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The G0 Experiment Parity-violating electron scattering from the nucleon Longitudinal beam polarization Strange quark contribution to elastic form factors Effective axial-vector elastic form factor Axial-vector N- transition Weak interaction contribution to pion photoproduction Single-spin asymmetries Transverse beam polarization •2 contribution to elastic scattering (Single spin asymmetry in pion photoproduction) D. Beck Mar. 2012

The G0 Experiment Parity-violating electron scattering from the nucleon –Longitudinal beam polarization Strange quark contribution to elastic form factors

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Page 1: The G0 Experiment Parity-violating electron scattering from the nucleon –Longitudinal beam polarization Strange quark contribution to elastic form factors

The G0 Experiment

• Parity-violating electron scattering from the nucleon– Longitudinal beam polarization

• Strange quark contribution to elastic form factors

• Effective axial-vector elastic form factor

• Axial-vector N- transition

• Weak interaction contribution to pion photoproduction

• Single-spin asymmetries– Transverse beam polarization

• 2 contribution to elastic scattering

• (Single spin asymmetry in pion photoproduction)

D. BeckMar. 2012

Page 2: The G0 Experiment Parity-violating electron scattering from the nucleon –Longitudinal beam polarization Strange quark contribution to elastic form factors

Strange Quark Observables• scalar matrix element

– .

• momentum carried by strange quarks– .

NuTEV hep-ex/9906037

– .

• spin carried by strange quarks– as determined in sum rule

s ~ -0.1 - 0

– as determined in semi-inclusive s(x)

• vector matrix elements

4.01.0~2 NdduuNNssN

06.007.042.02 dus

xsxs HERMES: Phys. Rev. D 89 (2014)

097101

0.02 0.006 0.029 0.007s

S. Alekhin et al. arXiv:1404.6469

Page 3: The G0 Experiment Parity-violating electron scattering from the nucleon –Longitudinal beam polarization Strange quark contribution to elastic form factors

Parity-Violating Electron Scattering

• Interference term violates parity: use

where

pZG ,

e,e

• contributes to electron scattering

- interference term: large x small

2ZMM

M ZM

22

2

5

24

10~

ME

AMEF

LR

LRPV

GG

AAAQG

A

e

AMWA

ZMMM

ZEEE

GGA

GGAGGA

2sin41

,

e p

Z

e p

2

2

2

12

11

,4

,2/tan121

pM

Q

Page 4: The G0 Experiment Parity-violating electron scattering from the nucleon –Longitudinal beam polarization Strange quark contribution to elastic form factors

:,, ,,, npZp GGG

Quark Currents in the Nucleon• Measure

– e.g.

– note

then

NqqeNG iii

i ~

psME

pdME

puME

pME GGGG ,

,,,

,,

,, 3

1

3

2

nsps

nupd

ndpu

GG

GG

GG

,,

,,

,,

charge symmetry

(see B. Kubis & R. Lewis, PRC 74 (06) 015204 and G. A. Miller PRC 57 (98) 1492.)

pZ

MEnME

pMEW

sME

pZME

nME

pMEW

dME

pZME

pMEW

uME

GGGG

GGGG

GGG

,,

,,

,,

2,

,,

,,

,,

2,

,,

,,

2,

sin41

sin42

sin43

dropping the p superscripts on the left

Page 5: The G0 Experiment Parity-violating electron scattering from the nucleon –Longitudinal beam polarization Strange quark contribution to elastic form factors

California Institute of Technology, Carnegie Mellon University,College of William and Mary, Grinnell College, Hampton University,

Hendrix College, Institut de Physique Nucléaire d'Orsay, J. Stefan Institute, Laboratoire de Physique Subatomique et de Cosmologie-Grenoble,

Louisiana Tech University, New Mexico State University, Ohio University, Thomas Jefferson National Accelerator Facility, TRIUMF, University of Illinois,

University of Kentucky, University of Manitoba, University of Maryland, University of Northern British Columbia, University of Winnipeg,

University of Zagreb, Virginia Tech, Yerevan Physics Institute

G0 Collaboration

Graduate Students:C. Capuano (2011 W&M), A. Coppens (2010 Manitoba), C. Ellis (2010 Maryland), J. Mammei (2010 VaTech), M. Muether (2010 Illinois), J. Schaub (2010 New Mexico State), M. Versteegen (2009 Grenoble); S. Bailey (2007 W&M)

Analysis Coordinator:F. Benmokhtar - Carnegie Mellon (Maryland)

SUPPORT: DOE, NSF, IN2P3, NSERC – Thank-you!

Page 6: The G0 Experiment Parity-violating electron scattering from the nucleon –Longitudinal beam polarization Strange quark contribution to elastic form factors

G0 Collaboration

Page 7: The G0 Experiment Parity-violating electron scattering from the nucleon –Longitudinal beam polarization Strange quark contribution to elastic form factors

G0 Experiment Overview• Measure ,

– different linear combination of u, d and s contributions than e.m. form factors

→strange quark contributions to sea (few % of overall G’s)

• Measure forward and backward asymmetries– recoil protons for forward

measurement– electrons for backward

measurements• elastic/inelastic for 1H,

quasi-elastic for 2H

Electron Beam

LH2 Target

SuperconductingCoils

Particle Detectors

Ebeam = 3.03 GeV, 0.33 - 0.93 GeV

Ibeam = 40 A, 80 A

Pbeam = 75%, 80%

= 52 – 760, 104 - 1160

= 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

GMZGE

Z

Page 8: The G0 Experiment Parity-violating electron scattering from the nucleon –Longitudinal beam polarization Strange quark contribution to elastic form factors

G0 in Hall C

beammonitoring girder

superconducting magnet (SMS)

scintillation detectors

cryogenic supply

cryogenic target ‘service module’

electron beamline

Page 9: The G0 Experiment Parity-violating electron scattering from the nucleon –Longitudinal beam polarization Strange quark contribution to elastic form factors

What Do We See?

• Different components separated by t.o.f.

• Background under elastic peak is main analysis issue

backelmeas AfAfA 1

• Background correction involves ‘dilution factor’, f and background asymmetry, Aback

Page 10: The G0 Experiment Parity-violating electron scattering from the nucleon –Longitudinal beam polarization Strange quark contribution to elastic form factors

Back Angle Layout

• Elastic, inelastic electron separation using FPD, CED

• Electron/pion separation using aerogel Cherenkov

Cherenkov

Electron Beam

Cryostat Exit Detector

Focal PlaneDetector

Shielding

Cryotarget

Single Octant Schematic

Page 11: The G0 Experiment Parity-violating electron scattering from the nucleon –Longitudinal beam polarization Strange quark contribution to elastic form factors

Back Angle Apparatus

Back angle detector package

Target system installation

FPD

CED

Cherenkov

SuperconductingMagnet

Page 12: The G0 Experiment Parity-violating electron scattering from the nucleon –Longitudinal beam polarization Strange quark contribution to elastic form factors

LH2, 678 MeV LH2, 687 MeV LH2, 362 MeV

LD2, 687 MeV LD2, 362 MeV

Electron Yields(quasi) elastic electrons

inelastic electrons

background regions

Page 13: The G0 Experiment Parity-violating electron scattering from the nucleon –Longitudinal beam polarization Strange quark contribution to elastic form factors

Combined Results (2010)• Using interpolation of G0 forward measurements

G0 forward/backward

PVA4: PRL 102 (2009)

Q2 = 0.1 GeV2 combined

Global uncertainties

G0 forward/backward

SAMPLE

Zhu, et al. PRD 62 (2000)

• also assuming

0 2 0 2,

0 2,

3

2

0 0.070

T T dipoleA NS A A

TA NS

F DG Q R G Q

G Q

Androić, et al. PRL 104 (2010) 012001

Page 14: The G0 Experiment Parity-violating electron scattering from the nucleon –Longitudinal beam polarization Strange quark contribution to elastic form factors

HAPPEx III Result

Z. Ahmed, et al. PRL 108 (2012) 102001

Q2 = 0.62 GeV2

Page 15: The G0 Experiment Parity-violating electron scattering from the nucleon –Longitudinal beam polarization Strange quark contribution to elastic form factors

Relative to Overall Form Factors

Z. Ahmed, et al. PRL 108 (2012) 102001

Page 16: The G0 Experiment Parity-violating electron scattering from the nucleon –Longitudinal beam polarization Strange quark contribution to elastic form factors

Combined Results with Theory

Androić, et al. PRL 104 (2010) 012001

Page 17: The G0 Experiment Parity-violating electron scattering from the nucleon –Longitudinal beam polarization Strange quark contribution to elastic form factors

PV: Inelastic Scattering/Pion Production• N- transition

– Dominant magnetic dipole (M1) transition in photoproduction• Coupling to vector current• Corresponds roughly to quark “spin flip” (via magnetic moment)

– Also study spin flip in axial current• e.g. charged pion electroproduction ep → e-++

A. Liesenfeld et al , Phys. Lett. B468 (1999) 20.

• “Pure” spin flip accompanied by flavor change

– We measure neutral current coupling to nucleon axial transition current: APV(inel)

• Like electroproduction, different flavor structure

• Pion production– Measure inclusive - from D target, dominated by

photoproduction– Asymmetry at Q2 =0 not zero (current conservation)– drelated to the anomalous S = 1 hyperon decays

S.-L. Zhu, C. Maekawa, B. Holstein & M. Ramsey-Musolf PRL 87 (2001) 201802

Page 18: The G0 Experiment Parity-violating electron scattering from the nucleon –Longitudinal beam polarization Strange quark contribution to elastic form factors

Inelastic Asymmetry

C. Capuano (thesis, W&M, 2011)

Proton

Deuteron: A = -43.6±14.6±6.2 ppm

Page 19: The G0 Experiment Parity-violating electron scattering from the nucleon –Longitudinal beam polarization Strange quark contribution to elastic form factors

Pion Asymmetries• Constrain small photoproduction asymmetry “d”

(OUT – IN)/2 = -0.56 ± 1.03 ppm[OUT + IN = 3.84 ± 2.15 ppm]

A. Coppens (thesis, Manitoba, 2010), arXiv:1112.1720, PRL 108 (2012) 122002

0.37 1.06 0.37 0.03

(8.1 23.7 8.3 0.7)

A

d g

Page 20: The G0 Experiment Parity-violating electron scattering from the nucleon –Longitudinal beam polarization Strange quark contribution to elastic form factors

Transverse Asymmetries• Elastic scattering

– Second order e.m. effects generate single-spin asymmetries

– Easy to measure with PV apparatus

• Pion production– Inclusive pion yield also has azimuthal dependence– Involves longitudinal/transverse interference (“5th structure fn.)

– Suppressed by ~me/E

– Calculation by A. Afanasev, et al.; T. S. H. Lee, et al.

Pasquini & Vanderhaeghen PRC 70 (2004) 045206

– Interference of 1 and 2 amplitudes; time reversal invariance requires An to involve the imaginary part of M2

– Real part of M2 related to important contribution to longitudinal scattering: GE/GM ratio

Ei = 570 MeV

Page 21: The G0 Experiment Parity-violating electron scattering from the nucleon –Longitudinal beam polarization Strange quark contribution to elastic form factors

Preliminary Transverse Asymmetries

Page 22: The G0 Experiment Parity-violating electron scattering from the nucleon –Longitudinal beam polarization Strange quark contribution to elastic form factors

Comparison of G0 Results with Theory

Proton

J. Mammei (thesis, VT, 2010), Androić, et al. PRL 107 (2011) 022501

Neutron: Bn(362 MeV) = +87±41 ppm (sign from GM)

Page 23: The G0 Experiment Parity-violating electron scattering from the nucleon –Longitudinal beam polarization Strange quark contribution to elastic form factors

Preliminary Pion Transverse Asymmetry

A. Coppens (Manitoba)

Page 24: The G0 Experiment Parity-violating electron scattering from the nucleon –Longitudinal beam polarization Strange quark contribution to elastic form factors

Summary• Comparison of electromagnetic and weak neutral elastic form

factors allows determination of strange quark contribution– large distance scale dynamics of the sea

• Contributions of and less than few % over measured range– why s, sbar not separated?

• First measurements of neutral current N transition around Q2 = 0.3 GeV2

• First measurements of PV asymmetry in inclusive - production at low Q2 – large d ruled out

• First measurements of transverse asymmetries in– back angle elastic scattering from H, D targets: Im(2)

– Inclusive - production: RLT’

sEG s

MG

Page 25: The G0 Experiment Parity-violating electron scattering from the nucleon –Longitudinal beam polarization Strange quark contribution to elastic form factors

Another Holt Measurement

• MDC ISO 400 gate valve has diameter of 16 in!