For the HAPPEX Collaboration

Thomas J eff erson National Accelerator Facility – Argonne National Laboratory – CSU, Los Angeles -William and Mary – Duke – DSM/ DAPNI A/ SPhN CEA Saclay - FI U – Harvard -

I NFN, Rome - I NFN, Bari – I AE, Beij ing – I PT Kharkov - J ozef Stefan I nstitute –Kent State - MI T – NPI RAS, St. Petersburg – ODU – Rutgers - Smith College –

Syracuse – Temple – U. Blaise Pascal – U. of I llinois Urbana-Champagne –UMass, Amherst – U. of Kentucky – U. of Virginia – UST, Heifei

Strange Quarks in the Nucleon Sea

Results from Happex II

Konrad A. Aniol, CSULA

Recent Talks by the HAPPEX Collaboration

http://hallaweb.jlab.org/experiment/HAPPEX/pubsandtalks.html

APS Meeting: Parity-Violation Electron Scattering on Hydrogen and Helium and Strangeness in the Nucleon, 23 April 2006 - Paul Souder (PPT)

TJNAF Seminar: Results from the 2005 HAPPEX-II Run, 21 April 2006 - Kent Paschke (PPT)

See these talks for greater detail

Kent Paschke, University of Massachusetts

Thesis Students

Lisa Kaufman, University of Massachusetts

Bryan Moffit, College of William and Mary

Hachemi Benaoum, Syracuse University

Ryan Snyder, University of Virginia

Structure of the Nucleon is of Fundamental Interest

99.9% of baryonic matter is contained in the nucleon

Molecules = atoms, massmolecule =massatoms

Atom = (nuclei + electrons), matom=mnuclei+melectrons

Nucleus = nucleons, mnucleus Zmp+Nmn

Nucleon=quarks+gluons), mnucleon mquarks !

A hierarchy of structures

From PDG, mu is 1.5 to 4 MeV

md is 4 to 8 MeV

Proton flavor content is uud, mp 2mu + md

Example of origin of proton’s mass, PRL 74 (1071) 1995, X. Ji

Quark kinetic + potential energy = 1/3 mnucleon

Total gluon energy = 7/12 mnucleon

Quark masses = 1/12 mnucleon

Conclude – nucleon mass has significant gluon field contribution expect significant amounts of pairs to be present.

qq

nucleon sea quarks are important components of the nucleon

How can we determine the quark content of the nucleon?

Constituent quarks are quasi-particles and become heavy fermions through the strong interactions.

g

qc

qc

A constituent u quark has spin ½ and is a dynamical system.

uc

g

uc

sdu ,,

sdu ,,

Charged-current neutrino and anti-neutrino scattering reveal the presence of strange and anti-strange quarks.

cs

The charm quarks decay semileptonically to positive muons. Muon neutrinos thus produce positive and negative muon pairs.

Likewise for muon anti-neutrinos: cs

)(

)(

Xs

Xs

Are strange sea quarks present in the nucleon?

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 BUT new HERMES data determine that s = 0 !

NssN 5

NssN

NssN Strange vector FF electromagnetic structure ?

Strange massN scattering: 0-30% of nucleon mass

Strange sea is well-known, but contributions to nucleon

matrix elements are somewhat unsettled

Static nucleon properties ?

Parts of the Lagrangian responsible for neutral current scattering

photon

Z boson

Electroweak coupling of charged fundamental particles

wv QIq 23 sin2 3Iqa

Note that the fermion fields i are the same for photon or Z boson coupling. Only the coupling constants change.

I3 weak

isospin

Q electric

charge

qv vector qa a axialaxial

vectorvector

u 1/2 2/3 ½ -4/3sin2w

1/2

d -1/2 -1/3 -½ +2/3sin2w

-1/2

-1/2 -1/3 -½ +2/3sin2w

-1/2

Electroweak coupling constants

wv QIq 23 sin2 3Iqa

s

e -1/2 -1-1/2 +2sin2W

-1/2

Electron Scattering off Nucleons & Nuclei

Neutral Currents andWeak-Electromagnetic

Interference

)(22

2

AMEF

PV AAAQG

A

22ME

ZEE

E GG

GGA

22

ME

ZMM

M GG

GGA

22

22 )1(1)sin41(

2

1

ME

NCAMW

A GG

GGA

2

2

4M

Q 12 ]

2tan)1(21[

Asymmetry terms for eP or eN scattering. HAPPEX is not sensitive to the AA term for forward angle scattering

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 symmetry

nsps

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

i

iii NqqeNG ~

])(2

[sin2

22

nE

pE

sE

WF

PV GG

GQGA

For 4He the asymmetry does not contain magnetic terms

Jefferson Laboratory

Polarized e-

Source

Hall A

AB

C

Continuous Electron Beam Accelerator Facility

CEBAF

Features:1. Polarized Source2. Quiet Accelerator3. Precision

Spectrometersin Hall A

The HAPPEX CollaborationCalifornia State University, Los Angeles -

Syracuse University -DSM/DAPNIA/SPhN CEA Saclay -

Thomas Jefferson National Accelerator Facility- INFN, Rome - INFN, Bari -

Massachusetts Institute of Technology - Harvard University – Temple University –

Smith College - University of Virginia - University of Massachusetts – College of William and Mary

1998-99: Q2=0.5 GeV2, 1H2004-06: Q2=0.1 GeV2, 1H, 4He 2008:Q2=0.6, 1H

HAPPEX Experiment

Target400 W transverse flow20 cm, LH220 cm, 200 psi 4He

High Resolution SpectrometerS+QQDQ 5 mstr over 4o-8o

Hall A at Jefferson Lab

Compton1.5-2% systContinuous

Møller2-3% syst

Polarimeters

Cherenkovcones

PMT

PMT

Elastic Rate:1H: 120 MHz4He: 12 MHz

High Resolution Spectrometers

100 x 600 mm

12 m dispersion sweeps away

inelastic events

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

Brass-Quartz Integrating Cerenkov Shower Calorimeter•Insensitive to background•Directional sensitivity •High-resolution•Rad hard

High-Power Cryogenic TargetNew "race track" design – 20 cm (transverse cryogen flow) CSULA design and fabrication.

20 cm 1.8% R.L. LH2

20 cm 2.2% R.L. 4He gas cell– Cold (6.6K), dense (230 psi)

Al wall thickness– 4 mils (H)– 10 mils (He)

controls

effective

analyzing

power

Tune residual

linear pol.

Slow helicityreversal

Intensity Attenuat

or(charge

Feedback)

Polarized Source

High Pe

High Q.E.

Low Apower

•Optical pumping of solid-state photocathode

•High Polarization

• Pockels cell allows rapid helicity flip

•Careful configuration to reduce beam asymmetries.

•Slow helicity reversal further to cancel beam asymmetries

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

Asym

metr

y

(pp

m)

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

Asym

metr

y

(pp

m)

Slug

June 2004HAPPEX-He• about 3M pairs at 1300 ppm

=> Astat ~ 0.74 ppm

June – July 2004HAPPEX-H• about 9M pairs at 620 ppm

=> Astat ~ 0.2 ppm

July-Sept 2005HAPPEX-He• about 35M pairs at 1130 ppm

=> Astat ~ 0.19 ppm

Oct – Nov 2005HAPPEX-H• about 25M pairs at 540 ppm

=> Astat ~ 0.105 ppm

HAPPEX-II

Q2=0.091 GeV2

Q2=0.099 GeV2

Q2=0.077 GeV2

Q2=0.109 GeV2

Example: The window pair statistical error is 620 ppm for 2004 HAPPEX-H.

Recent Happex Publications – 2004 runs

Phys.Rev. Lett. 96, 022003 (2006)

Parity-Violating Electron Scattering from 4He and the Strange Electric Form Factor fo the Nucleon

                             GEs = -0.038 0.042(stat) 0.010(syst)                                  

Constraints on the Nucleon Strange Form Factors at Q2 0.1 GeV2

Phys. Lett. B635 (2006) 275

GEs + 0.080GM

s = 0.030 0.025(stat) 0.006(syst) 0.012(FF)

Extrapolated from G0 Q2=[0.12,0.16]

GeV2

95% c.l.

2 = 1

Theory Calculations

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

18

17

16

19

21 22

HAPPEX-II 2005 Preliminary Results

A(Gs=0) = +6.37 ppm

GsE = 0.004 0.014(stat) 0.013(syst)

A(Gs=0) = -1.640 ppm 0.041 ppm

GsE + 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 HAPPEX 2005

data

World data confronts theoretical predictions

Preliminary results from 2005 data

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

A simple picture of GEs – Scattering from a group of

randomly oriented electric dipoles formed by the pairs. Average over cross sections and deduce <GE

S>.

beam

aa

1/3 e

-1/3 e

)sin(23

1aqG s

E

In this simple picture the dipoles would have a separation of 2a 0.014F if GE

S = 0.004.

ss

qBreit = 1.594 F-1, for HAPPEX-II data

A recent fit to the world’s data for Q2<0.3GeV2

R. D. Young et al., nucl-ex/0604010

GEs = sQ2. s = -0.06 0.41 GeV2

GMs = s. s = 0.12 0.55 0.07

Strange form factors of the proton

Includes data from SAMPLE, PVA4, G0, HAPPEX (2004)

Lattice QCD calculation of GMs

D. B. Leinweber et al., PRL 94(2005)212001

GMs = (-0.046 0.019)n

QNP06 – A. W. Thomas, HAPPEX II result plus Leinweber calculation means contribute 10 MeV or less to the nucleon’s mass.

ss

Summary

• Suggested large values at Q2~0.1 GeV2

• Ruled out

• Possible large values at Q2>0.4 GeV2

• G0 backangle, finished Spring 2007• 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% of p) maintains sensitivity to discover GM

S

Preliminary

0.6 GeV2

G0 backward

HAPPEX-III

GMs

GEs

Preliminary

References

mrst2004

Ann. Rev. Nucl. Part. Sci. 2001. 51:189-217, D. Beck, R. McKeown

Relative probabiliity for transition is circled

Detailed Formulae: Clean Probe of Strangeness

Inside the Nucleon

• Measurement of APV yields linear combination of GsE, G

sM

• Sensitive only to GsE

Hydrogen

4He

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

PV Electron Scattering to Measure Weak NC Amplitudes

EMEM JQ

M lQ

24

NCV

NCA

FNCPV JgJg

GM 5

5

22

Interference with EM amplitude makes NC amplitude accessible

22

~~Z

EM

NCPV

M

Q

M

M Z0

2~LR

LRPVA