strangeness in the nucleon kent paschke university of massachusetts einn ‘05 september 24, 2005
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Strangeness in the Nucleon
Kent PaschkeUniversity of Massachusetts
EINN ‘05September 24, 2005
Kent Paschke – University of Massachusetts
EINN ’05 Milos September 25, 2005
Strange Quarks in the NucleonStrange Seameasured inN scattering
Spin polarized DISInclusive: s = -0.10 ± 0.06
uncertainties from SU(3), extrapolationSemi-inclusive: s = 0.03 ± 0.03
fragmentation function
NssN 5
NssN
NssN Strange vector FF
Strange massN scattering: ~30%
Strange sea is well-known, but contributions to nucleon
matrix elements are somewhat unsettled
Kent Paschke – University of Massachusetts
EINN ’05 Milos September 25, 2005
pZG ,
Flavor Separation of Nucleon Form Factors
psME
pdME
puME
pME GGGG ,
/,/
,/
,/ 3
1
3
1
3
2
sMEW
dMEW
uMEW
ZME GGGG /
2/
2/
2/ sin
3
41sin
3
41sin
3
81
Measuringnp GG ,, , cannot separate all three flavors
(assumes heavy quarks are negligible)
Adding in a measurement of
and assuming charge symmetrynsps
nupd
ndpu
GG
GG
GG
,,
,,
,,
pZ
MEnME
pMEW
sME
pZME
nME
pMEW
dME
pZME
pMEW
uME
GGGG
GGGG
GGG
,,
,,
,,
2,
,,
,,
,,
2,
,,
,,
2,
sin41
sin42
sin43
then we can write
Kent Paschke – University of Massachusetts
EINN ’05 Milos September 25, 2005
Accessing Weak Neutral Current Amplitude
ApZME
pME
FZ
LR
LRPV GGG
QG
M
MMA ,,F
2,/
,/
2
2
Interference with EM amplitude makes NC amplitude accessible
22
~~Z
EM
NC
PVM
Q
M
MA
Longitudinal spin asymmetry violates parity (polarized e-, unpolarized p):
Kent Paschke – University of Massachusetts
EINN ’05 Milos September 25, 2005
Parity-violating electron scattering
p
AMEF AAAQGA
24
2
~ few parts per million
For a proton:
eAA
eA
sME
nME
nV
pME
pVW
ZME
RFsGG
GGRGRG
,,,2
, )1()1)(sin41(
For 4He: GEs alone
(but only available at low Q2)
Forward angle Backward angle
eA
pMWA
ZM
pMM
ZE
pEE GGAGGAGGA '2sin41 , ,
)(2
sin2
22
nE
pE
sE
WF
PV GG
GQGA
For deuterium: enhanced GA
e sensitivity
Kent Paschke – University of Massachusetts
EINN ’05 Milos September 25, 2005
Instrumentation for PVES
Large -Acceptance Detectors (G0, A4) Large kinematic range Large Detected Background
Spectrometer (HAPPEx) Good background rejection Small solid angle
Cumulative Beam Asymmetry• Helicity-correlated asymmetryx~10 nm, I/I~1 ppm, E/E~100 ppb
Helicity flips• Fast: Pockels cell• Slow: half-wave plate flips
!!!1010 1413 N
%52
11
NAAA610
PVA
Need• Highest possible luminosity• High rate capability• High beam polarization
Detectors Integrating (HAPPEx) vs. Counting (G0, A4)
Kent Paschke – University of Massachusetts
EINN ’05 Milos September 25, 2005
Beam helicity is chosen pseudo-randomly at 30 Hz
• Helicity state, followed by its complement• Data analyzed as “pulse-pairs”
Polarized Electron Source
Optical Pumping HV Extraction and Injection
LR
LRPVA
calculated at 15Hz
Kent Paschke – University of Massachusetts
EINN ’05 Milos September 25, 2005
Controlling Systematic Uncertainty
HAPPEX: Polarization monitored continuously with a Compton polarimeter.
(Average ~88% with superlattice photocathode.)
False Asymmetries• Beam Asymmetries – Source laser control, careful measurement and correction• Electronics pickup• Background Asymmetries
Normalization • Polarimetry – continuous measurement/monitoring. Control of systematic error• Linearity/Deadtime• Background Dilution
Polarimetry is dominant systematic error in two
recent experiments
Kent Paschke – University of Massachusetts
EINN ’05 Milos September 25, 2005
Experimental Overview
Electron Beam
LH2 Target
SuperconductingCoils
Particle Detectors
GMs, (GA) at Q2 = 0.1 GeV2
SAMPLE
HAPPEX GEs + 0.39 GM
s at Q2 = 0.48 GeV2
GEs + 0.08 GM
s at Q2 = 0.1 GeV2
GEs at Q2 = 0.1 GeV2 (4He)
Precision spectrometer, integrating
A4
open geometry, integrating
GEs + 0.23 GM
s at Q2 = 0.23 GeV2
GEs + 0.10 GM
s at Q2 = 0.1 GeV2
Open geometry
Fast counting calorimeter for background rejection
G0
GEs + GM
s over Q2 = [0.12,1.0] GeV2
GMs, GA
e at Q2 = 0.3, 0.5, 0.8 GeV2
Open geometry
Fast counting with magnetic spectrometer + TOF for background rejection
Kent Paschke – University of Massachusetts
EINN ’05 Milos September 25, 2005
Measure GMs at Q2 ~0.1 GeV2
Backward angle, H and 2H at low Q2
Air Cerenkov detector covers 2 sr from 130°-170°
Analog integrating electronics for asymmetry measurement
Pulse-Counting for background studies
SAMPLE at MIT-Bates
Theory prediction for anapole moment radiative correction.
Result of Zhu et al for GA commonly used to constrain GS
M result.
GsM(Q2=0.1) = 0.37 0.20 0.26
0.07
Kent Paschke – University of Massachusetts
EINN ’05 Milos September 25, 2005
HAPPEx-I in Hall A• GE
s + 0.39 GMs at Q2 =0.48 GeV2
• High Resolution Spectrometers eliminate background
• Analog integration of Cerenkov calorimeter for asymmetry measurement
• Tracking for background/kinematics studies
Kent Paschke – University of Massachusetts
EINN ’05 Milos September 25, 2005
HAPPEX-II: 1H and 4He
3 GeV beam in Hall A lab ~ 6 Q2 ~ 0.1 GeV2
Septum magnets (not shown) High Resolution Spectrometers
detectors
target
APV
Gs = 0 (ppm)
Stat. Error (ppm)
Syst. Error (ppm)
sensitivity(proposed)
1H -1.6 0.08 0.04 (GEs+0.08GM
s) = 0.010
4He +7.8 0.18 0.18 (GEs) = 0.015
Cherenkovcones
PMT
PMT
Elastic Rate:
1H: 120 MHz
4He: 12 MHz
Background ≤ 3%
Brass-Quartz integrating detector
Hall A at Jlab
Kent Paschke – University of Massachusetts
EINN ’05 Milos September 25, 2005
2004 HAPPEX-II Data
Araw = + 5.63 ppm ± .71 ppm (stat)
•Short run (~ 5 days)•Beam Polarization ~
86%•Beam asymmetries
small
•Background f <3% •Dense gas target
Araw correction < 0.2 ppm
Perfect sign-flip with /2 plate
Raw Asymmetry (after beam corrections)
pp
m
Helicity Window Pair Asymmetry
Araw = -0.95 ppm ± 0.20 ppm (stat)
Hydrogen 4He
•~1/2 proposed time•Beam asymmetries small
Araw correction ~ 0.06 ppm
•Background f ~1%•Beam Polarization ~ 80%
Kent Paschke – University of Massachusetts
EINN ’05 Milos September 25, 2005
PVA4 at MainzCalorimeter:1022 PbF2 crystals
20 cm LH2 target
20 A, 80% polarized beam
LuMo
MAMI Microtron, 2000-present
GEs + GM
s at Q2 = 0.23, 0.1 GeV2
Calorimeter distinguishes elastic via energy resolution, 0.8 sr from 30° to 40°
Elastic rate: 10 MHz, total rate 100 MHz
Kent Paschke – University of Massachusetts
EINN ’05 Milos September 25, 2005
G0 Experiment in Hall C•Measure forward and backward
asymmetries– recoil protons for forward
measurement: GEs, GM
s
– electrons for backward measurements: GM
s, GAe
•Fast Counting/Magnetic
spectrometer
Forward measurements complete(2004)
Back-angle measurements scheduled - 2006
Electron Beam
LH2 Target
SuperconductingCoils
Particle Detectors
Ebeam = 3.03 GeV, 0.33 - 0.93 GeVIbeam = 40 A, 80 APbeam = 75%, 80% = 52 – 760, 104 - 1160
= 0.9 sr, 0.5 srltarget = 20 cmL = 2.1, 4.2 x 1038 cm-2 s-1
A ~ -1 to -50 ppm, -12 to -70 ppm
Kent Paschke – University of Massachusetts
EINN ’05 Milos September 25, 2005
G0 Forward-angle Measurement
lead collimators
elastic protons
detectors
targetbeam
• TOF used to ID elastic recoil protons
• Measurement of yield and asymmetry of spectrum used to deduce background fraction and asymmetry
•Acceptance Q2=[0.12, 1.0] GeV2 for 3 GeV incident beam
•Time-of-flight measured over 32 ns beam bunch spacing
•Detector 15 acceptance: Q2=[0.44,0.88] GeV2 subdivided by TOF
Hear more tomorrow from Benoit Guillon
Kent Paschke – University of Massachusetts
EINN ’05 Milos September 25, 2005
G0 Backward Angle
Electron detectionTurn magnet/detector package
aroundAdd Cryostat Exit Detectors
(“CEDs”) to define electron trajectory
Add aerogel Cerenkovs to reject pions Begin Backward Angle installation in 2005
Planned measurements of H, 2H Q.E.
Combine with forward angle to separate Gs
E, GsM, GA at 2 or 3 Q2
pointsLikely to run in 2006 at Q2~0.3 GeV2, Q2~0.8 GeV2
Kent Paschke – University of Massachusetts
EINN ’05 Milos September 25, 2005
Results
Kent Paschke – University of Massachusetts
EINN ’05 Milos September 25, 2005
Extrapolated from G0 Q2=[0.12,0.16]
GeV2
95% c.l.
2 = 1
World Data at Q2 ~ 0.1 GeV2
GEs = -0.12 ± 0.29
GMs = 0.62 ± 0.32
Would imply that 7% of nucleon magnetic moment is Strange
Note: excellent agreement of world data set
Caution: the combined fit is approximate. Correlated errors and assumptions not taken into account
Kent Paschke – University of Massachusetts
EINN ’05 Milos September 25, 2005
Perspective at Q2 ~ 0.1 GeV2 1. Skyrme Model - N.W. Park and
H. Weigel, Nucl. Phys. A 451, 453 (1992).
2. Dispersion Relation - H.W. Hammer, U.G. Meissner, D. Drechsel, Phys. Lett. B 367, 323 (1996).
3. Dispersion Relation - H.-W. Hammer and Ramsey-Musolf, Phys. Rev. C 60, 045204 (1999).
4. Chiral Quark Soliton Model - A. Sliva et al., Phys. Rev. D 65, 014015 (2001).
5. Perturbative Chiral Quark Model - V. Lyubovitskij et al., Phys. Rev. C 66, 055204 (2002).
6. Lattice - R. Lewis et al., Phys. Rev. D 67, 013003 (2003).
7. Lattice + charge symmetry -Leinweber et al, Phys. Rev. Lett. 94, 212001 (2005).
-K oscillation of proton would produce a positive GE
s
Kent Paschke – University of Massachusetts
EINN ’05 Milos September 25, 2005
Anticipated Results from HAPPEX-II
2-3X improvement for each HAPPEX measurement
Q2 ~ 0.1 GeV2Experiment Running
NOW
Results available (early?) 2006
Result matching current central value:
• would convincingly establish a non-zero result
• would find GMs ~3
from zero
Kent Paschke – University of Massachusetts
EINN ’05 Milos September 25, 2005
G0 Forward - Measured Asymmetries
• “no vector strange” asymmetry, ANVS, is A(GEs, GM
s = 0)• inside error bars: stat, outside: stat & pt-pt
Global error accounts for large background corrections • f ~5-20%• A/ANVS ~40-60%
Kent Paschke – University of Massachusetts
EINN ’05 Milos September 25, 2005
World Forward-angle Hydrogen Data
~ Q2)
G0 Results are big news: • Amplifies interesting low Q2 structure• Strong constraint at Q2~0.2 GeV2
• Significant non-zero result at higher Q2
G0
Kent Paschke – University of Massachusetts
EINN ’05 Milos September 25, 2005
Possible interpretation of G0 results
• Fit world data set with dipole form for GM
s and GEn-
like behavior for GEs
• If not a statistical fluctuation, data implies large value of s and strong Q2-variation of GE
s
• Will be addressed by future measurements
Kent Paschke – University of Massachusetts
EINN ’05 Milos September 25, 2005
Future HAPPEx runPAC28 last month conditionally approved a new HAPPEx proposal to run at ~0.6 GeV2 to obtain an unprecedented precision (2007?)
• Requires 1% polarimetry
Kent Paschke – University of Massachusetts
EINN ’05 Milos September 25, 2005
Prospective JLab Data @ Q2 = 0.6, 0.23 GeV2
• G0 Run in March ’06 at Q2 = ~0.6 GeV2
• G0 Run in Summer of ‘06 at Q2 = ~0.23 GeV2
• HAPPEX-III Run at Q2 = ~0.6 GeV2 (not before 2007)• Also, A4 at 0.23 GeV2 or 0.5 GeV2?
G0 Backward
HAPPEX-III
GMs
GEs
0.6 GeV2
Kent Paschke – University of Massachusetts
EINN ’05 Milos September 25, 2005
Summary
GEs
0.6 GeV2
G0 backward
HAPPEX-III
GMs
• Suggested large values at Q2~0.1 GeV2
• HAPPEX-II, H and He running now!
• Possible large values at Q2>0.4 GeV2
• G0 backangle, approved for Spring ’06• HAPPEX-III, conditionally approved - 2007?• A4 backangle?
• Large possible cancellation at Q2~0.2 GeV2
• G0 backangle, conditionally approved for Summer ’06• A4 backangle?
Kent Paschke – University of Massachusetts
EINN ’05 Milos September 25, 2005
Transverse Asymmetry
Kent Paschke – University of Massachusetts
EINN ’05 Milos September 25, 2005
Interest in AT
AT is T-odd, P-even• As a radiative correction, it is similar to other T-odd QED
FSI that obscure measurements of nuclear -decay, neutron -decay, or other searches for T-odd, P-even interactions.
Probe of nucleon structure• Doubly virtual Compton scattering (VVCS) constrains
interpretation from DVCS
Dominated by spectrum of hadronic intermediate states
• Provides a clear and accessible window on the treatment of hadronic intermediate states in box diagrams.
GE/GM is influenced by the real part of 2- amplitude.AT is generated from the imaginary part of the 2-
amplitude.
“elastic” “inelastic”
Kent Paschke – University of Massachusetts
EINN ’05 Milos September 25, 2005
AT Data from 0.2 GeV-3 GeV
SAMPLE
“elastic”
“single pion”
sum
hep-ph/0405303
Pasquini &Vanderhaeghen
Resonance region treated in a model incorporating pion electroproduction amplitudes
A4
P&VdH
HAPPEX (prelim)
Afanasev and Merenkov,hep-ph/0406127
• Optical theorem: relate to tot((*)p)• Low Q2 and very forward angle• At fixed Q2, flat with energy
Kent Paschke – University of Massachusetts
EINN ’05 Milos September 25, 2005
AT at E158 (Azimuthal angle)
46 GeVep ep Sign: AT<0
Magnitude: ~2.5 ppm
Without enhancement by inelastic states, ATep ~
10-10
Q2 ~ 0.06 GeV2
46 GeVee ee
backward angle
Sign: opposite AT
ep?
Magnitude: ~3.5 ppm
Kent Paschke – University of Massachusetts
EINN ’05 Milos September 25, 2005
AT from Nuclei
Afanasev
Without inelastic states, 10-9
Predicted value, ~10-5 at 6 degrees, 3 GeV
Kent Paschke – University of Massachusetts
EINN ’05 Milos September 25, 2005
Backup
Kent Paschke – University of Massachusetts
EINN ’05 Milos September 25, 2005
World Data at Q2 ~ 0.1 GeV2
Extrapolated from G0 Q2=[0.12,0.16]
GeV2
95% c.l.
2 = 1
GEs = -0.020 ± 0.030
GMs = 0.72 ± 0.40
Kent Paschke – University of Massachusetts
EINN ’05 Milos September 25, 2005
LQCD prediction for s with Charge Symmetry
Leinweber et al.PRL 94, 212001 (2005)
• Use charge symmetry to relate valence quark magnetic dipole moments and loop contributions
• Use Lattice QCD only to calculate ratios of valence quark magnet dipole moments
• LQCD results in excellent agreement with measured octet magnetic moments
s = -(0.046 0.019)N
Lattice calculation
Kent Paschke – University of Massachusetts
EINN ’05 Milos September 25, 2005
Strange Vector FF and Lattice QCD
Lattice - Lewis, Wilcox & WoloshynPRD 67, 013003 (2003)
Chiral Quark Soliton Model - A. Sliva et al., Phys. Rev. D 65, 014015 (2001).
Kent Paschke – University of Massachusetts
EINN ’05 Milos September 25, 2005
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%
Kent Paschke – University of Massachusetts
EINN ’05 Milos September 25, 2005
Axial Form Factor
Axial 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
Kent Paschke – University of Massachusetts
EINN ’05 Milos September 25, 2005
EM Form Factors
uncertainty
(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