Contributions of Strange Quarks to Proton Structure Doug Beck UIUC - - PowerPoint PPT Presentation

Contributions of Strange Quarks to Proton Structure

Doug Beck UIUC 24 Apr 06

Outline:

• 1. Physics motivation
• 2. Experiments
• 3. Results
• 4. Speculation

Strange Quark Observables

• scalar matrix element

– .

• new review by M. Sainio (PANIC05)
• momentum carried by strange quarks

– .

NuTEV hep-ex/9906037

– .

• spin carried by strange quarks

– as determined in sum rule

• Δs ~ -0.1 - 0

– as determined in semi-inclusive Δs(x)

• HERMES result (PANIC05)
• vector matrix elements

4 . 1 . ~ 2 − + N d d u u N N s s N

( )

06 . 07 . 42 . 2 ± ± = + d u s

( ) ( )

x s x s ≅

0.1 0.2 0.3 0.4 0.5

x

0.01

• 0.01
• 0.02
• 0.03
• 0.04

x[s(x)-s(x)]

CTEQ6M, NLO NuTEV hep-ex/0405037

Vector Quark Currents in the Nucleon

• Measure

– e.g. – note then

: , ,

, , , n p Z p

G G G

γ γ

N q q e N G

i i i i μ

Γ

∑

~

( )

p s M E p d M E p u M E p M E

G G G G

, , , , , , , ,

3 1 3 2 + − =

γ n s p s n u p d n d p u

G G G G G G

, , , , , ,

= = =

charge symmetry

(see G. A. Miller PRC 57 (98) 1492.)

( ) ( ) ( )

p Z M E n M E p M E W s M E p Z M E n M E p M E W d M E p Z M E p M E W u M E

G G G G G G G G G G G

, , , , , , 2 , , , , , , , 2 , , , , , 2 ,

sin 4 1 sin 4 2 sin 4 3 − − − = − + − = − − =

γ γ γ γ γ

θ θ θ

dropping the p superscripts on the left

• spin current

– spin triplet: moments cancel – spin singlet: zero net moment, zero net convection – also requires separation

. , Non-Zero?

• charge distribution

– if s, s are separated, non-zero net contribution

• convection current

– if s, s are separated, non-zero net contribution

s μs

2 1 z s + =

μs

2 1 z s − =

s rs rs s s

GE

s

GM

s

Parity-Violating Electron Scattering

• Interference term violates parity: use

where

p Z

G

,

( )

e , e ′ r

• contributes to electron scattering
• interference term: large x small

2 Z

M M + ∝

γ

σ

γ

M

Z

M

( ) ( )

2 2 2 5

2 4 10 ~

γ γ

τ ε πα σ σ σ σ

M E A M E F L R L R PV

G G A A A Q G A + + + − = + − ≡

−

( )

( ) ( )

e A M W A Z M M M Z E E E

G G A G G A G G A

γ γ γ

θ ε θ τ θ ε ′ − − = = =

2

sin 4 1 ,

e p Z e p γ

( ) ( ) ( )

[ ]

( ) ( )(

)

2 2 2 1 2

1 1 , 4 , 2 / tan 1 2 1 ε τ τ θ ε τ θ τ θ ε − + = ′ = + + =

− p

M Q

Experiments

Summary of PV Electron Scattering Experiments

• K. Kumar

published, running published x2, running published (ing) published (ing)

2008 2006

SAMPLE Experiment

Ebeam = 200 MeV Ibeam = 40 μA Pbeam = 35% Δθ = 130 - 170o ΔΩ = 1.5 sr ltarget = 40 cm L = 4.3 x 1038 cm-2 s-1 A ~ -7 ppm

• Measure GM (Q2 = 0.1 GeV2)

for 1H,2H

Caltech, Illinois, Kentucky, LaTech, Maryland, MIT, Virginia Tech, W&M

Z

HAPPEx (JLab Hall A)

• Measured GE

s + 0.39 GM s at

Q2 = 0.48 GeV2

Electron Beam LH2 Target Pb-Sci Calorimeters HRS Spectrometers

Ebeam = 3.2 GeV Ibeam ~ 50 μA Pbeam = 80% θ = 60 ΔΩ = (3.7 msr) x 2 ltarget = 20 cm L = ~2 x 1038 cm-2 s-1 A ~ -2, +8 ppm

• 2004 runs: 1H, 4He at 0.11 GeV2

HAPPEx nucl-ex/0506010 10 5

• 5
• 10

1 2 3 4 5 6

Data Set Number Asymmetry (ppm)

PVA4 (Mainz)

Second measurement

Ebeam = 0.57 GeV Ibeam = 20 μA Pbeam = 80% θ = 350 ΔΩ = 0.7 sr ltarget = 10 cm L = 0.5 x 1038 cm-2 s-1 A ~ -2 ppm

• Measure GE

s + 0.11 GM s at Q2 = 0.1 GeV2

– have also measured at Q2 = 0.23 GeV2

• Q2=0.1 GeV2

– Ameas = -1.36 ± 0.29 ± 0.13 ppm – Ath = -2.06 ± 0.14 ppm

– PRL 94 (05) 152001

Channel Counts

G0 Experiment (JLab Hall C)

• Measure ,

– different linear combination

• f u, d and s contributions

than e.m. form factors →strange quark contributions to sea

• Measure forward and

backward asymmetries

– recoil protons for forward measurement – electrons for backward measurements

• elastic/inelastic for 1H,

elastic for 2H

• Forward measurements

complete (101 Coulombs)

Electron Beam LH2 Target Superconducting Coils Particle Detectors

Ebeam = 3.03 GeV, 0.36 - 0.69 GeV Ibeam = 40 μA, 80 μA Pbeam = 75%, 80% θ = 52 – 760, 104 - 1160 ΔΩ = 0.9 sr, 0.5 sr ltarget = 20 cm L = 2.1, 4.2 x 1038 cm-2 s-1 A ~ -1 to -50 ppm, -12 to -70 ppm

GM

Z

GE

Z

G0 in Hall C (JLab)

beam monitoring girder superconducting magnet (SMS) scintillation detectors cryogenic supply cryogenic target ‘service module’ electron beamline

Results

(Last Thursday)

• Strange quark contribution to asymmetry

Strange Quark Contribution

( )

p E p M i

G G E Q ε τ η = ,

2

http://www.npl.uiuc.edu/exp/G0/Forward

( )

) ( 2 2 2

1 2 4

V p E p M p E F

R G G G Q G + + ε τ ε πα

( )

NVS phys

A A − +

s E

G η =

s M

G

G0 Experimental Asymmetries

• “no vector strange” asymmetry, ANVS, is A( , = 0)

– em form factors: Kelly PRC 70 (2004) 068202

• inside error bars: stat, outside: stat. & pt-pt syst.

GE

s

GM

s

http://www.npl.uiuc.edu/exp/G0/Forward

• D. Armstrong, et al. PRL 95 (2005) 092001

Strange Quark Contribution to Proton

http://www.npl.uiuc.edu/exp/G0/Forward

• D. Armstrong, et al. PRL 95 (2005) 092001

Det 1-14 Background Correction

• Results of 2-step fitting

procedure: det 8

– fit Yback (poly’l of degree 4), Gaussian for elastic peak – then fit Aback (poly’l of degree 2), constant Ael

• asym: χ2 = 37.5/44

– f determined from Yback, Ymeas in subsequent analysis

• don’t use detailed shape of

elastic peak

• Det 14 similar except it has 2

elastic peaks

– Q2 = 0.41, 1.0 GeV2

Det 8

( )

back el meas

A f A f A + − = 1

• Det. 1-14 Background Uncertainty
• Background yield shape varied

within “lozenge”

– use a variety of shapes

• Similar approach for

asymmetry shape

– vary throughout range

• Then for each pair of shapes

distribution of gives systematic uncertainty

( )

back el meas meas back

fA A f A Y Y f + − = = ~ 1

el

A ~

Det 8

. , Data @ Q2 = 0.1 GeV2

= -0.013 ± 0.028

GE

s

GM

s = +0.62 ± 0.31

Contours 1σ, 2σ 68.3, 95.5% CL Theories

1. Leinweber, et al. PRL 94 (05) 212001 2. Lyubovitskij, et al. PRC 66 (02) 055204 3. Lewis, et al. PRD 67 (03) 013003 4. Silva, et al. PRD 65 (01) 014016

GE

s GM s

http://www.npl.uiuc.edu/exp/G0/Forward

(0.1 GeV2) = -1.42:

. , Data @ Q2 = 0.1 GeV2

= -0.013 ± 0.028

GE

s

GM

s = +0.62 ± 0.31

GM

p (0.1 GeV2) = 2.12:

u: 2.28 ± 0.21 d: 0.03 ± 0.11 s: -0.21 ± 0.11

GM

n

u: -0.07 ± 0.11 d: -1.14 ± 0.21 s: -0.21 ± 0.11

GE

s GM s

http://www.npl.uiuc.edu/exp/G0/Forward

Results

(Today)

1H Preliminary

Results

Q2 = 0.1089 ± 0.0011GeV2 Araw = -1.418 ppm ± 0.105 ppm (stat) Araw correction ~11 ppb Raw Parity Violating Asymmetry

Helicity Window Pair Asymmetry ~25 M pairs, width ~540 ppm

Asymmetry (ppm) Slug

4He Preliminary

Results

Q2 = 0.07725 ± 0.0007 GeV2 Araw = 5.253 ppm ± 0.191 ppm (stat) Raw Parity Violating Asymmetry

Helicity Window Pair Asymmetry 35 M pairs, total width ~1130 ppm Araw correction ~ 0.12 ppm

Slug Asymmetry (ppm)

HAPPEX-II 2005 Preliminary Results

A(Gs=0) = +6.37 ppm Gs

E = 0.004 ± 0.014(stat) ± 0.013(syst)

A(Gs=0) = -1.640 ppm ± 0.041 ppm Gs

E + 0.088 Gs M = 0.004 ± 0.011(stat) ± 0.005(syst) ± 0.004(FF)

HAPPEX-4He: HAPPEX-H:

Q2 = 0.1089 ± 0.0011 (GeV/c)2

APV = -1.60 ± 0.12 (stat) ± 0.05 (syst) ppm

Q2 = 0.0772 ± 0.0007 (GeV/c)2

APV = +6.43 ± 0.23 (stat) ± 0.22 (syst) ppm

HAPPEX-II 2005 Preliminary Results

Three bands: 1. Inner: Project to axis for 1-D error bar 2. Middle: 68% probability contour 3. Outer: 95% probability contour

Caution: the combined fit is

• approximate. Correlated errors and

assumptions not taken into account

Preliminary

World Data near Q2 ~0.1 GeV2

Caution: the combined fit is

• approximate. Correlated errors and

assumptions not taken into account

Preliminary

GM

s = 0.28 +/- 0.20

GE

s = -0.006 +/- 0.016

~3% +/- 2.3% of proton magnetic moment ~0.2 +/- 0.5% of Electric distribution

HAPPEX-only fit suggests something even smaller: GM

s = 0.12 +/- 0.24

GE

s = -0.002 +/- 0.017

World Data near Q2 ~0.1 GeV2

Preliminary

GM

s = 0.28 +/- 0.20

(0.1 GeV2) = -1.42:

GM

p (0.1 GeV2) = 2.12:

u: 2.06 ± 0.14 d: 0.15 ± 0.07 s: -0.09 ± 0.07

GM

n

u: -0.29 ± 0.07 d: -1.03 ± 0.14 s: -0.09 ± 0.07

Speculation

World data consistent with state of the art theoretical predictions

Preliminary

• 16. Skyrme Model - N.W. Park and H.

Weigel, Nucl. Phys. A 451, 453 (1992).

• 17. Dispersion Relation - H.W. Hammer,

U.G. Meissner, D. Drechsel, Phys.

• Lett. B 367, 323 (1996).
• 18. Dispersion Relation - H.-W. Hammer

and Ramsey-Musolf, Phys. Rev. C 60, 045204 (1999).

• 19. Chiral Quark Soliton Model - A.

Sliva et al., Phys. Rev. D 65, 014015 (2001).

• 20. Perturbative Chiral Quark Model -
• V. Lyubovitskij et al., Phys. Rev. C 66,

055204 (2002).

• 21. Lattice - R. Lewis et al., Phys. Rev. D

67, 013003 (2003).

• 22. Lattice + charge symmetry -

Leinweber et al, Phys. Rev. Lett. 94, 212001 (2005) & hep-lat/0601025

Summary

• Suggested large values at Q2~0.1 GeV2
• Ruled out
• Possible large values at Q2>0.4 GeV2
• G0 backangle, Running now!
• HAPPEX-III - 2008
• Large possible cancellation at Q2~0.2 GeV2
• Very unlikely given constraint at 0.1 GeV2
• G0 back angle at low Q2 (error bar~1.5%
• f μp) maintains sensitivity to discover GM

S

Preliminary

0.6 GeV2 G0 backward HAPPEX-III

GM

s

GE

s

Preliminary

Simple Fit to All Hydrogen Data

• Fit

( ) ( ) ( )=

+

2 2 2

, Q G E Q Q G

s M i s E

η

with simple forms for ,

GE

s

GM

s

( )

( ) (

)

( ) ( )

( )

2 2 2 2 2 2 2 2 , 2

1 1 6 . 5 1

s M s M s M s E s E s E

Q Q G Q G Q G Q G Λ + = = Λ + + = τ τ

Galster

Λ = Λ = Λ

s M s E

with

( )

) ( 2 2 2

1 2 4

V p E p M p E F

R G G G Q G + + ε τ ε πα

( ) ( )

i NVS phys

E Q A A ,

2

−

dipole

Simple Fit to All Hydrogen Data

• Fit

( )

22 . 39 . 95 . 80 .

2 ,

± = = ± − = Q G G

s M s E

22 / 8 . 19

2 = ν

χ

Simple Fit to All Hydrogen Data

• Fit

( )

26 . 40 . 11 . 1 83 .

2 ,

± = = ± − = Q G G

s M s E

22 / 8 . 20

2 = ν

χ

w/o SAMPLE

, Data @ Q2 = 0.23 GeV2

http://www.npl.uiuc.edu/exp/G0/Forward

GE

s GM s

Expected Results

• Assumes single measurement 50 d LH2

– total background uncertainty 2% (stat. unc. 2.8%)

PVA4 G0 Forward G0 Backward stat stat + sys stat + sys + model