~100%~100%

3. 3. tttt is a fundamental process for the is a fundamental process for the direct search of new physicsdirect search of new physics•• both production and decay: both production and decay: XX→→tttt, , tt→→XX, , ttXttX•• larger couplings with Higgs larger couplings with Higgs ––new physics?new physics?--•• top is background to many search channelstop is background to many search channels

The LHC will be a topThe LHC will be a top--factory !factory !•• σσNLONLO~830 ~830 pbpb : : 2 2 tttt events per second !events per second !•• more than 10 million more than 10 million tttt events expected per yearevents expected per year•• first physics in 2008 !first physics in 2008 !

from R. ChiericiICHEP ‘06


~4.1~4.1~4.0~4.0~0.7~0.7~0.1~0.1via crossvia cross--sectionsection

~1.1~1.1~0.6~0.6~1.0~1.0~0.2~0.2bqqbbqqbℓℓνν

~1.5~1.5~1.4~1.4~0.5~0.5~0.5~0.5exclusive exclusive J/J/ψψ decaysdecays

~4.2~4.2~3.5~3.5~2.3~2.3~0.2~0.2bqqbqqbqqbqq

~1.2~1.2~0.3~0.3~1.0~1.0~0.5~0.5bbℓℓννbbℓℓνν~1.7~1.7~1.4~1.4~0.9~0.9~0.2~0.2bqqbbqqbℓℓνν high high ppTT

δδmmtt

(GeV/c(GeV/c22))δδmmtt(s(systyst. . thth.).)

(GeV/c(GeV/c22) ) (2)(2)

δδmmtt(s(systyst. . instrinstr.).)(GeV/c(GeV/c22) ) (1)(1)

δδmmtt(s(stattat))(GeV/c(GeV/c22))

The key points for reducing the error on The key points for reducing the error on mmtt will be:will be:•• reduce systematic by using data to calibrate our measurements anreduce systematic by using data to calibrate our measurements and to d to

constrain our knowledge on simulationconstrain our knowledge on simulation•• combine analyses with a different systematic breakdown combine analyses with a different systematic breakdown

→→ many instrumental systematic errors are analysis correlatedmany instrumental systematic errors are analysis correlated→→ most theory systematic errors are also ATLAS/CMS correlatedmost theory systematic errors are also ATLAS/CMS correlated

⇒ ⇒ 1 GeV/c1 GeV/c22 error is anyway in reach !error is anyway in reach !

(1) jet and lepton energy scales, b(1) jet and lepton energy scales, b--tagging, luminosity,tagging, luminosity,……(2) radiation, fragmentation, MB/UE,(2) radiation, fragmentation, MB/UE,……

Estimated sensitivities as of today:Estimated sensitivities as of today:

LHC mt error breakdown from R. ChiericiICHEP ‘06


mmHH

SUSY mass scaleSUSY mass scale

MSSM MSSM ≈≈ SM SM

•• The experiments have now presented their realistic potential onThe experiments have now presented their realistic potential on top physics top physics measurements. Many ideas around on how to determine the top mmeasurements. Many ideas around on how to determine the top mass.ass.

•• By cBy combining all analyses, an estimation of ombining all analyses, an estimation of δδmmtt~1GeV/c~1GeV/c22 is realistic and totally is realistic and totally dominated by systematic error. dominated by systematic error.

→→ Conservatively estimated, especially when due to theoretical unConservatively estimated, especially when due to theoretical uncertaintiescertainties→→ The use of data for understanding detector and simulation will The use of data for understanding detector and simulation will be essentialbe essential

•• A precise measurement of the top quark mass willA precise measurement of the top quark mass willallow to:allow to:

→→ improve detector understandingimprove detector understanding→→ constrain standard physicsconstrain standard physics→→ look for presence of new physicslook for presence of new physics→→ constrain new physics !constrain new physics !

Impact of LHC W and Top measurements

Assuming Assuming δδmmWW=15 MeV/c=15 MeV/c22 and and also also ∆α∆αhadhad=0.00012=0.00012

→→ ((δδmmHH/m/mH H ≈≈ 25%)25%)

⇒⇒ Chances of ruling out the SMChances of ruling out the SM……

from R. ChiericiICHEP ‘06


Complementarityof sin2θWMeasurement


LHC expected to measure MHiggsComplementarity withprecision EW: predict MHiggs with precision, just as Mtop was predicted; if Mtop not where Z0 analysessaid it should be…then something else is in those loops

Similarly, if EW predictions of MHiggs are not verified byLHC measurement… something very exciting is up


Møller sensitivity to MHiggs

from E158PRL 95(2005) 081601-1-5



for projectederror of 2.5E-4



for projectederror of 2.5E-4and no ααααhad

(5)(Mz)error



from E158PRL 95(2005) 081601-1-5




but…new leptonmeasurementsshould be atleast 0.00021to have a big impact, beyondtesting for running


Additional (obvious) note on complementarity Møller and

High Energy Measurements of sin2θW

As experimentalistswe want to verifythe running asprecisely as possible,new physics could liein failure of thisrunning


Summary• Z0-pole measurements from LEP and SLC provide the

highest precision measurements of sin2θW but still make one uncomfortable:

Success of predicting top mass; yet there is a chance that the AFB

0,b is telling us something about new physics

• New precision measurements in leptonic-hadroniccouplings will come with AFB in Drell-Yan at the LHC

• Additional precision measurement in purely leptoniccouplings will be very useful to reinforce the LEP and SLC leptonic asymmetry data.


Summary• Additionally, very high energy LHC asymmetries and c

Møller measurements complementary to investigate running of a possible new effect

• Want to confront Higgs discovery at LHC with highest precision EW data possible: is it SM Higgs?

• LHC expected to give higher precision

top and W masses

• Much more precise sin2θW would be very usefulto help sort out what new physics might be at the LHC (but need improved ∆α(5)

had(Mz) to get there!)


Additional Slides


2

0 2 2

f 20 3 f

20 f

f0 3

2

f

2

determined by Higgs structure (e.g.=1 if only Higgs doublets)cos

(T Q sin )Q sin

or equivalently

(T 2Q

2 sinW

treeZ W

tree treeL Wtree treeR W

tree tree tr

F treeW W

eeV L R

mm

gg

g g g

Gm

ρθ

ρ θρ

θ

θ

πα

ρ

=

= −= −

= + = −

=

2

f0 3

2

0 2 2

sin )T

Modified by radiative corrections to propagators and vertices.In 'on-shell' renormalization scheme, keep form of

cosand use this to define the o

treeW

tree tree tree treeA L R R

W

Z W

g g g g

mm

θρ

ρθ

= − = =

=

Wn-shell EW mixing angle, , to all orders in terms ofW and Z masses.

θ


f f

fVf 3

Bulk of corrections to the couplings at the Z-pole absorbed into complex form-factors: for overall scale and for the on-shellEW mixing angle, these give complex effective couplings:

(T 2f= −

R K

G R 2f f

fAf 3

flavour-dependet vertex

propagator self energy correction

Q sin )T

In terms of the real parts

( ) 1 +

( ) 1

se

W

f

f f f

f f

RE

RE

ρ

θ

ρ ρ

κ

↓↓

=

≡ +

≡ +

∆= ∆

=

K

G R

R

K + se fκκ∆ ∆


2 2

f 2Vf 3 f

fAf 3

2Vf Vff

Af Af

H W

The effective EW mixing angle and real effective couplings aredefined as:sin sin

(T 2Q sin )T

So that:g 1 4 Q sing For m m the leading order

feff f W

ff eff

f

feff

gg

RE

θ κ θρ θρ

θ

≡≡ −≡

= = −

G

G

�

2 2 2 2

2 2 22

2 2 2 2

2 2 22

terms are:

The flavour dependent terms are small ex

3 sin 5ln ... cos 68 2

3 cos 9 5ln ... sin 1

cept

0 68

for b- r s

2

qua k .

F W t W Hse

W W W

F W t W Hse

W W W

G m m mm m

G m m mm m

θρθπ

θκθπ

∆ = − − +

∆ = − − +


2 22

2 22

2

(5)

(0) 1cos sin12

(0) 1cos si

The form of the SM relation is

n

p

12

.

( ) ( ) ( ) ( )(0)( )

1 ( )

reserve

..

d:

cos

W WZ F

f feff

e top had

eff fZ F

wf f

W

fW

Ww

rm G

rm Gr r

sr r

s

r

s

ss

r

sµτ

παθ θ

παθ θ

αα

α α α ααα

θ

αρ

=−∆

=−∆

∆ = ∆ + ∆∆ = ∆ +∆∆ = ∆ + ∆ + ∆

∆ =

=−∆

−∆ +

∆ = −

22

2

2 ...sin

often used to express the W mass in terms of more preciselydetermined paramete

11 1 42 12

rs:Z

W

W

F Z

mmrG m

ρθ

πα = + −

−

∆ +

∆

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