sld compton polarimeter-no atomic or nuclear physics corrections (ex. levchuk effect in moller...
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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