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4 He( p,2p ) reactions for studing in-medium NN interactions

4 He( p,2p ) reactions for studing in-medium NN interactions. S. Asaji Department of Physics, Kyushu University Collaborators T. Noro, K. Fujita 1 , Y. Hagihara, K. Hatanaka 1 , T. Ishida, M. Ito 1 , S. Kishi 2 , Y. Nagasue, M. Nakamura 2 ,

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4 He( p,2p ) reactions for studing in-medium NN interactions

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  1. 4He(p,2p) reactions for studing in-medium NN interactions S. Asaji Department of Physics, Kyushu University Collaborators T. Noro, K. Fujita1, Y. Hagihara, K. Hatanaka1, T. Ishida, M. Ito1 , S. Kishi2, Y. Nagasue, M. Nakamura2, K. Sagara, H. Sakaguchi2, Y. Sakemi1, Y. Shimizu1, H. Takeda3, Y. Tameshige1,S.Terashima2, M. Uchida2, T. Wakasa, Y. Yasuda2, H. P.Yoshida1, M.Yosoi2, and T. Yonemura Department of Physics, Kyushu University Research Center for Nuclear Physics, Osaka University1 Department of Physics, Kyoto University2 RIKEN3

  2. Introduction NN scattering in free space • Our interest is to study the NN interaction in the nuclear field. • A direct way is by examining the difference between the NN interactions in free space and in nuclear medium. • (p,2p) is a NN scattering which takes place in nuclear medium. NN scattering in nuclear medium

  3. Purpose of 4He(p,2p) measurement (1)Analyzing Power (Ay) • Ay reduced monotonically depending on effective mean density, and also on Q-value. • Determine the key parameter of Ay reduction by measuring Ay of 4He nucleus. Kinematics: θlab=25.5° Precoil=0MeV/c 4He (1s1/2) 4He (1s1/2)

  4. Distorted Wave Impulse Approximation (DWIA) χi(r): distorted waves of incident particles (i=0) outgoing particles (i=1,2) φ: bound wave function t : t-matrix for NN scattering σ: cross section

  5. Purpose of 4He(p,2p) measurement (2)Cross Section • A (p,2p) reaction is effective to study nuclear structure. • There are difficulties specific to studies of light nuclei such as recoil effect. • To examine how accurately we can deduce the momentum distribution of protons in the light nucleus. At Riken, study of unstable nuclei by (p,2p) reaction in inverse kinematics is schemed.

  6. Experiment • Facility • RCNP • Beam • 392MeV polarized proton beam • Two-armed spectrometer • Cooled Gas Target System

  7. Cooled Gas Target System Add drive unit Cryogenic Refrigerator Pressure Gauge & Transducer proton Aluminum Cover 4He Gas Reservoir Target Monitor Bearing p+αelastic scattering • Cooled down target to increase target density and to reduce background. Beam Heater Window Foil : Aramid 12.5μm Target Cell 4He Aramid Foil Target Cooled 4He Gas

  8. Energy Spectrum log scale log scale Pr=0MeV/c Pr=250MeV/c 4He(p,2p)3H 103 102 10 p+4He→p+p+n+d • Yield increased about 30 times higher than at room temperature by cooling the target. 10 Background from Aramid Foil Background from Aramid Foil Separation Energy Separation Energy

  9. Result of Ay • Ay is plotted as a function of the effective mean density and as a function of the Q-value. • Ay is better aligned with the Q-value.

  10. Additional Measurement on Other Light Nuclei 2D,3He,4He‥Gas 6Li,7Li, 9Be,10B,11B,16O,19F‥Solid • In order to examine systematics, we also measured Ay for many light nuclei.

  11. Ay of other nuclei ( ) ( ) • The ratios of observed Ay to DWIA calculations are plotted as a function of effective mean density and as a function of the Q-value. • The ratios are better aligned with the Q-value.

  12. off-energy-shell effect Calculated by H. Kamada (Kyushu Institute of technology), private communication • Non relativistic Ay calculations of p-p scattering including off-energy-shell effect. • The calculations show that off-energy-shell effect is smaller than a few percent.

  13. Cross section Measurement Kinematics • In order to determine the reliability of DWIA calculations, measurements have been performed for various kinds of kinematics.

  14. Result of Cross Section 1. θ1=const. 2. P0 // Pr 3. θ1,θ2=const. • The data for all kinds of kinematical conditions are consistent within 10% in FWHM.

  15. Result of Ay 1. θ1=const. 2. P0 // Pr 3. θ1,θ2=const. 2. 1. 3.

  16. Summary and Conclusion • Measurement • We measured cross section and Ay for the 4He(p,2p) reaction with various kinematics. • Cooled down target to increase target density and to reduce background. As a result, yield increased about 30 times higher than at room temperature. • Ay • Ay was reduced by 30% compared with DWIA calculations. (⇔50% reduction is expected from density dependence.)  Additional measurement for ten target nuclei • The ratio, Ay(exp)/Ay(DWIA), are better aligned with the Q-value. It implies that the Ay-reduction is caused by off-energy effect. but the non-relativistic off-energy-shell amplitude gives no reduction. • Cross section • The momentum width of bound wave function can be deduced within 10% accuracy by comparing with simple DWIA calculations. • Theoretical improvement is required for further study.

  17. Cross Section with various kinds of wave function • The data is also consistent within 10% in FWHM with various kinds of wave functions made in previous experimental and theoretical studies.

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