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Beautiful Physics with Precision Tracking at .

John Jaros Symposium17 May 2019

Stephane WillocqUniversity of Massachusetts

2 mm

Disclaimer: Many wonderful

results from SLD not shownThanks to Su Dong &

Marty for material

Contents• Brief history • Detector & running @SLC• Physics at the Z resonance• Physics with heavy quarks (pre-VXD3 era)

– B lifetimes– Z à bb & b-tagging

• VXD3: Reaching higher precision– Making the case– Precision alignment and vertexing

• Physics with heavy quarks (VXD3 era)– Z à bb, Z à cc, b- and c-quark asymmetries– Bs mixing

2

SLD: A brief history

3

C. Baltay @Leith Fest Dec’14


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Detector design• General purpose detector

– Precision tracking and vertex detector for chargedparticles in 0.6 T solenoidalmagnetic field

– Cherenkov ring-imagingdetector for particleidentification (! / K / p)

– Electromagnetic andhadronic calorimetersfor electron identificationand jet reconstruction

– Iron calorimeter formuon identification

7

• Ancillary detectors– Luminosity monitor– Compton polarimeter

Detector design• General purpose detector

– Precision tracking and vertex detector for chargedparticles in 0.6 T solenoidalmagnetic field

– Cherenkov ring-imagingdetector for particleidentification (! / K / p)

– Electromagnetic andhadronic calorimetersfor electron identificationand jet reconstruction

– Iron calorimeter formuon identification

8

4–94 8086A2

4

3

2

1

0

Dis

tanc

e

(m)

0 1 2 3 4 5Distance (m)

Vertex Detector

Luminosity Monitor

SLC Beamline

Warm Iron Calorimeter

Magnet Coil

Liquid Argon Calorimeter

Cherenkov Ring Imaging

Detector

Endc

ap D

C

Drift Chamber En

dcap

DC

Endcap CRID

Endcap LAC

Endcap WIC

Vertex detector• Key component for physics program

– VXD2: initial 3-D CCD pixel detector

9

Old Technology vs newThe fight for the VXD3 proposal

VXD3 Construction Strong collaboration of RAL, Yale, MIT, Oregon, SLAC, Brunel, U Mass, Col State, Washington, Wisconsin, Nagoya, Tohoku to build components.

Precision tracking• Key ingredients to high resolution track and displaced vertex

reconstruction:– Tiny interaction region (IR)– High resolution pixel detector– Low-X0 material to minimize MS– Short extrapolation between

1st track measurement and IR

10

0

1

2

3

4

5

6

7

8

9

10

1985 1990 1991 1992 1993 1994 1996 1998

Year

Bea

m S

ize

(mic

rons

)

0

1

2

3

4

5

6

7

8

9

10

σx ∗σ

y (m

icro

ns2 )

SLC Design

σX

σY

σX ∗ σy

What was SLD designed for?• Design Report (1984):

à e+e- collisions up to 100 GeVà Test of the Standard Model:

• Detailed measurement of Z boson mass, width, decay modes

• Search for top-quark in Z decays and toponium resonance

• Production and decay of heavy quarks

• Search for the Higgs boson

• Counting number of neutrino generations

• Lepton and quark couplings, quark and gluon jets, and polarization effects

à Physics beyond the Standard Model:

• Additional anomalous Z bosons

• Non-standard Higgs bosons

• Technicolor or Supersymmetry particles

• Heavy leptons

• Anomalous quark or lepton couplings11

What was SLD designed for?• Design Report (1984):

à e+e- collisions up to 100 GeVà Test of the Standard Model:

• Detailed measurement of Z boson mass, width, decay modes• Search for top-quark in Z decays and toponium resonance

• Production and decay of heavy quarks• Search for the Higgs boson

• Counting number of neutrino generations

• Lepton and quark couplings, quark and gluon jets, and polarization effects

à Physics beyond the Standard Model:• Additional anomalous Z bosons

• Non-standard Higgs bosons

• Technicolor or Supersymmetry particles

• Heavy leptons

• Anomalous quark or lepton couplings12

Topics actually studied

SLC: First linear collider• e+ and e- beams• E up to 50 GeV• Collision rate

120 Hz• e- beam with

longitudinalpolarization

13

Data taking• SLD physics runs from 1992 to 1998 @SLC

– Collected 550,000 Z-boson events

14Vanda 6/22/98

1992 - 1998 SLD Polarized Beam Running

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

20000

2-M

ay-9

26-

Jun-

9211

-Jul

-92

15-A

ug-9

2

20-M

ar-9

324

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29-M

ay-9

33-

Jul-9

37-

Aug

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23-J

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427

-Aug

-94

1-O

ct-9

45-

Nov

-94

10-D

ec-9

414

-Jan

-95

18-F

eb-9

56-

Apr

-96

11-M

ay-9

615

-Jun

-96

20-J

ul-9

613

-Jul

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17-A

ug-9

721

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730

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ar-9

819

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8

Z’s p

er W

eek

0

50000

100000

150000

200000

250000

300000

350000

400000

Tota

l Z’s

Z’s per WeekTotal Z’s

1992 1993 1994 - 1995 1996

22%

63%

78% 78%

1997-98

73%

Electron beam polarization• Beam polarization up to 78%

15

Strained Lattice Cathodefor 1993 SLD Run

SourceLaserWavelenghtOptimized


1996 Run


→

→

→

→

→

Z Count

Beam Polarization SLD 1992-1998 Data

Pola

riza

tion

of E

lect

ron

Beam

(%)

0

10

20

30

40

50

60

70

80

90

100

0 1000 2000 3000 4000 5000x 10

2

Physics at the Z boson resonance• e+ e- annihilation into fermion pairs:

16

Kal hit properties

Run 22591, EVENT 589 20-JUN-1993 04:52 Source: Run Data Pol: R Trigger: Energy CDC Hadron Beam Crossing 1764233295

KAL Subsystems LUM 0 LUM 1 LAC EM1 LAC EM2 LAC HAD1 LAC HAD2 WIC 1 WIC 2

Run 22591, EVENT 589 20-JUN-1993 04:52 Source: Run Data Pol: R Trigger: Energy CDC Hadron Beam Crossing 1764233295

Run 34356, EVENT 3419 28-MAY-1996 13:12 Source: Run Data Pol: R Trigger: Energy WAB Beam Crossing 1539736923

Run 34356, EVENT 3419 28-MAY-1996 13:12 Source: Run Data Pol: R Trigger: Energy WAB Beam Crossing 1539736923

~ 70%& → ( )(

~ 10% & → +,+-

~ 20%& → / )/

e+

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 220Centre-of-mass energy (GeV)

Cro

ss-s

ectio

n (p

b)

CESRDORIS

PEPPETRA

TRISTANKEKBPEP-II

SLCLEP I LEP II

Z

W+W-

e+e−→hadrons

Physics at the Z boson resonance• e+ e- annihilation into fermion pairs: 2 amplitudes

!" for &'&( → * → + +!- for &'&( → . → + +

/ &'&( → + + 0 !" +!-2

17

e+

e−

γ

f−

f

e+

e−

Z

f−

f

10

10 2

10 3

10 4

10 5


Cro

ss-s

ectio

n (p

b)CESRDORIS

PEPPETRA

TRISTANKEKBPEP-II

SLCLEP I LEP II

Z

W+W-

e+e−→hadrons

e+

e−

γ

f−

f

e+

e−

Z

f−

f

10

10 2

10 3

10 4

10 5


Cro

ss-s

ectio

n (p

b)

CESRDORIS

PEPPETRA

TRISTANKEKBPEP-II

SLCLEP I LEP II

Z

W+W-

e+e−→hadrons

Physics at the Z boson resonance• Differential cross section

• Parity-violating asymmetry parameters

• Forward-backward asymmetry

LEP:

SLC:

18

8 Oct 2001 11:14 AR AR140-11.tex AR140-11.SGM ARv2(2001/05/10) P1: GJC

SLD PHYSICS 369

respectively. The asymmetry parameter for a given fermion represents the extentof parity violation at the Z0 ! f f vertex and is defined as

A f =2gV gA

g2V + g2

A=

g2L � g2

Rg2

L + g2R. 9.

The parameter Af can be isolated by the measurement of various cross-sectionasymmetries, which is experimentally attractive because systematic effects areminimized. In addition, g2

V + g2A (or equivalently, g2

L + g2R) is determined from

the Z 0-decay partial widths, which are normalized by the hadronic decay partialwidth to control systematic effects.

The simplest of the asymmetries is the left-right cross-section asymmetry

A0LR =

�L � �R

�L + �R= Ae, 10.

for which all angular dependence and all dependence on the final state cancel.1As a result, ALR is a particularly robust quantity, with smaller systematic effectsthan any other asymmetry. This asymmetry provides a direct measurement of thecoupling between the Z 0 and the e+e� initial state, and provides, as we shall see,the best sensitivity to sin2 ✓W .

Asymmetries that retain angular information are sensitive to the final-state cou-plings. For Z 0 ! f f decays, the forward-backward asymmetry, measured at LEPfor lepton and heavy quark final states, can be expressed in terms of z = cos ✓ as

A fFB(z) =

� f (z) � � f (�z)� f (z) + � f (�z)

= Ae A f2z

1 + z2 . 11.

The asymmetry A fFB for fermions is a composite observable sensitive to both the

initial-state Ae and the final-state Af. For example, from the magnitudes of theparity violation parameters Af as listed in Table 4, it can be seen in the case of the bquark that the large value of Ab makes A f

FB particularly sensitive to Ae (and hence tosin2 ✓W ). In general, the final-state Z f f asymmetry parameter Af can be deduced bytaking the lepton coupling Ae’s from other measurements such as the ⌧ polarization,the lepton pair forward-backward asymmetries, and ALR. Note that A f

FB is subjectto systematic errors in the determination of detector acceptance and efficiency.

At the SLC, the polarized forward-backward asymmetry can be measured. Dueto the factor (Ae �Pe) in Equation 8, manipulation of the helicity of the e� beam(Pe < 0 for left-handed electrons) distinguishes two different forward-backwardasymmetries. In particular, for a highly polarized beam, the forward-backwardasymmetry is not only of the opposite sign for left-handed beam, the magnitude is

1The dependence of ALR on the final state couplings and polar (and azimuthal) angle com-pletely vanishes, provided that the efficiency for detecting a fermion at some polar angle(with respect to the electron direction) is equal to the efficiency for detecting an antifermionat the same polar angle. This condition is satisfied by the SLD detector.

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SLD PHYSICS 369


A f =2gV gA

g2V + g2

A=

g2L � g2

Rg2

L + g2R. 9.






A0LR =

�L � �R

�L + �R= Ae, 10.



A fFB(z) =

� f (z) � � f (�z)� f (z) + � f (�z)

= Ae A f2z

1 + z2 . 11.







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370 ROWSON ⌅ SU ⌅ WILLOCQ

TABLE 4 The approximate magnitude of the various fermion-to-Z 0

coupling parameters, for sin2 ✓ effW = 0.23

g fL g f

R R f = �(Z0! f f )�(Z0!hadrons) Af

�A f� sin2✓w

e, µ, ⌧ �0.27 �0.23 0.05 0.15 �7.9u, c 0.35 0.15 0.17 0.67 �3.5d, s, b �0.42 �0.08 0.22 0.94 �0.6

also expected to be larger compared with the asymmetry for right-handed beam.Separate measurements of the left and right cross sections can be combined intothe left-right forward-backward asymmetry

A fFB(z) =

⇥�

fL (z) � �

fL (�z)

⇤�

⇥�

fR (z) � �

fR (�z)

⇤⇥�

fL (z) + �

fL (�z)

⇤+

⇥�

fR (z) + �

fR (�z)

⇤ = |Pe|A f2z

1 + z2 . 12.

The use of A fFB eliminates the dependence on Ae and measures Af directly.

Compared with A fFB, A f

FB benefits from a large gain in statistical power for thedetermination of Af. Given an SLC electron beam polarization of ⇠75%, this im-provement factor is (Pe/Ae)2 ⇠ 25. The effects of nonuniformity of the detectoracceptance and efficiency cancel to first order for this double asymmetry. The SLDcollaboration has measured A f

FB for bottom, charm, and strange quarks, as wellas the charged leptons, providing direct measurements of the associated fermionasymmetry parameters. With the exceptions of Ae and A⌧ , these direct measure-ments are unique to SLD.

Measurements of partial Z 0-decay widths provide information complementingthat obtained from the asymmetries. Because

R f =0(Z0 ! f f )

0(Z0 ! hadrons)/ g2

L + g2R, 13.

Rf measures the Z0 ! f f coupling strength, whereas Af measures the extent ofparity violation at the Z 0 ! f f vertex. From another perspective, consider forexample the sensitivity of Rb and Ab to the left- and right-handed Zbb couplings:

�Rb/Rb ⇠ �3.57 �gbL � 0.65 �gb

R and

�Ab/Ab ⇠ �0.31 �gbL + 1.72 �gb

R . 14.

We see that Rb is more sensitive to the possible deviations in the left-handed Zbbcoupling, and Ab is more sensitive to deviations in the right-handed coupling. TheSLD collaboration has measured both Rb and Rc.

We have discussed how the well-determined constants MZ , GF , and ↵(M2Z )

constrain the standard model. However, these data are a sufficient set only at treelevel, and to test the standard model, including loop effects, at least one additional

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TABLE 4 The approximate magnitude of the various fermion-to-Z 0

coupling parameters, for sin2 ✓ effW = 0.23

g fL g f

R R f = �(Z0! f f )�(Z0!hadrons) Af

�A f� sin2✓w

e, µ, ⌧ �0.27 �0.23 0.05 0.15 �7.9u, c 0.35 0.15 0.17 0.67 �3.5d, s, b �0.42 �0.08 0.22 0.94 �0.6

also expected to be larger compared with the asymmetry for right-handed beam.Separate measurements of the left and right cross sections can be combined intothe left-right forward-backward asymmetry

A fFB(z) =

⇥�

fL (z) � �

fL (�z)

⇤�

⇥�

fR (z) � �

fR (�z)

⇤⇥�

fL (z) + �

fL (�z)

⇤+

⇥�

fR (z) + �

fR (�z)

⇤ = |Pe|A f2z

1 + z2 . 12.

The use of A fFB eliminates the dependence on Ae and measures Af directly.

Compared with A fFB, A f

FB benefits from a large gain in statistical power for thedetermination of Af. Given an SLC electron beam polarization of ⇠75%, this im-provement factor is (Pe/Ae)2 ⇠ 25. The effects of nonuniformity of the detectoracceptance and efficiency cancel to first order for this double asymmetry. The SLDcollaboration has measured A f

FB for bottom, charm, and strange quarks, as wellas the charged leptons, providing direct measurements of the associated fermionasymmetry parameters. With the exceptions of Ae and A⌧ , these direct measure-ments are unique to SLD.

Measurements of partial Z 0-decay widths provide information complementingthat obtained from the asymmetries. Because

R f =0(Z0 ! f f )

0(Z0 ! hadrons)/ g2

L + g2R, 13.

Rf measures the Z0 ! f f coupling strength, whereas Af measures the extent ofparity violation at the Z 0 ! f f vertex. From another perspective, consider forexample the sensitivity of Rb and Ab to the left- and right-handed Zbb couplings:

�Rb/Rb ⇠ �3.57 �gbL � 0.65 �gb

R and

�Ab/Ab ⇠ �0.31 �gbL + 1.72 �gb

R . 14.

We see that Rb is more sensitive to the possible deviations in the left-handed Zbbcoupling, and Ab is more sensitive to deviations in the right-handed coupling. TheSLD collaboration has measured both Rb and Rc.

We have discussed how the well-determined constants MZ , GF , and ↵(M2Z )

constrain the standard model. However, these data are a sufficient set only at treelevel, and to test the standard model, including loop effects, at least one additional

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SLD PHYSICS 369


A f =2gV gA

g2V + g2

A=

g2L � g2

Rg2

L + g2R. 9.






A0LR =

�L � �R

�L + �R= Ae, 10.



A fFB(z) =

� f (z) � � f (�z)� f (z) + � f (�z)

= Ae A f2z

1 + z2 . 11.







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as determined in the simulation. This muon selection also took advantage of theCRID to reject approximately half of the charged kaon and proton contaminationin most of the momentum range, and roughly a third of all charged pions withp < 6 GeV/c (with an efficiency loss of only 5%). Information from the pattern ofenergy deposition in the LAC was also used in the identification and was especiallyuseful at larger |cos ✓ |. Pion misidentification rates of about 0.3% were estimatedfrom K 0

S ! ⇡+⇡� and ⌧± decays in the data, in reasonable agreement with thesimulation.

5. ELECTROWEAK PHYSICS: Z 0 BOSON COUPLINGS

5.1. Introduction

In Section 1, we mentioned that in the standard model the Z f f couplings dependon the weak isospin of the fermions and on a single parameter, sin2 ✓W , but wedid not discuss the origin of this parameter. Recall that in the standard model,the weak isotriplet EAµ and the isosinglet Bµ gauge fields, with gauge couplingsg and g0, are mixed by electroweak symmetry breaking due to the finite vacuumexpectation value of the Higgs scalar field. The charged fields A1

µ and A2µ and

neutral fields Bµ and A3µ combine linearly into the physical charged W+ and W�

and the neutral photon and Z 0 gauge bosons. This change of basis is parameterizedby a weak mixing angle ✓W , given by g0 = g tan(✓W ), and the masses of the physicalgauge bosons (and the fermions) emerge as by-products of electroweak symmetrybreaking (the “Higgs mechanism”).

Electroweak tests of the standard model reached an important turning pointonce the Z 0 boson mass was determined at LEP to a precision of two parts in 105.The measurement of MZ provides a third precision constant, which together withthe Fermi constant GF (constrained by muon decay) and the fine structure constant↵ (evaluated at Q2 = M2

Z ) is sufficient to determine the three universal parametersof the electroweak standard model: the SU(2)L ⇥ U(1) couplings g and g0, and thevacuum expectation value of the Higgs field. The couplings of fermions to the Z 0

boson are, by virtue of weak mixing, a function of ✓W —hence, their determinationprovides a fundamental test of electroweak symmetry breaking and, if sufficientlyprecise, of higher-order corrections. The electroweak measurements made by theSLD collaboration can generally be described as measurements of the fermion-to-Z 0 couplings.

The differential cross section for e+e� ! Z0 ! f f is expressed as

d�

d cos ✓= (1 � Pe Ae)(1 + cos2 ✓ ) + 2 cos ✓ (Ae � Pe)A f , 8.

where cos ✓ is the cosine of the angle between the final-state fermion f and theincident electron directions, Pe is the electron beam longitudinal polarization, andAe and A f are the asymmetry parameters for the initial- and final-state fermions,

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Electron polarization

e- e+f

f

q

Physics with heavy quarks• Early measurements of relatively long b-hadron lifetime were first

indications that weak decays involving transitions between 3rd and 2nd generation quarks (b à c) are suppressed

• Encoded in small value of CKM quark-mixing matrix element Vcb

19

Physics with heavy quarks•

20

Is THERE LIFE AFTER ‘93 FOR HEAVY FLAVOR AND LEPTON PHYSICS IN SLD ?

I, B1G DISTICTINCTlONS BETWEEN LEP & SLDISLC:

0 POLARIZATION

0 VTX RES.+EFF. (PAT. REC. CAPABILITY) CRID PARTICLE ID

SLC IP STABILITY AND SIZE

- Heavy Flavor Physics Places Largest I3urden on Understanding the Detector of All Physics of SLD -

d) WE’VE ALWAYS ARGUED THAT AS MEASUREMENTS

FROM LEP BECOME IMPORTANT. REACH SYSTEMATICS LIMIT - OUR DIFFERENCES

a WHERE ARE WE ON ACHIEVING THESE DIFFERENCES

SLCSPOTS d 0 POLARIZATION d 0 VERTEX DETECTOR RESOL. + EFF. d

CENTRAL DRIFT CHAMBER d LAC +WIC MUONSELECTRONS I/

0 CRIDID I./

a THE GROWING CONFIDENCE IN THE STD. MODEL HAS MEANT THAT EXPT’S ARE MORE WILLING TO BE OPTIMISTIC (NOT CONSERVATIVE ) ON ERRORS

- MAKES OUR LIFE EVEN HARDER - 0 WE MUST MOVE ALONG FASTER BEFORE MANY OF

THE WINDOWS OF OPPORTUNITY CLOSE.

0 Other Standing Groups:

0 T~ Group (T. Johnson, J. Venuti ...) EPS C h i t ' .

- Impact Parameter Tests - 1st Move To Use Of Vertices For Analysis

0 ?b Group (Usher, Markiewicz,Punkar ...) EPS Tour.

- Impact Parameter Internal SLD T Check - Toward Use Of Cascade Vertices For Analysis

0 B anti B - Mixing Group (Zapalac, Jaros )

- Lepton+Vertex Analysis - Use Of Cascade Vertices

0 VERY WEAK POINTS OF SLD

0 WE ARE NOT TRYING TO ACTIVELY EXPLOIT VERTICES IN ANY ANALYSIS YET (Except T)

8 WE ARE NOT TRYING TO ACTIVELY EXPLOIT CASCADE VERTICES IN ANY ANALYSIS YET

@ WE ARE NOT TRYING TO USE THE CRID YET -

R.Schindler @Collab. Mtg May ’93

Early B lifetime at SLD• Impact parameter technique

– 50 K Z events collected in 1993– Z à bb events selected by requiring

at least 3 tracks with normalized 2D impact parameter > 3

21http://www-sld.slac.stanford.edu/sldwww/physics/bbmix/bbmix.html

SLAC-PUB-6595

DPF ’94

http://www-sld.slac.stanford.edu/sldwww/physics/bbmix/bbmix.html

http://www.slac.stanford.edu/cgi-wrap/getdoc/slac-pub-6595.pdf

Early B lifetime at SLD• Secondary vertex technique

– Same 50 K Z events collected in 1993– Reconstruct 3D secondary vertex

& measure decay length

– Much improved sensitivity (factor of ~2)

22

The lifetime is also extracted us-ing 3-D reconstructed vertices. Inthis technique we use quality tracksfrom b-tagged events to reconstruct allpossible geometrical vertices in threedimensions. The number of vertices isthen reduced by looking at the globalevent topology and by choosing theset of independent (i.e. not sharingany track) vertices that maximizes theproduct of the vertex fit probablities.Further cuts are applied to removevertices containing tracks originatingfrom the IP. In particular, the decaylength is required to be greater than1 mm. Only the vertex closest to theIP is kept in each event hemisphere.The final sample consists of 4294 b-tagged events with 5427 selected ver-tices. Monte Carlo studies indicate that88% of selected vertices carry B hadronlifetime information.

1

10

10 2

10 3

0 1 2

Data

MC

Figure 2. Decay length distribution forselected vertices.

The lifetime is extracted from the decay length distribution (Fig. 2) by followinga similar weighting and fit procedure as described above. The lifetime is measured tobe τB = 1.577±0.032(stat.)±0.046(syst.) ps, where the systematic error is dominatedby the uncertainty in the b-quark fragmentation. A complete account of this analysistechnique and results is given elsewhere.6

3. Conclusions

We have made preliminary measurements of the average B hadron lifetime using2-D impact parameters and 3-D vertices. Each of these measurements is currentlylimited by systematic errors which should decrease as we continue to improve ourunderstanding of the detector and the physics modeling. In addition, we hope to beable to extend the 3-D vertexing technique to study exclusive B decay lifetimes in thenear future.

References

1. See for example, W. Venus, Talk Presented at the 1993 Lepton-Photon InteractionsConference, August 10-15, 1993, Ithaca, New York.

2. SLD Design Report, SLAC-REPORT 273, 1984.3. The impact parameter resolution function is parametrized as α⊕ β/p

√sin3θ.

4. K. Abe et al., SLAC-PUB-6569, Aug. 1994.5. D. Fujino, SLAC-PUB-5635, Nov. 1991.6. K. Abe et al., SLAC-PUB-6586, July 1994.

First use of topologicalvertexing at SLD

PRL 75, 3624 (1995)

DPF ’94

Decay length

B+ and B0 lifetimes

23S.Willocq 5 October 2001 7

b

q–

W –l –, u–, c–

ν–, d, sc, u

q–

b

q–

W – u–, c–

d, s

c, u

q–

b

u–W –

u–, c–

d, s

b

d–W –

c

u–

B+ and B0 Lifetimes (I)

• Test b-decay transitionsand dynamics (strong interaction)

• Heavy Quark Expansion predictssmall differences betweenb-hadron types

τ(B+) / τ(B0) = 1 + O(5%)

0.9 < τ(Λb) / τ(B0) < 1.0

Bigi et al.

(somewhat contested by Neubert)

B+ and B0 lifetimes

24

S.Willocq 5 October 2001 8

B+ and B0 Lifetimes (II)

• Refined methods all based on vertexing (1994):

1. Lepton+D (G.Gladding, I.Karliner, T.Usher)

First results: summer 1995Published: PRL 79, 590 (1997) 1993-95 data sample: 150K evts

τ(B+) = 1.61 ± 0.13 ± 0.07 ps

τ(B0) = 1.56 ± 0.14 ± 0.10 ps

τ(B+) / τ(B0) = 1.03 ± 0.15 ± 0.09

B+ and B0 lifetimes

25S.Willocq 5 October 2001 9

B+ and B0 Lifetimes (III)2. Inclusive topological vertexing (D.Jackson)

first development and implementation of ZVTOP

- Select seed vtx with high track overlap density- Attach tracks with L/D > 0.3and T < 0.1 cm

- Lower quality tracks alsoattached to improve vtx charge

B+ and B0 lifetimes

26

S.Willocq 5 October 2001 10

B+ and B0 Lifetimes (IV)First results: summer 1995Published: PRL 79, 590 (1997) 1993-95 data sample: 150K evts

Topological analysis9719 candidate B decaysB purity = 98%

τ(B+) = 1.67 ± 0.07 ± 0.06 ps

τ(B0) = 1.66 ± 0.08 ± 0.08 ps

τ(B+) / τ(B0) = 1.01 ± 0.09 ± 0.05

Charged Neutral

53% B+

32% B025% B+

53% B0

Z à bb & b-tagging• Topological vertexing (ZVTOP) for b-tagging

à Inclusive approach to achieve high efficiencyà Tracks as Gaussian probability “tubes” !" #

à Vertices identified with vertex function

27

D.J. Jackson SLAC-PUB-7215

!" # $ #


Z à bb & b-tagging• Topological vertexing (ZVTOP) for b-tagging

à Discriminator: invariant mass of tracks associated with secondary vertex

à Benefits from b-hadron lifetime (~1.6 ps) & large mass (~ 5 GeV)

Raw mass (partially) corrected formissing neutral particles

28

PT corrected vertex mass• Applying a kinematic

correction to the Mvtxto recover neutral particle effect:

VTXT

VTXTVTXP PPMM

T++=

22

SLD collaboration PRL 80, 660 (1998)

PT corrected vertex mass• Applying a kinematic

correction to the Mvtxto recover neutral particle effect:

VTXT

VTXTVTXP PPMM

T++=

22

SLD collaboration PRL 80, 660 (1998)

.

DataSimulation

a) Charged Tracks Mass SLD

Mch (GeV/c2)

No.

of H

emis

pher

es

bc

uds

DataSimulation

b) Pt-Corrected Mass

M (GeV/c2)

No.

of H

emis

pher

es

bc

uds

0

500

1000

1500

2000

0 1 2 3 4 5 6

0

400

800

1200

1600

2000

0 1 2 3 4 5 6

�

Figure 2: Distribution of (a) Mch and (b) Pt corrected mass, M, for data (points) andMC which includes a breakdown of the b, c and uds contributions (open, hatched andcrosshatched histograms respectively).

9

SLAC-PUB-7481

MpT > 2 GeV: e = 35%, P = 98%

1993-95 dataD. Su

https://www-public.slac.stanford.edu/sciDoc/docMeta.aspx?slacPubNumber=SLAC-PUB-7481

Z à bb & b-tagging• Topological vertexing for b-tagging

– Measurement of Rb: Z à bb / Z à qq– Sensitive to higher order corrections

and BSM physics– ‘95 Rb crisis: world avg Rb 3s above SM

but most expts use b-tagging from impact parameter with significant charmcontamination and uncertainties

– SLD topological vtx tag greatly decreases charm contamination– Self-calibrating double-tag technique to measure both Rb and b-tag eff. !b

via single- and double-tag fractions in two event hemispheres:

small correlation Cb between hemispheres from MC simulation29


SLD PHYSICS 381

For most of the measurements in this section, the hadronic Z 0 events wereselected by requiring at least seven charged tracks and a visible charged energyof at least 18 GeV. The events were typically required to be well-contained inthe high-quality tracking fiducial volume of |cos ✓thrust| < 0.7. The flavor-taggingefficiencies referred to are generally for these selected fiducial events.

5.3.1. Rb AND Rc MEASUREMENTS The formulation of Rb and Rc as ratios of hadroniccross sections ensures that the propagator (oblique) electroweak radiative correc-tions and QCD radiative corrections that are common to all flavors largely cancel,isolating the heavy quark to Z 0 coupling vertex radiative corrections. In the stan-dard model, the large top quark mass introduces a �1.5% correction on Rb (42),compared with the tree-level prediction. Extensions to the standard model can alsoproduce potential deviations in Rb at ⇠1% (43). The effort toward <1% precisionRb measurements has therefore been one of the primary activities of the Z 0-poleexperiments. The Zcc vertex corrections in the standard model are much smaller,so that any deviations of the measured Rc from the standard model predictionwould signal exotic new physics processes.

At the peak of the Rb and Rc “crisis” in early 1996, the world average for Rbwas over 3� higher than the standard model, whereas that for Rc was over 2�

lower than the standard model (44). SLD’s crucial contribution was to introducean improved analysis method that was eventually adopted by other experiments,resulting in a significant increase in precision.

Rb Measurement Recent Rb measurements have generally adopted a double-tagtechnique to reduce modeling uncertainty. Events were divided into two hemi-spheres by the plane perpendicular to the thrust axis, and a b-tagging algorithm wasapplied to each hemisphere in turn. The measured hemisphere tag rateFs and event double-tag rate Fd allow the extraction of both Rb and the hemi-sphere b-tagging efficiency ✏b from the data by solving two simultaneous equa-tions:

Fs = ✏b Rb + ✏c Rc + ✏uds(1 � Rb � Rc),

Fd = Cb✏2b Rb + Cc✏

2c Rc + ✏2

uds(1 � Rb � Rc). 23.

The small background tagging efficiencies for uds and charm hemispheres, ✏uds and✏c, as well as the b-tagging hemisphere correlations Cb = ✏double

b✏2

band Cc = ✏double

c✏2

c,

were estimated from the Monte Carlo simulation. Furthermore, a standard modelvalue of Rc was assumed. The Rb statistical error is approximately / 1/✏b, whereasthe uds and charm systematic errors scale as ✏uds/✏b and ✏c/✏b, indicating the needto maintain both high efficiency and high purity for the b tag.

For the preliminary analysis of the 1996–1998 data, a cut on the neural-netc � b separation variable of Scb > 0.75 (see Section 4.3) was used as the b tag.Figure 13a shows the hemisphere tagging efficiencies and b purity for the 1997–1998 data as a function of the Scb cut. It can be seen that the measured b-tagging

Ann

u. R

ev. N

ucl.

Part.

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. 200

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-412

. Dow

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hers

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4/19

. For

per

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onl

y.

e+

e−

γ/Z

t−b−

Wt

b

e+

e−

γ/Z

W

b−

tW

b

e+

e−

γ/Z

t−b−

Wt

b

e+

e−

γ/Z

W

b−

tW

b

VXD3: Reaching higher precision• Upgrade: 307 Mega pixel

vertex detector

– Pixel size: 20 µm x 20 µm

– 5 µm hit resolution in 3D

– Reduced material

– Improved impact parameter

resolution à key for Bs mixing

– Full 3-layer coverage in phi

– Extended longitudinal

coverage à key for Ab, Ac

30

T. Usher

.11

t,

VXD3

“. .cosO=O.85 (=3 Hits) cos8=0.9 (22 Hits)-\ .

\ //\>

\\ /

\ //\—-—- ____ ____ __ -\’ —’________ —_____\\\

\\

1 , 1 I \, , ,

0 5 10 cose=o.75cm

VXD2

(22— Hits)

Figure ~, Comparison of VXD2 and VXD3 RZ profiles snowing bcarn pipe, beryllium support structure, ladders,and CCDS.

Figure 4

• Up

31

John @Feb’94 Collab.Mtg

• Up

32


Rb

Ab

• Up

33


VXD3: Reaching higher precision• Upgrade: 307 Mega pixel

vertex detector

34

I .

to a 0.125- 0.25% inefficiency. Also about 3-5 columns with smaller charge lossusua lly were seen in every channel.

Though such inefficiency is quite acceptable, some modifica t ions of the CCD designwere made to reduce the number of these charge t raps. The manufacturer believestha t mask misa lignments are the major cause of these t raps. Over lapping of I-clockst r ips was min imized in the design to reduce the capacitance, and misa lignment canproduce gaps between I-clocks phases. These gaps may crea te t raps due to chargeaccumula t ion in the silicon oxide passiva t ion below the polysilicon I-clock st r ips.The over lap will now be increased sligh t ly. Also, the supplementa ry channel,which was added to increase the radia t ion hardness of the CCD, will be removed,since it a lso may cont r ibu te to the observed t rapping. From test s we havedetermined tha t the radia t ion hardness of our detector s is much bet ter than weneed, and the supplementa ry channels a re unnecessary.

Radiation hardness.

One of the phase 1 CCDS was exposed to the radiation from a Co60 source with thetotal accumulated dose of 15 kRad. We measured the detector parameters a few timesduring the exposure and did not find any serious degradation in the detectorperformance. With the full dose, a small (-10%) loss of signal amplitude from theFe55 source is obse~ed.

u-Dgrade schedule

Product ion of the CCDS for VXD3 sta r t ed in Apr il, 1995 and will be accomplished in 9ba tches. The fir st ba tch is scheduled for delivery in J uly. The fina l ba tch will bedelivered in September . Ladder assembly, survey, and CCD test ing will st a r timmedia tely upon ar r iva l of the fir st ba tch , and a ll assembly and commission ing ofVXD3 will be fin ished by December 1995, when the next SLD run is scheduled tosta r t .

** The SLD-Collabora tors working on the VXD3 upgrade are: S. Hedges (BostonUniv.), N. Allen , P . Dervan, A. McKemey, S. Wat t s (Brunei Univ.), J . Har ton , M. Smy(Colo. Sta te U.), S. Her tzbach , R. Kofler , M. St rauss, A. Trandafir (Univ. ofMassachuset t s), P . Burrows, D. Dong, H. Kendall, V. Lia , L. Osborne, D. Ross, F . Taylor ,R. Verdier , (Massachuset t s Inst itu te of Technology), G. Bashindzhagyan, D.Karmanov, M. Mer t in (Moscow Sta te Univ.), C. Damerell, R. English , A. Gillman , D.J ackson , L. Lin tern , G. Tappern (Ruther ford-Appleton Labora tory), M. Breidenbach ,G. Crawford, G. Hailer , M. Hildreth , J . Hoeflich , M. Huffer , J . J a ros, K. Skarpaas VIII,Su Dong (SLAC), K. Abe, K. Hasuko, T. Nagamine, F . Suekane, H. Yuta (TohokuUniversity), A. Arodzero, J . Brau , R. Frey, J . Huber , N. Sinev (Univ. of Oregon), E .Weiss (Univ. of Washington), V. Serbo, G. Zapalac (Univ. of Wisconsin), C. Baltay, M.Liu , S. Manly, J . Snyder , W. Emmet , J . Sinnot t , A. Wandersee (Yale Univ.)

REFERENCES

1. G.D. Agnew et d, “Design and Per formance of the SLD Ver tex Detector , a 120MPixel Tracking System,” Proceedings of the XXVI In terna t iona l Conference onHigh Energy Physics, Dallas, TX, 1992.--2. The CCDS are being manufactured by the EEV Company, Chelmsford, Essex,England.

7

SLAC-PUB-6950John’s contributions:VXD3 proposal,physics case, tracking,Bs mixing

VXD3 installed prior to 1996 SLC run

VXD3: Furthering precision• Why

à A

35

VXD3: Reaching higher precision• Alignment a major challenge!

– Optical survey [at room temp!]:CCD bowing

– Use tracks to determineboth internal alignment andglobal alignment relative todrift chamber

– Use various geometric overlaps

36

0.02

0–0.02–0.04–0.06

50

–5–40

–20 0

South CCD

North CCD

All Dimensions in mm

8262A154–97

20 40

0.06

0.04

0.02

0

–0.02

50

–5–40

–20 0 20 40

Fig. 20

account the errors and correlations in the residual fits. Abetter solution can be obtained by redefining the basis ofcoefficients from each of the residual fits such that themodified coefficients from each fit have a unit covari-ance matrix.

The equation to be solved then becomes TAx =Tc, where T provides the suitable change of basis forthe coefficients c. The elements of T are calculated fromthe covariance matrices of the residual fits. Solving thisequation with SVD effectively gives a more optimal ¬2

fit for the unknown CCD misalignments x.

7.3 CCD misalignments and hit residualsFigure 7.2 shows the degrees of freedom allowed in thisanalysis for a pair of CCDs on one of the 48 ladders ofVXD3.

Fig. 7.2: Definition of the CCD translation ±z, ±r, ±¥ and ro-tation ±Æ, ±Ø, ±∞ corrections to be determined, indicated fortwo CCDs on the same ladder

The parameters consist of three translations, par-allel to the edges of the rectangular CCD and normalto the CCD plane, and three rotations about the normalpoint in the CCD plane (i.e., the point in the plane clos-est to the IP)

– ±z : Translation in CCD plane in z direction– ±¥ : Translation in CCD plane in ¡ direction– ±r : Translation normal to CCD– ±Æ : Pitch – Rotation axis along width of CCD– ±Ø : Yaw – Rotation axis normal to CCD– ±∞ : Roll – Rotation axis along length of CCD.

Figure 7.2 also shows how the hit • in a CCD isspecified by the angle ∏ in the rz plane relative to z = 0

about the IP, and the distance L¡ across the CCD in theCCDs own reference system. The alignment proceduredescribed here assumed that each CCD was approxi-mately flat, with small shape corrections as measuredin the optical survey having been applied (see furtherdiscussion on CCD shapes in Section 7.6).

Fig. 7.3: The effect on the apparent hit position in a CCD dueto adjustments in the six degrees of freedom

Figure 7.3 illustrates the effect on the apparenthit position within a CCD for a track of fixed trajectorywhen the CCD position is adjusted by movements in thesix degrees of freedom. Misalignments of the CCDscause the measured hit on the CCD to be displaced fromthe true track trajectory by a residual amount ±z alongthe CCD length and ±L¡ across its length. The sign of±z is such that it measures the z location of the hit mi-nus the z location of the actual track in the plane of theCCD. If the only degree of freedom of the CCD was the±z correction, then ±z = °±z, and it would be trivial to‘unfold’ the required CCD alignment correction ±z fromthe measured residual ±z . Straightforward geometric ar-guments show that the more general form for the ±z and±L¡ residuals can be approximated as:

±z = °±z+±r tan∏+±Æ r tan2 ∏+±∞L¡ tan∏+±ØL¡

(7.1)

±L¡ = °±¥+±rr

L¡ +±∞

rL¡

2+±ÆL¡ tan∏°±Ør tan∏

(7.2)where both residuals are measured in the plane of theCCD.

Since the true track trajectory is unknown itis necessary to identify hits on several (usually three)CCDs associated with a track reconstructed in the CDC.Good quality tracks were selected with a momentum ofat least 1 GeV. In general the track was constrained topass through two of the CCD hits and the correspond-ing residual measured to the third, reference, CCD. Thesmall curvature effect of the charged track of known mo-mentum in the SLD magnetic field (0.6 T) was takeninto account in the r¡ plane. The relative lever-armweights with which each of the three CCDs contributeto the observed residual was determined from the idealgeometry to within a very good approximation (sincethe alignment corrections are very small compared withthe dimensions of the detector), in all cases the refer-

− Requires 578 alignment correctionsassuming optical survey distortionsaccurate

− But distortions found not to matchtrack data well

− Additional 288 alignment corrections needed to determine CCD shapes from track data

VXD3: Reaching higher precision• Alignment a major challenge!

– Optimal resolution achieved after full internal alignmentincluding fit for CCD shape distortions

37

The functional forms used after the shape correc-tions had been included are listed in Table 7.2. Sincethere was no track data to constrain the shape in thehigh | tan∏| region of layer 2 and particularly layer 1CCDs (as can be seen from Fig. 7.1(a) tracks from theIP that traverse any part of a layer 3 CCD can only in-tersect about half of a layer 1 CCD), a further 866 rows,each with only one non-zero element, were appended tothe matrix A and the array c was extended downwardswith 866 zero elements. These extra lines were usedto apply conservative restraints on the geometry by ef-fectively combining the dummy measurements ±z, ±r =

0±10 µm, ±¥ = 0±2 µm, ±Æ, ±Ø, ±∞ = 0±0.05 mradand ±q, ±h, ±t = 0 ± 5 µm (±x and ±y for the IP werenot ultimately constrained in this way) into the SVD ¬2

minimization fit. The complete 5026£866 element ma-trix A

0 and the 5026 element vector c0 were obtained

from A and c, respectively, by Eq. (7.7) using the 16 332non-zero elements of the effective matrix T. The latterwas obtained in turn from the residual fit covariance er-ror matrices (plus the corresponding error terms fromthe dummy measurements added above) as described inthe previous section. The matrix A

0 was inverted usingSVD and the VXD3 geometry was corrected with the866 elements of the solution vector x = A

0+c

0.

7.6.2 Achievement of design performance

The alignment procedure described in the previous sec-tions requires only a single iteration to a given data setto determine the corrected geometry. In practice, dueto a difference in run conditions and as the algorithmdeveloped, several aligned geometries were determinedfor the data taken in 1996/98. Details of these can befound in Ref. [6].

Figure 7.7 shows the Triplet ±z and ±L¡ residu-als obtained with the aligned detector together with thepre-alignment residuals derived from the optical surveygeometry. Since the Triplets cover the full volume of thedetector, that is over the full region of track acceptancefor all CCDs in all three layers, they provide a represen-tative indication of the local alignment. The data usedfor these Triplet plots correspond to charged tracks se-lected with momentum greater than 5 GeV/c to suppressthe multiple scattering contribution.

The post-alignment RMS of the residual distri-butions was found to be around a factor of four im-proved over the pre-alignment RMS values. Similarplots for all residual types, along with the mean andRMS measurements, were a major guide in debuggingand refining the alignment algorithm. Indeed, only af-ter taking into account the full residual fit error matri-ces, with the operation of T as expressed in Eq. (7.7),were the post-alignment residual plots observed to standout in a manner approaching the ideal performance, i.e.,with an RMS dominated by the intrinsic CCD hit reso-

lution about an essentially zero mean as seen in Fig. 7.7.Fitting a single Gaussian curve to each of the post-alignment histograms in Figs 7.7(a) and (b) yielded awidth of 4.45 µm in each case. This number, dependingon the three Triplet CCDs, is divided by the geometricweight factor

p1.02 + 0.52 + 0.52 to yield 3.63 µm as

the single CCD hit resolution for both ±z and ±L¡ af-ter the alignment, well within the initial target goal of5 µm and close to the intrinsic hit resolution. Erraticvariations in the residual distribution mean as a functionof the Triplet index that had been observed in the initialdata were reduced to the 1 µm level, as can be seen inFig. 7.8.

Fig. 7.7: Triplet residuals for 1997/1998 data obtained withthe original survey geometry (broad histograms with thick out-line) and after the alignment (narrow shaded histograms)

The magnitudes of the measured geometry cor-rections were typically O(10 µm) with the largest effectsbeing perpendicular to the CCD plane. A second itera-tion of the global alignment, described in Section 7.1,was performed after the internal alignment and gaveonly minor corrections for the six rigid body degrees offreedom of the detector as a whole. It should be notedthat the SVD procedure does not need to be iterated onthe same data set. This was expected given the relativelyminor nature of the approximations made in the analysisand was confirmed by the observed negligible effect ofperforming a second iteration of the internal alignment.

After the final alignment, the one hit resolutionfor the Shingle, Doublet, Triplet and Pair residuals overthe whole detector was in general found to be consis-tently better than 4.0 µm in both the rz and r¡ planes,very close to the true intrinsic CCD resolution, and de-sign performance had been achieved.

Single-hit resolution of 3.6 µm achieved!

D.J. Jackson, D. Su, F.J. WickensSLAC-PUB-13025

CCD shape fromoptical survey

CCD shape distortionsfrom internal alignment


VXD3: Reaching higher precision• Significant improvements in impact parameter resolution

• Significant gains in b-tagging efficiency

38

rz

VXD2VXD3

VXD2

6–978262A35

VXD3

rφ

(µm

)

(µm

)

Fig. 34

Z à bb or cc & b- or c-tagging• Topological vertexing for b- & c-tagging, 400K evts, 96-98 SLC runs

– Measurement of Rb: best b-tagging achieved with VXD3

– Measurement of Rc:precision with double-tag techniqueproportional to c-tag efficiency squaredè not accessible at LEP

Neural network for classification of events as b, c, or uds based on

• pT-corrected vertex mass• total vtx momentum• decay length• number of tracks assoc. vtx

39

DataMC

Mass (GeV/c 2)

No.

of H

emis

pher

es

bc

0

500

1000

1500

2000

2500

3000

3500

0 1 2 3 4 5 6

cuds

DataMC

Mass (GeV/c 2)N

o. o

f Hem

isph

eres

bc

0

500

1000

1500

2000

2500

3000

3500

0 1 2 3 4 5 6

cuds

SLAC-PUB-9941

https://arxiv.org/abs/hep-ex/0503005

Z à bb or cc & b- or c-tagging• Rb = Z à bb / Z à qq Rc = Z à cc / Z à qq

• Competitive Rb measurement• Dominant Rc measurement

40

LEP+SLD 0.21629 ± 0.00066

SLD vtx mass 1993-98

0.21576 ± 0.00094 ± 0.00076

OPAL mult 1992-95

0.2176 ± 0.0011 ± 0.0012

L3 mult 1994-95

0.2166 ± 0.0013 ± 0.0025

DELPHI mult 1992-95

0.21643 ± 0.00067 ± 0.00056

ALEPH mult 1992-95

0.2158 ± 0.0009 ± 0.0009

0.214 0.216 0.218Rb

LEP+SLD 0.1721 ± 0.0030

OPALcharm count. 1991-93

0.164 ± 0.012 ± 0.016

DELPHIcharm count. 1991-95

0.1693 ± 0.0050 ± 0.0092

ALEPHcharm count. 1991-95

0.1735 ± 0.0051 ± 0.0110

SLDmass+lifetime 1993-98

0.1741 ± 0.0031 ± 0.0020

OPALD-meson 1990-95

0.177 ± 0.010 ± 0.012

DELPHID-meson 1991-95

0.161 ± 0.010 ± 0.009

ALEPHD-meson 1991-95

0.1682 ± 0.0082 ± 0.0082

ALEPHlepton 1992-95

0.1685 ± 0.0062 ± 0.0080

0.16 0.18Rc

LEP+SLD 0.21629 ± 0.00066

SLD vtx mass 1993-98

0.21576 ± 0.00094 ± 0.00076

OPAL mult 1992-95

0.2176 ± 0.0011 ± 0.0012

L3 mult 1994-95

0.2166 ± 0.0013 ± 0.0025

DELPHI mult 1992-95

0.21643 ± 0.00067 ± 0.00056

ALEPH mult 1992-95

0.2158 ± 0.0009 ± 0.0009

0.214 0.216 0.218Rb

LEP+SLD 0.1721 ± 0.0030

OPALcharm count. 1991-93

0.164 ± 0.012 ± 0.016

DELPHIcharm count. 1991-95

0.1693 ± 0.0050 ± 0.0092

ALEPHcharm count. 1991-95

0.1735 ± 0.0051 ± 0.0110

SLDmass+lifetime 1993-98

0.1741 ± 0.0031 ± 0.0020

OPALD-meson 1990-95

0.177 ± 0.010 ± 0.012

DELPHID-meson 1991-95

0.161 ± 0.010 ± 0.009

ALEPHD-meson 1991-95

0.1682 ± 0.0082 ± 0.0082

ALEPHlepton 1992-95

0.1685 ± 0.0062 ± 0.0080

0.16 0.18Rc

SLAC-R-774


b- and c-quark asymmetry• Topological vertexing for b- or c-tagging and charge reconstruction

400K Z events from ’96-98 SLC runsà Measurement of parity-violating Ab and Ac– Discrimination between bottom quarks and antiquarks based on

sec. vtx charge (incl. VXD3 standalone tracks) charge of kaon attached to vtx

41

b- and c-quark asymmetry• Measurement of parity-violating Ab and Ac

– b-quark angular distributions based on vtx charge

42

0

5000

10000

-1 -0.5 0 0.5 1cosθ

Entri

es /

0.1

ALEPH DATASimulationb → l

(a)

0

5000

10000

15000

-1 -0.5 0 0.5 1cosθ

(b)

c → l

cosθthrust

tagg

ed e

vent

s

L polarizationSLD

cosθthrust

tagg

ed e

vent

s

R polarization

Large forward-backward asymmetry evident!

Becomes a tool to determine B or B nature for Bs mixing studies

e- e+b

b

q

Ab & Ac

43

SLAC-R-774

No LEP measurement!

Ratio of AFB for b and c@LEP yields Ab / Ac


Bs mixing• How to compute sensitivity to

Bs oscillations?

44

John’s notes

Bs mixing: Theory• Why look for Bs oscillations?

à A measurement of oscillation frequency provides an importantconstraint on tests of CP violation in B meson decays

• Why CP violation?à It is a required ingredient to explain the preponderance of

matter over anti-matter in our Universe• Why are Bs oscillations hard to find?

1. Must produce and identify large enough sample of Bs mesons2. Must determine whether a given Bs meson was born as B or B3. Must determine whether a given Bs meson decayed as B or B4. Must measure decay time precisely to resolve fast oscillations

SLD was excellent at points 2, 3 & 4 but not at point 1

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Bs mixing: Ingredients

47

Bs mixing: Reconstruction of Bs decay

48

Bs mixing: Reconstruction of Bs decayDs + tracks Vertex charge dipole

49

Kaon IDwith CRID

dq = (QD – QB) * DistanceB to D

Use B à D cascade structure

Ds à KKp

Bs mixing: Flavor tagging

50

Bs mixing: Sensitivity vs. LEP

SLD l+D and dipole analyses among 3 most sensitive at Δms = 17 ps-1

Sensitivity = Δms value for which oscillation amplitude has σA = 1 / 1.645= expected 95% CL lower limit on Δms

51

Bs mixing: Oscillation amplitude

SLD 400K Z0: Sensitivity = 13.4 ps-1 LEP 12M Z0: Sensitivity = 15.4 ps-1

52

Bs mixing: Oscillation amplitude

SLD most significant oscillation @ Δms = 19 ps-1 CDF @ Δms = 17.75 ps-1

2002

A/sA = 6A/sA = 2

2006

HFAG 2016 world average: Δms = 17.757 ± 0.021 ps-1

53

Mega-Z runextension?

• Making the case foran extension basedon Bs mixingà John’s notes

54

Mega-Z runextension?

• Making the case foran extension basedon Bs mixingà Sensitivity up

to Dms of 20 ps-1

with 1M Z events

55

http://www-sldnt.slac.stanford.edu/sld/sld2000/

http://www-sldnt.slac.stanford.edu/sld/sld2000/


56



0 POLARIZATION









0 CRIDID I./






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0 POLARIZATION









0 CRIDID I./





0 Other Standing Groups:

0 T~ Group (T. Johnson, J. Venuti ...) EPS C h i t ' .

- Impact Parameter Tests - 1st Move To Use Of Vertices For Analysis

0 ?b Group (Usher, Markiewicz,Punkar ...) EPS Tour.

- Impact Parameter Internal SLD T Check - Toward Use Of Cascade Vertices For Analysis

0 B anti B - Mixing Group (Zapalac, Jaros )

- Lepton+Vertex Analysis - Use Of Cascade Vertices

0 VERY WEAK POINTS OF SLD

0 WE ARE NOT TRYING TO ACTIVELY EXPLOIT VERTICES IN ANY ANALYSIS YET (Except T)

8 WE ARE NOT TRYING TO ACTIVELY EXPLOIT CASCADE VERTICES IN ANY ANALYSIS YET

@ WE ARE NOT TRYING TO USE THE CRID YET -

✓✓

✓

✓ ✓

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SLAC Summer Institute Jul-Aug ’93

SLD mug shots

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SLD Collab. Mtg Jun’99

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Chateau La CrestaSaratoga

SLD Collab. Mtg Oct’01

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St Francis Yacht ClubSan Francisco

SLD Collab. Mtg Oct’01

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St Francis Yacht ClubSan Francisco

SLD: Epilogue• SLD @SLC was an amazing experiment with many unique aspects

– Polarized electron beam for precise Electroweak measurements at the Z boson resonance

• Many have not been measured elsewhere since (ALR, Ab, Ac)

– Tiny SLC beam spot– Exquisite spatial resolution with pixel detector à heavy flavor physics– Particle ID

• John made key contributions – Building the case for an upgraded vertex detector (VXD3)– Pushing the boundaries of the physics program

& exploiting SLD’s unique strengths– Improving track reconstruction – Much encouragement and support to reach our goals

63

beautiful physics with precision tracking at › johnjarossymposium › sites › ... ·...

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