S. Sakaguchi

Analyzing power in elastic scattering of 6He from a polarized proton target at 71 MeV/nucleon

The vector analyzing power has been measured for the elastic scattering of neutron-rich {sup 6}He from polarized protons at 71 MeV/nucleon making use of a newly constructed solid polarized proton target operated in a low magnetic field and at high temperature. Two approaches based on local one-body potentials were applied to investigate the spin-orbit interaction between a proton and a {sup 6}He nucleus. An optical model analysis revealed that the spin-orbit potential for {sup 6}He is characterized by a shallow and long-ranged shape compared with the global systematics of stable nuclei. A semimicroscopic analysis with an {alpha}+n+n cluster folding model suggests that the interaction between a proton and the {alpha} core is essentially important in describing the p+{sup 6}He elastic scattering. The data are also compared with fully microscopic analyses using nonlocal optical potentials based on nucleon-nucleon g matrices.

Candidate Resonant Tetraneutron State Populated by the He 4 (He 8, Be 8) Reaction

A candidate resonant tetraneutron state is found in the missing-mass spectrum obtained in the double-charge-exchange reaction ^{4}He(^{8}He,^{8}Be) at 186  MeV/u. The energy of the state is 0.83±0.65(stat)±1.25(syst)  MeV above the threshold of four-neutron decay with a significance level of 4.9σ. Utilizing the large positive Q value of the (^{8}He,^{8}Be) reaction, an almost recoilless condition of the four-neutron system was achieved so as to obtain a weakly interacting four-neutron system efficiently.

Three nucleon force effects in intermediate-energy deuteron analyzing powers for dp elastic scattering

A complete high precision set of deuteron analyzing powers for elastic deuteron-proton (dp) scattering at 250 MeV/nucleon (MeV/N) has been measured. The new data are presented together with data from previous measurements at 70, 100, 135 and 200 MeV/N. They are compared with the results of three-nucleon (3N) Faddeev calculations based on modern nucleon-nucleon (NN) potentials alone or combined with two models of three nucleon forces (3NFs): the Tucson-Melbourne 99 (TM99) and Urbana IX. At 250 MeV/N large discrepancies between pure NN models and data, which are not resolved by including 3NFs, were found at c.m. backward angles of {theta}{sub c.m.} > or approx. 120 deg. for almost all the deuteron analyzing powers. These discrepancies are quite similar to those found for the cross section at the same energy. We found small relativistic effects that cannot resolve the discrepancies with the data indicating that other, short-ranged 3NFs are required to obtain a proper description of the data.

Analyzing power for proton elastic scattering from the neutron-rich He6 nucleus

Vector analyzing power for the proton-{sup 6}He elastic scattering at 71 MeV/nucleon has been measured for the first time, with a newly developed polarized proton solid target, which works at a low magnetic field of 0.09 T. The results are found to be incompatible with a t-matrix folding model prediction. Comparisons of the data with g-matrix folding analyses clearly show that the vector analyzing power is sensitive to the nuclear structure model used in the reaction analysis. The {alpha}-core distribution in {sup 6}He is suggested to be a possible key for understanding the nuclear structure sensitivity.

Precision measurement of vector and tensor analyzing powers in elastic deuteron-proton scattering

Abstract.High-precision vector and tensor analyzing powers of elastic deuteron-proton ( d + p) scattering have been measured at intermediate energies to investigate effects of three-nucleon forces. Angular distributions in the range of 70°-120° in the center-of mass frame for incident-deuteron energies Edlab = 130 and 180 MeV were obtained using the RIKEN facility. The beam polarization was unambiguously determined by measuring the ^12C (d, α)^10B(2+) reaction at 0°. Results of the measurements are compared with state-of-the-art three-nucleon calculations. The present modeling of nucleon-nucleon forces and its extension to the three-nucleon system is not sufficient to describe the high-precision data consistently and requires, therefore, further investigation.

Proposal on the measurements of d–p elastic scattering analyzing powers at 0.3–2.0 GeV at the Internal Target Station of the Nuclotron

A new high-energy beam polarimeter is proposed for Nuclotron, which uses the Internal Target Station (ITS). This polarimeter based on a measurement of asymmetry for the d–p elastic scattering will allow one to measure simultaneously both vector and tensor components of deuteron beam polarization. For this purpose an analyzing powers measurement for the d–p elastic scattering at energies T d = 0.88–2 GeV is proposed. The precise measurements of the deuteron analyzing powers over the energy range T d = 300–2000 MeV can give an irreplaceable clue to the study of the spin dependence of three nucleon forces.

Measurement of the vector and tensor analyzing powers for dp-elastic scattering at 880 MeV

The vectorAy and tensor analyzing powers Ayy andAxx for dpelastic scattering were measured at T lab d = 880 MeV over the c.m. angular range from 60 ◦ to 140 at the JINR Nuclotron. The data are compared with prediction s of different theoretical models based on the use of nucleon-nucleon forces only. The observed disc repancies of the measured analyzing powers from the calcula tions require the consideration of additional mechanisms. PACS: 24.70.+s, 25.10. +s, 21.45. +v

Shallow and diffuse spin-orbit potential for proton elastic scattering from neutron-rich helium isotopes at 71 MeV/nucleon

Vector analyzing powers for proton elastic scattering from 8He at 71 MeV/nucleon have been measured using a solid polarized proton target operated in a low magnetic field of 0.1 T. The spin-orbit potential obtained from a phenomenological optical model analysis is found to be significantly shallower and more diffuse than the global systematics of stable nuclei, which is an indication that the spin-orbit potential is modified for scattering involving neutron-rich nuclei. A close similarity between the matter radius and the root-mean-square radius of the spin-orbit potential is also identified.

The 270 MeV deuteron beam polarimeter at the Nuclotron Internal Target Station

A deuteron beam polarimeter has been constructed at the Internal Target Station at the Nuclotron of JINR. The polarimeter is based on spin-asymmetry measurements in the d − p elastic scattering at large angles and the deuteron kinetic energy of 270 MeV. It allows to measure vector and tensor components of the deuteron beam polarization simultaneously.

Investigation of the angular dependence of the analyzing powers in the deuteron-proton elastic scattering at the nuclotron

New polarimeter based on the asymmetry measurement in dp-elastic scattering has been constructed at internal target at Nuclotron (JINR). The result on the deuteron analyzing powers Ay, Ayy and Axx in the deuteron-proton (dp) elastic scattering at the energies of 880 and 2000 MeV are presented. They are compared with different theoretical approaches.