study of strange quark in the nucleon with neutrino scattering

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


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


Neutrino Scattering

e

e’

W

d

u

lepton number conservation, charge conservation

)(

0Z

)(

W

d

u

cf.


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)


])(

)()()()[(

),()()()(

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


'EE

2Q

40 GeV0

80GeV2

x = 1

x < 1

mQ

x2

2

Bjorken

1

Resonance region


‘Proton Spin Problem’ by EMC and 　 Neutrino Cross Sections


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


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


Quark Helicity Distributions, Flavor Separation

Double-spin asymmetry

)()(

)()(),(

xx

xxzxA

1

XeNe

Polarized beam and polarized target

....

.... ....

....NucleonVirtual photon

How was it measured?


Asymmetry, Polarized Quarks

)()()( xqxqxq Quark Helicity Distribution

)()(),( zDxqezx hq

qqh 2

)()()( xqxqxq Quark Density Distribution

)()(

)()(),(

xx

xxzxA

1

( quark distribution ) x ( fragmentation function )


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


Flavor Separation of Quark Helicity Distributions

)(),(),(),(),( xsxdxuxdxu

as a function of x


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


Precision measurements of asymmetry )(, xA p1

)()(

)()(),(

xx

xxzxA

1


Hadron identificationat 2-15 GeV/cwith RICH


Detector

Target

HERMES @DESY- HERA1995 --

27.6 GeV

Polarized Internal gas targets

(H, D,3He)

e


HERMES Spectrometer


Kd

Kd AA ,, 11

x

Deuterium Target

A1 increases with x

)(hd, xA1

K K

Asymmetry, Hadron detection


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.


Strangeness Helicity Distribution

syst.)(.stat.)(.. :Integral 010030030

,.. 300230 x x integral of ,)(xs

Strangeness Spin

)()( xsxs or

)(xs

in the measured region


Stepwise approach before Neutrino Factories:

‘Strangeness with Neutrino Scattering’ Working Group for J-PARC

feasibility studies, compilation of existing data, theoretical investigations, …


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


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

study of strange quark in the nucleon with neutrino scattering

Documents

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