strangeness in the nucleon kent paschke university of massachusetts einn ‘05 september 24, 2005

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 Strange vector FF

Strange massN scattering: ~30%

Strange sea is well-known, but contributions to nucleon

matrix elements are somewhat unsettled

Flavor Separation of Nucleon Form Factors

pME GGGG ,

ZME GGGG /

2/ sin

Measuringnp GG ,, , cannot separate all three flavors

(assumes heavy quarks are negligible)

Adding in a measurement of

and assuming charge symmetrynsps

then we can write

Accessing Weak Neutral Current Amplitude

LRPV GGG

MMA ,,F

Interference with EM amplitude makes NC amplitude accessible

Longitudinal spin asymmetry violates parity (polarized e-, unpolarized p):

Parity-violating electron scattering

AMEF AAAQGA

~ few parts per million

For a proton:

GGRGRG

, )1()1)(sin41(

For 4He: GEs alone

(but only available at low Q2)

Forward angle Backward angle

pEE GGAGGAGGA '2sin41 , ,

For deuterium: enhanced GA

e sensitivity

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

NAAA610

Need• Highest possible luminosity• High rate capability• High beam polarization

Detectors Integrating (HAPPEx) vs. Counting (G0, A4)

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

calculated at 15Hz

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

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

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

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

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

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

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

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

Elastic Rate:

1H: 120 MHz

4He: 12 MHz

Background ≤ 3%

Brass-Quartz integrating detector

Hall A at Jlab

2004 HAPPEX-II Data

Araw = + 5.63 ppm ± .71 ppm (stat)

•Short run (~ 5 days)•Beam Polarization ~

86%•Beam asymmetries

•Background f <3% •Dense gas target

Araw correction < 0.2 ppm

Perfect sign-flip with /2 plate

Raw Asymmetry (after beam corrections)

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%

PVA4 at MainzCalorimeter:1022 PbF2 crystals

20 cm LH2 target

20 A, 80% polarized beam

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

G0 Experiment in Hall C•Measure forward and backward

asymmetries– recoil protons for forward

measurement: GEs, GM

– 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

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

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

Results

Extrapolated from G0 Q2=[0.12,0.16]

95% c.l.

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

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

Anticipated Results from HAPPEX-II

2-3X improvement for each HAPPEX measurement

Q2 ~ 0.1 GeV2Experiment Running

Results available (early?) 2006

Result matching current central value:

• would convincingly establish a non-zero result

• would find GMs ~3

from zero

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%

World Forward-angle Hydrogen Data

G0 Results are big news: • Amplifies interesting low Q2 structure• Strong constraint at Q2~0.2 GeV2

• Significant non-zero result at higher Q2

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

• Will be addressed by future measurements

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

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

0.6 GeV2

Summary

0.6 GeV2

G0 backward

HAPPEX-III

• 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?

Transverse Asymmetry

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”

AT Data from 0.2 GeV-3 GeV

SAMPLE

“elastic”

“single pion”

hep-ph/0405303

Pasquini &Vanderhaeghen

Resonance region treated in a model incorporating pion electroproduction amplitudes

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

AT at E158 (Azimuthal angle)

46 GeVep ep Sign: AT<0

Magnitude: ~2.5 ppm

Without enhancement by inelastic states, ATep ~

Q2 ~ 0.06 GeV2

46 GeVee ee

backward angle

Sign: opposite AT

Magnitude: ~3.5 ppm

AT from Nuclei

Afanasev

Without inelastic states, 10-9

Predicted value, ~10-5 at 6 degrees, 3 GeV

Backup

World Data at Q2 ~ 0.1 GeV2

Extrapolated from G0 Q2=[0.12,0.16]

95% c.l.

GEs = -0.020 ± 0.030

GMs = 0.72 ± 0.40

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

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).

Extraction of SVFF from APV

GGGGRR

)0()8(0)3(122

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

Total: (APV) = 0.62 ppm, 2.8%

Axial Form Factor

Axial Form Factor: Uncertainty dominated by “anapole moment”

014.001.0

024.006.00

[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

EM Form Factors

uncertainty

(APV)/APV

2%negligibl

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

strangeness in the nucleon kent paschke university of massachusetts einn ‘05 september 24, 2005

background rejectionsample

mitbatesmeasure gms

counting g0

4he3 gev beam

asymmetry measurement

careful measurement

dominant systematic

asymmetry measurementpulse

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