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PR-05-109: A Measurement of the Strange Nucleon Form Factors at High Q 2 Kent Paschke University of Massachusetts, Amherst Paul Souder Syracuse University

PR-05-109: A Measurement of the Strange Nucleon Form Factors at High Q 2

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PR-05-109: A Measurement of the Strange Nucleon Form Factors at High Q 2. Paul Souder Syracuse University. Kent Paschke University of Massachusetts, Amherst. “global” experimental uncertainty. Recent Results for the Strange Vector FF. - PowerPoint PPT Presentation

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Page 1: PR-05-109: A Measurement of the Strange Nucleon Form Factors at High Q 2

PR-05-109: A Measurement of the Strange Nucleon Form Factors at

High Q2

Kent PaschkeUniversity of Massachusetts,

Amherst

Paul SouderSyracuse University

Page 2: PR-05-109: A Measurement of the Strange Nucleon Form Factors at High Q 2

PR-05-109: HAPPEX High-Q2

Recent Results for the Strange Vector FF

• Deviation from APV(Gs=0) averages ~17% for Q2>0.4 GeV2

G0 Results are big news: amplifies interesting low Q2 structure, strong constraint at Q2~0.2 GeV2, and significant non-zero result at higher Q2

~ Q2

“global” experimental uncertainty

Page 3: PR-05-109: A Measurement of the Strange Nucleon Form Factors at High Q 2

PR-05-109: HAPPEX High-Q2

Focusing on High Q2

• In this range, background corrections are large, on order 40-60% of APV.

• Combining data points reduces point-to-point uncertainty, correlated error dominatesQ2 >0.35 GeV2: Gs

E + GsM = 0.046 + 0.022

Page 4: PR-05-109: A Measurement of the Strange Nucleon Form Factors at High Q 2

PR-05-109: HAPPEX High-Q2

Proposal(GE

s + 0.48 GMs) = 0.0082 (experimental) at Q2 = 0.6

GeV2

• Very different experimental technique, with very low backgrounds

• In the heart of the suggested positive contribution

• Precise error bar needed to impact global fitQ = 0.63 Gev2 alone: 5.5

Q= [0.4,1] GeV2: 4

Page 5: PR-05-109: A Measurement of the Strange Nucleon Form Factors at High Q 2

PR-05-109: HAPPEX High-Q2

K.A. Aniol and D.J. Margaziotis - California State University, Los Angeles

D.S. Armstrong, J.M. Finn, T. Holmstrom, B. Moffit, and V. Sulkosky - College of William and Mary

F. Bataru, Z.-E. Meziani, B. Sawatzky, P. Solvignon, and H. Yao - Temple

University

H. Benaoum, R. Holmes, and P.A. Souder - Syracuse University

R. Carlini, J.-P. Chen, R.J. Feuerbach, J. Grames, D.W. Higinbotham, C.W. de Jager, R. Michaels, B. Reitz, J. Roche, and A. Saha - TJNAF

G.D. Cates, N. Liyanage, V. Nulyubin, J. Singh, R. Snyder, and W.A. Tobias - University of Virginia

E. Cisbani, F. Cusanno, S. Fullani, F. Garibaldi, and G.M. Urciuoli - INFN Sezione

Sanita

P. Decowski - Smith College

L.J. Kaufman, K.S. Kumar, and K.D. Paschke - University of Massachusetts, Amherst

S. Kowalski - Massachusetts Institute of Technology

L. Lagamba, R. De Leo, and S. Marrone - INFN Bari

D. Lhuillier and C. Munoz-Camacho - CEA Saclay, DAPNIA/SPhN

P. Markowitz - Florida International University

P. Reimer and X. Zheng - Argonne National Laboratory

R. Wilson - Harvard University

HAPPEX High-Q2 Collaboration

Page 6: PR-05-109: A Measurement of the Strange Nucleon Form Factors at High Q 2

PR-05-109: HAPPEX High-Q2

HAPPEX

target

Q2

[GeV2

]

APV

Gs = 0 (ppm)

Stat. Error (ppm)

Syst. Error (ppm)

sensitivity

1H 0.48 -14.9 0.98(6%)

0.56(3%)

GsE + 0.39Gs

M = 0.014

± 0.020 (exp) ± 0.010 (FF)

1H 0.11 -1.4 0.08(5.7%

)

0.04(2.9%

)

(GsE + 0.08Gs

M ) = 0.010

4He 0.11 +7.8 0.18(2.2%

)

0.18(2.1%

)

(GsE ) = 0.015

Page 7: PR-05-109: A Measurement of the Strange Nucleon Form Factors at High Q 2

PR-05-109: HAPPEX High-Q2

Proposed Measurement: HAPPEX High-Q2

Configuration: • 20 cm cryogenic Hydrogen Target• 100 A• 80% polarization

Kinematics: E = 3.42 GeV, =13.7o, E’ = 3.1 GeV, Q2 = 0.6 GeV2

Rate: 1.1 MHz per arm (3700 ppm width per arm, 2600 ppm per pair)APV (assuming no strange vector FF):

APVNS = -22.1 ppm ± 0.62 ppm (form factor/radiative

correction)Anticipated results:

APV = 0.55 ppm (stat) ± 0.33 ppm (syst)

(GsE + 0.48 Gs

M) = 0.0070 (stat) ± 0.0042 (syst) ± 0.0079 (FF)

Page 8: PR-05-109: A Measurement of the Strange Nucleon Form Factors at High Q 2

PR-05-109: HAPPEX High-Q2

Improvements since HAPPEX-I• P2L (statistical power)

• HAPPEX-I ran with 100 A and 38% polarization, or 35 A and 71% polarization

• Now 100 A at 75% polarization is routine.

• Target thickness: 15cm -> 20cm

• Precision polarimetry

• HAPPEX-I: (Pbeam) = 3.2%

• Planned Compton upgrade: (Pbeam) = 1%

• Q2 determination

• HAPPEX-I: (Q2) = 1.2%

• Nuclear Recoil method: (Q2) = 0.5%

Page 9: PR-05-109: A Measurement of the Strange Nucleon Form Factors at High Q 2

PR-05-109: HAPPEX High-Q2

Target Spectrometer: QQDQ

Hall A

Cherenkovcones

PMT

Compton Moller Polarimeters

Page 10: PR-05-109: A Measurement of the Strange Nucleon Form Factors at High Q 2

PR-05-109: HAPPEX High-Q2

Cherenkovcones

PMT

PMT

High Resolution Spectrometers

Very clean separation ofelastic events by HRS optics

Overlap the elastic line above the focal plane and integrate the flux

Large dispersion and heavy shielding reduce backgrounds at the focal plane: typically fi < 1.5%Standard detector package used to track individual electrons to measure kinematics, study background, in dedicated low-current studies.

12 m dispersion sweeps away

inelastic events

Hydrogen elastic distribution, Q2=0.1 GeV2

Page 11: PR-05-109: A Measurement of the Strange Nucleon Form Factors at High Q 2

PR-05-109: HAPPEX High-Q2

False Asymmetries

It is requested the machine be optimized for longitudinal polarization to Hall A, to minimize the transverse spin asymmetry.

Araw

= Adet

- AQ +

E+

ix

i

HAPPEX-H (2004 results):

APV = -1.14 0.24 (stat) 0.06 (syst) ppm

Systematic error due to helicity correlated beam dynamics controlled below the level required for HAPPEX-High Q2 (60

ppb).

Page 12: PR-05-109: A Measurement of the Strange Nucleon Form Factors at High Q 2

PR-05-109: HAPPEX High-Q2

Background

Measured using:• Dedicated runs at very low current using track reconstruction of the HRS• Dedicated integrating runs

The probability of rescattering inside the

spectrometer as measured by a dipole field scan

Al Quasi-elastic

Spectrometer

Rescatter

HAPPEX-I (0.48 GeV2)

fraction 1.4% 0.2%

(APV)/APV 0.3% 0.1%

This proposal

(0.6 GeV2)

fraction 1.4% 0.4%

(APV)/APV 0.3% 0.1%

G0: typical dilution factor at high Q2 ~ 20%

Page 13: PR-05-109: A Measurement of the Strange Nucleon Form Factors at High Q 2

PR-05-109: HAPPEX High-Q2

Measuring Q2

Nuclear recoil, using water cell optics target: p between elastic and excited state peaks reduces systematic error from spectrometer calibration.

At Q2~0.1 GeV2 (6o) in 2004:

Achieved ~ 0.3%

%5.02 QGoal:

Q2 measured using standard HRS tracking package, with reduced beam current

• Central scattering angle must be measured to < 0.25%• Asymmetry distribution must be averaged over finite acceptance

Page 14: PR-05-109: A Measurement of the Strange Nucleon Form Factors at High Q 2

PR-05-109: HAPPEX High-Q2

Compton Polarimeter Upgrade

3kW Green Fabry-Perot Cavity Twice the Analyzing power of present IR

cavityTwice the luminosity

New Electron Detector High resolution silicon

microstrips

Integrating Photon Detector Electronics

Improve systematic uncertainties

Upgrade required for E05-007 (PV-DIS) and E03-011 (PREx)Goal of the upgrade: 1-2% at 850 MeV. 1% at 3.4 GeV is expected.

Page 15: PR-05-109: A Measurement of the Strange Nucleon Form Factors at High Q 2

PR-05-109: HAPPEX High-Q2

Compton Upgrade Status • Optics

– Green Laser, Optics, HF mirrors procured– Low power optics commissioning completed– Prototype FP Cavity built and tested

• Photon Detector– Prototype integrating data acquisition electronics

installed– Commissioning in progress during HAPPEX-2005

• Electron detector– Design completed

Project completion target: Spring 2007

Page 16: PR-05-109: A Measurement of the Strange Nucleon Form Factors at High Q 2

PR-05-109: HAPPEX High-Q2

APV / APV (GEs +

GMs)

Polarization 1.0% 0.0028

Q2 Measurement 0.8% 0.0022

Backgrounds 0.3% 0.0009

Linearity 0.6% 0.0017

Finite Acceptance 0.3% 0.0009

False Asymmetries

0.3% 0.0009

Total Systematic

1.5% 0.0042

Statistics 2.5% 0.0070

Total Experimental

2.9% 0.0082

Error Budget

Page 17: PR-05-109: A Measurement of the Strange Nucleon Form Factors at High Q 2

PR-05-109: HAPPEX High-Q2

Extraction of SVFF from APV

sAAA

TAA

TAp

MpE

pMWF

sMp

MpE

pM

VF

sEp

MpE

pE

VF

pM

pE

nM

pM

nE

pEn

VpVW

FPV

GGGGG

GQG

GGG

GR

QG

GGG

GR

QG

GG

GGGGRR

QGA

)0()8(0)3(122

22

22)0(

2

22)0(

2

222

2

sin41

24

124

124

11sin4124

Electromagnetic FF

Axial FF (GAZ)

Including radiative corrections, APV from hydrogen is:

Axial FF: (APV) = 0.33 ppm

EMFF: dominated by GnM, (APV) = 0.53

ppm

Total: (APV) = 0.62 ppm, 2.8%

Page 18: PR-05-109: A Measurement of the Strange Nucleon Form Factors at High Q 2

PR-05-109: HAPPEX High-Q2

Axial Form FactorAxial Form Factor: Uncertainty dominated by “anapole moment”

014.001.0

024.006.00

1

TA

TA

R

R

[Zhu et al , 2000]

Assume dipole FF, with MA = 1.001 GeV (GA

Z) ~ 0.12,

E04-115 G0 Backward Angle

(GAZ) ~ 0.14

Compatible with Phys. Rev. C 69, 065501 (2004)

[Maekawa et al , 2000]

(APV) = 0.33 ppm

Page 19: PR-05-109: A Measurement of the Strange Nucleon Form Factors at High Q 2

PR-05-109: HAPPEX High-Q2

EM Form Factorsuncertain

ty(APV)/

APV

Gp

M

2%negligibl

e

GpE 1.5%

0.24 ppm

GnE 8%

0.26 ppm

GnM 2%

0.44 ppm

Total 0.53 ppm

But: 2-photon effects can complicate this picture at 2-4% level

Experimental constraint:

E04-116 in Hall B (approved): precision comparison of elastic positron-proton and electron-proton scattering, with very good coverage at this Q2

Page 20: PR-05-109: A Measurement of the Strange Nucleon Form Factors at High Q 2

PR-05-109: HAPPEX High-Q2

APV / APV (GEs +

GMs)

Total Systematic

1.5% 0.0042

Statistics 2.5% 0.0070

Total Experimental

2.9% 0.0082

Axial FF 1.5% 0.0042

EM FF 2.4% 0.0067

Total FF 2.8% 0.0079

TOTAL: 4.0% 0.011

Estimated Precision

Page 21: PR-05-109: A Measurement of the Strange Nucleon Form Factors at High Q 2

PR-05-109: HAPPEX High-Q2

Beam Request• 30 Days

• includes 3 days commissioning/study

• Proposed at 100 A, 80% polarization, 20 cm LH2 target

• adjust runtime based on P2I

• Special scheduling requirements:

• optimized for longitudinal polarization

• control of source parameters for “parity-quality”

• sufficient ESR power or CHL supplement for cryotarget

•No major, non-standard equipment or specialized installation required.

• APPROVED, at “A-” rating! Conditionality now removed (Q2=0.63GeV2). Possible run 2008 (2007, depending on 6GeV Hall A experiments)

Page 22: PR-05-109: A Measurement of the Strange Nucleon Form Factors at High Q 2

PR-05-109: HAPPEX High-Q2

HAPPEX-III(GE

s + 0.48 GMs) = 0.0082 (experimental)

• Very different experimental technique, with very low backgrounds

• 4-sigma measurement in the middle of the suggested positive contribution

• No major new technology or special equipment

± 0.0079 (FF)