Study of Strange Quark in the Nucleon with Neutrino Scattering

Transcription

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

2 Contents: 3. 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 G A s Δs Δq x T.-A. Shibata, NuFact04 2

3 Strangeness in the nucleon, s(x) π N scattering OZI suppressed σ term: production p>= uud>+ ε uud s s φ Neutrino scattering p s s p p u ud ds s p 0. 2 u, d Strange quark polarization in the nucleon, Δs(x) Polarized deep inelastic scattering (inclusive) ν N elastic scattering Baryon magnetic moments Lattice calculations Δs 0.15 Δs 0. 2 Δs 0.1 Polarized deep inelastic scattering (hadron detection) T.-A. Shibata, NuFact04 3 s s Δs 0.1 Δs 0

4 Neutrino Scattering ν μ ν μ Z 0 ν μ ν μ ν μ d W μ u cf. e e ν μ u W μ d lepton number conservation, charge conservation T.-A. Shibata, NuFact04 4

5 Selective reactions on quark flavor Distinction between quark and antiquark νd μ u νu μ d s νu μ d νd μ u (anti-)neutrino is 100 polarized Selective reactions with quark helicity (spin) T.-A. Shibata, NuFact04 5

6 electron muon deep inelastic scattering: F 2 x =x[ 4 9 u x u x 1 9 d x d x 1 9 s x s x ] neutrino scattering F 3 ν p x =u x d x s x, dσ ν ν dxdy s =G2 2 π F 11 y 2 2 x [ y 2 2 x F 3 x F 2 x ] T.-A. Shibata, NuFact04 6

7 Q 2 Bjorken x = Q2 2 m ν x = 1 80 GeV 2 Resonance region x < GeV ν=e E ' T.-A. Shibata, NuFact04 7

8 Proton Spin Problem by EMC and Neutrino Cross Sections T.-A. Shibata, NuFact04 8

9 Spin of Proton SU(6) Quark Wave Functions of Baryons Sum of Spins of u u d Quarks = Spin of Proton 1 / =1 2 1 / = - 1 / 2 1 / 2 T.-A. Shibata, NuFact04 9

10 Spin of Proton 1 / =1 2 q Δq Δ q ΔGL q L G 1 / 2 EMC Experiment (1988) - 1 / 2 1 / ΔuΔdΔs=0.06±0.047± ±9± % of Nucleon Spin Slightly negative Δs T.-A. Shibata, NuFact04 10

11 How was it measured? Quark Helicity Distributions, Double-spin asymmetry Flavor Separation e N e ' X Polarized beam and polarized target Virtual photon... Nucleon A 1 x, z= σ x σ x σ x σ x T.-A. Shibata, NuFact04 11

12 Asymmetry, Polarized Quarks σ h x, z q e q 2 q x D q h z ( quark distribution ) x ( fragmentation function ) A 1 x, z= σ x σ x σ x σ x q x =q x q x Quark Density Distribution Δ q x =q x q x Quark Helicity Distribution T.-A. Shibata, NuFact04 12

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, ν (mean energy 1.3 GeV), (1.2 GeV) ν ν p and ν p elastic events. axial vector dipole mass needs to be determined. M A 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 G s A Q 2 =0=Δs E ν = GeV, ν + p, ν + n elastic cross sections LSND at LAMPF SAMPLE, G0 Experiments T.-A. Shibata, NuFact04 13

14 Flavor Separation of Quark Helicity Distributions Δu x, Δd x, Δ u x, Δ d x, Δs x as a function of x T.-A. Shibata, NuFact04 14

15 Δu x, Δd x, Δ u x, Δ d x, Δs 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) 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/ T.-A. Shibata, NuFact04 15

16 Precision measurements of asymmetry A 1, p x A 1 x, z= σ x σ x σ x σ x T.-A. Shibata, NuFact04 16

17 Hadron identification at 2-15 GeV/c with RICH T.-A. Shibata, NuFact04 17

18 Detector HERA Polarized Internal gas targets (H, D, 3 He) 27.6 GeV e Target T.-A. Shibata, NuFact04 18

19 HERMES Spectrometer T.-A. Shibata, NuFact04 19

20 A h 1, d x Asymmetry, Hadron detection Deuterium Target π π K K A 1 increases with x K A 1, d K A 1, d x T.-A. Shibata, NuFact04 20

21 Systematic Errors: Light Error Bar Fragmentation Models Dark Error Bar - Asymmetries Positive Negative Nearly Zero Δu x Δd x Δ q x x bin by bin analysis. SU(3) Symmetry not assumed. T.-A. Shibata, NuFact04 21

22 Strangeness Spin Δs x Strangeness Helicity Distribution 0.023x0.3, x integral of Δs x, Δs x Δs x or Integral: 0.03 ±0.03 stat. ±0.01 syst. in the measured region T.-A. Shibata, NuFact04 22

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 23

24 What is new with Neutrino Factories hydrogen and deuteron targets in counter experiments (non-bubble chamber) polarized hydrogen and deuteron targets E ν up to 30 GeV, ν and ν 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 ν ν T.-A. Shibata, NuFact04 24

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 Δq x Neutrino reaction is a promising approach to determine strange quark contributions to the nucleon spin G s A. At Neutrino Factories neutrino reactions on polarized targets are expected. T.-A. Shibata, NuFact04 25