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?