Search

Space Star (SS) anomaly in nd breakup cross section was first reported in 1989 at E n = 13 MeV (Strate et al. in Nucl Phys A 501:51, 1989), but its origin has not been found yet. In order to obtain suggestions for its origin, we made systematic measurements of pd breakup cross section around SS. In SS configuration, three outgoing nucleons form an equilateral triangle and the triangle is perpendicular to the beam axis. Necessity of the equilateral and perpendicular conditions of SS anomaly was investigated by systematic experiments. Also energy dependence of SS anomaly is being studied at energies from E p = 7.5 to 13 MeV.

Space Star anomaly in Nd breakup reaction below 20 MeV is well-known. Also, Quasi-Free Scattering (QFS) anomaly in Nd breakup reaction below 40 MeV has been reported from several experiments. Origin(s) of QFS anomaly has not been known, similarly to origin(s) of SS anomaly. We have been making a systematic measurement on pp-QFS cross section, previously at Ep = 9.5 MeV and 13 MeV and recently at 7.5 and 19 MeV. We used an unpolarized p-beam to correctly measure only cross section. Our data agreed well with pd calculation by A. Deltuva. So far, no pp-QFS anomaly has been found in our experiments.

Cross sections of pd breakup reaction at E p = 250 MeV were measured systematically in single-proton detection and in two-proton coincidence detection. Measured cross section is up to two times higher than calculated ones. The enhancement of breakup cross section is similar to reported enhancement in pd elastic scattering cross section. Origins of this enhancement are discussed.

We measured pd breakup cross section at E d = 19 MeV (E/A = 9.5 MeV) at Star configuration at 120° ≤ inclination angle α ≤ 180°, i.e. apart from Space Star configuration (α = 90°), and found that pd Star cross section at 120° ≤ α ≤ 180° agree with pd calculation, contrary to Koln data. By our systematic experiments on Star configurations so far and recent reliable pd calculations, existence of Space Star anomaly has been established in pd breakup at E/A = 9.5 and 13 MeV. Also it has been confirmed that no anomaly exist at Star configurations apart from Space Star.

Cross section and analyzing power Ay of [Formula: see text] reaction at [Formula: see text] were measured and large disagreements with 3N calculations were found especially at forward angles. Effects of 2π3NF are too small to explain the discrepancy. To microscopically investigate the discrepancy, a 2 H (p, pp)n experiment is planned.

We made again an experiment of pd radiative capture at [Formula: see text], and obtained Axx, Ayy and Azz (= -Axx - Ayy) data using a newly-developed data-analysis method of high detection efficiency. Re-analysis of previous data on Axx and Ayy was also made using a new method. All the new and previous data at 197 MeV agree to each other, and Axx anomaly has been confirmed.

At Ed = 26 MeV , H (d,pp)n cross section was measured at 4 angle pairs corresponding to off-plane star and compared with recent pd calculations. A rotary foil target was developed for this experiment. The present data and previous data revealed dependence of the star anomaly on the star-inclination angle α. The angular dependence at Ep = 13 MeV differs much with that at 9.5 MeV.

Inclusive measurements of the D(p, p)pn reaction were made at incident proton energies of 248 MeV and 13 MeV, to investigate the global feature of the pd breakup reaction at intermediate and low energies. At 248 MeV, the cross section and analyzing power A y were measured at four angles from 7° to 20°. The data largely disagree with Faddeev calculations even if 2π-exchange three-nucleon force (2π3NF) or Δ-isobar is included, and the disagreement increases at forward angles. At 13 MeV, the cross section was measured at eight angles from 10° to 70°. The data are well reproduced by a recent pd Faddeev calculation, and the effects of Δ-isobar at 13 MeV are very small.

We made three kinds of measurements at E p = 13 MeV ; i) D ( p , p p ) n experiment at pp FSI, ii) D ( p , p ) p n experiment at θ p = 10 ° – 60 ° , and iii) D ( p , p p ) n experiment at many angle pairs around the space star. For an easy estimate of Coulomb effects in pd breakup reaction, we proposed Watson- Migdal & Faddeev calculation which was found to give nearly the same results as the pd calculation by Deltuva et al. . Cross sections of i) and ii) are well reproduced by the pd calculation, however, 10-15% discrepancy has been found between the cross section of iii) and the calculation.

Differential cross sections of isoscalar and isovector spin-M1 (0(+)→1(+)) transitions are measured using high-energy-resolution proton inelastic scattering at E(p)=295 MeV on (24)Mg, (28)Si, (32)S, and (36)Ar at 0°-14°. The squared spin-M1 nuclear transition matrix elements are deduced from the measured differential cross sections by applying empirically determined unit cross sections based on the assumption of isospin symmetry. The ratios of the squared nuclear matrix elements accumulated up to E(x)=16 MeV compared to a shell-model prediction are 1.01(9) for isoscalar and 0.61(6) for isovector spin-M1 transitions, respectively. Thus, no quenching is observed for isoscalar spin-M1 transitions, while the matrix elements for isovector spin-M1 transitions are quenched by an amount comparable with the analogous Gamow-Teller transitions on those target nuclei.

Differential cross sections of isoscalar and isovector spin-M1 (0(+)→1(+)) transitions are measured using high-energy-resolution proton inelastic scattering at E(p)=295 MeV on (24)Mg, (28)Si, (32)S, and (36)Ar at 0°-14°. The squared spin-M1 nuclear transition matrix elements are deduced from the measured differential cross sections by applying empirically determined unit cross sections based on the assumption of isospin symmetry. The ratios of the squared nuclear matrix elements accumulated up to E(x)=16 MeV compared to a shell-model prediction are 1.01(9) for isoscalar and 0.61(6) for isovector spin-M1 transitions, respectively. Thus, no quenching is observed for isoscalar spin-M1 transitions, while the matrix elements for isovector spin-M1 transitions are quenched by an amount comparable with the analogous Gamow-Teller transitions on those target nuclei.

In our previous inclusive experiment on 2H(p, p)pn at 247 MeV, the measured cross section at forward angles is about twice larger than 3N calculation with ππ 3NF. Therefore, we have made an exclusive experiment on 2H(p, p1 p2)n at the same energy. The preliminary data suggest that the cross section was enhanced at forward angle of θ1 and θ2.

Cross section of pd breakup at Star configuration (equilateral triangle) was systematically measured at E = 9.5 and 13 MeV/A with varying an angle α between the Star plane and the beam axis. At 13 MeV/A, Star anomaly appears only around Space Star (α = 90°) configuration. At 9.5 MeV/A, same feature was found in our experimental data at α = 0°−105°, but large difference of about −25% at α = 124°−180° was reported by Koln group.

Systematic measurement of the D(p, pp)n cross section at Ep = 13 MeV at star configurations at various inclined angle α is in progress at Kyushu University tandem accelerator laboratory (KUTL). The measured cross section at space star (α = 90°) is about 12% below the recent pd calculation. The next measurement is being made at 0° < α < 90° to see if the large anomaly of about 25% found by the Koln group (2006) at backward α exists also at forward α.

In our previous measurement of pd radiative capture at Ed = 137 and 196 MeV, we found an interesting fact that the measured tensor analyzing powers show the relation Axx ≈ Ayy, although calculated Axx and Ayy are apparently different, Axx ≠ Ayy. The measured Ayy agrees fairly well with the 3N calculations, and the measured Axx largely disagrees with calculated Axx. Similar experiments on pd capture have been made at KVI at nearly the same energies of 130–180 MeV. The KVI data also support Axx ≈ Ayy relation, but absolute values of Axx and Ayy at KVI are about half of RCNP data. Therefore, we made a new experiment of pd capture at Ed = 196 MeV. Azz was measured in three different ways, and data analysis is in progress. Preliminary data seem to support our previous data.

Extraction of anti-analog giant dipole resonance and neutron skin thickness for 208Pb Jumpei Yasuda1,∗, Tomotsugu Wakasa1, Midori Okamoto1, Masanori Dozono1, Kichiji Hatanaka3, Munetake Ichimura2, Sho Kuroita1, Yukie Maeda4, Tetsuo Noro1, Yasuhiro Sakemi5, Masaki Sasano2, and Kentaro Yako6 1Department of Physics, Kyushu University, Higashi, Fukuoka 812-8581, Japan 2RIKEN Nishina Center for Accelerator-Based Science, The Institute of Physical and Chemical Research, Wako, Saitama 351-0198, Japan 3Research Center for Nuclear Physics, Osaka University, Ibaraki, Osaka 567-0047, Japan 4Department of Applied Physics, University of Miyazaki, Miyazaki, Miyazaki 889-2192, Japan 5Cyclotron and Radioisotope Center, Tohoku University, Sendai, Miyagi 980-8578, Japan 6Center for Nuclear Study, University of Tokyo, Bunkyo, Tokyo 113-0033, Japan ∗E-mail: yasuda@phys.kyushu-u.ac.jp

We report measurements of cross sections and analyzing powers for reaction angles of θlab = 0.0°-10.0° and complete sets of polarization transfer observables and induced polarizations at θlab = 0.0°-7.0° for the 208Pb(p,n) reaction at a bombarding energy of Tp = 296 MeV. A multipole decomposition technique was applied to the data to extract the spin-dipole (SD) components from the continuum. The polarization observables were also used, for the first time, to separate the SD components into different spin-parity transfer (ΔJπ = 0−, 1−, and 2−) contributions. The SD strength distributions were clearly dependent on ΔJπ, which is reasonably reproduced by Hartree-Fock (HF) plus random phase approximation (RPA) calculations that include the Skyrme interaction with tensor components [C. L. Bai et al., Phys. Rev. C 83, 054316 (2011)].

We report measurements of cross sections and analyzing powers for reaction angles of ${\ensuremath{\theta}}_{\mathrm{lab}}={0.0}^{\ensuremath{\circ}}$--${10.0}^{\ensuremath{\circ}}$ and complete sets of polarization transfer observables and induced polarizations at ${\ensuremath{\theta}}_{\mathrm{lab}}={0.0}^{\ensuremath{\circ}}$--${7.0}^{\ensuremath{\circ}}$ for the ${}^{208}\mathrm{Pb}(\stackrel{P\vec}{p},\stackrel{P\vec}{n})$ reaction at a bombarding energy of ${T}_{p}=296$ MeV. A multipole decomposition technique was applied to the data to extract the Gamow-Teller (GT) and spin-dipole (SD) components from the continuum. The polarization observables were also used, for the first time, to separate the SD components into different spin-parity transfer ($\ensuremath{\Delta}{J}^{\ensuremath{\pi}}={0}^{\ensuremath{-}}$, ${1}^{\ensuremath{-}}$, and ${2}^{\ensuremath{-}}$) contributions. A significant strength with $\ensuremath{\Delta}{J}^{\ensuremath{\pi}}={1}^{+}$ is identified in the continuum beyond the GT giant resonance, which is due to configuration mixing effects and the isovector spin monopole (IVSM) contribution. The SD strength distributions were clearly dependent on $\ensuremath{\Delta}{J}^{\ensuremath{\pi}}$, which is reasonably reproduced by Hartree-Fock (HF) plus random phase approximation (RPA) calculations that include the Skyrme interaction with tensor components [Phys. Rev. C 83, 054316 (2011)].

In our previous inclusive experiment on pd breakup at Ep = 247 MeV, we found experimental cross section is about twice larger than 3N calculation with ππ 3NF at forward angle. Therefore we made exclusive measurement of 2 H(p, p1 p2)n cross section at the same 247 MeV. Preliminary data indicate that the cross section enhancement appears at forward angles of θ 1 and θ 2. We made also inclusive experiment again and confirmed the previous data.

The cross sections and analyzing powers for $(p,n)$ reactions on $^{3}\mathrm{He}$ and $^{4}\mathrm{He}$ have been measured at a bombarding energy of ${T}_{p}=346$ MeV and reaction angles of ${\ensuremath{\theta}}_{\mathrm{lab}}=9.{4}^{\ifmmode^\circ\else\textdegree\fi{}}\text{\ensuremath{-}}{27}^{\ifmmode^\circ\else\textdegree\fi{}}$. The energy transfer spectra for ${}^{3}\mathrm{He}(p,n)$ at large ${\ensuremath{\theta}}_{\mathrm{lab}}$ ($\ensuremath{\geqslant}{16}^{\ifmmode^\circ\else\textdegree\fi{}}$) are dominated by quasielastic contributions and can be reasonably reproduced by plane-wave impulse approximation (PWIA) calculations for quasielastic scattering. By contrast, the known $L=1$ resonances in $^{4}\mathrm{Li}$ are clearly observed near the threshold in the ${}^{4}\mathrm{He}(p,n)$ spectra. Because these contributions are remarkable at small angles, the energy spectra are significantly different from those expected for quasielastic scattering. The data are compared with the PWIA calculations, and it is found that the quasielastic contributions are dominant at large ${\ensuremath{\theta}}_{\mathrm{lab}}$ ($\ensuremath{\geqslant}{22}^{\ifmmode^\circ\else\textdegree\fi{}}$). The nuclear correlation effects on the quasielastic peak for ${}^{4}\mathrm{He}(p,n)$ are also discussed.

We report measurements of the cross-section and a complete set of polarization transfer coefficients for the ${}^{3}\mathrm{He}(p,n)$ reaction at a bombarding energy ${T}_{p}=346$ MeV and a reaction angle ${\ensuremath{\theta}}_{\mathrm{lab}}={0}^{\ifmmode^\circ\else\textdegree\fi{}}$. The data are compared with the corresponding free nucleon-nucleon values on the basis of the predominance of quasielastic scattering processes. Significant discrepancies have been observed in the polarization transfer ${D}_{\mathit{LL}}({0}^{\ifmmode^\circ\else\textdegree\fi{}})$, which are presumably the result of the three-proton $T=3/2$ resonance. The spin-parity of the resonance is estimated to be $1/{2}^{\ensuremath{-}}$, and the distribution is consistent with previous results obtained for the same reaction at ${T}_{p}=48.8$ MeV.

Inclusive experiments for D(p,p)pn breakup were performed at incident proton energies of 247 MeV and 13 MeV. At 247 MeV, the cross sections and analyzing power Ay measured at angles from 7 ° to 20 ° largely disagree with calculations even if a 2π‐exchange three‐nucleon force (2π3NF) effects are included, and the disagreement increases at forward angles. At 13 MeV, cross section measured at angles from 10 ° to 70 ° agrees well with pd calculation and 2π3NF effects are small. The large disagreement in pd breakup at 247 MeV may have some relationship with disagreements in pd scattering at 250 MeV.

Space star anomalies in nd and pd breakup reactions are peculiar phenomena, different from other discrepancies in the 3N systems. Recently progress on the pd star anomaly has been made both in experiment and in theoretical calculations. We have started systematic experiments on the pd star, and some preliminary data are presented.

We carried out the experiment of the 1H(d,pp)n reactions at Ed = 26 MeV at RCNP and that of the 2H(p, pp)n reactions at Ep = 13 MeV at KUTL. The data of the differential cross sections was measured and compared with the Faddeev calculations based on the various nucleon-nucleon (NN) interactions with/without the Coulomb interactions or the three-nucleon force (3NF). The data is overestimated by the theoretical predictions by less than 10 %. This result is very different from the data at E=9.5 MeV reported from Koln, which showed the large discrepancies between the data and the Faddeev calculations.

Space Star (SS) anomaly in Nd breakup cross section is well known. SS anomaly has large charge asymmetry; exp eriment is larger than calculation at nd SS and exp eriment is smaller than calculation at pd SS. There are also rep orts on anomaly in quasi-free scattering (QFS) cross section in Nd breakup reaction. At nd QFS, exp erimental cross section was found to be larger than calculation. On the contrary, pd QFS cross section measured by Köln group is smaller than pd calculation. We measured QFS cross section in pd breakup reaction, and compared the data with recent pd calculations to see angular dep endence of QFS anomaly.