HAPPEX-II Status Report

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HAPPEX-II Status Report
Robert J. Feuerbach Jefferson Lab Constructed
from contributions from the HAPPEX Collaboration
Hall A Collaboration Meeting December 5, 2005
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Strange-form factors
At Q20.11 GeV2, APV can access Hydrogen
(GsE 0.08GsM ) Helium GsE
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How is the PV Asymmetry Measured?
1 ppm 5 measurement gt 4x1014 counts
Beam Helicity - 30 Hz
PV asymmetry between window pair is measured. 34M
(He) and 24M (H) good pairs collected.
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Beam Asymmetries
Araw Adet - AQ ??E ??i?xi

• natural beam jitter (regression)
• beam modulation (dithering)

Slopes from
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Hall A
Spectrometer QQDQ
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The Goal
The goal was to improve on the error bars of last
year by a factor of 3.
2004 Helium APV s 0.84 ppm
(11.2)
Hydrogen APV s 0.24 ppm (17)

• This required
• higher luminosity
• similar to the previous years tight control over
  systematics uncertainties.

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Some Improvements for this year

• Sweeper Magnet
• IbHe 28uA to 36uA
• IbH 35uA to 58uA
• S0 trigger
• Beam quality
• In development
• Integrating Compton
• Cavity monitors

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Run Summary
Helium Eb2.75 GeV
Scheduled 48 days
July 9 Aug 7 Aug 7 Aug 31
July 28 Sept 1 Sept 9 Sept 27
Actual 55 days

• Late start due to
• installation
• sweeper/septum and spectrometer commissioning
• beamline commissioning

18 day parasitic extension (to Hall C) was
very important
Scheduled 39 days
Hydrogen Eb3.18 GeV
Oct 15 Nov 23
Actual 36 days
Oct 16 Nov 21
Last day for PREx tests
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Auxiliary Studies

• Al (target wall) Backgrounds 1.8 (He), 0.7
  (H)
• Inelastics (quasi-elastic)
• Rescattering probability with dipole scan
• He Prelim estimate lt2 He QE, 1.8 Al, lt0.6
  rescatter
• H Prelim estimate 0.7 Al, lt0.2 rescatter
• Q2 measurement (scans, Counting DAQ, optics,
  angle)
• Polarimetry Compton and Moller in good agreement

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Optics with Sweeper
Sweeper induces simple shifts of phi and
Z. Angle found with nuclear-recoil method.
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Polarimetry Results
Helium

• Discrepancy of 0.6 in the transfer function
  (LvsR) compared to last year and last absolute
  measurement in 2001.
• Will be opening up the Compton to re-measure the
  transfer function to understand the effect.

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New Challenges

• Electronics pickup between an (unconnected)
  helicity module and magnet controls
• 100nm beam-position difference
• Transverse asymmetry
• 3 vertical polarization, He AT 13 ppm -gt
  suggests 0.8 ppm difference
• AL AR is large (0.9 ppm), with correct sign!
• Compton power dropped 1200W -gt300W
• cleaning optics brought it to 500W
• excellent beam quality resulted in 20 S/B

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Physics Asymmetry
Helium
2004
APV s 0.21 ppm (3.5)
APV s 0.84 ppm (11.2)
GEs s 0.014
GEs s 0.042
Hydrogen
2004
APV s 0.24 ppm (17)
APV s 0.12 ppm (8)
GEs0.080GMs s 0.025
GEs0.084GMs s 0.012
NOTE Statistical error only!
Systematic error will likely increase Helium
error bar by 40, and Hydrogen by about 25
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Online Raw Asymmetry (blinded)
Helium
ltAgt (ppm) RMS (ppm) Regress Correction
Left 4.38 0.26 1495 0.43 ppm
Right 3.45 0.25 1466 -0.18 ppm
Avg 3.91 0.18 1047 0.12 ppm
Hydrogen
ltAgt (ppm) RMS (ppm) Regress Correction
Left -1.32 0.15 757 0 ppb
Right -1.46 0.16 762 5 ppb
Avg -1.39 0.11 537 3 ppb
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Impact of the Measurement

He nucl-ex/0506010 (reviewed and recommended
for PRL) H nucl-ex/0506011 (under revision for
submission to PL)
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Future

• Analysis is beginning (continuing).
• Knowledge transfer to next generation of students
• Next collaboration meeting in late February 2006.
• P-REX and HAPPEX-3 will benefit greatly from high
  current/high beam polarization now available
• 100uA _at_ 80 vs. 35uA _at_ 71
• Manpower needed for the Compton upgrade.
• data in 2008, graduate 2009?