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Study of Strange Quark in the Nucleonwith Neutrino Scattering
T.-A. Shibata
Tokyo Institute of Technology
Ｊｕｌｙ 28, 2004
NuFact 04, Osaka
T.-A. Shibata, NuFact04 2
Contents:
1. 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
s
)(xq
sAG
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Strangeness in the nucleon, s(x)
N scattering term:
OZI suppressed production
du,
s
s
20.||
||
pssdduup
pssp
Strange quark polarization in the nucleon, Δs(x)
))((||| ssuuduudp
Polarized deep inelastic scattering (inclusive)
N elastic scatteringBaryon magnetic moments
Lattice calculations
Polarized deep inelastic scattering (hadron detection)
10.s
150.s
20.s
10.s
0s
Neutrino scattering
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Neutrino Scattering
e
e’
W
d
u
lepton number conservation, charge conservation
)(
0Z
)(
W
d
u
cf.
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Selective reactions on quark flavor
Distinction between quark and antiquark
(anti-)Neutrino is polarized%100
ud du
du ud )(s
Selective reactions with quark helicity (spin)
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])(
)()()()[(
),()()()(
scattering neutrino
))]()(())()(())()(([)(
:scattering inelastic deep (muon) electron
)(
p
xF
xFxyyxF
sG
dxdy
d
xsxdxuxF
xsxsxdxdxuxuxxF
2
322
2
2
3
2
2
11
2
11
2
9
1
9
1
9
4
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'EE
2Q
40 GeV0
80GeV2
x = 1
x < 1
mQ
x2
2
Bjorken
1
Resonance region
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‘Proton Spin Problem’ by EMC and Neutrino Cross Sections
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Spin of Proton
Sum of Spins of u u d Quarks = Spin of Proton
2
1
2
1
2
1
2
1
SU(6) Quark Wave Functions of Baryons
+ + =
1 / 2
1 / 2- 1 / 2
1 / 2
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Spin of Proton
2
106800470060
2
1 ...)( sdu
)%( 14912
EMC Experiment (1988)
20 – 30 % of Nucleon SpinSlightly negative
Gqq
LLGqq )(2
1
2
1
1 / 2
1 / 2- 1 / 2
1 / 2
s
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Quark Helicity Distributions, Flavor Separation
Double-spin asymmetry
)()(
)()(),(
xx
xxzxA
1
XeNe
Polarized beam and polarized target
....
.... ....
....NucleonVirtual photon
How was it measured?
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Asymmetry, Polarized Quarks
)()()( xqxqxq Quark Helicity Distribution
)()(),( zDxqezx hq
qqh 2
)()()( xqxqxq Quark Density Distribution
)()(
)()(),(
xx
xxzxA
1
( quark distribution ) x ( fragmentation function )
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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.
pp
AM
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
sQGsA )( 02
E
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Flavor Separation of Quark Helicity Distributions
)(),(),(),(),( xsxdxuxdxu
as a function of x
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A. 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) 012005
hep-ex/0307064
‘Quark Helicity Distributions in the Nucleon for up-, down-, and strange-quarks from Semi-inclusive Deep-inelastic Scattering’submitted to Phys. Rev. Dhep-ex/0407032
)(),(),(),(),( xsxdxuxdxu
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Precision measurements of asymmetry )(, xA p1
)()(
)()(),(
xx
xxzxA
1
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Hadron identificationat 2-15 GeV/cwith RICH
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Detector
Target
HERMES @DESY- HERA1995 --
27.6 GeV
Polarized Internal gas targets
(H, D,3He)
e
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HERMES Spectrometer
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Kd
Kd AA ,, 11
x
Deuterium Target
A1 increases with x
)(hd, xA1
K K
Asymmetry, Hadron detection
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Positive )(xu)(xdNegative
Nearly Zero )(xq
Light Error Bar – Fragmentation Models
Dark Error Bar - Asymmetries
Systematic Errors:
x bin by bin analysis.
SU(3) Symmetry not assumed.
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Strangeness Helicity Distribution
syst.)(.stat.)(.. :Integral 010030030
,.. 300230 x x integral of ,)(xs
Strangeness Spin
)()( xsxs or
)(xs
in the measured region
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Stepwise approach before Neutrino Factories:
‘Strangeness with Neutrino Scattering’ Working Group for J-PARC
feasibility studies, compilation of existing data, theoretical investigations, …
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What is new with Neutrino Factories
hydrogen and deuteron targetsin counter experiments (non-bubble chamber)
polarized hydrogen and deuteron targets
GeV,to up 30E 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
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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.
)(xq
)( sAG