Post on 05-Sep-2020
LEP, SLC and the
Standard ModelFinal - and not so final - electroweak results
e+
e−γ /Z
f−
f
e+
e−
γ
Z
f−
f
e+
e−
νeW
We+
e− γ WW
e+
e− Z WW
e+
e− Z(∗) Z(∗)
H
Dave CharltonThe University of Birmingham
SLAC Summer Institute Topical Conference, August 2002
Most of the averages and plots shown were prepared by the LEP electroweak
working group – particular thanks are due to them
High Energy e e
�
Colliderse+
e−γ
f−
f
e+
e− Z
f−
f
10
10 2
10 3
10 4
10 5
0 20 40 60 80 100 120 140 160 180 200 220
Centre-of-mass energy (GeV)
Cro
ss-s
ecti
on (
pb)
CESRDORIS
PEP
PETRATRISTAN
KEKBPEP-II
SLC
LEP I LEP II
Z
W+W-
e+e−→hadrons
SLC 1989-1998
�� � ,� 20 pb
� �
� �
polarisation� 75%
LEP-1 1989-199588 � � � 94 GeV
� 160 pb
� � 4
LEP-2 1996-2000130 � � � 209 GeV
� 700 pb
� � 4
Millions of Z’s, tens of thousands of W’s
Dave Charlton LEP/SLD Electroweak (2) August 2002
The Z Lineshape
Ecm [GeV]
σ had
[nb]
σ from fitQED corrected
measurements, error barsincreased by factor 10
ALEPHDELPHIL3OPAL
σ0
ΓZ
MZ
10
20
30
40
86 88 90 92 94
� ��� � � � � � � � measured over�� 3 GeV
Initial-state radiation (ISR): bigeffect
�� 91.1875� 0.0021 GeV
� � 2.4952� 0.0023 GeV
�� ��� � � � � �� ���
� � � � � �� � �
gives access to � �� � � � via
� �� � � ��� � �� � � � � �� � � �
Using ! � �� � � � " � ! ! �$# � we find
! �% &'( � � )% ) )'*
Dave Charlton LEP/SLD Electroweak (3) August 2002
The Z Lineshape: High Statistics!
peak-2
9.9
10
10.1
10.2
89.44 89.46 89.48Ecm [GeV]
σ had
[nb]
ALEPH
DELPHI
L3
OPAL
1990-1992 data
1993-1995 datatypical syst. exp.luminosity error
theoretical errors:QEDluminosity
peak
30
30.2
30.4
30.6
30.8
91.2 91.25 91.3Ecm [GeV]
peak+2
14
14.25
14.5
14.75
92.95 92.975 93 93.025Ecm [GeV]
Dave Charlton LEP/SLD Electroweak (4) August 2002
Z Decay Widths: Heavy Quarks
Decay Length Significance
DELPHI
bcuds
0 1 2 3 4 5 60
200
400
600
800
1000
1200
1400
1600
1800
M / GeV
SLD
bc
� � ��� � �� � � � �� �
Z lineshape � � e, � , � , � � �
Also measure Z � , Z �
Main b tags: � � , � , � � High performance multivariate b tags:
� from data – “double tag” method
0.16
0.17
0.18
0.19
0.214 0.216 0.218 0.22
R0b
R0 c
Preliminary
68% CL
95% CL
SM
By convention � � � � � �� ���
� � )% � � �( ( � )% ) ) ) ��Dave Charlton LEP/SLD Electroweak (5) August 2002
Asymmetries at the Z
e−
FB
µ−
� � ��� � � � � �
��� � � � � �
Asymmetry parameters �
� � � �� �
� ���� � ��� � � � ��
� �
�� �
� �( � �� � � � ���Various asymmetries:
� forward-backward
� �� � �� � �
� tau polarisation � � , � � � � �
� left-right polarisation � � �
� forward-backward left-right
Superscript 0 denotes “Z-pole” quantities
� � measured for e, � , � , b and c
Dave Charlton LEP/SLD Electroweak (6) August 2002
Left-Right Polarization Asymmetry
Strained Lattice Cathodefor 1993 SLD Run
SourceLaserWavelenghtOptimized
Strained Lattice Cathodefor 1994 SLD Run
1996 Run
Strained Lattice Cathodefor 1997 SLD Run
→
→
→
→
→
Z Count
Beam Polarization SLD 1992-1998 Data
Pol
ariz
atio
n of
Ele
ctro
n B
eam
(%
)
0
10
20
30
40
50
60
70
80
90
100
0 1000 2000 3000 4000 5000x 10
2
0LRA
0.10 0.12 0.14 0.16
92
93
94-95
96
97-98
Average
0.004 0.044 ±0.100
0.0028 0.0071 ±0.1656
0.0011 0.0042 ±0.1512
0.0010 0.0057 ±0.1593
0.0010 0.0024 ±
±
±
±
±
±0.1491
0.0022±0.1514
/DOF=7.4/4 Prob.=11.4%2χ
Measured by SLD, polarized� �
beam
Counting experiment:
� � � � � � �
� � � � ��
� � � �
� � � � mean polarization, three measure-ments
With � � � , convert to
�� � �% � � �� � �% � �� �
Overall, SLD obtain
�� � ��� � ���� �% � � �� � � �% � � �� �
Most precise measurement of �� � � � ��
Dave Charlton LEP/SLD Electroweak (7) August 2002
Leptonic Couplings
-0.041
-0.038
-0.035
-0.032
-0.503 -0.502 -0.501 -0.5
gAl
g Vl
68% CL
l+l−
e+e−
µ+µ−
τ+τ−
mt
mH
∆α
Combining leptonasymmetry results
� )% �� ) � � )% ) ) � �
Combine also with leptonicpartial widths
Test of NC leptonuniversality
Strong sensitivity to radiativecorrections
Preference for small H massin SM framework
Dave Charlton LEP/SLD Electroweak (8) August 2002
Heavy Quark Asymmetries
0
200
400
600
800
1000
1200
1400
-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1Q tag class 4
even
ts /
0.02
OPAL1994 databbcuds
b
b
uds c
�� � and �� � measured at LEP/SLD
Needs good flavour and charge tagging
For �� � , powerful lifetime tags need
charge measure – multivariate techniquescalibrated from data
Lepton tags probe b charge via �
0.055
0.065
0.075
0.085
0.09 0.1 0.11
A0,bfb
A0,
cfb
Preliminary
68% CL
95% CL
mHmt
SM
For � �� � �� � � , sensitivity to �� � � � ��
mainly via � � � �� � � � ���
SLD also measure � , � via polarized� �
Dave Charlton LEP/SLD Electroweak (9) August 2002
Effective Weak Mixing Angle
10 2
10 3
0.23 0.232 0.234
Preliminary
sin2θlept
eff = (1 − gVl/gAl)/4
mH [
GeV
]
χ2/d.o.f.: 10.2 / 5
A0,l
fb 0.23099 ± 0.00053
Al(Pτ) 0.23159 ± 0.00041
Al(SLD) 0.23098 ± 0.00026
A0,b
fb 0.23217 ± 0.00031
A0,c
fb 0.23206 ± 0.00084
<Qfb> 0.2324 ± 0.0012
Average 0.23148 ± 0.00017
∆αhad= 0.02761 ± 0.00036∆α(5)
mZ= 91.1875 ± 0.0021 GeVmt= 174.3 ± 5.1 GeV
Asymmetries mostly measure�� � � � � � ���
A posteriori, see that two most
precise �� � � ��� � ���� measurementsagree only at 2.9 � level
Old problem: discrepancy around 3 � for six
years, though errors improved by factor 1.5
In context of SM: �� � prefers
� � 400 GeV — unlike mostother observables which prefer low
�
Dave Charlton LEP/SLD Electroweak (10) August 2002
Fermion Pairs at LEP-2
10 2
10 3
10 4
10 5
80 100 120 140 160 180 200
120 140 160 180 200
√s / GeV
Cro
ss-s
ecti
on /
pb
OPALpreliminary
e+e-→hadrons
e+e-→hadrons; s′/s>0.7225
√s
´ (GeV)
Num
ber
of e
vent
s / 4
GeV
Data 207 GeV
hadrons(γ)
e+e−hadrons
W+W−
others
L3preliminary
0
100
200
300
400
50 75 100 125 150 175 200
��� � � � �
e+
e−(γ/Z)*
f−
f
e+
e−
γ
Z
f−
f
radiative return
non-radiative
Dave Charlton LEP/SLD Electroweak (11) August 2002
LEP-2 Fermion Pair PropertiesNon-radiative events � � � � � � � � �
� � � � � � �
Cro
ss s
ectio
n (p
b)
√s
´/s
> 0.85
e+e−→hadrons(γ)e+e−→µ+µ−(γ)e+e−→τ+τ−(γ)
LEPpreliminary
√s
(GeV)
σ mea
s/σ S
M
1
10
10 2
120 140 160 180 200 220
0.8
0.9
1
1.1
1.2
120 140 160 180 200 220
For
war
d-B
ackw
ard
Asy
mm
etry √s
´/s
> 0.85
e+e−→µ+µ−(γ)e+e−→τ+τ−(γ)
LEPpreliminary
√s
(GeV)
AF
B
mea
s -AF
B
SM
0
0.2
0.4
0.6
0.8
1
120 140 160 180 200 220
-0.2
0
0.2
120 140 160 180 200 220
SM continues to describe � � at LEP-2Dave Charlton LEP/SLD Electroweak (12) August 2002
W Pair Productione+
e−
νeW
We+
e− γ WW
e+
e− Z WW
√s (GeV)
σ WW
(pb
)
YFSWW and RacoonWW
LEP PRELIMINARY
13/07/2002
0
10
20
160 180 200
16
17
18
190 195 200 205
Around 12000 WW / experiment
46% WW � � � � �
� 4 jets
44% WW � � � � �
2 jets, charged lepton, missing p
10% WW � ��
��
2 leptons, missing p
Selection � � � typically 80-90%
� � � � � to� 1%
New O( � )-corrected predictionsshift � � � by � 2.5� 0.5%
� � � well-described byO( � ) calculations
Dave Charlton LEP/SLD Electroweak (13) August 2002
Gauge Boson Self-Couplings
0
10
20
30
160 180 200
√s (GeV)
σ WW
(pb
)
YFSWW/RacoonWWno ZWW vertex (Gentle)only νe exchange (Gentle)
LEPPRELIMINARY
16/07/2002
Direct measurements possible at LEP-2
Several channels, WW is most powerful
e+
e− γ /Z WW?
Sensitivity via � � � , production polarangle, W polarisation
O( � ) corrections � current precision – now included in analyses
Vertex coupling parameters: (preliminary)
� � � 0.943 � 0.055 SM: 1
� � � � 0.020 � 0.024 0
�� � 0.998 ��� � � �� � � � 1
SM gauge structure of boson self-couplings demonstrated
Dave Charlton LEP/SLD Electroweak (14) August 2002
W Mass from LEP-2
W mass (GeV/c 2 ) ev
ents
/ 1
GeV
/c 2
0
20
40
60
80
100
120
140
50 55 60 65 70 75 80 85 90 95 100
L3
minv [GeV]
Num
ber o
f Eve
nts
/ 1 G
eV
Data qqeνM.C. reweighted
M.C. background (a)
preliminary
MW = 79.99 ± 0.22 GeV
0
20
40
60
50 60 70 80 90
0
10
20
30
40
50
60
70
80
50 55 60 65 70 75 80 85 90
MW (GeV/c2)
Eve
nts
per
1 G
eV/c
2
ALEPHµνqq selection
√s = 188.6 GeV
Data
MC (mW = 80.27 GeV/c2)
Non-WW background
OPAL √s=189 GeV
0
10
20
30
40
50
60
70
70 80 90mrec/GeV
Eve
nts
WW→qqτν
Primarily from WW � � � � �
and � � � �Reconstruct (jet, ) angles and
energies
Kin. fit improves resolution:
� (E,p)�� � �� ( � ,0)
� � � � �
Fit to extract � (+ � � )
Statistical power:
� � � � � � � � �
Systematic errors significant
Dave Charlton LEP/SLD Electroweak (15) August 2002
Final-State Interactions
γ,Z
W–
W+
πo πo
K+ K+
π– π–
ColourReconnection
Bose-Einstein
WW � � � � � may suffer from “final-stateinteractions”: if the two hadronic W decays don’t
develop independently
Non-perturbative hadronisation process: needsmodels
Models of two types: “colour reconnection” (CR)and Bose-Einstein correlations (BE)
Ongoing work to compare models with data:
� BE between W decay hadrons small, so give low � shift
� CR studies focus mainly on particle flow - but several models givequite different effects
Dave Charlton LEP/SLD Electroweak (16) August 2002
Particle Flow & Colour Reconnection
10-1
1
0 1 2 3 4rescaled angle (φresc)
1/N
evt d
n/dφ
189-207 GeV (preliminary)W1 W2
L3 Data- WW → qqqq
A C B D
A
BC D
jet 2jet 1
jet 3jet 4
� ��� ��
� �� � �� �
� ��� � � � � � �
1
1.2
1.4
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1particle flowparticle flowparticle flowparticle flowparticle flow
φr
R
ALEPH data (189-207 GeV)
KoralW (JETSET)
KoralW (SKI 100%)
ALEPHpreliminary
0
2
4
6
0.8 1 1.2 1.4
OPAL
L3
DELPHI
ALEPH
LEP 0.969±0.015
r at 189 GeV
SK
-I 100%
No C
R
� � � �
� � � �� � � �� � � � � ��� ��
�
� � � �� � � �� � � � � �� ��
, � � �� �� ����� �� � �� ��
LEP combination now available, full LEP-2 data
Hints of CR effects, data-driven error on
� ( � � � � channel) from CR� 90 MeV
Dave Charlton LEP/SLD Electroweak (17) August 2002
W Mass Results
80.3 80.4 80.5 80.6 80.7MW[GeV]
ALEPH 80.458±0.055
DELPHI 80.404±0.074
L3 80.376±0.077
OPAL 80.490±0.065
LEP preliminary 80.447±0.042
CDF 80.433±0.079
D0 80.483±0.084
Tevatron Run-1 80.454±0.059
World average 80.450±0.034
In LEP � average, weightof � � � � channel just 9%
Also find
��� ��� � ��� � � ��
� � ��� � � �� � � ��
� � � ��� � � � � � GeV
2
2.1
2.2
2.3
80.2 80.3 80.4 80.5
MW [GeV]
Γ W
[GeV
]
Preliminary
68% CL
SMmHmt
∆α
Good agreement LEP-Tevatron,comparable precision per experiment
Dave Charlton LEP/SLD Electroweak (18) August 2002
Global Electroweak TestsUse precise LEP/SLD and Tevatron EW data to probe SM
(other inputs from NuTeV and atomic parity violation)
SM predictions from ZFITTER and TOPAZ0 electroweak libraries
Parameters:
� measured precisely by LEP-1 Z data
� � � �� � measured precisely by LEP-1 Z data
� � � � �� � calculated from low-energy measurements
� , � may be either predicted, or put in as measured
� may be predicted in this framework
Dave Charlton LEP/SLD Electroweak (19) August 2002
Predicting and
�
80.2
80.3
80.4
80.5
80.6
130 150 170 190 210
mH [GeV]114 300 1000
mt [GeV]
mW
[G
eV]
Preliminary
68% CL
∆α
LEP1, SLD Data
LEP2, pp− Data
LEP-1/SLD Z data, � � � � �� � ,NuTeV and APV results used to
predict � , �Compare with direct
measurements (Tev/LEP-2),and with SM relation between
� , � , �
Electroweak fit correctlypredicts the masses of the
heavy particles (W,top)
Both sets of data prefer a lightHiggs in the SM framework
Dave Charlton LEP/SLD Electroweak (20) August 2002
Fit to all Electroweak Data
Measurement Pull (Omeas−Ofit)/σmeas
-3 -2 -1 0 1 2 3
-3 -2 -1 0 1 2 3
∆αhad(mZ)∆α(5) 0.02761 ± 0.00036 -0.24
mZ [GeV]mZ [GeV] 91.1875 ± 0.0021 0.00
ΓZ [GeV]ΓZ [GeV] 2.4952 ± 0.0023 -0.41
σhad [nb]σ0 41.540 ± 0.037 1.63
RlRl 20.767 ± 0.025 1.04
AfbA0,l 0.01714 ± 0.00095 0.68
Al(Pτ)Al(Pτ) 0.1465 ± 0.0032 -0.55
RbRb 0.21644 ± 0.00065 1.01
RcRc 0.1718 ± 0.0031 -0.15
AfbA0,b 0.0995 ± 0.0017 -2.62
AfbA0,c 0.0713 ± 0.0036 -0.84
AbAb 0.922 ± 0.020 -0.64
AcAc 0.670 ± 0.026 0.06
Al(SLD)Al(SLD) 0.1513 ± 0.0021 1.46
sin2θeffsin2θlept(Qfb) 0.2324 ± 0.0012 0.87
mW [GeV]mW [GeV] 80.449 ± 0.034 1.62
ΓW [GeV]ΓW [GeV] 2.136 ± 0.069 0.62
mt [GeV]mt [GeV] 174.3 ± 5.1 0.00
sin2θW(νN)sin2θW(νN) 0.2277 ± 0.0016 3.00
QW(Cs)QW(Cs) -72.18 ± 0.46 1.52
Summer 2002
Full electroweak fit of all results,including � and �
Overall consistency �� /dof is
29.7/15 (1.3% probability)
Large �� contribution from NuTeV,
without it fit probability is 11%
Standard Model parameters ( �
etc) little affected by NuTeV
Go on to see what the SM fit saysabout �
Dave Charlton LEP/SLD Electroweak (21) August 2002
Constraining the SM Higgs
0
2
4
6
10020 400
mH [GeV]
∆χ2
Excluded Preliminary
∆αhad =∆α(5)
0.02761±0.00036
0.02747±0.00012
Without NuTeV
theory uncertaintyFit to all electroweak data inStandard Model framework
Theory uncertainty includesZFITTER/TOPAZ0 options,
partial two-loop calculations
NuTeV has little impact on �
results, but may affect whetherto believe the SM fit...
From the fit, obtain
� ' � �� �� � � � �
� � � &* GeV at 95% CL
Dave Charlton LEP/SLD Electroweak (22) August 2002
A Hint of the Higgs?
DALI
Run=56065 Evt=3253 ALEPH
4 Gev EC10 Gev HC
(φ−43 )*SIN(θ)
θ=180 θ=0
−xx
x
x
−
x
x
−
−x
−
x
x
−−
x −x xx
x
−
x
x
x−
−− x−
−
x
−
−
x
−x
x
−
−
−x
−
− −
−
x o
ooooooo
oo
oo
o
o
oo
o
oooo
o
oooo o
o
o
o
o
oo
o
ooo
oo
o
oo
22. GeV
P>2 Z0<5 D0<2 YX
0 −0.8cm 0.7cmX
0 −0.8cm
0.7cm
Y
e+
e− Z(∗) Z(∗)
H At LEP-2, main process is� � � � � ZH � � �
Rely on good b tagging and mass reconstruction
In September 2000, ALEPHreported an excess (3
events) in the � � channelconsistent in mass with a
115 GeV H
LEP run extended for 1month...
Dave Charlton LEP/SLD Electroweak (23) August 2002
LEP Higgs Search: Final Results
10-5
10-4
10-3
10-2
10-1
1
100 102 104 106 108 110 112 114 116 118 120
mH(GeV/c2)
1-C
Lb
3σ
2σ
4σ
LEP
ObservedExpected for signal+backgroundExpected for background
10-6
10-5
10-4
10-3
10-2
10-1
1
100 102 104 106 108 110 112 114 116 118 120
mH(GeV/c2)
CL
s
114.4 115.3
LEP
ObservedExpected forbackground
Final data, analyses and calibrations:
� no confirmation of ALEPH � �
excess
� no significant excess in final com-bined sample ( � 8%)
but extra statistics too limited to excludea 115 GeV SM Higgs
Sophisticated statistical combination ofchannels/experiments
Final direct search result:
� � 114.4 GeV (95% CL)(expected limit 115.3 GeV)
Dave Charlton LEP/SLD Electroweak (24) August 2002
HighlightsWealth of precise electroweak measurements from LEP and SLD
(and the Tevatron)
Amongst hundreds of other results, LEP/SLD have:
� shown there are three light neutrino species
� demonstrated radiative loop corrections
� predicted the top quark mass
� verified SM triple gauge couplings
� put many strong constraints on physics beyond the SM
� indicated where to look for the SM Higgs (and ”nearly” found it)...
LEP and SLD have provided a huge step forward for the Standard Model– but the Higgs sector waits for another day
Dave Charlton LEP/SLD Electroweak (25) August 2002