M. Woods, SLAC

SLDSLD Compton PolarimeterCompton Polarimeter(also Compton polarimetry at NLC, DIS-Parity)

SLD Compton Polar imeter at SLC

Compton Polar imetry at NLC

Compton Polar imeter for DIS-Par ity LOI

JLAB Polar imetry Workshop June 9-10, 2003Mike Woods, SLAC

M. Woods, SLACM. Woods, SLAC

SLDSLD Experiment at the SLAC Linear ColliderExperiment at the SLAC Linear Collider

M. Woods, SLAC

Simple Cuts to select hadronic Z events• Energy imbalance < 0.6

• >22 GeV energy in calorimeter

• 3 or more charged tracks

LReRL

RLm A|P|

NN

NNA =

+−=

AALR LR Measurement at Measurement at SLDSLD

Simple Counting Exper iment• can use all final states (no particle ID)• no kinematic reconstruction• no need to distinguish fermion from

anti-fermion• no final state interaction effects

M. Woods, SLAC

1.6%

0.64%

0.07%

0.15%

0.39%

0.50%

1997-8

0.63%0.75%1.7%3.6%Total Systematic

3.7%2.8%4.3%44%Statistics

0.16%0.17%1.1%-Chromatic Effects

0.05%0.06%0.1%2.4%Bkg., detector ,…

0.37%0.33%--Energy Scale

0.50%0.64%1.3%2.7%Polar imetry

19961994-519931992

SLDSLD AALRLR result and result and SystematicsSystematics

00027.023097.0sin

00216.015138.02

0

±=

±=eff

W

LRA

θ

ALR Statistics and Systematic Errors

M. Woods, SLAC

Experimental Constraints on the Higgs MassExperimental Constraints on the Higgs Mass

Established measurements of the Z boson mass at LEP and the top quark mass at the Tevatron allow predictions of the Higgs mass from precise measurements of the weak mixing angle, the W mass and the Z width. The yellow region is excluded by direct searches at LEP.

M. Woods, SLAC

Focusing and Steering Lens

Compton Polarimeter Compton Polarimeter

M. Woods, SLAC

M. Woods, SLAC

Features of Features of SLDSLD Compton polarimeterCompton polarimeter

Physics is well understood QED; radiativecorrections <0.1%- no atomic or nuclear physics corrections (ex. Levchuk effect

in Moller polarimetry)- reference for O(α3) corrections: M. Swartz, Phys.Rev.D58:014010,1998

Electron beam backgrounds measured with laser off pulses

Polar imetry data taken parasitic to physics data (electron detector only)

Scatter ing rate is high; ~1% polarization determination in a few minutes

Laser helicity selected with a pseudo-random sequence

Laser polar ization determined to 0.1%

Beam-beam depolar ization effects can be measured by compar ing measurements with and without collisions

M. Woods, SLAC

Electron Cherenkov Detector (CKV)Electron Cherenkov Detector (CKV)

8mm Pb radiator

EGS4 simulation for shower from 1 electron

EGS-generated response function for CKV-7, with (solid line) and without (dashed line) 8mmlead pre-radiator.

Gas is propane at 1atm; 11 MeV threshold

M. Woods, SLAC

Raw Data from CKV DetectorRaw Data from CKV Detector(during e- - only running)

M. Woods, SLAC

Compton Scattering KinematicsCompton Scattering Kinematics

The cross section for Compton scatter ing is

( ) ( ) ( )[ ]yAPPyy e γσσ += 10 where 0

'

E

Ey =

The measured asymmetry in a channel is

γPPaNNN

NNA eioff

iii

iimi =

−+−= →←→→

→←→→

2

Where the analyzing power is calculated from the Compton Cross section and the channel response function, Ri.

( ) ( )

( )�

�=

dxxRdx

d

dxxRxAdx

d

a

i

i

i0

0

σ

σ

M. Woods, SLAC

CKV Analyzing Power DeterminationCKV Analyzing Power Determination(Table Scans)

Detector resolution modifies theoretical analyzingpower by <2% for CKV7 at Compton Edge

• 10 MeV detector threshold ensures EGS-based simulation is reliable

Table scans sweep detector channels thru Compton Edge• done daily• give spectrometer calibration, locate Compton edge,

track detector channel gains• determine CKV7 analyzing power to 0.2%

Use pulse height ratios for CKV7/CKV6 andCKV8/CKV6 to track analyzing powers between table scans. Resulting uncertainty in CKV7 AP is 0.3%.

References: SLD Physics Note 50; E. Torrence Ph.D. thesis, SLAC-Report-509.

M. Woods, SLAC

Radiative Radiative Corrections to Analyzing PowersCorrections to Analyzing Powers1st-order (α3) corrections

<0.1% correction to analyzing powerat Compton Edge

<0.2% corrections to cross section

See M. Swartz, Phys. Rev. D58, 014010 (1998)

M. Woods, SLAC

CKV LinearityCKV Linearity

Measurement of electronics linearitywith pulser

Study measured Compton asymmetry as aFunction of background level.

0.2% linear ity systematic

( )( )onlyelectron

collisionsRatio

P

P=

M. Woods, SLAC

λλλλ/2plate

Spectra Physics GCR-130

CPPS

L,R Photodiodes

Intensity Photodiode

LaserPhotodiode

Pockels Cells

Polarizer

Polarizer Polarizer

Remote Steering, Focusing Control

Remote Intensity Control λλλλ/2

plate

λλλλ/4plate

Calcite Prism

Compton Laser BenchCompton Laser Bench

CCD Camera

LaserTransport L ine

Remote Polarization Control

M. Woods, SLAC

Compton Laser Transport SystemCompton Laser Transport System

• 40 meters from laser to Compton IP• Each Mirror Box has 2 helicity-compensating

mirrors•Transport line operates at +3psi nitrogen• Laser focused to ~0.5mm rms at Compton IP

(50mJ in 7ns FWHM pulse)

M. Woods, SLAC

Laser Polarization Control And AnalysisLaser Polarization Control And Analysis

Pockels Cell used for CP, PS Calcite Pr ism used in Helicity Filter

M. Woods, SLAC

( )���

�

�

���

�

�

�

��

�

��

=+

2cos

2sin

2 CPi

CP

PSeE δ

δ

δπ

Electr ic Field Vector after PS Cellin Jones Matr ix notation:

Laser Polarization ControlLaser Polarization Control

Allow for imperfect Pockels cells and phase shifts in downstream optics:

( )

( ) ( )

( ) ( )LR

LRs

VU

VUs

YX

YXs

PSCP

PSCP

CP

+−==

+−==

+−==

δδ

δδ

δ

cossin

sinsin

cos

3

2

1

( ) 12223

22

21 =+=++ CLsss

Stokes parameters for laser polar ization:

CPPS

Pockels Cells

PolarizerRemote Polarization Control

( ) ��

���

⋅+

��

���

⋅+=

2cos

2sin

4/4/3

πδπδλλ

PS

TCPPS

CP

TCPCP

V

VV

V

VVCIPs

M. Woods, SLAC

Laser Polarization ScansLaser Polarization Scans(and the laser polarization systematic error)

0.1% systematic er ror

Abo

xPD

(ad

cco

unts

)

CP Voltage (Volts) CP Voltage (Volts)Res

idua

ls (

adc

coun

ts) LPSCANS

• done once per hour; readout photodiodes only• ability to extinguish laser light after

Helicity Filter determines polarization purity

Laser Polarization at Compton IP (%)CP Voltage (Volts)

CK

V7

Raw

Asy

mm

etry

• monitor phase shifts in laser Polarization with continuous Pockelscell scans

• only 1/3 of data is at nominal voltages

ESCANS

M. Woods, SLAC

Photon CrossPhoton Cross--check Polarimeter Detectorscheck Polarimeter Detectors

PGC (polarimeter gamma counter): - threshold gas (14 MeV; 1 atm ethylene) Cherenkov counter - insertable lead pre-radiator; 1 PMT

QFC (quartz fiber calorimeter): - quartz fibers with tungsten radiators; 0.2 MeV threshold(34 longitudinal sections, each 1 radiation length)

- 24 PMTs (10X, 10Y, SUMX, SUMY, 2 Bkgd)

24 PMTsPMT

InsertablePb pre-radiators

M. Woods, SLAC

QFC Data and QFC Data and SystematicsSystematics

Measurement, MC<0.1%Optical cross talk

0.6%Total

In situ study0.1%Laser pickup

In situ study0.1%Electronics cross-talk

LED study, beam test0.5%Electronics linear ity

MC, in situ study<0.1%Re-scattered electrons

MC simulation<0.1%Angular acceptance, beam size

Beam test, MC 0.1%Detector mis-alignment

Beam test, MC0.3%Detector non-uniformity

Beam test, MC0.2%Energy Response

MethodErrorSystematic

D. Onoprienko, SLD-Note-267, 1999 and Ph.D. thesis, SLAC-Report-556, 2000.

M. Woods, SLAC

PGC Data and PGC Data and SystematicsSystematics

PGC analysis described in R. Frey, SLD-Note-266, 1999,and IEEE Trans. Nucl. Sci. 45, 670, 1998.

T-4100.5” Pb

T-4101.0” Pb

T-4101.5” Pb

SLC data with e- only, 1” Pb

0.6%Total

In situ study0.1%Laser pickup

In situ study0.3%Detector effects (uniformity, geometry,

linear ity)

Beam test, MC0.5%Energy Response

MethodErrorSystematic

No e-

e-, no laser

Jz = 1/2

Jz = 3/2

M. Woods, SLAC

Analyzing Power Systematic ErrorAnalyzing Power Systematic Error

Estimate CKV7 systematic error in analyzing power at 0.3% from table scan data that determines location of Compton edge and accuracy of modeling detector response function

Results from cross-check Polar imeters

0.4% systematic er ror

Residual of CKV7 polarization to results from PGC and QFC was ∆P/P=(0.30±0.39)%.

M. Woods, SLAC

0.52%0.52%0.67%1.7%2.7%TOTAL

0.15%0.16%0.17%1.1%0.2%Lum-wtingCorrection

0.2%0.2%0.2%0.2%0.4%Laser Pickup

0.4%0.4%0.3%0.6%1.0%Analyzing Power

0.2%0.2%0.5%0.6%1.5%Detector L inear ity

0.1%0.1%0.2%1.0%2.0%Laser Polar ization

1997/9819961994/9519931992Systematic

72.92 ± 0.38 %76.16 ± 0.40 %77.23 ± 0.52 %63.0 ± 1.1%22.4 ± 0.6 %Lum-wtedPolar ization

1997/9819961994/9519931992

Polarization Summary for all SLD RunsPolarization Summary for all SLD Runs

Ph. D. Students: R. Elia, SLAC-Report-429, 1994; R. King, SLAC-Report-452, 1994;A. Lath, SLAC-Report-454, 1994; T. Junk, SLAC-Report-476, 1995; E. Torrence, SLAC-Report-509, 1997; J. Fernandez, SLAC-Report-519, 1999;P. Reinertsen, SLAC-Report-537, 1998; D. Onoprienko, SLAC-Report-556, 2000.

M. Woods, SLAC

The “ 17Hz Problem” in the 1994 runThe “ 17Hz Problem” in the 1994 run

Reflection from inverter (added due to BPM miswiring in downtime) causes every 7th pulse to be off-energy

Observe i) phasing of off-energy pulse wrt laser pulse shifts every 40sii) large scatter in electron polarization measurements

Implemented tr igger ing of laser on 6th machine pulse rather than the 7th machine pulse every ~10 seconds, to ensure beam backgrounds for laser off pulses identical to beam backgrounds for laser on pulses.

M. Woods, SLAC

Arc Spin RotationArc Spin RotationSpin precession in the SLC arc is nearly resonant with vertical betatron oscillation

1. Vertical betatron oscillation in a quadrupole string

2. Vertical betatron oscillation with horizontal dipoles added

Spinaxis perpendicularto trajectoryelectron trajectory

SLC arc consists of 23 achromats. Each achromat:

• 20 combined function magnets• Spin precession of 10850

• Betatron phase advance of 10800

SLC arc consists of 23 achromats• Launch into arc with electron spin ver tical• Two or thogonal ‘spin bumps’ allow arbitrary control• Optimize spin bumps to minimize total precession in

the arcs reducing polar ization dependence on energy

M. Woods, SLAC

LuminosityLuminosity--weighted Beam Polarizationweighted Beam Polarization

( ) ( ) ( )( ) ( )�

�=−

dEELEn

dEELEPEnP wtlum

e

( ) ( )( )�

�=dEEn

dEEPEnPCompton

e

1. Chromatic Effect

2. Spin Diffusion- incoming beam divergence- disruption angles

ξξξξdiv====(-0.24 ± 0.08)% correction for 1997/98 run

3. Depolarization due to beamstrahlung spin flip- expect effect to be <0.1%- effect measured to be <0.001 by comparing polarization measurements with and

without positrons presentξξξξdiv====(0.0 ± 0.1)%

( )ξ+=− 1Comptone

wtlume PP

- determine n(E) from automated wire scans (every 4 hours) at point of high dispersion;P(E) by varying beam energy (optimize spin bumps to minimize)L(E) from optics models and measured dependence of Z production on

beam energyξξξξdiv====(+0.12 ± 0.08)% for 1997/98 Run

M. Woods, SLAC

0.25%0.50%TOTAL

0.05%0.2%Electronic Noise

0.1%0.2%Linear ity

0.2%0.4%Analyzing Power

0.1%0.1%Laser Polar ization

NLC Goal

δδδδP/P

SLD

δδδδP/P

Uncer tainty

Goals for Compton PolarimetryGoals for Compton Polarimetry SystematicsSystematicsat NLCat NLC

Improve linear ity by: - higher resolution adcs (16-bit rather than 11-bit)- blue diode laser calibration and bias system - compare laser jitter, toroid jitter with detector jitter- use of Compton laser power scans

Improve analyzing power by: - more segmentation of channels near Compton edge in CKV detector- careful design and simulation of spectrometer and detector

(original design goal for SLD was 1%)- detailed systematics data taking- cross-checks (if possible): Compton gamma detectors,

W-pair asymmetries, polarized Moller asymmetriesElectronic Noise includes crosstalk and laser pickup: reduce by careful setup and accurate measurements

M. Woods, SLAC

Polarimetry Options at a future LCPolarimetry Options at a future LC

Mott Polarimeter at Source for commissioning

Compton Polarimeterbefore IPafter IP+ after energy collimation for fixed target

Blondel scheme if both beams polarized

W-pair asymmetry- with only electrons polarized- better with both beams polarized

M. Woods, SLAC

Improved Weak Mixing angle determination at Improved Weak Mixing angle determination at GigaGiga--ZZvia Avia ALRLR measurementmeasurement

(positrons unpolarized)

M. Woods, SLAC

Polarimetry using WPolarimetry using W--pair asymmetriespair asymmetries

Can we use asymmetry in forward W pairs as a polar imeter?

Yes, if can achieve backgrounds below 1%.(This level of backgrounds is achieved for LEP200 W massmeasurements, if require one W to decay to ee or µµ.)If positron beam is also polarized, can use Blondel-type scheme to

fit for beam polarizations as well as physics asymmetry andeliminate sensitivity to backgrounds

• advantage wrt Compton polarimetry is that anydepolarization in beam-beam interaction is properlyaccounted for (need to be above W-pair threshold though)

• disadvantage wrt Compton polarimetry is Compton canachieve 1% accuracy in a few minutes

e-

e+

W-

W+

ν

M. Woods, SLAC

Blondel Blondel scheme with electron and positron beams scheme with electron and positron beams both polarizedboth polarized

%50%,90 == +− PP

%25.0%,25.0 == +

+

−

−

P

P

P

P δδ%55.96

1=

++= +−

+−

PP

PPPeff

%10.0=eff

eff

P

PδLReff

RLLR

RLLR APNN

NN =+−

Can also use ‘Blondel scheme’ to determine beam polar izations directly:

LRLLRLRR

LLRLRR

LRRRRLLL

RRRLLL

APNNNN

NNNN

APNNNN

NNNN

LR

LR

LR

LR

+

−

=+++−−+

=+++−−+

- using Blondel technique, just need Compton polarimeters for measuring polarization differences between L,R states;and only need to spend approx. 10% of running time in NRR, NLL states

- this technique directly measures lum-wted polarizations (any depolarizationeffect properly taken into account)

M. Woods, SLAC

Extraction Line Design at NLCExtraction Line Design at NLC

Location for Compton IP (also for wire scanner to measurebeam energy distribution)- secondary focus with 20mm dispersion

Detailed design for polarimeter in progress

M. Woods, SLAC

Compton Kinematics and Cross SectionsCompton Kinematics and Cross Sectionsat NLC/TESLAat NLC/TESLA

-can have a large separation between the kinematic endpoint energythe beam energy

- large Compton asymmetry at high energy

(500 GeV electrons, 1.165 eV photons)

Spectrum of Compton-scattered electrons

M. Woods, SLAC

Total

Depolarization Effects at NLCDepolarization Effects at NLC(see SLAC PUB 8716, K. Thompson Jan. 2001)

Lum-wted depolarization is approx.25% of average depolarization

Depolarization can be large for beam particles thatlose significant energy to beamstrahlung

Depolarization can be large for large vertical offset(may have large effect for first bunches in

train)

BMT: spin precession effects S-T: Sokolov-Ternov spin flip effects

BMT

S-T

Total

S-T

BMT

M. Woods, SLAC

DISDIS--PARITYPARITYSearch for New Physics through Par ity Violation

in Deep Inelastic Electron Scatter ing

LOI submitted for SLAC PAC meetingnext week

Aim for 0.3% systematic error on beam polarization

M. Woods, SLAC

SummarySummarySLD Compton Polar imeter

• 0.5% precision achieved• enabled precise parity violation measurements by SLD,

including the best measurement of the weak mixing angle and best indirect search limits for the SM Higgs boson

Polar imetry at a future LC• requires 0.25% precision or better• currently designing Compton polarimeter to achieve this• better precision is possible if positrons also polarized• physics asymmetry with forward W-pair events is promising

Polar imetry for SLAC DIS-Par ity LOI• 0.6% statistical error on physics asymmetry requires

0.3% precision for polarimetry• use SLD’s Compton polarimeter with some upgrades• can be a testbed for demonstrating precision required for LC