PR-05-109: A Measurement of the Strange Nucleon Form Factors at High Q 2 Kent Paschke University of...
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Transcript of PR-05-109: A Measurement of the Strange Nucleon Form Factors at High Q 2 Kent Paschke University of...
PR-05-109: A Measurement of the Strange Nucleon Form Factors at
High Q2
Kent PaschkeUniversity of Massachusetts,
Amherst
Paul SouderSyracuse University
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
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
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
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
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
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)
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%
PR-05-109: HAPPEX High-Q2
Target Spectrometer: QQDQ
Hall A
Cherenkovcones
PMT
Compton Moller Polarimeters
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
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).
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%
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
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.
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
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
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%
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
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
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
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)
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)