40th ssi: 23 years of precision electroweak physics file1 40th ssi: 23 years of precision...

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40th SSI: 23 Years of Precision Electroweak Physics

Johns Hopkins University

M. Swartz

2

• 1957: Schwinger proposes unifying weak and em interactions• 1961: Glashow proposes SU(2)xU(1) but no SSB• 1964: Brout, Englert, Higgs, Guralnik, Hagen, Kibble propose relativistic

Spontaneous Symmetry Breaking• 1967-1968: Weinberg, Salam add SSB/Higgs Mechanism to SU(2)xU(1)• 1971: ‘t Hooft proves renormalizability• 1973: Neutral currents seen in Gargamelle• 1977-1978: Observation of tree-level ew interference - divergent results from optical rotation in atomic Bi spectra- polarized asymmetry in eD scattering here at SLAC (E122)

• 1983: Observation of W and Z at CERN SppS Collider• 1987-1996: Tevatron Run I: CDF, D0• 1989-1998: “Golden Era” of e+e- Z-pole EW measurements- SLC: MkII (1989-1990), SLD (1991-1998), polarized 1992+- LEP (1989-1995): Aleph, Delphi, L3, Opal

Electroweak Timeline

3

• early 1989: MZ and MW known at 1-2 GeV level- everything until now is known at “tree-level” accuracy- define “Precise” to mean “loop-level” accuracy

• SSI 1989: first precise measurements of MZ

- ±0.36 GeV (CDF) and ±0.12 GeV (MkII)- by late autumn, LEP ran and reduced this to ±0.02-0.03 GeV level

(enroute to ±0.002 GeV level)• 1995: observation of the top quark by CDF, D0• 1996-1997: NuTeV at FNAL• 1996-2001: LEP 2 • 2001-2003: E158 (polarized e-e-) at SLAC• 2001-2011: Tevatron Run II• 2011-2012: LHC • summer 2012: observation of a Higgs candidate by Atlas, CMS- we finally have everything we need to TEST the EW SM!

Electroweak Timeline

PrecisionEW

Begins

4

Electroweak TimelineThe field of Precision Electroweak Tests was born at SSI 1989 and now reaches full maturity (maybe?) at SSI 2012. This is a long time but it’s also a familiar period to the parents of children:

4

Stanford, CA Summer 1989


4

Pittsburgh, PA Summer 2012Stanford, CA Summer 1989


5

Three series of three lectures (9 hours!):• SSI 1987: “Physics with Polarized Beams” (25 years ago!!!)• SSI 1989: “Precision Experiments in Electroweak Interactions”• SSI 1995: “Precise Electroweak Measurements: The View from Below”

MS and the SSI

L =� g

2p2 f�µ (1� �5) {⌧+W+

µ + ⌧�W�} f

� gg0p

g2 + (g0)2Qf f�µ1 fAµ

�p

g2 + (g0)2

4 f

n

�

2IL3 � 4Qf sin2 ✓W

�

| {z }

vf

�µ +�

�2IL3�

| {z }

af

�µ�5o

fZµ

sin ✓W =g0

p

g2 + (g0)2, MW =

gp2h�i, MZ =

r

g2 + (g0)2

2h�i

6

depends entirely on 3 parameters:• g - SU(2) coupling constant• g’ - U(1) coupling constant• <f> - Vacuum expectation value of the Higgs field

Precision Electroweak PhysicsThe interaction of the gauge bosons with fermions at tree-level in the MSM is described by

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• we can predict any quantity at tree-level• a 4th accurately measured quantity TESTS the model?- well, not really: higher order corrections involve all of the other

parameters of the theory.- in 1989, there were two important and unknown MSM states: the

top quark and the Higgs boson- in 2012, we’ve finally arrived at the ability to test the theory at

the <10-3 level‣ Higgs (?) discovered, top mass measured to < 1 GeV‣ can look more sensitively for unknown physics

We can derive these parameters from 3 precisely measured quantities

Quantity EW Parameters Current Value Precision

a (gg’)2/{4p[g2+(g’)2]} [137.035999679(94)]-1 0.68 ppb

GF <f>-2(8)-1/2 1.16637(1)x10-5 GeV-2 9 ppm

MZ <f>{[g2+(g’)2]/2}1/2 91.1876(21) GeV 23 ppm

f

Z f

e-

e+

f

Z f

e-

e+ Z

Tree-level

f

A f

e-

e+Interference

f

Z f

e-

e+Externalradiation

f

Z f

e-

e+Vertexcorrection

Vacuumpolarization“oblique”

8

• Z-A interference can make large corrections- sensitive to energy scale- not particularly sensitive to new

physics• External rad does affect observables- not sensitive to new physics- gluon radiation sensitive to as

• Vertex corrections can be sensitive to new physics- (mundane) strong vertex

corrections are sensitive to as

• VPol corrections can be sensitive to new physics- strong corrs to A are not reliably

calculable

Radiative CorrectionsRadiative corrections affect all particle physics measurements. They fall into less and more interesting categories:

f

fA A �↵(q2) =

↵(q2)� ↵0

↵(q2)= ⇧0

��(q2)�⇧0

��(0)

�↵had(q2) =

↵0

3⇡P

Z 1

4m2⇡

dsq2

s(q2 � s)Rhad(s)

10. Electroweak model and constraints on new physics 5

Table 10.1: Recent evaluations of the on-shell !!(5)had(MZ). For better comparison

we adjusted central values and errors to correspond to a common and fixed value of!s(MZ) = 0.120. References quoting results without the top quark decoupled areconverted to the five flavor definition. Ref. [33] uses "QCD = 380± 60 MeV; for theconversion we assumed !s(MZ) = 0.118 ± 0.003.

Reference Result Comment

Martin, Zeppenfeld [23] 0.02744 ± 0.00036 PQCD for!

s > 3 GeV

Eidelman, Jegerlehner [24] 0.02803 ± 0.00065 PQCD for!

s > 40 GeV

Geshkenbein, Morgunov [25] 0.02780 ± 0.00006 O(!s) resonance model

Burkhardt, Pietrzyk [26] 0.0280 ± 0.0007 PQCD for!

s > 40 GeV

Swartz [27] 0.02754 ± 0.00046 use of fitting function

Alemany et al. [28] 0.02816 ± 0.00062 incl. " decay data

Krasnikov, Rodenberg [29] 0.02737 ± 0.00039 PQCD for!

s > 2.3 GeV

Davier & Hocker [30] 0.02784 ± 0.00022 PQCD for!

s > 1.8 GeV

Kuhn & Steinhauser [31] 0.02778 ± 0.00016 complete O(!2s)

Erler [19] 0.02779 ± 0.00020 conv. from MS scheme

Davier & Hocker [32] 0.02770 ± 0.00015 use of QCD sum rules

Groote et al. [33] 0.02787 ± 0.00032 use of QCD sum rules

Martin et al. [34] 0.02741 ± 0.00019 incl. new BES data

Burkhardt, Pietrzyk [35] 0.02763 ± 0.00036 PQCD for!

s > 12 GeV

de Troconiz, Yndurain [36] 0.02754 ± 0.00010 PQCD for s > 2 GeV2

Jegerlehner [37] 0.02765 ± 0.00013 conv. from MOM scheme

Hagiwara et al. [38] 0.02757 ± 0.00023 PQCD for!

s > 11.09 GeV

Burkhardt, Pietrzyk [39] 0.02760 ± 0.00035 incl. KLOE data

Hagiwara et al. [40] 0.02770 ± 0.00022 incl. selected KLOE data

Jegerlehner [41] 0.02755 ± 0.00013 Adler function approach

Davier et al. [20] 0.02750 ± 0.00010 e+e! data

Davier et al. [20] 0.02762 ± 0.00011 incl. " decay data

Hagiwara et al. [42] 0.02764 ± 0.00014 e+e! data

is, however, some discrepancy between analyses based on e+e! " hadrons cross-sectiondata and those based on " decay spectral functions [20]. The latter utilize data fromOPAL [43], CLEO [44], ALEPH [45], and Belle [46] and imply lower central values

June 18, 2012 16:19

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Rhad(s)=s(e+e-->hadrons)/s(e+e-->m+m-)• Integral is dominated by low energy

(1-5 GeV e+e- cross section)- multiple data and theory-based

evaluations- Dahad(MZ) = 2.75-2.80x10-2

- take Dahad(MZ) = (2.752±0.010)x10-2

• Total correction is ~6%

They can be reliably calculated for lepton-loops [Dalep(MZ) = 3.1498x10-2] but not for quark loops. The quark contributions are extracted from a dispersion integral

Vacuum polarization corrections to the photon propagator modify the em coupling constant at larger mass scales,

fromRPP 2012

a(0)

GF

MZ

Mt

Dahad

MH

Tree-level

EW-interference

External radiation

Vertex corrections

Oblique corrections

Radiative Corr Simulation

ExperimentalObservable(s)

Pseudo-Observable

as(MZ)

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• Use a full EW + detector simulation to model data- assume MSM is correct- adjust input parameters to

achieve good model• Use same simulation to

calculate a closely-related “Pseudo-Observable”- remove experimental

effects- remove “uninteresting”

radiative effects

ObservablesExperiments measure quantities that are not simple electroweak parameters: they include experimental acceptance, efficiency, + resolution effects in addition to all of the classes of radiative corrections.

- try to avoid “disturbing” the vpol and vtx effects or biasing answer‣ scheme mostly succeeds except in the case of neutrino x-section

ratios where quoted parameter has nothing to do with observable

ZFITTER 6.43

d�obs

ff

d⌦(s) =

d�Z

ff

d⌦(s) +

d�Z�

ff

d⌦(s) +

d��

ff

d⌦(s).

d�

obs

ff

d⌦(s) =

Zdx1dx2De

(x1, s)De

(x2, s)d�

obs

ff

d⌦(sx1x2)

Year Centre-of-mass Integrated

energy range luminosity

[GeV] [pb

�1]

1989 88.2 – 94.2 1.7

1990 88.2 – 94.2 8.6

1991 88.5 – 93.7 18.9

1992 91.3 28.6

1993 89.4, 91.2, 93.0 40.0

1994 91.2 64.5

1995 89.4, 91.3, 93.0 39.8

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• The electron structure functions represent the probabilities that the primary electron and positron retain a fraction x of their momenta after radiation of 1-x in photons

• The LEP/SLC experiments were operated near the Z-pole energy- interference terms formally vanish on

the Z-pole energy but initial state radiation smears energies

Z-Pole Results (1989-1998)The cross section for e+e-->ff near the Z-Pole has significant corrections from photon x-change and initial state radiation,

LEP Z-pole operations

d�ffZ

d⌦=

9

4

sM2

Z�ee�ff

(s�M2Z)

2 + s2

M2Z�2Z

�(1 + c2)[1� PAe] + 2cAf [Ae � P ]

d�ffZ

d⌦=

9

4

sM2

Z�ee�ff

(s�M2Z)

2 + s2

M2Z�2Z

⇢(1 + c2) +

8

3cAf

FB

�, Af

FB =3

4AeAf

�ffZ = �0

ff

s�2Z

(s�M2Z)

2 + s2

M2Z�2Z

, �0ff =

12⇡

M2Z

�ee�ff

�2Z

�f ¯f =NcGFM3

Z

24⇡p2

�v2f + a2f

�

⇥ [1 + �vtx

+�vtx

]

�Z =X

f

�f ¯f

Af =2vfafv2f + a2f

=(gfL)

2 � (gfR)2

(gfL)2 + (gfR)

2

12

• Lineshape is sensitive to mass + widths- total width includes “invisible” partial

width from neutrino final states• Angular distribution is sensitive to the

Af parameters• Vertex corrections to partial widths- all: dvtx = 3Qf2a(MZ)/(4p) + ...- quarks: Dvtx = as(MZ)/p + ...

The Z-pole cross section can be expressed in a relatively model-ind way,

• Electron polarization (P) modulates the symmetric angular dist (total x-section) and increases the cos(theta)-odd term

1 kmLEP

ALEPH

L3DELPHI

OPAL

SPS

PS

France

JuraMountains

Geneva Airport

Switzerland

FinalFocus IP

ComptonPolarimeter

Collider Arcs

Linac

e+ Source

e+ Return Line

Spin RotationSolenoids

ThermionicSource

Polarized e< Source

Electron SpinDirection

e+Damping Ring

e<Damping Ring e< Spin

Vertical

e< Extr. Line Spectrometer

e+ Extr. Line Spectrometer

(LTR Solenoid)

1 km

13

• The LEP beam energy calibration was based upon resonant depolarization of S-T transverse pol (20-30%) that could be developed from special tunes:- single beam energy scale ±0.2 MeV- transfer to collision tunes + tracking

in time worsens Ecm scale to 2 MeV‣ ground deformation, tides, and

electric trains caused drift- physics running w/ unpolarized beams

• The SLC operated with large (73-77%) average longitudinal beam polarization from GaAs photoemission gun- Ecm scale is ±29 MeV from precisely

calibrated spectrometers‣ checked with 3-point resonance

scan at end of last run

LEP and SLCLEP was the last high energy circular e+e- collider. SLC was the first (and hopefully not last) linear e+e- collider. Polarized beams played a role at both:

Ecm [GeV]

AF

B(µ

)

AFB from fit

QED correctedaverage measurements

ALEPHDELPHIL3OPAL

MZ

AFB0

-0.4

-0.2

0

0.2

0.4

88 90 92 94Ecm [GeV]

mha

d [n

b]

m from fitQED corrected

measurements (error barsincreased by factor 10)

ALEPHDELPHIL3OPAL

m0

KZ

MZ

10

20

30

40

86 88 90 92 94

Number of EventsZ0 ! qq Z0 ! `+`�

Year A D L O LEP A D L O LEP

1990/91 433 357 416 454 1660 53 36 39 58 1861992 633 697 678 733 2741 77 70 59 88 2941993 630 682 646 649 2607 78 75 64 79 2961994 1640 1310 1359 1601 5910 202 137 127 191 6571995 735 659 526 659 2579 90 66 54 81 291Total 4071 3705 3625 4096 15497 500 384 343 497 1724

14

The LEP experiments (Aleph, Delphi, L3, Opal) acquired a total Z-peak sample of more than 16M events.

Z-Resonance Parameters

They simultaneously fit angle-integrated hadronic and angle-dep leptonic final states to the smeared

The leptonic FB asymmetries are sensitive to very energy dependent interference corrections and are included in the MZ analysis to reduce systematics.

lineshape fcn to extract MZ, GZ, shad, Rl= Ghad/Gll, AFB(l) with and without lepton universality assumptions (electron final states have t-channel A and need special handling).

ALEPH

DELPHI

L3

OPAL

LEP

91.1893±0.0031

91.1863±0.0028

91.1894±0.0030

91.1853±0.0029

91.1875±0.0021common: 0.0017r2/DoF = 2.2/3

mZ [GeV]91.18 91.19 91.2

ALEPH

DELPHI

L3

OPAL

LEP

2.4959±0.0043

2.4876±0.0041

2.5025±0.0041

2.4947±0.0041

2.4952±0.0023common: 0.0012r2/DoF = 7.3/3

KZ [GeV]2.48 2.49 2.5 2.51

ALEPH

DELPHI

L3

OPAL

LEP

41.559±0.057

41.578±0.069

41.536±0.055

41.502±0.055

41.540±0.037common: 0.028r2/DoF = 1.2/3

m0 had [nb]

41.4 41.5 41.6 41.7

ALEPH

DELPHI

L3

OPAL

LEP

20.729±0.039

20.730±0.060

20.809±0.060

20.822±0.044

20.767±0.025common: 0.007r2/DoF = 3.5/3

R0l

20.7 20.8 20.9

ALEPH

DELPHI

L3

OPAL

LEP

0.0173±0.0016

0.0187±0.0019

0.0192±0.0024

0.0145±0.0017

0.0171±0.0010common: 0.0003r2/DoF = 3.9/3

Afb0,l

0.015 0.02 0.025

0

10

20

30

86 88 90 92 94Ecm [GeV]

mha

d [n

b]

3i

2i

4i

average measurements,error bars increased by factor 10

ALEPHDELPHIL3OPAL

15

• GZ - has interesting sensitivity to the vpol corrections• shad, GZ, Rl determine Ginvis + the num of light neutrinos Nn [2.984±0.008]• shad and Rl accurately and cleanly determine as(MZ) from vtx corrections• AFB(l) is an important ingredient in the determination of Al

-40

-20

0

20

40

6E

[MeV]

16

The systematic uncertainties on these measurements are small but from several sources:• Event Selection: ±0.04-0.1% (qq) and ±0.1-0.7% (ll)• Luminosity: - ±0.033-0.09% experimental- ±0.054-0.06% Bhabha xsection [B. Ward et al., PL B450, 262 (1999)]

• QED Corrections: ±0.02% on shad and ±0.5 MeV on MZ, GZ

• Beam Energy Calibration: approx ±1.8 MeV on MZ, and ±1.15 MeV on GZ

A` =2v`a`v2` + a2`

=2(1� 4 sin2 ✓e↵W )

(1� 4 sin2 ✓e↵W )2 + 1=

(g`L)2 � (g`R)

2

(g`L)2 + (g`R)

2

17

is a particularly interesting quantity: • it is nearly linear in the accidentally small |vl|~0.07- relative size of |vl| vpol corrections are magnified by an order of

magnitude wrt |al| or |vq|• The leptonic FB asymmetry is quadratic in Al: AFB(l) = 0.75(Al)2- experimentally quite small- measured asymmetry is insensitive to Al near the quadratic minimum

• Final state t-lepton polarization is sensitive to Al

• Initial state beam polarization asymmetry is sensitive to Al: ALR(P) = PAl

• The hadronic FB asymmetries are linear in Al: AFB(q) = 0.75AqAl

Measurement of AlThe coupling constant combination

P⌧ (c) =� A⌧ (1 + c2) + 2Aec

1 + c2 + 2A⌧Aec, P⌧ = �A⌧

s

io

o<

/<

po

e�

1

�

d�

d cos ✓⇤=

1

2

(1� P⌧Q⌧ cos ✓⇤)

1

�

d�

dx

= 1� P⌧Q⌧ (2x� 1) = A(x) + P⌧B(x)

1

�

d

N�

dx

N= A(x1...xN ) + P⌧B(x1...xN )

18

can extract both simultaneously from the angular dist of Pt. The t-pol is determined from 5 decay modes: t±->p±n, r±n, a1±n, enn, mnn. Since the t decays via a pure V-A current, each mode has a polarization-dependent decay distribution in lab variables. For example, the center-of-mass angular distribution of p- from the decay of a spin-polarized t- is very asymmetric,

Tau PolarizationThe polarization of final state t-leptons depends upon both Ae and At

or in terms of scaled lab energy x=Ep/Eb

The general case is where N = 1 (pn, lnn ), 3 (rn), 6 (a1n )

Final State e⌫⌫ µ⌫⌫ ⇡⌫ ⇢⌫ a1⌫

Branching Ratio (%) 18 18 12 24 8

Acceptance 0.4 0.7 0.6 0.5 0.5

Analyzing Power ap 5 5 1.8 2.3 3.1

Relative Precision 2.7 2.1 1.0 1.0 2.2

Al (LEP)=0.1465±0.0033 r2/DoF=4.7/7

ALEPH

DELPHI

L3

OPAL

Ao (LEP)

0.1451±0.0060

0.1359±0.0096

0.1476±0.0108

0.1456±0.0095

0.1439±0.0043

ALEPH

DELPHI

L3

OPAL

Ae(LEP)

0.1504±0.0068

0.1382±0.0116

0.1678±0.0130

0.1454±0.0114

0.1498±0.0049

0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 0.22 0.24

Ae,o

Measured Po vs coseo

-0.4

-0.3

-0.2

-0.1

0

0.1

-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1

Po

coseo

ALEPH

DELPHI

L3

OPAL

no universalityuniversality

-

-

19

The statistical uncertainty dPt expected for Ndec decays can be parameterized by dPt =ap[Ndec ]-1/2. Most power comes from pn and rn

ALR =1

Pe

NZ(L)�NZ(R)

NZ(L) +NZ(R)= Ae

20

• beam helicity was flipped pseudorandomly pulse to pulse- same luminosities in both helicity states

• All hadronic Z events (loose cuts) in both subsamples are counted- doesn’t need to use leptonic final states (4% visible BR per species)- exclude e+e- final states (t-channel subprocess)

• A polarization measurement Pi is assoicated with each event, the average includes small corrs (j=0.001-0.002) for chromatic + transport effects

• Correct for residual background+asymmetries in lum, pol, energy,etc- DALR/ALR ~ 10-3

• Correct for EW interference (DALR/ALR ~2%) to extract final result

Measurement of ALRThe left-right asymmetry was a particularly simple and powerful measurement performed at the SLC during 1992-1998

Pe = (1 + ⇠)1

NZ

NZX

i

Pi

SLD

MirrorBox

Mirror Box(preserves circular

polarization)

Focusingand

Steering Lens

AnalyzingBend Magnet

Laser BeamAnalyzer and Dump Compton

Back Scattered e–

532 nmFrequency Doubled

YAG Laser

Circular Polarizer

“Compton IP”

e–

e+

CerenkovDetector

Quartz FiberCalorimeter

Polarized Gamma Counter21

Vanda 6/22/98

1992 - 1998 SLD Polarized Beam Running

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

200002-

May

-92

6-Ju

n-92

11-J

ul-9

2

15-A

ug-9

2

20-M

ar-9

3

24-A

pr-9

3

29-M

ay-9

3

3-Ju

l-93

7-A

ug-9

3

23-J

ul-9

4

27-A

ug-9

4

1-O

ct-9

4

5-N

ov-9

4

10-D

ec-9

4

14-J

an-9

5

18-F

eb-9

5

6-A

pr-9

6

11-M

ay-9

6

15-J

un-9

6

20-J

ul-9

6

13-J

ul-9

7

17-A

ug-9

7

21-S

ep-9

7

26-O

ct-9

7

30-N

ov-9

7

4-Ja

n-98

8-Fe

b-98

15-M

ar-9

8

19-A

pr-9

8

24-M

ay-9

8

Z’s

per

Wee

k

0

50000

100000

150000

200000

250000

300000

350000

400000

Tot

al Z

’s

Z’s per WeekTotal Z’s

1992 1993 1994 - 1995 1996

22%

63%

78% 78%

1997-98

73%

SSI 1987: Physics with Polarized Beams

• we learned many things in 11 years - strained lattice cathodes- load lock guns- spin transport in resonant arcs- scanning polarimetry- Moller target effects- .....

Strained Lattice Cathodefor 1993 SLD Run

SourceLaserWavelenghtOptimized


1996 Run


A

A

A

A

A

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

22

Year NZ Pavg A0LR

1992 10k 0.22460.006 0.09760.044(stat)60.004(sys)

1993 47k 0.62660.012 0.165660.0073(stat)60.0032(sys)

1994/5 94k 0.77260.005 0.151260.0042(stat)60.0011(sys)

1996 52k 0.76260.004 0.159360.0057(stat)60.0010(sys)

1997/8 332k 0.72960.004 0.149160.0024(stat)60.0010(sys)

total 535k 0.72160.004 0.1513060.00207*

*Includes leptonic final states

• Largest systematics are: - pol uncertainty:

DA/A=0.5%- beam energy calibration:

DA/A=0.4%• Final result is still statistics

dominated • Final result also includes

leptonic final states

Proposed 1986:• Luminosity: 6x1030 cm-2s-1

• Z events: >106

• Polarization: 40-50%• DP/P: 3-5%• DALR: 0.005

Achieved 1998:• Luminosity: 4x1030 cm-2s-1

• Z events: 0.5x106

• Polarization: 72%• DP/P: 0.5%• DALR: 0.002

23

SLC Polarization Proposal: Propaganda+Reality

achieved

0 1 2 3 4 5 6 70

100

200

300

400

500

600

700

800

900htempNent = 24468 Mean = 2.32562RMS = 1.21238

M1C (M1C>0)

M (Gev)

B .C .

UDS

htempNent = 24468 Mean = 2.32562RMS = 1.21238

24

Hadronic FB Asymmetries

• Flavor tag the jets- high P,PT lepton tags- lifetime tags + jet mass‣ topological vtxing and enhanced

mass from SLD

The quark FB asymmetries are also linear in Al: AFB(q) = 0.75AqAl This usually involves three steps:

- reconstruct final state particles: B, D, ...- many techniques self-calibrate if samples are pure‣ number of single vs double tags

• Reconstruct thrust axis

- find axis which maximizes T (thrust axis)- divides event into two hemispheres- determines the cos(q) direction modulo a sign- interacts with final state radiative correction

T =

Pi |~pi · T |P

i |~pi|

QfF =

P~pi·T>0i |~pi · T |qi

P~pi·T>0i |~pi · T |

, QfB =

P~pi·T<0i |~pi · T |qi

P~pi·T<0i |~pi · T |

QfFB = Qf

F �QfB = �fA

fFB

hQFBi =X

q

RqAqFB�qCq, �q = sq hQ� �Q+i

25

• Sign the thrust hemispheres to determine fermion (vs anti-fermion) dir- sign of large P,PT lepton- topological vtx charge (self calibrates)- K± Sum: use sum of K± charges from b->c->s (or c->s) cascade:

needs particle ID- jet charge: reconstruct momentum-weighted hemisphere

charges and form the FB charge asymmetry,

‣ self-calibrating from sums and differences (except for hemisphere correlation effects)

• Inclusive Hadronic Charge Asymmetry - apply jet charge technique to an unseparated sample of qq final states: Rq is fraction of sample and Cq is acceptance of quark species

- lots of systematics to consider

ALEPH

DELPHI

L3

OPAL

0.2322 ± 0.0008 ± 0.0011

0.2345 ± 0.0030 ± 0.0027

0.2327 ± 0.0012 ± 0.0013

0.2321 ± 0.0017 ± 0.0029

(90-94)

(90-91)

(91-95)

(90-91)

LEP 0.2324 ± 0.0012

0.225 0.23 0.235 0.24sin2e

eff

lept

LEP 0.0992 ± 0.0016

OPALinclusive 1991-2000

0.0994 ± 0.0034 ± 0.0018

L3jet-chg 1994-95

0.0948 ± 0.0101 ± 0.0056

DELPHIinclusive 1992-2000

0.0978 ± 0.0030 ± 0.0015

ALEPHinclusive 1991-95

0.1010 ± 0.0025 ± 0.0012

OPALleptons 1990-2000

0.0977 ± 0.0038 ± 0.0018

L3leptons 1990-95

0.1001 ± 0.0060 ± 0.0035

DELPHIleptons 1991-95

0.1025 ± 0.0051 ± 0.0024

ALEPHleptons 1991-95

0.1003 ± 0.0038 ± 0.0017

0.08 0.09 0.1A

FB

0,b

LEP 0.0707 ± 0.0035

OPALD* 1991-95

0.0761 ± 0.0109 ± 0.0057

DELPHID* 1992-95

0.0695 ± 0.0087 ± 0.0027

ALEPHD* 1991-95

0.0698 ± 0.0085 ± 0.0033

OPALleptons 1990-2000

0.0643 ± 0.0051 ± 0.0037

L3leptons 1990-91

0.0834 ± 0.0301 ± 0.0197

DELPHIleptons 1991-95

0.0725 ± 0.0084 ± 0.0062

ALEPHleptons 1991-95

0.0734 ± 0.0053 ± 0.0036

0.06 0.08 0.1A

FB

0,c26

The QFB measurements are not easily interpreted by similar pseudo-observables and are converted to sin2qWeff . The FB symmetries for b- and c-quarks are quoted as relevant observables.

Effective Weak Mixing Angle

50

CMS: First measurement at the LHC

sin2 θeff = 0.2287 ± 0.0020 (stat) ± 0.0025 (syst)

11

FIG. 6: Comparison of measured sin2 !!

e! with results fromother experiments. The average is a combination of A0,!

F B,Al(P" ), Alr(SLD), A0,b

F B, A0,cF B, and Qhad

F B measurements fromthe LEP and SLD Collaborations.

for zgrad2.

(GeV)eeM100 1000

FBA

-0.5

0

0.5

1

50 70 100 300 500 1000

PYTHIAZGRAD2

Statistical uncertaintyTotal uncertainty

DØ 5.0 fb-1

FIG. 7: Comparison between the unfolded AF B (points) andthe pythia (solid curve) and zgrad2 (dashed line) predic-tions. The boxes and vertical lines show the statistical andtotal uncertainties, respectively.

MEASUREMENT OF gu(d)V

AND gu(d)A

FROM THE

UNFOLDED DISTRIBUTION

We extract the individual quark couplings by compar-ing the unfolded AFB distribution to templates generatedwith resbos for di!erent values of the Z-light quark cou-

plings. To determine gu(d)V and gu(d)

A , the couplings ofelectrons to Z bosons are fixed to their SM values andsin2 !!

e! is fixed to the global fit value 0.23153 [15]. A two-dimensional "2 fit [38] is used to constraint the couplings,and a four-dimensional fit is presented as reference. Thetwo-dimensional fit is performed by fixing the u quark(d quark) couplings to their SM values when fitting dquark (u quark) couplings, while the four-dimensional fitis performed by letting the u quark and d quark cou-plings vary simultaneously. The best fit values, togetherwith results from other experiments, are shown in Ta-ble VIII. Figure 8 depicts the 68% C.L. contours of the"2 fit and the contours of the theoretical uncertainty fromthe PDF uncertainties determined using the CTEQ pre-scription [5]. The correlation coe"cients between gu

V , guA,

gdV , and gd

A are shown in Table IX, without the PDF un-certainty included. The comparisons between di!erentmeasurements from LEP [15], H1 [37], CDF [21], andD0 are shown in Fig. 9. Because of the high statisticsof our data sample, and the reduced ambiguity in thequark content of the initial state, these are the world’smost precise direct measurements of gu

V , guA, gd

V , and gdA

to date.

CONCLUSIONS

We have measured the forward-backward charge asym-metry in pp ! Z/#! ! e+e" events and extracted

sin2 !!

e!, gu(d)V and gu(d)

A using 5.0 fb"1 of integrated lumi-nosity collected by the D0 experiment at

"s = 1.96 TeV.

The measured forward-backward charge asymmetry inthe range 50 < Mee < 1000 GeV agrees with the theo-retical predictions. The measured sin2 !!

e! value can bedirectly compared with the LEP and SLD results, and theoverall sin2 !!

e! uncertainty for light quarks obtained issmaller than the combined uncertainty in the LEP mea-surements of the inclusive hadronic charge asymmetry.We also present the most precise direct measurement todate of gu

V , guA, gd

V , and gdA.

Although the uncertainty of our sin2 !!

e! measurementis still larger than that of the current world average, withabout 10 fb"1 of integrated luminosity expected by theend of Tevatron Run II, a combined result of CDF andD0 AFB measurements in both dielectron and dimuon

CMS

27

sin2qWeff SummaryObservations:• The two most precise measurements

AFBb and ALR are 3.15s apart• All of the measurements involving

lepton couplings are self-consistent - sin2qWeff =0.23113±0.00020- x2/dof=1.66/2

• All of the measurements involving hadron couplings are self-consistent - sin2qWeff =0.23222±0.00027- x2/dof=0.02/2

• The two groups are 3.25s apartIs there physics here?

• M. Chanowitz, Phys. Rev. D66, 073002 (2002)• this paper was the basis of workshop ELECTROWEAK PRECISION

DATA AND THE HIGGS MASS, Zeuthen Germany, February 2003

J. Guimarães da Costa, ICHEP 2012

Z

e-

e+ W

W e-

e+n

W

W

f

fff

f

fff

W Mass at LEP2

L3

minv [GeV]

Num

ber o

f Eve

nts

/ 1 G

eV

1999 Data qqliM.C. reweightedM.C. background (d)

preliminary

MW = 80.35 ± 0.14 GeV

0

50

100

150

60 70 80 90 100

0

25

50

75

100

125

150

175

200

65 70 75 80 85 90 95m / GeV

Eve

nts

/ GeV

qqqq 4-jet

OPAL 192-202 GeV preliminary

• Perform maximum likelihood MW

fit to data

• Reweight simulation

• Compare (smeared) Breit-Wigner

calibrate with simulation

event by event resolution

Chris Parkes XXXVIIth Recontres de Moriond, March 2002

28

W-Mass Measurements: LEP 2

• Unlike the measurement of MZ, this is not a scanning measurement- most sensitive energy is near threshold where the cross section is

small: would seriously limit other W measurements and other physics• MW is measured by direct reconstruction of qqqq, qqln, (and l+l-nn )- (E,p)1 = (E,p)2 and M1=M2 constraints are applied to improve resolution - 35k events by the four experiments (~700 pb-1/experiment)- lots of simulation/fitting to achieve best result with smallest biases

Along with sin2qWeff, the other “most important” electroweak observable is the mass of the W boson MW. It was measured by the 4 LEP experiments during operation between Ecm = 161-209 GeV (above W-pair threshold)

0

0.25

0.5

0.75

1

80 80.280.480.680.8 81

Entries 0

80.0 81.0

MW[GeV] (non-4q)

LEP EWWGcorrel. with 4q = 0.20

ALEPH [final] 80.429±0.059

DELPHI [final] 80.339 ±0.075

L3 [final] 80.212±0.071

OPAL [final] 80.449±0.063

LEP 80.372±0.036

Summer 2006 - LEP Preliminary

0

0.25

0.5

0.75

1

80 80.280.480.680.8 81

Entries 0

80.0 81.0

MW[GeV] (4q)

LEP EWWGcorrel. with non-4q = 0.20

ALEPH [final] 80.475±0.081

DELPHI [final] 80.311±0.137

L3 [final] 80.325±0.080

OPAL [final] 80.353±0.083

LEP 80.387±0.059


0

0.25

0.5

0.75

1

80 80.280.480.680.8 81

Entries 0

80.0 81.0

MW[GeV]

LEP EWWGc2/dof = 49 / 41

ALEPH [final] 80.440±0.051

DELPHI [final] 80.336±0.067

L3 [final] 80.270±0.055

OPAL [final] 80.416±0.053

LEP 80.376±0.033


W Mass at LEP2

Err

or C

ompo

nent

(MeV

)

0

5

10

15

20

25

30

35

40

45

50

Stat Syst Det. Frag. FSI LEP

Stat.

Syst.

Systematics on MW

• Systematics dominated measurement

• Inter-experiment collaboration

- LEP WW workshops

• Detector E!ects • Fragmentation

• FSI • EBeam

• O(!)

Chris Parkes XXXVIIth Recontres de Moriond, March 2002

29

C. Parkes XXXVIIth Recontres de Moriond, March 2002

u W l-

d np

pq

e-

q

n

qPT =

MW

2sin�

produces Jacobian peak

dN

dPT=

dN

d cos ✓· 2PT /MWq

1� (2PT /MW )

2

30

W-Mass Measurements: Tevatron

• The lepton PT distributions peak at MW/2 - shape near peak is sensitive to GW, the W boson PT distribution, and

detector resolution• MT=[2 PT l PT

n(1-cosf)]1/2 is less sensitive to the W boson PT distribution• The new analyses use simultaneous template fits to all 3 distributions• Detailed knowledge (simulations) of all three quantities are needed to

extract precise values of MW

- the results are completely dominated by the systematics of technique• There are new results from CDF (m and e) and D0 (e only)

The Tevatron expts have logged large numbers (1-2x106) of qq->W->ln events during the last decade. They are distinguished by Jacobian peaks in the lepton and neutrino PT distributions,

) (GeV)µ(T

p30 40 50

even

ts /

0.25

GeV

0

5000

10000

15000

) MeVstat 18± = (80348 WM

/dof = 54 / 622r

-1 2.2 fb5 L dt 0CDF II preliminary

) (GeV)i(µT

p30 40 50

even

ts /

0.25

GeV

0

5000

10000

) MeVstat 22± = (80406 WM

/dof = 79 / 622r


) (GeV)iµ(Tm60 70 80 90 100

even

ts /

0.5

GeV

0

5000

10000

15000

) MeVstat 16± = (80379 WM

/dof = 58 / 482r


)-1> (GeVµ

T<1/p

0 0.2 0.4 0.6

p/p

6

-0.002

-0.0015

-0.001


data (stat. only) µµAsJ/

data (stat. only) µµA[

data (stat. only) µµAZ

eventsiµA syst.) for W� p/p (stat. 6combined

31

The CDF muon analysis is an example of the new work. The momentum scale is derived from 3 resonances.

80200 80400 80600

Mass of the W Boson

[MeV]WM March 2012

Measurement [MeV]WM

CDF-0/I 79±80432

-I�D 83±80478

CDF-II )-1(2.2 fb 19±80387

-II�D )-1(1.0 fb 43±80402

-II�D )-1 (4.3 fb 26±80369

Tevatron Run-0/I/II 16±80387

LEP-2 33±80376 World Average 15±80385

32

Source Uncertainty (MeV)

Lepton energy scale and resolution 7

Recoil energy scale and resolution 6

Lepton removal 2

Backgrounds 3

pT (W ) model 5

Parton distributions 10

QED radiation 4

W -boson statistics 12

Total 19

The new CDF result has a 19 MeV uncertainty which follows from years of work understanding the electron, muon, and neutrino energy scales. It is smallest of many analyses. The world average uncertainty is now only 15 MeV!

CDF 2012

⇢ =

M2W

M2Z cos

2 ✓W' 1 +

3GF

8⇡2p2

M2t

WWt

b

33

Top Quark

This should be compared with the logarithmic loop-level contributions of other heavy states. An accurate knowledge of the top mass is necessary to constrain or determine other contributions.

q

q

t

t

t

tg

g t

tg

gdominates at Tevatron dominates at LHC

The top quark plays a particularly important role in the study of precision electroweak physics. The large t-b mass splitting breaks the custodial SU(2) symmetry that keeps the r parameter near unity and contributes a quadratic mass dependence at next-to-leading order,

The top quark was discovered at the Tevatron in 1995 and has been studied extensively there and now at the LHC

• Tevatron production dominated by qq: total of ~100K produced events• LHC production dominated by gg: total of ~1.5M produced events (2011)- present production rate is ~1.6 t-tbar pairs per expt per second

q/g

f1

q/gt

t

W+

W-

b

b

f4

f2

f3

Top Pair Production and Decay at the LHC

Top pair production happens via gluon fusion (mainly), and qq anihilationapprox. NNLO: �tt(LHC@7TeV) = 163 pb, �tt(LHC@8TeV) = 225 pb

Top quark decays almost exclusively via the W decay

Measurements done according to the decay channel

Decay channelRdtL (fb�1)

dilepton (e, µ) @ 7 TeV 2.3dilepton (⌧ , e/µ) @ 7 TeV 2.0-2.2lepton (e/µ) + jets @ 7 TeV 0.8-1.1

⌧ + jets @ 7 TeV 3.9all hadronic @ 7 TeV 1.1

dilepton (e, µ) @ 8 TeV 2.4lepton (e/µ) + jets @ 8 TeV 2.7-2.8

A.Y. Rodrıguez-Marrero (IFCA) Top production at CMS July 5th , 2012 2 / 13

34

• 2 b-jets always present- W boson masses can be used as constraints esp

for the Jet Energy Scale (JES)• Both Ws decay hadronically: 4 additional jets- largest BR (46%)- larger backgrounds from QCD- intrinsically poorer resolution- need to understand JES for light-quark + b-jets

• One leptonic, one hadronic W: 2 add jets, l, n- still large BR (eff 30%)- much smaller backgrounds- charged lepton well measured, but neutrino

resolved only through missing PT, longitudinal P creates 2-fold ambiguity even w/ mass constr

- JES issues smaller than all jets decay• Two leptonic W: 2l, 2n

- small BR (4%)- “good” backgrounds- good lepton resolution, two missing neutrinos‣ significant loss of statistical analyzing power

The t-tbar final state has 6 final state particles/jets:

A.Y. Rodrıguez-Marrero, ICHEP 2012

ICHEP2012 , Hyun Su Lee, Ewha Womans University

Use full dataset (8.7 fb-1)

8

Most Precise single measurement to data 172.85 ±0.71(stat.) ±0.85(syst.)=172.85 ± 1.11 GeV/c2

Updated with full data (additional gain of 25% respect to luminosity increasing)

Working on the publication ICHEP2012 , Hyun Su Lee, Ewha Womans University

Systematic uncertainty

9

Most Precise single measurement to data 172.85 ±0.71(stat.) ±0.85(syst.)=172.85 ± 1.11 GeV/c2

Updated with full data (additional gain of 25% respect to luminosity increasing)

Working on the publication 35

• The actual analyses differ in final state, control of energy scale issues, and approach to fitting for Mt

- template fitting makes use of full simulation to generate simplified 1,2,3-d likelihood functions of mass sensitive variables

- “matrix-element” fitting uses full multidimensional cross section but it must be convolved with appropriate resolution functions in “real time”

Presently, the best single measurement comes from a ln +4jet CDF analysis

Mt = 172.85 ±0.71(stat.) ±0.85(syst.) = 172.85 ± 1.11 GeV/c2

Hyun Su LeeICHEP 2012

160 170 180 190

Mass of the Top Quark [GeV]

Lepton+jets

Lepton+jets

Lepton+jets

Lepton+jets

Alljets

Alljets

Dileptons

Dileptons

Dileptons

Dileptons

ET+jets

Decay length

Tevatron Combination 2012

Run II

Run II

Run I

Run I

Run II

Run I

Run II

Run II

Run I

Run I

Run II

Run II

CDF

D

CDF

D

CDF

CDF

CDF

D

CDF

D

CDF

CDF

1.06

1.24

5.3

3.9

1.40

5.7

3.13

1.44

4.9

3.6

1.82

2.82

0.75

0.65

0.83

5.1

3.6

1.43

10.0

1.95

2.36

10.3

12.3

1.80

9.00

0.56

173.00

174.94

176.1

180.1

172.47

186.0

170.28

174.00

167.4

168.4

172.32

166.90

173.18

GeV

GeV

GeV

GeV

GeV

GeV

GeV

GeV

GeV

GeV

GeV

GeV

GeV

LHC top-quark mass combination result

Χ2/dof = 2.5/6, prob = 86%

36

The Tevatron combined result currently has less than 1 GeV uncertainty

Mt = 173.18 ± 0.94 GeV/c2

VVH

p

VV HVV

H

37

Higgs Boson

So, what mass should we assume?

This is the “Summer of the Higgs” and has been discussed at length at this SSI. We don’t know that it’s the “one and only MSM Higgs”, but we do know that it couples to ZZ with more or less “standard” strength. Let’s assume that this state has all standard MSM couplings to Z, W and contributes to the VPol corrections as we expect

• CMS: MH = 125.3 ± 0.5 ± 0.4 GeV/c2 = 125.3 ± 0.64 GeV/c2

• Atlas: “around 126 GeV”• OK ... so how do we average them?• Don’t try ... take CMS number (apologies to Atlas)- ln(MH) isn’t very sensitive anyhow

38

Observable Pull

Mw 1.05

sin2qs(Rn) 2.03

MZ 0.02

GZ -0.33

shad 1.75

Rl 1.16

AFB l 0.92

At -0.78

Ae 0.52

ALR 1.95

Rb 0.76

Rc -0.06

AFB b -2.57

AFB c -0.90

Ab -0.59

Ac 0.08

sin2qWeff (QFB) 0.76

as(MZ) -0.15

Dahad(MZ) 0.13

Mt -0.74

QW(Cs) 1.94

QW(Tl) 0.62

MH -1.44

OK, after waiting for 23 years (!), we are ready to go. Let’s make a x2 fit to the MSM (ZFITTER)

• Choose 23 “precisely measured” quantities: MZ, MW, sin2qs(Rn), GZ, shad, Rl, AFB l, At, Ae, ALR, Rb, Rc, AFB b, AFB c, Ab, Ac, sin2qWeff (QFB), QW(Cs), QW(Tl), as(MZ), Dahad(MZ), Mt, MH.

- use published correlation matrices for Z-pole resonance and heavy flavor parameters

- fit for 5 parameters: MZ, as(MZ), Dahad(MZ), Mt, MH

• And the answer is: x2/dof = 26.95/18 (8%)- the MSM is alive and well :))

• OK ... well what else?- the pulls show that ALR and AFB b disagree!‣ (MSM falls midway between them)

- the NuTeV result looks kind of strange too!• I thought we already knew those things?

MSM Fit

After 23 years, is this all we get?

Model Independent Interpretation

There are several “equivalent” three-parameter schemes to describeelectroweak measurements. What follows the the S,T ,U scheme ofPeskin and Takeuchi [PRL 65, 964 (1990)]:

Begin by making a Taylor expansion of the four vacuum polarizationamplitudes,

W

W

W

W

W1 1

3

3 3

gg

g

P11(q2)JP P(0) (0)q 2

+112 S

P (q2)J P (0)q 22 S

P (q2)JP P(0) (0)q 2

+ 2 SP (q2)J P (0)q 22 S

33 33 33

11

3Q 3Q

QQ QQ

where ⇧QQ(0) = ⇧

3Q(0) = 0 is required by gauge invariance (thisexpansion is valid of all new states are much heavier than the W andZ).

Of the 6 nonzero coe�cients, 3 are absorbed into the definitions of↵(M2

Z), GF , MZ and the remaining three can be used to definedthree finite parameters,

↵S = 4e2

⇧

033

(0) � ⇧

03Q(0)

↵T =

e2

s2c2M2

Z

[⇧

11

(0) � ⇧

33

(0)]

↵U = 4e2

⇧

011

(0) � ⇧

033

(0)

The requirement that the mass scale of new physics be much heavierthan MW ,MZ can be relaxed [see Bamert and Burgess Z.Phys. C66,495 (1995)].

↵S = 4e2⇥⇧0

33(0)�⇧03Q(0)

⇤

↵T =e2

s2c2M2Z

[⇧11(0)�⇧33(0)]

↵U = 4e2 [⇧011(0)�⇧0

33(0)]

T ' const +

3

16⇡s2c2M2

t

M2Z

� 3

16⇡c2lnM2

H

U ' const +

1

2⇡lnM2

t39

Model Independent Interpretation There are several 3-parameter schemes. Use S,T,U scheme of Peskin and Takeuchi [PRL 65, 964 (1990)]. Based upon Taylor expansion of 4 VPol amplitudes: gauge invariance requires PQQ(0) and P3Q(0) to vanish, leaves 6 parameters. Absorb 3 into 3 input parameters (a,GF,MZ) and define the 3 remaining ones as

• S is weak isospin symmetric

• T characterizes global SU(2) breaking (rescaling of Dr)

• U is generally small and has no MH dependence in leading order,

S ' const +

1

12⇡lnM2

H � 1

6⇡lnM2

t

Oi = OMSMi (M ref

t ,M refH ) + aiS + biT + ciU + [diW + eiX + fiY + giZ]

W = ↵s(M2Z)� ↵ref

s (M2Z), X = �↵had(M

2Z)��↵ref

had(M2Z)

Y = Mt �M reft , Z = MH �M ref

H

40

Since S,T,U characterize very small (~10-3) corrections, the dependence of any observable can be represented by a linear expansion about a MSM reference value (from ZFITTER 6.43) at chosen Mt, MH reference values

• Assume that U=0 to simplify analysis (only affects MW)- MSM contributions to U are small

• Each observable determines a band in S-T space after integration over the constrained variables- Different S-T slopes, mi = −ai/bi provide different information about

vacuum polarization corrections

Where W, X, Y, Z represent “nuisance” parameters that are used to introduce uncertainties from constraints added to a global fit on all observables

41

The x2 includes the measured values of: MW, Rn-, QW(Cs), GZ, shad, Rl, AFB l,

At, Ae, ALR, AFB b, AFB c, sin2qWeff (QFB), QW(Tl), Dahad(MZ), Mt, MH.The best fit is x2/dof = 21.8/11 (2.6%) and yields the confidence regions

• Most precise measurements are MW, sin2qWeff (all Z pole asy), and GZ

• Ellipses are 2D 68% and 95% confidence regions• MSM at S,T = 0,0

42

Zoom and remove the Oi bands

• MSM is between the 68% and 95% 2D-bands

43


• MSM is between the 68% and 95% 2D-bands• MSSM from Pierce, Bagger, Matchev, Zhang, Nucl.Phys. B491 (1997) 3- keep only models with lightest Higgs near 125 (disfavor a few)

44


• MSM is between the 68% and 95% 2D-bands• MSSM from Pierce, Bagger, Matchev, Zhang, Nucl.Phys. B491 (1997) 3- keep only models with lightest Higgs near 125 (disfavor a few)

• Add heavy degenerate fermion doublet (Nc=3)- doesn’t decouple at high mass (excl @ 90% in 1D, more in 2D)

45

You’ve come a long way baby!

Like my son, the field of Precision Electroweak Physics has finally matured:• The MSM is alive and well• We can put interesting limits on new particle content• The field will improve only incrementally in the near term• The best way to find new physics is with bumps in mass spectra :)

46

Extra Slides

VOLUME 63, NUMBER 7 PHYSICAL REVIEW LETTERS 14 AUGUST 1989

Measurement of the Mass and Width of the Z Boson at the Fermilab Tevatron

F. Abe, D. Amidei, G. Apollinari, " M. Atac, P. Auchincloss, ' A. R. Baden, A. Bamberger, A.Barbaro-Galtieri, V. E. Barnes, ' F. Bedeschi, " S. Behrends, ' S. Belforte, " G. Bellettini, " J. Bellinger, '

J. Bensinger, A. Beretvas, J. P. Berge, " S. Bertolucci, S. Bhadra, M. Binkley, R. Blair, ' C. Blocker,A. W. Booth, G. Brandenburg, D. Brown, E. Buckley, '" A. Byon, ' K. L. Byrum, ' C. Campagnari, M.Campbell, R. Carey, W. Carithers, D. Carlsmith, ' J. T. Carroll, R. Cashmore, F. Cervelli, " K.Chadwick, G. Chiarelli, W. Chinowsky, S. Cihangir, A. G. Clark, D. Connor, i' M. Contreras, t ) J.Cooper, M. Cordelli, D. Crane, M. Curatolo, C. Day, S. Dell'Agnello, " M. Dell'Orso, " L.DeMortier, P. F. Derwent, T. Devlin, ' D. DiBitonto, ' R. B. Drucker, J. E. Elias, R. Ely, S. Errede,B. Esposito, B. Flaugher, ' E. Focardi, " G. W. Foster, M. Franklin, J. Freeman, H. Frisch, Y.Fukui, Y. Funayama, t' A. F. Garfinkel, ' A. Gauthier, S. Geer, i P. Giannetti, "i N. Giokaris, ' i P.Giromini, L. Gladney, ' M. Gold, K. Goulianos, ' H. Grassman, " C. Grosso-Pilcher, C. Haber, S. R.Hahn, R. Handler, ' K. Hara, ' R. M. Harris, J. Hauser, T. Hessing, ' R. Hollebeek, ' L. Holloway,P. Hu, ' B. Hubbard, B. T. Huffman, ' R. Hughes, ' P. Hurst, J. Huth, M. Incagli " T. Ino ' H.Iso, ' H. Jensen, C. P. Jessop R. P. Johnson, U. Joshi, R. W. Kadel, T. Kamon ' S. Kanda, ' D. A.Kardelis, i I. Karliner, E. Kearns, R. Kephart, P. Kesten, R. M. Keup, H. Keutelian, S. Kim, ' L.Kirsch, K. Kondo, ' S. E. Kuhlmann, ' E. Kuns, ' A. T. Laasanen, ' J. I. Lamoureux, ' W. Li, ' T. M.Liss, t i N. Lockyer, t' i C. B. Luchini, t P. Maas, M. Mangano, " J. P. Marriner, R. Markeloff, t' ) L. A.Markosky, ~' R. Mattingly, P. McIntyre, ' A. Menzione, " T. Meyer, ' S. Mikamo, R. Mikawa, M.Miller, t3i T. Mimashi, t'6i S. Miscetti, t i M. Mishina, t i S. Miyashita, t' Y. Morita, '6i S. Moulding, t i A.Mukherjee, L. Nakae, I. Nakano, ' C. Nelson, C. Newman-Holmes, J. S. T. Ng, M. Ninomiya, ' L.Nodulman, t' S. Ogawa, ' R. Paoletti, " A. Para, E. Pare, J. Patrick, T. J. Phillips, i R. Plunkett, t L.Pondrom, t' J. Proudfoot, ' G. Punzi, " D. Quarrie, K. Ragan, t' G. Redlinger, t i J. Rhoades, ' i F.Rimondi, t''i L. Ristori, " T. Rohaly, ' A. Roodman, ) A. Sansoni, R. D. Sard, A. Savoy-Navarro, i V.Scarpine, P. Schlabach, E. E. Schmidt, M. H. Schub, ' R. Schwitters, A. Scribano, " S. Segler, Y.Seiya, ' M. Sekiguchi, ' P. Sestini, " M. Shapiro, M. Sheaff, ' M. Shochet, J. Siegrist, P. Sinervo, ' ~ J.Skarha, ' i K. Sliwa, ' D. A. Smith, ' ' F. D. Snider, R. St. Denis, A. Stefanini, " R. L. Swartz,Jr., M. Takano ' K. Takikawa, ' S. Tarem D. Theriot, M. Timko, ' P. Tipton, S. Tkaczyk, A.Tollestrup, G. Tonelli, " J. Tonnison, ' i W. Trischuk, Y. Tsay, ' F. Ukegawa, ' D. Underwood, ' R.Vidal, R. G. Wagner, ' R. L. Wagner, J. Walsh, ' T. Watts, ' R. Webb, ' C. Wendt, ' W. C. Wester,III, T. Westhusing, " S. White, ' A. Wicklund, ' H. H. Williams, ' B. Winer, A. Yagil, A.

Yamashita, ' K. Yasuoka, ' G. P. Yeh, J. Yoh, M. Yokoyama, ' J. C. Yun, and F. Zetti "' Argonne National Laboratory, Argonne, Illinois 60439

Brandeis University, 8'altham, Massachusetts 02254' University of Chicago, Chicago, Illinois 60637Fermi National Accelerator Laboratory, Batavia, Illinois 60510

Laboratori Nazionali di Frascati, Istituto Nazionale di Fisica Nucleare, Frascati, ItalyHarvard University, Cambridge, Massachusetts 02138

' iUniversity of Illinois, Urbana, Illinois 61801National Laboratory for High Energy Physics IKEK), Tsukuba gun, Ibaraki ken -305, Japan-

Lawrence Berkeley Laboratory, Berkeley, California 94720t' iUniversity of Pennsylvania, Philadelphia, Pennsylvania 19104

t"'Istituto Nazionale di Fisica Nucleare, University and Scuola Norrnale Superiore ofPisa, I-56100 Pisa, Italyt'2iPurdue University, West Lafayette, Indiana 47907

t'"Rockefeller University, 1Vew York, New York 10021Rutgers University, Piscataway, New Jersey 08854

Texas AckM University, College Station, Texas 77843' iUniversity of Tsukuba, Ibaraki 305, Japan

Tufts University, Medford, Massachusetts 02155' iUniversity of Wisconsin, Madison, Wisconsin 53706

(Received 19 July 1989)

720

Accepted without review at the request of John Peoples under policy announced 26 April 1976

l989 The American Physical Society

VOLUME 63, NUMBER 20 PHYSICAL REVIEW LETTERS 13 NOVEMBER 1989

Measurements of Z-Boson Resonance Parameters in e+

e Annihilation

G. S. Abrams,'

C. E. Adolphsen, D. Averill, J. Ballam, B. C. Barish, T. Barklow, B. A.

Barnett, J. Bartelt, S. Bethke,'

D. Blockus, G. Bonvicini, A. Boyarski, B. Brabson,

A. Breakstone, J. M. 8rom, F. Bulos, P. R. Burchat. , D. L. Burke, R. J. Cence,

J. Chapman, M. Chmeissani, D. Cords, D. P. Coupal, P. Dauncey, H. C. DeStaebler, D. E.

Dorfan, J. M. Dorfan, D. C. Drewer, R. Elia, G. J. Feldman, D. Fernandes, R. C. Field,

T. Ford, C. Fordham, R. Frey, D. Fujino, K. K. Gan, E. Gero, G. Gidal,'

T. Glanzman, G. Goldhaber,' J. J. Gomez Cadenas, G. Gratta, G. Grindhammer,

P. GrosseWiesmann, G. Hanson, R. Harr,' B. Harral, F. A. Harris, C. M. Hawkes,

K. Hayes, C. Hearty,'

C. A. Heusch, M. D. Hildreth, T. Himel, D. A. Hinshaw, S. J.

Hong, D. Hutchinson, J. Hylen, W. R. Innes, R. G. Jacobsen, J. A. Jaros, C. K. Jung,

J. A. Kadyk,' J. Kent, M. King S. R. Klein, D. S. Koetke, S. Komamiya, W. Koska,

L. A. Kowalski, W. Kozanecki, J. F. Kral,'

M. Kuhlen, L. Labarga, A. J. Lankford, R. R.

Larsen, F. Le Diberder, M. E. Levi,'

A. M. Litke, X. C. Lou, V. Liith, J. A. McKenna,

J. A. J. Matthews, T. Mattison, B. D. Milliken, K. C. MoA'eit, C. T. Munger, W. N.

Murray, J. Nash, H. Ogren, K. F. O'Shaughnessy, S. I. Parker, C. Peck, M. L. Perl,

F. Perrier, M. Petradza, R. Pitthan, F. C. Porter, P. Rankin, K. Riles, F. R. Rouse, D. R.

Rust,"

H. F. W. Sadrozinski, M. W. Schaad,' B. A. Schumm,

'A. Seiden, J. G. Smith,

A. Snyder, E. Soderstrom, D. P. Stoker, R. Stroynowski, M. Swartz, R. Thun, G. H.

Trilling,' R. Van Kooten, P. Voruganti, S. R. Wagner, S. Watson, P. Weber, A. Weigend,

A. J. Wein stein, A. J. Weir, E. Wicklund, M. Woods, D. Y. Wu, M. Yurko,

C. Zaccardelli, and C. von Zanthier

t'iLawrence Berkeley Laboratory and Department of Physics,

University of California, Berkeley, California 94720

University of California at Santa Cruz, Santa Cruz, California 95064

oStanford Linear Accelerator Center, Stanford University, Stanford, California 94309

Indiana University, Bloomington, Indiana 47405

5'California Institute of Technology, Pasadena, California 91125

Johns Hopkins University, Baltimore, Maryland 21218

iUniversity ofMichiganAnn Ar, bor, Michigan 48109t

iUniversity of Hawaii, Honolulu, Hawaii 96822

University of Colorado, Boulder, Colorado 80309

(Received 12 October 1989)

We have measured the mass of the Z boson to be 91.14+ 0.12 GeV/ cand its width to be 2.42 —+II' i

GeV. If we constrain the visible width to its standard-model value, we find the partial width to invisible

decay modes to be 0.46+ 0.10 GeV, corresponding to 2.8 ~ 0.6 neutrino species, with a 95%-

confidence-level upper limit of 3.9.

PACS numbers: 14.80.Er, 13.38.+c, 13.65.+i

We present an improved measurement of the Z-boson

resonance parameters. The measurement is based on a

total of 19 nb'

of data recorded at ten different

center-of-mass energies between 89.2 and 93.0 GeV by

the Mark II detector at the SLAC Linear Collider. This

data sample represents approximately 3 times the in-

tegrated luminosity presented in an earlier Letter.'

The

statistical significance of the luminosity measurement is

further improved by including a detector component

—the mini-small-angle monitor (MiniSAM) —not used

in the previous analysis. The larger data sample and im-

proved luminosity measurement result in a significant

reduction in the resonance-parameter uncertainties. In

particular, our observations exclude the presence of a

fourth standard-model massless neutrino species at a

confidence level of 95%.

The Mark II drift chamber and calorimeters provide

the principal information used to identify Z decays.

Charged particles are detected and momentum analyzed

in a 72-layer cylindrical drift chamber in a 4.75-kG axial

magnetic field. The drift chamber tracks charged parti-

cles withicosBi & 0.92, where 8 is the angle to the in-

cident beams. Photons are detected in electromagnetic

calorimeters that cover the regionicosB

i& 0.96. The

calorimeters in the central region (barrel calorimeters)

are lead-liquid-argon ionization chambers, while the

end-cap calorimeters are lead-proportional-tube count-

ers.

There are two detectors for the small-angle e+e

(Bhabha) events used to measure the integrated luminos-

ity. The small-angle monitors (SAM's) cover the angu-

lar region of 50 (8 & 160 mrad. Each SAM consists of

1989 The American Physical Society 2173

47

Summer 1989

40th ssi: 23 years of precision electroweak physics file1 40th ssi: 23 years of precision...

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