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W Boson Properties

Eric Torrence University of Oregon

formerly Enrico Fermi Institute University of Chicago
Eric Torrence Physics in Collision June 2001


Overview

Ç Introduction

Ç W Boson Production

Ç Decay Branching Fractions

Ç Electroweak Couplings

Ç W Mass and Width

Ç Conclusions All numbers from Moriond 2001
http://www.cern.ch/torrence/talks/PIC01
Eric Torrence Physics in Collision June 2001


Introduction

Eric Torrence

Physics in Collision

June 2001


Precision EW Tests Tree Level Parameters g g'
0

SU(2)L weak isospin coupling U(1) weak hypercharge coupling Vacuum EV of the Higgs field

Need three precision measurements
em : F: Z: 1 ( gg' ) 2 ----- ----------------4 g 2 + g' 2 11 ------ ----------2 8 0 0 ----------- g 2 + g' 2 (Electron g-2) (Muon Lifetime)
2

0.004 ppm 9 ppm 23 ppm

G m

(LEP I lineshape) 2

Measure

m

W,

sin

w to test theory!

Radiative corrections W t W b m
2 W

= ------------------------------- ( 1 + r ) 2 2 sin W G F

r = f ( m t2, ln ( m H ) )
Eric Torrence Physics in Collision June 2001


The LEP Collider at CERN

L3
e+e- collisions LEP I LEP II ~ 91 GeV 161 - 209 GeV (1990 - 1995) (1996 - 2000)

Eric Torrence

Physics in Collision

June 2001


The Tevatron at FNAL

pp collisions Run I Run II
Eric Torrence

1800 GeV 1960 GeV
Physics in Collision

(1992 - 1995) (2001 - 200?)
June 2001


Data Samples e+e- W +W
W
-

W

W


W

Z
W


W



WW

( 200 GeV ) 17 pb (2700 pb-1)

LEP II Total: 35k W pairs pp W X q qW
Trigger on W Å l only

l



WX

B ( W l ) 2.4 nb 200k W events
Physics in Collision

Run I Total:
Eric Torrence

(200 pb-1)
June 2001


W Production and Decay

Eric Torrence

Physics in Collision

June 2001


LEP WW Decay Modes W + W - lvlv SM Rate: 10.6%
Ç Two Leptons Ç Little Mass Information

~ 60-80%

~ 90%

W + W - qqlv SM Rate: 43.8%
Ç One Lepton, Two Jets Ç Low Backgrounds Ç Golden channel for mass

~ 70-85%

~ 90%

W + W - qqqq SM Rate: 45.6%
Ç Four Jets Ç Significant Backgrounds Ç No Missing Momentum

~ 80-90%
Eric Torrence

~ 80%
Physics in Collision June 2001

Worse performance with taus


Four Fermion Amplitudes CC03 Amplitudes:
W W W


W

Z
W


W

Convenient definition of resonant production Other diagrams with identical final states!

e + e - qqev
e e e

W

q q

W

q q

W

q q

Rely on complete 4f Monte Carlo Non-CC03 diagrams ~5%

Eric Torrence

Physics in Collision

June 2001


WW Cross Section
02/03/2001

LEP
20

Preliminary

RacoonWW / YFSWW 1.14

WW [pb]

15

10
18

YFSWW 1.14 RacoonWW

5

17

16

0

160

170

180

190

200

210

Ecm [GeV]

Complete Order Calculations
RacoonWW: Denner, Dittmaier, Roth, Wackeroth YFSWW: Jadach, Placzek, Skrzypek, Ward, Was
Eric Torrence Physics in Collision June 2001


LEP W Branching Fractions Leptonic Branching Fractions Br (WÅe): Br (WÅÅ): Br (WÅ):
2

10.54 Á 0.17 % 10.54 Á 0.16 % 11.09 Á 0.22 %

/ dof = 14.9 / 9

SM: 10.83% Assume Lepton Universality Br (WÅqq):
2

67.92 Á 0.27 %

/ dof = 18.8 / 11

SM: 67.51% CKM Interpretation
Br ( W q q ) ---------------------------------------- = ( 1 + s ( m W ) / ) 1 - Br ( W q q )
( u, c

, ), ( d

V
s, b )

ij

2

( u, c

), ( d,
cs

V
s, b )

ij

2

= 2.039 Á 0.025

V

= 0.996 Á 0.013
[Winter 01 Preliminary LEP Combined]

Eric Torrence

Physics in Collision

June 2001


Charm Production
Number of Vertices
10
3

OPAL
183-189 GeV

10

2

Data charm uds Non-WW

10

1

0

2.5

5

7.5

10

12.5

15

17.5 20 22.5 25 Decay Length Significance

Number of Jets

10

3

OPAL
183-189 GeV

Data charm uds Non-WW

10

2

10 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Combined Likelihood Output

R

W c

= 0.481 Á 0.042 ( stat ) Á 0.032 ( syst )
cd 2

3 CG F m W Using ( W c X ) = -------------------- ( V 6 2

+V

cs

2

+V

cb

2

)

V
Eric Torrence

cs

= 0.969 Á 0.058
[Opal Collaboration, Phys. Lett. B490 (2000) 71] Physics in Collision June 2001


Tevatron W/Z Cross Sections

s = 1800 GeV
3

W Ç B (nb)

Dè W l

CDF

O(s2) Theory (van Neerven et al.)

2.5

e
2

e Å
+ Zl l -

e

Å



0.3

Z Ç B (nb)

0.25

0.2

e Å

e

e

e Å

Å

0.15

Å 94/96 92/93 94/96

Data set: 92/93

Note different normalization: (CDF) = 1.06 (D0) Experimental Uncertainty ~ 2% Luminosity Uncertainty ~ 4% Theory Uncertainty ~ 3%

(Dominated by PDFs)

Use Br (WÅe) to measure Run II Lumi?
Eric Torrence Physics in Collision June 2001


Tevatron Cross Section Ratio Z W (W e) Br ( W e ) ------- -------------------------- ------------------------------------------------------------------ = Z ( Z e e ) W Br ( Z e e ) W / Z from QCD
[Hamberg, van Neerven, Matsuura]

Br ( Z e e ) from LEP I Extract branching fraction Br ( W e ) = 10.45 Á 0.20 %
(CDF+D0)

Indirect Width Assume SM partial width ( W e ) = 226.5 Á 0.3 MeV
[Rosner, Worah, Takeushi]

Extract W width W ( CDF + D 0 ) = 2.167 Á 0.040 GeV W ( SM ) = 2.093 Á 0.003 GeV
[PDG 2000]

Eric Torrence

Physics in Collision

June 2001


Gauge Boson Couplings

Eric Torrence

Physics in Collision

June 2001


Charged Triple Gauge Couplings Non-Abelian Gauge Theory
W W


W

Z
W

Lorentz invariance Need 2 ç 7 parameters... Gauge invariance, C, P, CP conservation
Z { , Z, , Z, g1 } In SM, =
Z

=g

Z 1

= 1 , =

Z

=0
W

Magnetic Dipole Moment: Å

W

= e ( 1 + + ) / 2 m
W

Electric Quadrupole Moment: Q

= -e ( - ) / m

2 W

Measure deviations allowed by LEP I = - 1 , g
Eric Torrence

Z 1

Z = g1 - 1 ,

Physics in Collision

June 2001


LEP TGC Results
W e

W W

/
W

W

W

Fit Production and Decay Cross Sections
0.3

LEP

0.3
Preliminar y

LEP

Preliminar y

0.15

0.15



0


68% CL 95% CL -0.15

0

-0.15 SM 0 0.15 0.3

-0.15 68% CL 95% CL -0.15 SM 0 0.15 0.3

-0.3 -0.3

-0.3 -0.3



gZ 1



gZ 1

Single Parameter Fits* k = - 0.002 Á 0.066 g = - 0.025 Á 0.026
Z 1

*Summer 2000 Order(EM) effects not yet included...
June 2001

= - 0.036 Á 0.028
Eric Torrence

Physics in Collision


Tevatron TGC Analyses Associated production
W

/ W Pair production /
W W



l+ lll lqq qqll

WZ final states marginal at Run I



ll qql

D0 combined analysis (l+, ll, qql) Measure cross sections and p - 0.25 0.31 ( = 0 ) - 0.18 0.18 ( = 0 ) [95% CL] Expect ~2-3X better at Run II [Competitive with single LEP experiment]
Eric Torrence Physics in Collision June 2001

W T


Charged Quartic Gauge Couplings
W

W /
W
SM prediction negligible at LEP II



W

Look for anomalous QGCs Lorentz Structure
e 2 a0 -L 0 = - ----- ----- F 16 2 e 2 ac -L c = - ----- ----- F 16 2
Å

F

Å

W W W W






CP conserving (WW) CP conserving (WW)

Å

F

Å



[Belanger and Boudjema, Nucl. Phys. B288, 201 (1992)]

e 2 an -L n = - i ----- ----- ijk W 16 2

(i) Å

W

( j)

W

( k ) F Å

CP violating (WWZ)

[Stirling and Werthenback, EPJ C14, 103 (2000)]

Measure cross sections, E , or m
Eric Torrence Physics in Collision

recoil
June 2001


LEP QGC Results

Events

30 25 20 15 10 5 0 5

L3 preliminary

Data 189-202 GeV ISR an/ = 0.4 GeV FSR Bkg WW, ZZ, Zee, qq
2 -2

10

15

20

25

30

35

E



GeV

Unofficial LEP combination
Aleph L3

(M. Musy Moriond `01) Opal

WW

189-202 GeV 183-202 GeV 189 GeV 183-202 GeV 189 GeV

95% CL limits (in GeV-2): - 0.022 < a 0 / 2 < 0.021 - 0.043 < a c / 2 < 0.058 - 0.22 < a n / 2 < 0.20
Eric Torrence Physics in Collision June 2001


W Boson Mass

Eric Torrence

Physics in Collision

June 2001


Tevatron Mass Analysis g
W

q q

l



l
Spectator


U

QCD ISR

Transverse Mass m
T

=

l 2 E T E T ( 1 - cos l )

Missing Transverse Momentum:

p

T

l = -( pT + U )

MC Spectrum m T ( m W )
l Ç Energy scale and resolution E T m W ~ Á ( 80 25 ) MeV

Ç QCD Recoil model (U) m W ~ Á 40 MeV Ç PDF model (W Rapidity) m W ~ Á 15 MeV
Eric Torrence Physics in Collision

P P

W T W Z

June 2001


Run I Mass Results
# Events 2000
CDF(1B) Preliminary We

1500

/df = 82.6/70 (50 < MT < 120) 2 /df = 32.4/35 (65 < MT < 100) Mw = 80.473 +/- 0.065 (stat) GeV Backgrounds KS(prob) = 16%

2

1000

500 Fit region 0 50 60 70 80 90 100 110 120 Transverse Mass (GeV)

CDF Ç Use W e e and Å Ç Central only l < 1
Å

m W ( CDF ) = 80.433 Á 0.079 GeV D0
e Ç Use W e e only, also fit p T & p T Ç Include forward electrons 1.5 < l < 2.5

m W ( D 0 ) = 80.482 Á 0.091 GeV*
Eric Torrence Physics in Collision June 2001


Run I Systematics "Typical" Uncertainties per Channel Uncertainty Statistical scale resolution backgrounds recoil PDF HOC Systematic [MeV] 60-100 80 25 15 40 15 15 95
[D.Glenzinski, Moriond 2001]

largely statistical (constrain with data) correlated between channels correlated between experiments Significant room for improvement at Run II m W ( 2 fb - 1 ) < 40 MeV/exp ???
Eric Torrence Physics in Collision June 2001


D0 Energy Scale
number of events

Calibrate using data E = E
meas

300 250 200 150 100 50 0 60

+

Z ee

0 eeee J / ee Z 0 ee

70

80

90

100

110

120

m(ee) (GeV)

EM

0.960 0.958 0.956 0.954 0.952 0.950 0.948 0.946 0.944 0.942
0.955 0.954 0.953 0.952 0.951 -0.25

-0.2

-0.15

-0.1

Z 0 J/ EM (GeV)

0.940 -0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5

Eric Torrence

Physics in Collision

June 2001


CDF Production Model
# Events # Events 160 140 120 100 80 60 40 20 0 50 40 30 20 10 0 -10 -20 -30 -40 -50 Uncertainty in pT(W) % 0 10 20 30 40 pT(ee) (GeV) /df=0.82
2

350 300 250 200 150 100 50 0 0 10 20 30 40 50 pT(Z)ÅÅ /df = 1.28
2

CDF(1B) Preliminary Zee

CDF(1B) Preliminary ZÅÅ

Uncertainty from Z statistics

pT(W) in MC 0.04

0.02
Theory Uncertainty (PDFs, Input pT)

0

10

20

30 40 pT (GeV)

0

0

10

20 30 pT(W) : W Å

Eric Torrence

Physics in Collision

June 2001


LEP Mass Analysis Kinematic fitting e+
W+ W-

e-

E

0

=

2E m
+ w

beam

,

p

0

=

0

4 Constraints 1 Constraint

=m

- w

WW



qqlv q
WW

l

3 Unknowns

q WW


5 - 3 = 2C Fit

qqqq q
WW

q q
Physics in Collision

0 Unknowns

q
Eric Torrence

5 - 0 = 5C Fit

June 2001


LEP Mass Spectrum
Expected Events
Breit Wigner Reconstructed mW = 80.330 GeV W = 2.093 GeV

60

70

80 90 100 qql Invariant Mass (GeV)

Initial State Radiation: Detector Resolution: Non-CC03 Diagrams:

E0 2E mw (
rec

beam

) m w ( true )

qqev, qqqq

Cannot directly fit Breit-Wigner Aleph, L3, Opal: Delphi:
Eric Torrence

Reweight MC to Data Likelihood Convolution

Physics in Collision

June 2001


WW



qqqq Jet Pairing

Expected Events

Correct Incorrect

All Combinations

60

70

80

90

100

Selected Pairing

60

70

80 90 100 qqqq Invariant Mass (GeV)

Aleph, Opal: L3: Delphi:
Eric Torrence

Jet pairing selection Highest 5C fit probability Use all Combinations
Physics in Collision June 2001


W Mass Spectra qqe
Events per 1 GeV/c Events per 1 GeV/c
80 70 60 50 40 30 20 10 0 50 55 60 65 70 75 80 85 90 95 100
2

qqÅ
80 70 60 50 40 30 20 10 0 50 55 60 65 70 75 80 85 90 95 100
2 2

2

ALEPH Preliminary
eqq selection
Data (Luminosity = 217 pb ) MC (mW = 80.80 GeV/c2) Non-WW background
-1

s > 202 GeV

ALEPH Preliminary
Åqq selection
Data (Luminosity = 217 pb ) MC (mW = 80.31 GeV/c2) Non-WW background
-1

s > 202 GeV

MW (GeV/c )

MW (GeV/c )

qq

qqqq

Aleph 2000 data (preliminary)

Eric Torrence

Physics in Collision

June 2001


LEP W Mass Results

LEP W-Mass (171-209 GeV)
Winter 2001 Preliminary

Aleph Delphi L3 Opal LEP

80.477 Á 0.049 GeV 80.378 Á 0.072 GeV 80.389 Á 0.069 GeV 80.486 Á 0.065 GeV 80.447 Á 0.040 GeV LEP 0.017 GeV 2 /dof = 30/33

Delphi & Opal [171-202] GeV

80

80.2 80.4 80.6 80.8 MW (GeV)

LEP Combined (preliminary) m W ( LEP ) = 80.446 Á 0.040 GeV
[Including threshold cross section]
Eric Torrence Physics in Collision June 2001


LEP Systematic Uncertainties Direct Reconstruction Results (preliminary) m
W

= 80.447 Á 0.026 ( stat ) Á 0.030 ( syst ) Systematics Limited!

Moriond 2001 Combination Ç Preliminary Procedure Ç Conservative Correlations Uncertainty qql [MeV] qqqq [MeV] Detector 11 8 ISR/FSR 8 8 Hadronization 19 17 LEP Beam Energy 17 17 Bose - Einstein Corr. 25 Color Reconnection 40
[Component of total error indicated]

Weight from qqqq only 0.27 m
Eric Torrence

W

(no syst) = 22 MeV
Physics in Collision June 2001


LEP Detector Systematics Calibration Data: Z l l , Z 0 qq
0

+-

Ç Jet/Lepton Energy/Angle Scale/Resolution Ç Detector Alignment/Biases
1.05 1.04 1.03 1.02 1.01

ALEPH
Jet Energy Corrections

1.00
0.99 0.98 -1

-0.6

-0.2

0.2

0.6

1 cos

Mixed Lorentz Boosted Z (Delphi)

+

=

Ç Boost to match WW Monte Carlo Ç Useful for Fragmentation as well
Eric Torrence Physics in Collision June 2001


Final State Interactions ++ W+ / 00 WK-K-

CR

BE

Interactions between decay products shift in MW MW(qqqq) - MW(qql) = + 18 Á 46 MeV Color Reconnection
Ç Strong (QCD) interactions in non-perturbative phase Ç Only a few models exist, difficult to calculate

Bose-Einstein Correlations
Ç Well established in single W or Z decays Ç Difficult to model properly in WW system

Constrain using Data!
Eric Torrence Physics in Collision June 2001


Color Reconnection
1/Nevtd/d
n

6

data (189 GeV) WW (jetset) ZZ, qq

ALEPH preliminary

4

W-jets

W-jets

2

A

C

B

D

0 0

0.5

1

1.5 2 2.5 3 norm. particle flow

3.5

4 n

1/Nevtd/dr(A+B)/(C+D)

1.5

data (combined 189 - 208 GeV) KoralW (jetset) KoralW (sk1 100%) KoralW (ariadne crc2)

1

0
Eric Torrence

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
Physics in Collision



1
r

June 2001


Bose-Einstein Correlations

+
=
WW

=
W WW mix

- 2 - 2

1 dn pairs where = --- ---------------N dQ

Model Independent!
20

data inter-W no inter-W

L3

(Á,Á) [GeV ]

-1

15 10 5 0 -5

-10 0

PRELIMINARY 98+99 DATA
0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

Q [GeV]

No evidence for inter-W BE correlations
Eric Torrence Physics in Collision June 2001


LEP II Beam Energy
E
Beam

(GeV)
Beam Energy in Physics

from RDP

apolation Extr
60 50 40
Simultaneous Measurements

445

555

665

1000

B

NMR

(Gauss)

Ç Resonant Depolarization Ebeam< 1 MeV Limited to Ebeam < 60 GeV Ç NMR Extrapolation Ebeam= 20 MeV MW = 17 MeV Extrapolation Checks Ç Inline Spectrometer Ebeam= 20 MeV? Ç Synchrotron Qs vs. VRF Ebeam= 20 MeV? Work continues...
Eric Torrence Physics in Collision June 2001


LEP II Radiative Returns f e+e- Å f f Statistics
Channel Ebeam

1 f
Number of Events / 1 GeV

2

sin 1 + sin 2 - sin ( 1 + 2 ) s' -- = -----------------------------------------------------------------------sin 1 + sin 2 + sin ( 1 + 2 ) s

300

Data qq M.C. reweighted M.C. background 183 GeV Data MZ = 91.172 Á 0.098 GeV

L3

qq ÅÅ

~ 20 MeV ~ 50 MeV

200

LEP Combined Statistics Only

100

0 70

80

90

100

110

m

inv

[ GeV]

Systematics
Ç Theoretical Description Ç Hadronization Uncertainties Ç Detector Understanding Preliminary Estimates qq Ebeam ~ 70 MeV ÅÅ Ebeam ~ 40 MeV

Eric Torrence

Physics in Collision

June 2001


World W Mass Results
Aleph * Delphi L3 * Opal LEP
* [171-202] GeV Only

80.477 80.378 80.389 80.486 80.446 2

/dof = 30/33

Á Á Á Á Á

0.049 0.072 0.069 0.065 0.040

CDF D0 Hadron Colliders World Average NuTeV LEP1/SLD/N
80.2 80.4

80.433 Á 0.079 80.482 Á 0.091 80.452 Á 0.062 80.448 Á 0.034
[Winter 2001 Preliminar y]

80.25 Á 0.11 80.357 Á 0.033
80.6

MW (GeV)

Ç LEP II Final

MW ~ 20 MeV (stat) ~ 35 MeV (total)?

Ç Run IIa (2 fb-1) MW ~ 40 MeV (each)? MW ~ 20 MeV by 2006 Ç LHC (10 fb-1)
Eric Torrence

MW ~ 20 MeV (each)??
June 2001

Physics in Collision


Direct Width
Aleph Delphi L3 Opal LEP CDF direct Direct Average CDF/D0 indirect Standard Model
1.9 2 2.1 2.2 2.3

2.13 Á 2.10 Á 2.14 Á 2.04 Á 2.148
2

/dof = 18/21

0.14 0.14 0.19 0.18 Á 0.095

2.06 Á 0.12 2.114 Á 0.076
[Winter 2001 Preliminar y]

2.167 Á 0.040 2.093 Á 0.003 W (GeV)

LEP W ( qqqq ) - W ( qql ) useful for CR?
Not all LEPII data analyzed...

Tevatron D0 direct width coming this summer

Eric Torrence

Physics in Collision

June 2001


Global Results

Eric Torrence

Physics in Collision

June 2001


Standard Model Consistency

80.6
LEP1, SLD, N Data - LEP2, pp Data 68% CL

80.5

[GeV] m
W

80.4

80.3 mH [GeV] 113 300 1000 80.2 130 150 170
Preliminary

190

210

mt [GeV]
Direct measurements on the SUSY-side Light Higgs preferred!

Eric Torrence

Physics in Collision

June 2001


SM Higgs Boson

6

theor y uncer tainty

(5) had

=

0.02761Á0.00036 0.02738Á0.00020

4

2
2 Excluded 10
Simple Parameterization sin
2 eff W

0

Preliminary
2

mH [GeV]

,m

W

= f (m

2 top

, ln ( m H ),

QED

)

[Degrassi et al.]

Poor man's ZFITTER!
Eric Torrence Physics in Collision June 2001


SM Higgs Constraint Using m
W

= f (m

2 top

, ln ( m H ),

QED

)

ln ( m H ) = Á 0.60 Á 0.55 ( m t ) Á 0.11 ( h ) = Á 0.82 ( total )

Using sin

2 eff W

= f (m

2 top

, ln ( m H ),

QED

)

ln ( m H ) = Á 0.32 Á 0.31 ( m t ) Á 0.24 ( h ) = Á 0.51 ( total )

After Run IIa (2 fb-1) m t = 3 GeV, m
W

= 20 MeV (expected)

Using m

W

alone

ln ( m H ) = Á 0.34 Á 0.32 ( m t ) Á 0.11 ( h ) = Á 0.49 ( total )

Using sin

2 eff W

alone

ln ( m H ) = Á 0.32 Á 0.18 ( m t ) Á 0.24 ( h ) = Á 0.44 ( total )

Eric Torrence

Physics in Collision

June 2001


Summary Final LEP II Performance Ç Ç Lint ~ 650 pb-1 per experiment ECM 209 GeV Br (WÅqq): V
cs

Physics Highlights 67.92 Á 0.27 % = 0.996 Á 0.013

Triple Gauge Couplings: 3-6% precision achieved W Boson Mass: m
W

= 80.446 Á 0.034 GeV

Five Year Plan Run IIa: Lots of EW physics in 2 fb-1 m W 20 MeV m
top

3 GeV

Time for more hadrons!

Eric Torrence

Physics in Collision

June 2001