1. Study of Strange Quark in the Nucleon with Neutrino Scattering
Ｊｕｌｙ　28, 2004
NuFact 04, Osaka
Study of Strange Quark in the Nucleon with Neutrino Scattering
T.-A. Shibata
Tokyo Institute of Technology

2. --- Quark Structure of the Nucleon
Contents:
Physics Motivation
　　　 --- Quark Structure of the Nucleon
--- Proton Spin Problem and Strange Quark Spin
2. Strange Quark with Neutrino Scattering,
3. Flavor Decomposition of Quark Helicity Distributions
4. Conclusions
T.-A. Shibata, NuFact04

3. Strangeness in the nucleon, s(x)
N scattering term:
OZI suppressed production
Neutrino scattering
Strange quark polarization in the nucleon, Δs(x)
Polarized deep inelastic scattering (inclusive)
N elastic scattering
Baryon magnetic moments
Lattice calculations
Polarized deep inelastic scattering (hadron detection)
T.-A. Shibata, NuFact04

4. e’ e Neutrino Scattering cf. lepton number conservation,
charge conservation
T.-A. Shibata, NuFact04

5. Selective reactions on quark flavor
Distinction between quark and antiquark
(anti-)Neutrino is polarized
Selective reactions with quark helicity (spin)
T.-A. Shibata, NuFact04

6. T.-A. Shibata, NuFact04

7. x = 1 80 GeV2 x < 1 1 40 GeV Resonance region
40 GeV
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8. ‘Proton Spin Problem’ by EMC and Neutrino Cross Sections
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9. + Spin of Proton = SU(6) Quark Wave Functions of Baryons
Sum of Spins of u u d Quarks = Spin of Proton
1 / 2
- 1 / 2 + =
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10. Spin of Proton EMC Experiment (1988) 20 – 30 % of Nucleon Spin
1 / 2
- 1 / 2
EMC Experiment (1988)
20 – 30 % of Nucleon Spin
Slightly negative
T.-A. Shibata, NuFact04

11. Double-spin asymmetry
How was it measured?
Quark Helicity Distributions, Flavor Separation
Double-spin asymmetry
Polarized beam and polarized target
Virtual photon
Nucleon
T.-A. Shibata, NuFact04

12. Asymmetry, Polarized Quarks
( quark distribution ) x
( fragmentation function )
Quark Density Distribution
Quark Helicity Distribution
T.-A. Shibata, NuFact04

13. After EMC experiment, low energy neutrino-nucleon cross sections attracted attention from viewpoint of strange quark contriutions to the nucleon spin.
G.T. Garvey et al., Phys. Rev. C48 (1993) 761
Reanalysis of BNL734 experiment
Neutrino beam from AGS on proton,
(mean energy 1.3 GeV) , (1.2 GeV)
and elastic events.
axial vector dipole mass needs to be determined.
G.T. Garvey et al., Prog. Part. Nucl. Phys. 34 (1995) 245.
Neutral current neutrino-proton and -neutron scattering cross section
Strange form factors. Axial vector form factor
　　　0.1 – 0.25 GeV , p, n elastic cross sections
LSND at LAMPF
SAMPLE, G0 Experiments
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14. Flavor Separation of Quark Helicity Distributions
as a function of x
T.-A. Shibata, NuFact04

15. ‘Flavor Decomposition of the Sea Quark Helicity Distributions
Airapetian et al., HERMES
‘Flavor Decomposition of the Sea Quark Helicity Distributions
in the Nucleon from Semi-inclusive Deep-inelastic Scattering’
Phys. Rev. Lett. 92 (2004)
hep-ex/
‘Quark Helicity Distributions in the Nucleon for up-, down-,
and strange-quarks from Semi-inclusive Deep-inelastic Scattering’
submitted to Phys. Rev. D
hep-ex/
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16. Precision measurements of asymmetry
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17. Hadron identification at 2-15 GeV/c with RICH
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18. e Detector HERMES @DESY- HERA 1995 -- 27.6 GeV Target
Polarized Internal gas targets
(H, D,3He)
HERA
27.6 GeV
Target e
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19. HERMES Spectrometer
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20. Asymmetry, Hadron detection
Deuterium Target x
A1 increases with x
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21. Positive Negative Nearly Zero Systematic Errors:
Light Error Bar – Fragmentation Models
Dark Error Bar - Asymmetries
Positive
Negative
Nearly Zero
x bin by bin analysis.
SU(3) Symmetry not assumed.
T.-A. Shibata, NuFact04

22. Strangeness Helicity Distribution
Strangeness Spin
Strangeness Helicity Distribution
x integral of or
in the measured region
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23. Stepwise approach before Neutrino Factories:
‘Strangeness with Neutrino Scattering’ Working Group
for J-PARC
feasibility studies,
compilation of existing data,
theoretical investigations, …
T.-A. Shibata, NuFact04

24. What is new with Neutrino Factories
hydrogen and deuteron targets
in counter experiments (non-bubble chamber)
polarized hydrogen and deuteron targets
and beams with low contaminations,
small beam diameter, beam is polarized (!)
Deep inelastic scattering on the nucleon at high energies
quark and antiquark structure in the nucleon
spin of quarks in polarized nucleon
in particular, strangeness in the nucleon
tests of fundamental sum rules
combined analysis with e and muon scatterings
Elastic scattering on the nucleon at low energies
form factors both with and beams
T.-A. Shibata, NuFact04

25. Conclusions
Neutral and charged current neutrino interactions are useful tools to study the properties of the nucleon.
Neutrino reacts on the quark flavor selectively. Neutrino beam is 100% polarized. Selective reactions with quark helicity (spin).
‘Proton Spin Problem’ is an important challenge for QCD (EMC,1988). Strange quark is suggested to be negatively polarized.
Hadron detection in electron deep inelastic scattering (HERMES) provides flavor separation of quark helicity distributions
Neutrino reaction is a promising approach to determine strange quark contributions to the nucleon spin 　.
At Neutrino Factories neutrino reactions on polarized targets are expected.
T.-A. Shibata, NuFact04