Robert J. Feuerbach Jefferson Lab Constructed from contributions from the HAPPEX Collaboration Hall A Collaboration Meeting December 5, 2005 HAPPEX-II.
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Robert J. FeuerbachJefferson Lab
Constructed from contributionsfrom the HAPPEX Collaboration
Hall A Collaboration Meeting December 5, 2005
HAPPEX-II Status Report
Strange-form factors
At Q2=0.11 GeV2, APV can accessHydrogen: (Gs
E + 0.08GsM )
Helium: GsE
How is the PV Asymmetry Measured?
Beam Helicity - 30 Hz
1 ppm: 5% measurement —> 4x1014 counts
PV asymmetry between window pair is measured.34M (He) and 24M (H) good pairs collected.
Beam Asymmetries
Araw
= Adet
- AQ +
E+
ix
i
•natural beam jitter (regression) •beam modulation (dithering)Slopes from
Target Spectrometer: QQDQ
Hall A
Cherenkovcones
PMT
Compton Moller Polarimeters
The Goal
2004: Helium APV: ~ 0.84 ppm (11.2%) Hydrogen APV: ~ 0.24 ppm
(17%)
The goal was to improve on the error bars of last year by a factor of ~3.
This required•higher luminosity•similar to the previous year’s tight control over systematics uncertainties.
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
Run SummaryHelium
Eb=2.75 GeV
Scheduled: 48 days
Actual: 55 days
July 9 – Aug 7Aug 7 – Aug 31July 28 – Sept 1Sept 9 – Sept 27
Late start due to • installation• sweeper/septum and spectrometer commissioning• beamline commissioning
Hydrogen
Eb=3.18 GeV
Scheduled: 39 daysActual: 36 days
Oct 15 – Nov 23
Oct 16 – Nov 21
Last day for PREx tests
~18 day “parasitic” extension (to Hall C) was very important
Auxiliary Studies•Al (target wall) Backgrounds: ~1.8% (He), ~0.7% (H)
•Inelastics (quasi-elastic)
•Rescattering probability with dipole scan
•He: Prelim estimate: <2% He QE, ~1.8% Al, <0.6% rescatter
•H: Prelim estimate: ~0.7% Al, <0.2% rescatter
•Q2 measurement (scans, Counting DAQ, optics, angle)
•Polarimetry: Compton and Moller in good agreement
Optics with Sweeper
Sweeper induces ~simple shifts of phi and Z.Angle found with nuclear-recoil method.
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.
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 -
> suggests 0.8 ppm difference– AL – AR is large (0.9 ppm), with correct sign!
• Compton power dropped 1200W ->300W– cleaning optics brought it to 500W– excellent beam quality resulted in ~20 S/B
Physics Asymmetry
Hydrogen
HeliumAPV: ~ 0.21 ppm (3.5%)GE
s: ~ 0.014
2004:
APV: ~ 0.84 ppm (11.2%)GE
s: ~ 0.042
APV: ~ 0.12 ppm (8%)GE
s+0.084GMs: ~ 0.012
2004:
APV: ~ 0.24 ppm (17%)
GEs+0.080GM
s: ~ 0.025
NOTE: Statistical error only!
Systematic error will likely increase Helium error bar by ~40%, and Hydrogen by about 25%
Online Raw Asymmetry (blinded)Helium
Hydrogen
<A> (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
<A> (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
Impact of the Measurement
2 = 1
95% c.l.
He: nucl-ex/0506010 (reviewed and recommended for PRL) H: nucl-ex/0506011 (under revision for submission to PL)
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 @ 80% vs. 35uA @ 71%
• Manpower needed for the Compton upgrade.– data in ~2008, graduate 2009?
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