1. Shibata lab. Ogoshi Shun P. Amaudruz et al., New Muon Collaboration Phys. Rev. Lett. 66 (1991) 2712 [Contents] 1.Introduction 2.Deep inelastic scattering 3.Experiment 4.Results 5.Summary 1

2. u d u q 1. Introduction Valence Quarks and Sea Quarks in the Proton 2 Are sea quarks flavor symmetric or asymmetric ? proton gluon

3. 2. Deep inelastic scattering Lepton Beam (electron, muon) p’p’ p 3 P : Bjorken scaling variable is a Lorentz invariant mass, total hadron mass after scattering. Elastic Scattering ( ) Inelastic Scattering ( )

4. 4 Structure Function( 構造関数 ) Structure Function in the parton model Structure Function in the proton Structure Function in the neutron

5. 5 Isospin Symmetry between proton and neutron Gottfried Sum If sea quarks are flavor symmetric,

6. 66 3. Experiment NMC at CERN ( Deep inelastic scattering ) Measured From the world data (1) (2) (3) 90 or 280 GeV

7. 7 4. Results Fig.1 7 Fig.2 Measured x region

8. 8 Sea quarks are flavor–asymmetric. Extrapolation to There is more than in the proton.

9. 9 5. Summary 9 ・ Gottfried sum is under assumption of parton model and isospin symmetry between a proton and a neutron. ・ The value for the Gottfried sum estimated in this experiment is ・ A flavor asymmetric sea is a likely explanation. There is more than in the proton. ・ The experimental results shows ・ Extrapolation to x=0(x=1)

10. 以下、補足スライド 10

11. Flavor-asymmetric sea 11 There is more than in the proton. Proton u, u, d Neutron u, d, d