Search

The giant resonance regions of ${}_{}{}^{144,154}{}_{}{}^{}\mathrm{Sm}$, ${}_{}{}^{159}{}_{}{}^{}\mathrm{Tb}$, ${}_{}{}^{165}{}_{}{}^{}\mathrm{Ho}$, ${}_{}{}^{169}{}_{}{}^{}\mathrm{Tm}$, and ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ have been investigated by inelastic scattering of 80-MeV ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ ions. The shapes of the resonance structure were observed to be quite similar for each target studied here. Comparison of the experimental cross sections with energy-weighted sum rules implies that the observed structure is probably comprised of more than just an isoscalar $E2\mathrm{}$ excitation.

NUCLEAR REACTIONS ${}_{}{}^{144,154}{}_{}{}^{}\mathrm{Sm}$ ${}_{}{}^{159}{}_{}{}^{}\mathrm{Tb}$, ${}_{}{}^{165}{}_{}{}^{}\mathrm{Ho}$, ${}_{}{}^{169}{}_{}{}^{}\mathrm{Tm}$, and ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$(${}_{}{}^3{}_{}{}^{}\mathrm{He}$, ${}_{}{}^3{}_{}{}^{}\mathrm{He}$'), $E_{{}_{}{}^3{}_{}{}^{}\mathrm{He}}\approx 80$ MeV, $E_x=0-40\mathrm{}$ MeV; measured $\sigma (E_x, \theta )$; discuss giant resonances.

Distorted wave Born approximation calculations of differential cross sections for inelastic excitation of the giant dipole resonance with helium projectiles through the Coulomb field are presented. Competition with the nuclear excitation of the giant monopole resonance is discussed.

NUCLEAR REACTIONS ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$($\alpha$,${\alpha }^{\prime }$); $E_{\alpha }=96, 172.5, 480$ MeV; calculated $\sigma \left(\theta \right)$, giant resonances, Coulomb excitation.

The ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$${+}^{12}$C reaction at an incident energy E/A of 38 MeV has been investigated experimentally. Singles energy spectra and the angular distribution of reaction residues having 3≤Z≤9 were measured. A small low-energy cutoff in the spectra combined with measurements at large angles (up to 70°) allowed a study of the systematics involved in the production of low-energy reaction residues. A target-related origin is proposed for these yields. Cascade model calculations are presented which support this hypothesis.

A precision measurement by the Alpha Magnetic Spectrometer on the International Space Station of the positron fraction in primary cosmic rays in the energy range from 0.5 to 350 GeV based on $6.8\times {10}^6$ positron and electron events is presented. The very accurate data show that the positron fraction is steadily increasing from 10 to $\sim 250\mathrm{GeV}$, but, from 20 to 250 GeV, the slope decreases by an order of magnitude. The positron fraction spectrum shows no fine structure, and the positron to electron ratio shows no observable anisotropy. Together, these features show the existence of new physical phenomena.

The atmospheric muon and neutrino flux have been simulated using the same approach which successfully accounted for the recent secondary proton, electron, and positron flux measurements in orbit by the AMS experiment. For the muon flux, good agreement is obtained with the CAPRICE and HEAT data for altitudes ranging from sea level up to about 38 km. The general features of the calculated atmospheric neutrino flux are reported and discussed. The flux obtained at the Super-Kamiokande experiment location are reported and compared with other calculations. For low neutrino energies the flux obtained is significantly smaller than that used in the data analysis of underground experiment. The simulation results for the SOUDAN experiment site are also reported.

We have measured the production of strange baryons and antibaryons in 340-GeV/c ${\Sigma }^{-}+\mathrm{C}$ and 260-GeV/c $n+\mathrm{C}$ interactions. The single $x_F$ distributions show the expected leading particle effect, and the single $p_t^2$ distributions show a distinct nonthermal behavior. The $x_F$ distributions of Λ-Λ pairs indicate two different phase space distributions for the two coincident baryons. On the other hand two $\overline{\Lambda }\mathrm{’}\mathrm{s}$ show identical distributions. Momentum conservation during the formation process may represent a significant source for the observed behavior.

Inelastic scattering of 163- and 241-MeV positive pions by ${}_{}{}^{\mathrm{nat}}{}_{}{}^{}\mathrm{Ca}$ has been studied with special attention paid to the giant-resonance region. Pronounced giant resonance structures are observed at both incident energies. The analysis indicates a strong excitation of the giant quadrupole resonance at 18.2 MeV ($\Gamma \sim 3-3.5$ MeV).

Neutron hole states were investigated in the ${}_{}{}^{207,206,205}{}_{}{}^{}\mathrm{Pb}$ isotopes up to 25 MeV excitation energy using the (${}_{}{}^3{}_{}{}^{}\mathrm{He}$,$\alpha$) reaction at 100 MeV incident energy with 100 keV energy resolution. Above the well-matched low-lying levels corresponding to high angular momentum transfers, new peaks are identified. In addition, three gross structures, riding on a continuous background, are observed in each of the three isotopes, with some fine structures showing up to 10 MeV excitation energy. For ${}_{}{}^{207}{}_{}{}^{}\mathrm{Pb}$, angular distributions have been obtained for the low-lying levels as well as for the deeply bound hole states. The data have been analyzed with distorted-wave Born-approximation calculations and spectroscopic factors extracted. It has been found that the low-lying levels do not exhaust the $1i\frac{13}{2}$ and $1h\frac{9}{2}$ neutron hole strengths. Corrections for exact finite-range effects, form factor shapes, and indirect pickup contributions have been calculated, and modify significantly the $2f\frac{7}{2}$ spectroscopic measured strength but not the $1i\frac{13}{2}$ and the $1h\frac{9}{2}$ ones. Most of the $1i\frac{13}{2}$ and $1h\frac{9}{2}$ missing strengths are found in the "bump" located at about 5 MeV excitation energy. The highly fragmented bump observed at about 8 MeV excitation energy is shown to arise from $1h\frac{11}{2}$ neutron pickup exhausting 45% of the sum-rule limit. Finally, the very smooth structure extending to 21 MeV excitation energy is tentatively attributed to $1g\frac{7}{2}+1g\frac{9}{2}$ neutron holes with 80% of the total strength. In ${}_{}{}^{207}{}_{}{}^{}\mathrm{Pb}$, the four first isobaric analog states are observed as narrow structures around 20 MeV excitation energy.

NUCLEAR REACTIONS ${}_{}{}^{208,207,206}{}_{}{}^{}\mathrm{Pb}$ (${}_{}{}^3{}_{}{}^{}\mathrm{He}$, $\alpha$), $E=101.75\mathrm{}$ MeV; measured $\sigma (E_{\alpha }, \theta )$, ${}_{}{}^{207,206,205}{}_{}{}^{}\mathrm{Pb}$ deduced levels, $\mathrm{Ex}$, $l$, $J$, $\pi$, $C^{2}S$; ${}_{}{}^{207,206,205}{}_{}{}^{}\mathrm{Pb}$ inner shell spectroscopic factors: enriched targets, magnetic spectrometer.

The isoscalar giant resonance region has been investigated in ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$, ${}_{}{}^{92}{}_{}{}^{}\mathrm{Mo}$, and ${}_{}{}^{120}{}_{}{}^{}\mathrm{Sn}$ nuclei by inelastic scattering of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ particles at small angles where the quadrupole and monopole states can be distinguished through their angular distributions. A monopole resonance is observed in the three nuclei, exhausting, respectively, 23%, 85%, and 110% of the E0 energy weighted sum rule.

Inelastic scattering spectra have been measured with 245 MeV incident energy ${}_{}{}^9{}_{}{}^{}\mathrm{Be}$ ions on a ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ target. They show large excitation of the ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ giant quadrupole resonance. Distorted-wave Born-approximation calculations are reported and compared with the data.

NUCLEAR REACTIONS ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$(${}_{}{}^9{}_{}{}^{}\mathrm{Be}$, ${}_{}{}^9{}_{}{}^{}\mathrm{Be}\prime$) $E=245\mathrm{}$ MeV; measured giant quadrupole resonance $\sigma \left(\theta \right)$; DWBA analysis.

We report on a high-statistics search for the $\Theta (1540){}^{+}$ resonance in ${\Sigma }^{-}$-nucleus collisions at 340 GeV/c. No evidence for this resonance was found in our data sample which contains 13 million $K_s^0\to {\pi }^{+}{\pi }^{-}$ decays above background. For the decay channel ${\Theta }^{+}\to K_s^{0}p$ and the kinematic range $x_F>$ 0.05, we find the production cross section to be $\mathrm{BR}({\Theta }^{+}\to K_s^{0}p){\sigma }_0<1.8$ μb per nucleon at 99% C.L.

The geometrical interpretation of high-energy hadronic cross sections is discussed. Evidence is provided, by means of a simple model, that hadron-hadron total cross sections are not governed by geometry only, and that the interaction dynamics is flavor dependent and determines to a large extent the cross section of hadronic systems. The same conclusion is reached in a numerical approach of the problem.

The dipole strength has been measured in ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ between 22- and 27-MeV excitation energy by inelastic scattering of 45- and 155-MeV protons. The dipole cross section is compared to the results of isovector-collective-model, distorted-wave Born-approximation calculations and to photonuclear experimental results.

The elastic scattering and one-proton transfer reactions induced by 312.6-MeV ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ ions on ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ are investigated and compared with data at lower incident energies. A conventional distorted-wave Born approximation analysis can account for the qualitative features of the energy spectra but overestimates the energy dependence of the observed absolute cross sections by almost an order of magnitude between 140 and 312.6 MeV.

The atmospheric secondary proton flux is studied for altitudes extending from sea level up to the top of the atmosphere by means of a three-dimensional Monte Carlo simulation procedure successfully used previously to account for flux measurements of protons, light nuclei, and electron-positron pairs below the geomagnetic cutoff (satellite data), and of muons and antiprotons (balloon data). The calculated fluxes are compared with the experimental measurements from sea level up to high float balloon altitudes. The agreement between data and simulation results is very good at all altitudes, including the lowest ones, where the calculations become extremely sensitive to the proton production cross section. The results are discussed in this context. The calculations are extended to the study of quasitrapped particles above the atmosphere to about five earth radii, for prospective purpose.

The ${\pi }^{+}$ production in $85A$-MeV C+C and C+Au reactions has been studied for $20 \mathrm{MeV}<~E_{\pi }<~80 \mathrm{MeV}$ and ${\theta }_{\mathrm{lab}}>55\mathrm{}°$. The cross sections, $\frac{d^2\sigma }{d\Omega \mathrm{dE}}$, fall exponentially with $E_{\pi }$ and are 9 times larger for C+Au than for C+C. The angular distribution is backward peaked for C+Au in the nucleon-nucleon c.m. system, while it is weakly forward peaked in the nucleus-nucleus c.m. system. An independent nucleon-nucleon scattering model can explain the data only if diffuse internal momentum distributions are introduced.

It is shown that a simplified Glauber approach using an experimental nucleon-nucleon forward amplitude and a Gaussian nucleus density reproduces fairly well both nucleus-nucleus reaction cross sections and elastic scattering differential cross sections over a broad energy range.

NUCLEAR REACTIONS ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$+${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ elastic scattering, $\frac{E}{A}=25, 30, \mathrm{and} 85$ MeV, optical limit of Glauber theory, reaction cross section.

The atmospheric secondary antiproton flux is studied for detection altitudes extending from sea level up to about three earth radii, by means of a three-dimensional Monte Carlo simulation, successfully applied previously to other satellite and balloon data. The calculated antiproton flux at mountain altitude is found to be in fair agreement with the recent BESS measurements. The flux obtained at balloon altitude is also in agreement with calculations performed in previous studies and used for the analysis of balloon data. The flux at sea level is found to be significant. The antineutron flux is also evaluated. The antiproton flux is prospectively explored up to around $2\times {10}^4\mathrm{km}$ from the Earth. The results are discussed in the context of the forthcoming measurements by large acceptance experiments.

For the previously reported Gamow-Teller transition centered in ${}_{}{}^{90}{}_{}{}^{}\mathrm{Nb}$ at 8.4 MeV, two components are observed in the ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}({}_{}{}^3{}_{}{}^{}\mathrm{He}, t){}_{}{}^{90}{}_{}{}^{}\mathrm{Nb}$ reaction at 80 MeV. The first one of $M1\mathrm{}$ type is centered at 7.2 MeV, the other one of unknown multipolarity at 9.7 MeV.

NUCLEAR REACTIONS ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}({}_{}{}^3{}_{}{}^{}\mathrm{He}, t)$, $E=80\mathrm{}$ MeV; measured $\sigma \left(\theta \right)$ IAS and Gamow-Teller states.