electroweak physics at slc/sld

Electroweak Physics at SLC/SLD

M. Swartz

The SLD experiment operated from 1991-1998 at the SLAC Linear Collider studying the process e+e- -> f-fbar. It was able to compete successfully against the aggregate of four LEP experiments and their combined ~30 times larger data sample. It succeeded because of some unique features. In particular:

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SLD Electroweak Physics

• a spin polarized electron beam with Pe = 70-80%

• the world’s most precise vertex detector, VXD3, that was very close [28mm] to a very small luminous region [1.5µm x 0.7µm x 700µm]

These features were made possible by the nature of the SLC, the world’s first [and so far, only] linear collider:

• can use a polarized electron source

‣ polarizing the beam does not reduce the luminosity [unlike LEP]

• repetition rate of the machine is low [120 Hz]

‣ can use a slow, relatively rad-soft, but very precise tracking technology like CCDs

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• The left- and right-handed helicity states of an electron are very nearly pure chiral eL and eR.

‣ with spin polarized beams, we can change the weak charges of the incident beam by flipping its spin state

‣ powerful tool for investigating the the Standard Model

• spin flipping is done by flipping the circular polarization of a laser with a birefringent Pockel’s cell

‣ does not affect the beam intensity

‣ can make very sensitive measurements

Polarized Beams

Fermion Qf I3L YνL 0 +1/2 -1eL -1 -1/2 -1uL 2/3 +1/2 1/3dL -1/3 -1/2 1/3νR 0 0 0 eR -1 0 -2uR 2/3 0 4/3dR -1/3 0 -2/3

The Standard Model treats the left- and right-chiral projections of our fermions as differentparticles with different electroweak quantum numbers.

spin spinright-handed left-handed

• the initial and final state coupling asymmetries Ae and Af interact with the polarization

‣ the product PeAe modulates the total cross section

‣ the sum Ae-Pe increases/decreases the angular asymmetry

• the asymmetry Ae [Aℓ] is particularly interesting because because ve [vℓ] is accidentally small

‣ quantum corrections due to new particles/physics are fractionally larger and more observable [~4.5-6 times more sensitive]

The differential cross section for e-(Pe) - e+ -> Z -> f - fbar can be expressed in a fairly model independent form as

4

Af =2vfafv2f + a2f

�f = NcGFM3

Z

24⇡p2(v2f + a2f )[1 + �vtx +�vtx] �Z =

X

f

�ff

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f

f

e+!

( )Pe"

d�ffZ

d⌦=

9

4M2Z

s�ee�ff

(s�M2Z)

2 + s2�2Z/M

2Z

�(1 + cos2 ✓)[1� PeAe] + 2 cos ✓Af [Ae � Pe]

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• can be measured using all visible final states except e+e- [which needs a more sophisticated treatment due to t-channel exchanges]

‣ negligible backgrounds

‣ count events only [don’t need any reconstructed quantities]

‣ independent of absolute acceptance

‣ independent of relative acceptances/eff of various final states in lowest order (need them for Z-γ interference corrections)

‣ independent of QCD corrections

‣ measured asymmetry is large (0.11-0.12): insensitive to many subtle problems

• often converted into an effective weak mixing angle for leptons

The comparison of the cross sections with left- and right-handed beams leads to a very powerful test of the SM

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ALR =1

P

�(�|P |)� �(+|P |)�(�|P |) + �(+|P |) = Ae =

2veaev2e + a2e

=2(1� 4 sin2 ✓e↵W )

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• fits to distributions are generally more precise than asymmetry measurements

‣ backgrounds from other Z final states

‣ independent of absolute acceptance

‣ QCD corrections for hadronic final states

The final state coupling asymmetries Af can be determined from fitting the angular distribution of particular final state or by defining an asymmetry

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AfFB =

�fF � �f

B

�fF + �f

B

=3

4

✓�P +Ae

1� PAe

◆Af

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VVH

p

VV HVV

H

ALR determines the initial state coupling asymmetry Ae, which is sensitive to quantum corrections that involve all of the SM particle content,

deviations can indicate new physics that has not been otherwise observed.

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• The SLC conceptual design report (SLAC R-229) of June 1980 contains a polarized source and a discussion of the impact of polarization on the determination of sin2θw

‣ no details about spin transport, manipulation, or monitoring

‣ influence of SLD co-founder C.Y. Prescott who had performed an iconic EW interference experiment [in DIS] using a polarized gun/beam in 1977/8

• The details were worked out over the next 2 years and are described in SLC Workshop on Experimental Use of the SLAC Linear Collider (SLAC R-247) in March 1982

‣ not included in the original SLC project

• Polarization was treated as an upgrade and described in SLAC-PROPOSAL-SLC-UPGRADE-01 (April 1986)

‣ SLCPOL group was formed to implement the needed elements

SLC EW Physics History

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SLC Polarization GroupEarly in 1986, a group of MkII and SLD physicists formed the SLC Polarization Group to implement the hardware needed to produce/monitor polarized electrons

• Co-Spokesmen: K. Moffeit and H. Steiner

• Some of the original proponents dropped out

• Between April 1986 and the end of 1990, a number of new collaborators joined/contributed: H. Band, S. Bethke, R. Elia, E. Garwin, M. Kowitt, F. Perrier, D. Pripstein, B. Schumm, M. Swartz, A. Weigend, M. Woods

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There were 7 parts of the project that needed to work (some more than others):

• Polarized Source

• Spin Rotation System

• Linac Polarimeter

• Compton Polarimeter

• Extraction Line Polarimeter

• SLC

• detector … like SLD - see talk by C. Baltay

SLC Polarization Hardware

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• triode gun was built and tested by C. Sinclair in the early 1980’s

• gun installed on SLC in winter 1987-1988, vacuum testing only?

‣ SLC mired in technical difficulties

‣ some politics too?

• first HV voltage tests in spring 1990 - failed

‣ begin Techical Division project to build several new diode guns with improved vacuum performance (HV improvements not obvious)

• Flashlamp-pumped dye laser/optics were developed by D. Cords/F. Perrier/M. Woods

• In the end, everything was replaced with better technology

Polarized Electron Gun

-. -^ -.,..: :

‘..

GAASCLBNLYNEXliQ~ED PW9TKW FW ACWA%W, /- WJumv

c

ULVE I 4177A72

Fig. 1. The high current polarized electron gun for the SLC. The gallium arsenide cathode is shown in the extracted position where it is activated with cesium and oxygen. In the normal position, polarized electrons are photoemitted from the cathode with a polarized laser beam, not shown.

Spin Rotation System

Linac

LTR Solenoid

2

5RTL Solenoid

Off

On

Linac Solenoid

8-886104A2

BSolenoid

Bd = 6.34Tm

e

Pθs

θPB

θ sg-22= γ θP

90 = 2.74 x 32.8

3

1

North Damping Ring (e )

3 x 32.8

5 x 32.8

4

6RTL Solenoid On

RTL Solenoid Off

7

Linac Solenoid On

Linac Solenoid Off

B

B

Be

e from South Ring

+ e+

-

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• designed to insert vertically polarized e- into damping ring and to allow for arbitrary polarization in the linac

• used three 6.3 T-m superconducting solenoids

‣ K. Moffeit + S. St. Lorant

‣ delivered under budget from small East-Bay company that manufactured MRI magnets

‣ lots of details but they just worked!

‣ R. Elia helped with testing/software?

• in the end, only 1 was needed for operations but all 3 were used for important diagnostic purposes

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Linac Møller PolerimeterLinac Moller Polarimeter

Target Collimator Detector

PC- φ

SLC

PEP e

PEP e +

Linac

20

40

60

80

100

04 8 12 16 20

y

(mm

)

5.51 mrad

0

PEP Beam Line

B2

B1

SLC Beam Line

METERS

Moller Scatters

6.81 mrad

10-88 7268A3

40 PR1 Collimator

Momentum Slit Preamplifier

Crate

Pb Shielding

Helmholtz Coils

6004A105–94

Target Holder

• used PEP injection line septum as analyzing magnet

• diagnostic only

• target design/calibration by H. Band/R. Prepost

‣ cloned for use in extraction line polarimeter

• Would lead to an interesting physics quandry in 1993

‣ solution would teach use more about magnetized target physics than we really wanted to know

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Compton Polarimeter

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 Counter

• best technique for polarimetry

‣ large QED asymmetry (“easily” understood)

‣ target has known quantum state of large polarization

‣ no intrinsic background

‣ machine backgrounds are directly measurable

‣ expensive/complex

• laser/optical transport built by SLAC/LBL

• prototype detector H. Steiner/G. Shapiro

• final 9 channel detector by B. Schumm

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Extraction Line Polarimetere+

SEPTUM MAGNE

TUNGSTEN RADIATOR

12-81 PWC HODOSCOPE 1 4177AA3

• only change from early design

‣ to accommodate SLC energy spectrometer, CYP negotiates a compromise with M. Levi

• new polarimeter is fatally flawed (can’t expose main beam to B-field)

• handed to MS to implement in late 1986 (took ~2 years to understand background problem)

• energy spectrometer more important than redundant Møller

• operated once in 1992 w/o B-field to check beam helicity

• simulation used in 1993 to solve polarization problem

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SLC• Machine completed and declared operational in April 1987

‣ B. Richter promises “only” 15 Z events per day

‣ no measurable luminosity in 1987

• 1988 - Mk II Collaboration stands shifts during the entire summer

‣ total integrated luminosity ~0.7 Z events equivalent, no events observed

• 1989: The SLC produced the world’s first e+e- -> Z -> hadrons event in early 1989. By the Autumn, it had produced a sample of about 500 Zs.

‣ Mk II scanned the Z-peak at 10 energies: measured MZ = 91.14±0.12 GeV, Nν = 2.8±0.6

‣ best day in 1989: 14 Z events!

• 1989: LEP Physics program starts in autumn: ~20,000 Zs/experiment in 4 months

‣ LEP combined results: MZ = 91.171±0.012±0.030 GeV, Nν = 3.04±0.12

• SLC would be totally outclassed from now on: except for beam polarization and vertexing

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SLC• SLC 1990

‣ triode gun HV voltage tests in spring 1990 fail

✴ begin Techical Division project to build several new diode guns with improved vacuum performance + HV improvements

‣ Mark II vertex detectors installed

✴ operates for ~ 3 months, logs ~150 Z events

✴ J. Jaros promoted to Mark II spokesman (Gary, Jonathan, Gerson head for hills)

‣ best SLC day in 1990: 15 Z events on Oct 28, 1990!

✴ BR’s boast is fulfilled!

✴ Or not: Oct 28 is a 25 hour day - 15th event comes in last hour ….

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MIB and SLCThe lab management responded to the disasterous early years of SLC operation with all kinds of re-organizations. BR knew who to lean on when the things weren’t going well.

• Aug 1988 - Emergency Task Force: BR in charge of SLC, MIB controls, TS software

• Dec 1989 - SLC Whitepaper: MIB, Burke, Himel, Patterson, Ruth, Seeman, Sheppard

• 1991 SLC Steering Committee

‣ MIB/Ross lead reliability assessment

• MIB would remain deeply [unofficially] involved with the machine until the end

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SLD Electroweak Working GroupStarting in 1991, the SLC Polarization Group integrates/morphs into the SLD Electroweak Working Group:

• Mark II members of the pol group are sent a really obnoxious letter inviting them to join SLD

‣ Marty would explain later that it was “toned down” from the original version pushed by some senior members of the collaboration

• Co-Leaders: P. Rowson and MS

• Many new collaborators join the work on ALR: R. Ben-David, G. Blaylock, W. Bugg, D. Calloway, J. Fernandez, M. Fero, R. Frey, S. Hertzbach, E. Hughes, T. Junk, R. King, A. Lath, D. Onoprienko, H. Park, M. Petradza, K. Pitts, K. Reeves, P. Reinertsen, E. Torrence, J. Yamartino, G. Zapalac, M. Zolotorev

• Roughly at the same time, CYP steps down as Research Division leader and agrees to lead the polarized gun project

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Spring 1991-Spring 1992• The gun project prospered under CYP’s leadership: diode guns were made operational

‣ R. Kirby [Garwin group] develops load lock for the diode guns: improves operability

✴ solves two problems: baking the gun poisons photocathodes, activating photocathodes with Cs is bad for HV performance if the Cs goes anywhere else

• Group of E. Garwin, T. Maruyama, R. Prepost, G. Zapalac develop usable strained lattice photocathode: high polarization [70-80%] now achievable

‣ importance cannot be overstated: reduced required # of events by [0.73/0.4]2 = 3.3

• 1991 SLD commissioning run is as bad as you might expect: 364 Z events (unpolarized)

• Witherell HEPAP Subpanel - visits lab and is told:

‣ 1992: SLD will log 104 Z events with polarization ~ 40%

‣ 1993: SLD will log 105 Z events with polarization ~ 40%

‣ committee is skeptical ....

• Feb-Mar 1992: SLC begins to improve - 1010 Z events logged by SLD

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April 1992Witherell HEPAP Subpanel: official recommendations (DOE/ER-0542P)

• sure ... give SLD until the end of 1993, let it produce what it can: then kill it

• luckily, this was only advice to DOE

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April 21,1992• Compton polarimeter (PR and MF) sees 3-5% polarization on midnight shift

‣ puzzling ... expect 30-35% from bulk GaAs cathode?

‣ maybe spin transport in arc is wrong?

• MS spends day developing the 3-state measurement

‣ determines max P and optimal orientation in linac

‣ at 17.00, MS calls KD to say he will be home late: she says NO, come home NOW!

‣ M. Petradza + W. Spence make measurement, find P~23%

• Tests of cathodes later confirm 20-25% polarization

• T. Fieguth later realizes that the arc lives on a spin resonance: spin orientation is sensitive to details of orbit - important, will be used to rotate spins and reduce number of arc precessions

First accelerated beam from polarized source!

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April 21,1992• Compton polarimeter (PR and MF) sees 3-5% polarization on midnight shift

‣ puzzling ... expect 30-35% from bulk GaAs cathode?

‣ maybe spin transport in arc is wrong?

• MS spends day developing the 3-state measurement

‣ determines max P and optimal orientation in linac

‣ at 17.00, MS calls KD to say he will be home late: she says NO, come home NOW!

‣ M. Petradza + W. Spence make measurement, find P~23%

• Tests of cathodes later confirm 20-25% polarization

• T. Fieguth later realizes that the arc lives on a spin resonance: spin orientation is sensitive to details of orbit - important, will be used to rotate spins and reduce number of arc precessions

First accelerated beam from polarized source!

Talia Swartz 12:20 am

Apr 22, 1992 7lbs, 11oz

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1992 SLD Run• After 5 terrible years, the SLC began to WORK!

‣ after lots of work by many people and many improvements to the machine

✴ one of them was the large scale use fast feedback [T. Himel]

• SLD logs 10,000 Z events with P=22.4%

‣ initially measures ALR = -0.100±0.044 !!!!

‣ expect ALR ~ +0.15, DO WE HAVE THE SIGN WRONG?, Is the SM really right-handed?

✴ LEP FB asymmetries are insensitive, Pτ is sensitive assuming LH W

‣ use sign of the Compton asymmetry to determine e- helicity at SLC IP

✴ need to know absolute laser γ helicity at Compton IP and sign of Compton theoretical asymmetry

✴ γ helicity is a mess of conflicting terminology and conventions ... some textbooks like Born+Wolf are wrong. It is very subtle,

AMAZING things happened during the summer of 1992:

RH helicity= LCP : ~E=E0 (x+ iy)ei(kz�ωt)

LH helicity= RCP : ~E=E0 (x+ iy)e�i(kz�ωt)

• Absolute helicity of the laser at the Compton IP - use many independent checks: 1/4 wave plate labelling (ambiguous), total internal reflection, vitamin B12, helical liquid crystal polarizer, Berek’s Compensator

• Check e- helicity at end of linac with Moller polarimeter

• Sign of the Compton Asymmetry for backscattered electrons (same conventions issues):

‣ Calculation by M. Peskin: σ(1/2) > σ(3/2)

‣ Physical argument by S. Drell: σ(3/2) > σ(1/2) [wins dime from MP]

• Check e- helicity using extraction line Moller with magnets off

• Final answer: ALR = +0.100±0.044 (agrees w/ SM)23

Great Sign Problem of 1992

e- !

Jz=1/2Jz=3/2

24

MIB and the EW GroupMarty is well known for his technical leadership skills, his hardware aesthetics, and his high standards that apply to everyone. I never felt effects of those standards except for one morning, early in the spring/summer of 1992. I arrived at the lab and learned that the Compton Polarimeter had stopped taking data in the night. I went off to the “laser shack” near the SLC Collider Hall and noticed that the polarimeter trigger had been “re-wired” by 2-3 of our junior colleagues in the night. It looked like they had tried to add an additional gate but hadn’t realized that it would add delay. Additionally, they needed an extra cable, and took a really long one: the two ends emerged from a large coil on the floor. Suddenly the door opened and Marty charged in:

MIB: WHAT THE HELL HAPPENED LAST NIGHT?MS: well … it looks like they tried to add a gate to the trigger and threw everything out of time ….. I guess they didn’t check the timing with an oscilloscopeMIB: USE A SCOPE? WHAT A GOOD IDEA, but I doubt that they even know how to …The conversation then became friendlier.

24

MIB and the EW GroupMarty is well known for his technical leadership skills, his hardware aesthetics, and his high standards that apply to everyone. I never felt effects of those standards except for one morning, early in the spring/summer of 1992. I arrived at the lab and learned that the Compton Polarimeter had stopped taking data in the night. I went off to the “laser shack” near the SLC Collider Hall and noticed that the polarimeter trigger had been “re-wired” by 2-3 of our junior colleagues in the night. It looked like they had tried to add an additional gate but hadn’t realized that it would add delay. Additionally, they needed an extra cable, and took a really long one: the two ends emerged from a large coil on the floor. Suddenly the door opened and Marty charged in:

MIB: WHAT THE HELL HAPPENED LAST NIGHT?MS: well … it looks like they tried to add a gate to the trigger and threw everything out of time ….. I guess they didn’t check the timing with an oscilloscopeMIB: USE A SCOPE? WHAT A GOOD IDEA, but I doubt that they even know how to …The conversation then became friendlier.We were encouraged to teach our younger colleagues simple rules like “NEVER, EVER, EVER, TOUCH THE ELECTRONICS WHEN YOU ARE ON SHIFT”

25

MIB and the EW GroupThe helicity state of the polarized source was chosen pseudo-randomly using a hardware random number generator copied straight out of “Horowitz and Hill”

Art of Electronics Third Edition 13.14.2. Feedback shift register sequences 975

With just a few chips you can generate sequences that lit-erally go on for centuries without repeating, making thisa very accessible and attractive technique for the genera-tion of digital bit sequences or analog noise waveforms.When generating eye diagrams (e.g., Figures 12.132 and14.33), or testing serial links for bit error rates (BERs), itis common to use a PRBS source. PRBSs are used alsoto “scramble” (deterministically) the serial data in gigabitEthernet communications, in order to generate a lively bitpattern for the ac-coupled (transformer) physical link; thescrambling is reversed at the receive end, by XOR-ing witha synchronized PRBS running the same sequence.

A. Analog noiseSimple lowpass filtering of the output bit pattern of a PRBSgenerates bandlimited white Gaussian noise, i.e., a noisevoltage with a flat power spectrum up to some cutoff fre-quency (see Chapter 8 for more on noise). Alternatively,a weighted sum of the shift-register contents (via a set ofresistors) performs digital filtering, with the same result.Flat noise spectra out to several megahertz can easily bemade this way. As you will see later, such digitally syn-thesized analog noise sources have many advantages overpurely analog techniques such as noise diodes or resistors.

B. Other applicationsBesides their obvious applications as analog or digitalnoise sources, pseudorandom bit sequences are useful ina number of applications that have nothing to do withnoise. As just mentioned, they are used for pattern gen-eration in serial link testing (eye diagrams, bit error rate),and for bit scrambling (as opposed to real encryption)in serial network protocols like Ethernet. They are usedin “direct-sequence” spread-spectrum digital communica-tions (in which each bit to be transmitted is sent as a pre-determined sequence of shorter “chips”); such a techniqueis used, for example, in CDMA (code-division multiple-access) cellular phone systems, and in the airlink privacycipher of the GSM cellular standard. They’re also usedin digital TV broadcasting. These sequences are used ex-tensively in error-detecting and error-correcting codes, be-cause they allow the transcription of blocks of data insuch a way that valid messages are separated by the great-est “Hamming distance” (measured by the number of biterrors). Their good autocorrelation properties make themideal for radar-ranging codes, in which the returned echo iscompared (cross-correlated, to be exact) with the transmit-ted bit string. They can even be used as compact modulo-ndividers.

13.14.2 Feedback shift register sequences

The most popular (and the simplest) PRBS generator isthe linear feedback shift register (LFSR, Figure 13.111).A shift register of length m bits is clocked at some fixedrate, f0. An exclusive-OR gate generates the serial inputsignal from the exclusive-OR combination of the nth bitand the last (mth) bit of the shift register. Such a circuitgoes through a set of states (defined by the set of bits in theregister after each clock pulse), eventually repeating itselfafter K clock pulses; i.e., it is cyclic with period K.

PRBS out

shift register (clocked)

1 2 3 4 n m

Figure 13.111. Pseudorandom bit sequence generator.

The maximum number of conceivable states of an m-bitregister is K = 2m, i.e., the number of binary combinationsof m bits. However, the state of all 0s would get “stuck” inthis circuit, because the exclusive-OR would regenerate a 0at the input. Thus the maximum-length sequence you canpossibly generate with this scheme is 2m−1. It turns outthat you can make such “maximal-length shift-register se-quences” if m and n are chosen correctly, and the resultantbit sequence is pseudorandom.136 As an example, considerthe 4-bit feedback shift register in Figure 13.112. Begin-ning with the state 1111 (we could start anywhere except0000), we can write down the states it goes through:

111101110011000110000100001010011100011010110101101011011110

We have written down the states as 4-bit numbers

136 The criterion for maximal length is that the polynomial 1+xn+xm be

irreducible and prime over the Galois field GF(2).

A 31-bit shift register and an XOR gate generate a sequence of 231-1 bits. This information must be transmitted from the source area to the experiment 3km away. Any corruption or loss of the this information would dilute all measured asymmetries. Data integrity is essential.

• Original solution: use the Klystron Veto Module system

‣ signal is received and re-transmitted at each of the 240 klystrons

‣ there is traffic on the bus during operation [klystrons dropping out/returning]

• No one liked this idea, we decided to use an available coaxial cable called Mach Line

‣ MIB hated this too … aesthetics aside, if they disagree … what do you do?

26

MIB and the EW GroupMarty [and helpers] designed and built a 3rd system called Polmon using new technology.

At some point, someone [T. Junk, T. Johnson, MIB?] realized that we could verify the sequence after reading the states of 31 consecutive pulses and emulating the [very simple] hardware. Was done online and offline. In the end,

System Error RateKVM few %

Mach Line 10-4

Polmon <10-9

Polmon never made a mistake in Nx109 pulses!

27

1993 SLD RunFeatured significant changes to SLC operation:

• Flat beam operation increases luminosity

‣ turn-off RTL and linac spin rotators, accelerate vertical pol in linac

‣ use arc resonance to rotate spins w/ orbit bumps (P.Emma)

• First use of strained-lattice cathode + loadlock gun increases P to 63%

• SLD logs 47,000 Z events with P=62.6%

• SLD measures ALR = 0.1656±0.0073(stat)±0.0032(sys)

‣ result is slightly more precise than promise to Witherell Committee

‣ very exciting result about 16% larger than LEP Ae = 0.1425±0.0048

‣ H. Band and R. Prepost operate linac Møller, find PMøl = 1.21 Pcompton

✴ after correcting for calculated 5% loss in arc, PMøl = 1.16 Pcompto

✴ Maybe the Ae discrepancy is due to incorrect Compton measurement?

28

Great Polarization Problem of 1993In the autumn of 1993, MS finds preprint by L.G. Levchuk [KFTI 92-32] (via M. Woods?):

• suggests that Møller polarimeters may be affected by momenta of bound e-

‣ polarized M-shell e- less affected than unpolarized inner shells

‣ estimates size of effect using simplified momentum distributions

‣ claims effect is small in large acceptance SLAC polarimeters [in preprint, not in published version]

• But SLAC polarimeters have high resolution:

‣ use realistic distributions in full simulation

‣ broadens peak: improves fit

‣ increases analyzing power: changes PMøl by 1/1.16 = 0.86

• Now find PMøl = Pcompton, measured ALR is OK!

0.1

7667A125–94

0

Pol

ariz

atio

n

Measurement

0.7

0.8

0.6

4 8

!2

( bou

nd e

– )

!2

(fre

e e–

)

Compton measurement

(a)

Bound e– hypothesis Free e– hypothesis

(b)

0.9

Averages (incl. syst. error)

X

120

0.2

0

4

Detector Channel (0.6 mm pitch)7667A15–94

0 20 40 60

N–shell

8

12

M

L

KSig

nal/

Tar

get e

– (

arb

units

)

polarizedelectrons

29

1994/5 SLD RunThings continued to improve in the 1994/5 run

• SLD logged 94,000 Z events with P=77%

‣ improved final focus optics

‣ optimized photocathode


‣ smaller than 1993, but still larger than LEP average

‣ Compton systematic uncertainty down to ΔP/P = 0.64%

✴ MW implements tunable elliptical polarization at Compton laser bench to compensate transport line phase shifts: increase Pγ to nearly 100% (decreasing uncertainty to ~0.2%)

✴ implement table scans to monitor analyzing power

‣ Reduce transport related effects on polarization uncertainty

30

1996 SLD RunThings take a bit of a downturn on Feb 10, 1996

• A senior accelerator division engineering physicist decides to take a shortcut to solve a tripping vacuum pump problem in the North Damping Ring

‣ calling in a vacuum tech on a weekend will waste valuable time

‣ physicists know everything and can do anything [I can’t really argue with that :)]

• Resulting fire in NDR delays start of run by ~2 months [maybe we should have waited for the tech?]

‣ smoke residue has lingering affect on reliability of NDR components

• SLD logs only 52,000 Z events with P=76%


‣ achieve ΔP/P = 0.5%

31

1997/8 SLD Run• SLC luminosity rises to 400 Z/hr in Apr/May 1998

‣ due to efforts of a few diehards: P. Emma, N. Phinney, and P. Raimondi

‣ prorated for 120 Hz, achieves design luminosity (after 11 years)

• SLD logs 334,000 Z events with P=73%

Vanda 6/22/98

1992 - 1998 SLD Polarized Beam Running

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

20000

2-May-92

6-Jun-92

11-Jul-92

15-A

ug-92

20-M

ar-93

24-A

pr-93

29-M

ay-93

3-Jul-93

7-Aug

-93

23-Jul-94

27-A

ug-94

1-Oct-94

5-Nov

-94

10-D

ec-94

14-Jan-95

18-Feb-95

6-Apr-96

11-M

ay-96

15-Jun

-96

20-Jul-96

13-Jul-97

17-A

ug-97

21-Sep-97

26-O

ct-97

30-N

ov-97

4-Jan-98

8-Fe

b-98

15-M

ar-98

19-A

pr-98

24-M

ay-98

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%


‣ run polarimeter with interleaved e+ dumper: very robust result

‣ cross-check polarimeter w/ PGC (RF) and QFC (BB, DO)

‣ HB and PCR do Posipol (prove P+=0)

‣ miniscan of peak (establish Ecm scale to ±30 MeV)

• Vacuum leak in e+ source killed SLC after it’s best 24 hours ever ....

32

SLD EW Physics

• Most precise single determination of Ae [sin2θWeff]

‣ still statistics dominated

‣ systematic uncertainty ~ 1/2 of the stat uncertainty

‣ Too bad the program ended in 1998 [another 1-2 years would have had real impact]

Year NZ Pavg ALR

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

0.1513860.00216

The total ALR results are are based on hadronic final states and are summarized below

33

Leptonic FB Asymmetries

• plot shows only most precise single measurements

• tension with Ae determined from LEP AbFB measurements

‣ 3+ sigma difference

‣ SM with mH=125 is 0.23152

The leptonic final states were handled separately using angle information: they determine both Ae and Aℓ

Ae = 0.1558±0.0064, Aμ = 0.137±0.016, Aτ = 0.142±0.016They are consistent with lepton universality and are combined with ALR to produce a final Aℓ,

Aℓ = 0.15130±0.00207

sin2θWeff = 0.23098±0.00026

William Barter (University of Manchester) Slide 3Weak Mixing Angle Measurements HL/HE-LHC: June 2018

Weak Mixing Angle – current status

Only showing explicitly the most precise measurements at LEP/SLD; overall average from all LEP/SLD measurements shown as gold band.

LEP/SLD average

Tevatron combination reaches uncertainty of 0.00033; compatibility of measurements 2.6%.

Current ATLAS analysis only uses 7 TeV data.

Current CMS analysis uses sophisticated techniques to reduce statistical and PDF uncertainties.Current LHCb analysis has smaller PDF uncertainties than ATLAS, but a larger stat. unc (lower lumi).

from talk by W. Barter, 2018

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

34

Hadronic FB Asymmetries

• polarized beam allows the direct measurement of Ab

• we had VXD3, the best vertex detector ever

• we had D. Jackson who realized that we could partly correct the vertex mass for the missing ν’s in the B hadron decays

‣ really enhanced the vertex mass sensitivity

‣ required all of VXD3 resolution, didn’t work at LEP

The tension between ALR and AbFB=0.75AeAb made the determination of Ab quite interesting [also, the Z->bbar branching fraction result from ALEPH appeared to be anomalous]SLD had several strengths:

primary vtx

secondary vtx

pTmiss

The b and bbar directions were identified using 4 techniques [vtx chrg, jet chrg, lepton chrg, K±]. Combined result,

Ab = 0.905±0.017(stat)±0.020(sys)It’s a little smaller than the SM value of 0.935 but would be adjusted in LEPEWWG fits 0.923

35

What does it mean?Using the model independent approach of Peskin and Takeuchi,

• SM seems to work really well

• We can exclude the existence or parameter space of many possible extensions

‣ for example: sequential fermions [the kind we know and love] of all masses are excluded or disfavored … most LHC searches focus on “vector-like” fermions

36

Marty’s RoleMarty’s technical leadership was a crucial part of the whole SLC/SLD adventure. He is a rare individual who has a clear vision and remarkable taste. He holds others to the same very high standards that he applies to himself … digress here

36


In May of 1995, PBS broadcast a 3 part TV series entitled “Triumph of the Nerds” on the history of the personal computer. Some of that history played out in the “old” Panofsky Auditorium and featured Steve Jobs. SJ was a man of vision and taste, and held his subordinates to very very high standards … some of his behavior was downright despicable. As I watched it, hmmm … echos of Marty … but Marty is a fundamentally kind/caring human being and SJ is not.

36


In May of 1995, PBS broadcast a 3 part TV series entitled “Triumph of the Nerds” on the history of the personal computer. Some of that history played out in the “old” Panofsky Auditorium and featured Steve Jobs. SJ was a man of vision and taste, and held his subordinates to very very high standards … some of his behavior was downright despicable. As I watched it, hmmm … echos of Marty … but Marty is a fundamentally kind/caring human being and SJ is not.

The next morning, I crossed paths with T. Schalk. Our conversation went something like this:MS: did you see Triumph of the Nerds last night?TS: yes, it was really interesting … tell me, does Steve Jobs remind you of someone we know?MS: I thought exactly the same thing, but our guy isn’t nearly as extreme and demandingTS: Oh, Marty is a pussycat compared to Steve Jobs …

37

Marty’s RoleAnother very special aspect of Marty is his deep understanding all kinds of technical issues and complex systems. This high level understanding of low level stuff is quite rare. Have I ever met anyone else like him?

37


The only person who came to mind, but not someone that I knew terribly well, is W.K.H. Panofsky. It was really quite appropriate that Marty was awarded the APS Panofsky prize in 2000.

37



OK, we’ve now established that Marty manifests some characteristics of Pief and some of Steve Jobs. Yesterday, he described some of his efforts to build a compact linear accelerator/linear collider. What should it be called?

37



OK, we’ve now established that Marty manifests some characteristics of Pief and some of Steve Jobs. Yesterday, he described some of his efforts to build a compact linear accelerator/linear collider. What should it be called?

iLC?

Best wishes for a really busy, happy, and rewarding retirement.

electroweak physics at slc/sld

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