E-158 : A precise measurement of at low

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E-158 A precise measurement of
at low
Antonin VACHERET CEA SACLAY PAVI 2004,
June 10
The 2 miles long LINAC at SLAC
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• Physics Motivation
• Apparatus
• Control of systematics
• Analysis
• Run III preliminary results
• Conclusion

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Extracting the weak charge at low
Møller scattering - Sensitive to e, Qw
Parity violation asymmetry
Tree level Moller asymmetry
Qw
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Radiative corrections

• 1 loop corrections change the relation between
• Aee and

3 corrections to
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Sensitivity

Aim to measure to 0.001 level
6.5s significance level to radiative
corrections effect. 1. Precise measurement away
from Z pole complementary to e-e
colliders 2. Sensitive to new physics scenarii

Z (GUT) boson MZ 0.8 TeV
Electron compositness L 10 TeV
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SLAC E158

• SLAC
• Smith College
• Syracuse
• UMass
• Virginia

• UC Berkeley
• Caltech
• Jefferson Lab
• Princeton
• Saclay

SLAC
A-line

• Sep 97 EPAC approval
• 1998-99 Design and Beam Tests
• 2000 Funding and construction
• 2001 Engineering run
• 2002 Physics Runs I, II
• 2003 Physics Run III

ESA
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Experiment principle
Raw Asymmetry 1.3x10-7 (130 ppb) D(Apv) 10-8
(10 ppb) Need
1016 electrons
DETECTOR
BEAM
N,N-
TARGET
4-7 mrad
LH2
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Polarized beam

• Optical pumping
• Helicity sequence
• Quadruplet RLLR,LLRR,

Very high-charge polarized electron beams are
possible (Pe85)

• Beam helicity is chosen
• pseudo-randomly at 120 Hz
• Data analyzed as pulse-pairs

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Liquid Hydrogen target
Length 1.54 m Refrigeration capacity 1 kW Beam
heat deposit 800W Operating temperature 20K Flow
rate 5 m/s
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Spectrometer
e-e
60 m

• Dipole Magnetic chicane cut particles
• lt 10 GeV
• Quadrupoles focus Møller electrons
• Synchrotron light blocked with Collimators.

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Electron Detector

• Full Azimuthal acceptance
• Radiation hard
• Fast pure Cerenkov signal
• Insensitive to low energy
• backgrounds

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Statistics and systematics

• Integrating counting rate
• 1. Additional random fluctuations
• affect statistical precison
• 2. Constant shift
• false asymmetry
• Origin
• beam parameters variations (E,X,Y, qx,qy)
• Physics backgrounds
• Electronic crosstalk

Pulse pair width 200 ppm Raw asymmetry 150 ppb
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Precise beam diagnostics

• High resolution BPM cavity monitors (energy
  position, angle)
• Toroids (beam current)

?BPM 2 microns
?toroid 30 ppm
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Luminosity Monitor
more than 108 scattered electrons per spill at
?lab 1 mrad

• Density fluctuations monitor

• Null asymmetry test

• Enhanced sensitivity to beam fluctuations

Parallel plates
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Minimizing beam asymmetries
Natural pulse to pulse jitter
AI0.5
AE0.1

Feedback loop (Cumulative)
(run I data)
Cumulative asymmetries with feedback on
AIlt 200 ppb /- 5 ppb
AElt 20 ppb /- 3 ppb
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Backgrounds controls
Flux integration includes various residual
backgrounds
False asymmetry
eP ring
eP asymmetry
Dilution effect
Flux Radial and azimuthal scans
Pion flux and asymmetry
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Scattered flux profile

• Very good agreement between Flux scans and MC
  (run I)
• Q2 determination ltQ2gt 0.0266 GeV-2

Radial and azimuth agreement
Flux vs radial distance agreement
e-e
e-p
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Correcting beam fluctuations

• Beam jitter enlarge distribution of asymmetry
  pairs.
• Two complementary method to correct for the beam
  noise
• DITHERING
• REGRESSION
• Two main steps
• determine the dependance a of the detector
  integrated flux to beam parameters variations
• Correct the detector asymmetry

Klystron
dX
Y
dY
E
X
An
a
Areg
Ax
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Corrections method
Run I DAPV(regression-dithering) (3.1 11.8)
ppb Run II DAPV(regression-dithering) (4.8
4.2) ppb
Very good agreement !
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Analysis
Raw asymmetry distribution by runs
Raw asymmetry distribution by pairs Gaussian over
5 orders of magnitude

• Blinded asymmetry

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Slow reversal
Split data in four exclusive states
1. Insertable Half Wave Plate
2. Energy change 45 -gt 48 GeV
g-2 precession in A-Line
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Systematics summary
Source Run I II
DA (ppb) Dilution
Beam 1st order 0 /- 2 -
Beam 2nd order 0 /- 9 -
Transverse polarization -12 /- 2 -
eP Background -30 /- 5 0.071 /- 0.008
High energy g 3 /- 3 0.004 /- 0.002
Synchrotron g 0 /- 2 0.0015 /- 0.0005
Neutrons -2.5 /- 1.5 0.0015 /- 0.0005
Pions 0.5 /- 0.8 0.0014 /- 0.0011
Normalization factors
Polarimetry 0.847 /- 0.046
Geometry 0.989 /- 0.011
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Run III Preliminary
Q2 0.027 GeV2)
Official Run I result PRL hep/ex0312035
First observation of parity violation in
Møller scattering 5 s
Run I APV -175 ? 30 (stat) ? 20 (syst) ppb
Run II APV -144 ? 28 (stat) ? 23 (syst) ppb
APV -161 ? 21 (stat) ? 17 (syst) ppb Run I II
(preliminary)
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The Weak Mixing Angle
sin2?eff(Q20.026 GeV2) 0.2379 0.0016
0.0013 (Run I II, preliminary) Agreement with
theory at the level of uncertainty prediction
0.2386 0.0006
(stat)
(syst)
sin2?(MZ2)
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Physics implication

• Parity is violated in Møller scattering
• Limit on ?LL
• LLL gt 7,4 TeV
• L-LL gt 6,4 TeV
• Limits on extra Zs at the level of 700 GeV

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Toward the final result

• Run III data analysis is being finalized
• Preliminary result on full data set very soon
• Systematics will improve
• Significant complementary constraint on new
  physics

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Conclusion

• Preliminary result on APV -161 21 17 ppb
• sin2?Weff 0.2379 0.0016 0.0013
  (preliminary)
• Inelastic e-p asymmetry at low Q2 consistent with
  quark picture
• First measurement of e-e transverse asymmetry
• Preliminary result for all three runs soon !
• - 10 ppb statistical error
• - Systematic error will be less than statistical
  error

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Physics Runs
Run 1 Apr 23 1200 May 28 0000, 2002 Run 2
Oct 10 0800 Nov 13 1600, 2002 Run 3 July 10
0800 - Sep 10 0800, 2003

• One g-2 flip in each run
• ?/2 flip roughly once in two days
• Run I data divided into 24 slugs

Run 1 Spring 2002 Run 2 Fall 2002 Run 3
Summer 2003
1020 Electrons on Target
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Higher orders

• Beam spotsize higher moment in residual
  polarisation effect at the photocathode.
• Beam sub pulse fluctuations
• - Evidences in Run II analysis
• - monitored during Run III in order to
  estimate the systematics.
• - affect the OUT only

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No sign of charge limit!
Very high-charge polarized electron beams are
possible.
Small anisotropy in strain results in 3
analyzing power for residual linear polarization.
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Acceptance segmentation

• Dividing the acceptance
• 1. Monitoring the counting statistics versus f
  and q
• 2. Checking systematics building
  monopoles,dipoles amplify false asymmetries.

X DIPOLE
Y DIPOLE
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End Station A setup
Target chamber
Quadrupoles
Detector Cart
Concrete Shielding
Dipoles
Drift pipe
60 m
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Results of corrections
cxp
pxp
cxc
pxc
Asym width goes form 500 ppm to 200 ppm
Run I DAPV(regression-dithering) (3.1 11.8)
ppb Run II DAPV(regression-dithering) (4.8
4.2) ppb
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from APV to sin2qWeff
where
is an analyzing power factor depends on
kinematics and experimental geometry.
Uncertainty is 1.7. (y Q2/s)

• Fbrem (0.90 0.01) is a correction for ISR and
  FSR
• (but thick target ISR and FSR effects are
  included in the analyzing power
• calculation from a detailed MonteCarlo study)
• qWeff is derived from an effective coupling
  constant, geeeff , for the Zee coupling,
• with loop and vertex electroweak corrections
  absorbed into geeeff

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ep Detector Data

• Radiative tail of elastic ep scattering is
  dominant background
• 8 under Moller peak
• Additional 1 from inelastic e-p scattering
• Coupling is large similar to 3 incoherent quarks
• Reduced in Run II with additional collimation

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Backgrounds
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Polarized Source Laser System
CID Gun Vault
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rf Cavity BPMs for E-158
476 MHz
RF Cavity BPM
Mixer
Rf cavities resonate at 2856 MHz X cavity is
TM210 Y cavity is TM120 Q cavity is
TM010
ANALYSIS OF AN ASYMMETRIC RESONANT CAVITY AS A
BEAM MONITOR (David H. Whittum (SLAC), Yury
Kolomensky (Caltech). SLAC-PUB-7846
published in Rev.Sci.Instrum.702300-2313,1999.)
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Beam Performance
Quantity Run 1 Achieved
AQ Alcove 219 319 ppb
?(AQ) -8.4 7.8 ppb

AE -0.1 1.4 keV -1.2 14.8 ppb
?(AE) -0.01 0.24 keV 0.05 2.6 ppb

(?x, ?y)target (-16.6 5.6 nm, -3.1 4.0 nm)
?(?x, ?y)target (1.0 0.6 nm, -0.01 0.9 nm)

(?x, ?y)angle (15.9 9.4 nm, 4.8 2.7 nm)
?(?x, ?y)angle (-2.7 2.0 nm, 0.9 1.0 nm)

(?x, ?y)spotsize (0.7 1.9 nm, -1.7 1.9 nm)
Delivered (May 2002)
Quantity
Electrons / pulse 6 x 1011 _at_ 45 GeV, 3.5 x 1011 _at_ 48 GeV
Rep. rate 120 Hz
Intensity jitter 0.5
Position jitter 50 µm
Spot size jitter 5 of spot size
Energy jitter 0.03 rms
Energy spread 0.1 rms
Polarization (85 5)
Efficiency (65-70)
All proposal goals achieved or exceeded
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Luminosity Monitor Data

• Null test at level of 20 ppb

• Target density fluctuations small
• Limits on second order effects

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Collimators
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Pion Detector

• 0.5 pion flux
• 1 ppm asymmetry
• lt 5 ppb correction

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Future Possibilities
Part per billion measurements are now
feasible future measurements could improve
sensitivity
Challenging experiments
E158 (projected)
Interest will depend on discoveries (or lack
thereof) over the next few years, including LHC