Influence of single-neutron stripping on near-barrier ⁶He+²⁰⁸Pb and ⁸He+²⁰⁸Pb elastic scattering

The influence of single-neutron stripping on the near-barrier elastic scattering angular distributions for the 6,8He+208Pb systems is investigated through coupled reaction channels (CRC) calculations fitting recently published data to explore the differences in the absorptive potential found in the scattering of these two neutron-rich nuclei. The inclusion of the coupling reduces the elastic cross section in the Coulomb-nuclear interference region for 8He scattering, whereas for 6He its major impact is on the large-angle elastic scattering. The real and imaginary dynamic polarization potentials are obtained by inverting the CRC elastic scattering S-matrix elements. These show that the main absorptive features occur between 11 and 12 fm for both projectiles, while the attractive features are separated by about 1 fm, with their main structures occurring at 10.5 fm for 6He and 11.5 fm for 8He

alpha-particle production in the scattering of 6He by 208Pb at energies around the Coulomb barrier

New experimental data from the scattering of 6He+208Pb at energies around and below the Coulomb barrier are presented. The yield of breakup products coming from projectile fragmentation is dominated by a strong group of $\alpha$ particles. The energy and angular distributions of this group have been analyzed and compared with theoretical calculations. This analysis indicates that the $\alpha$ particles emitted at backward angles in this reaction are mainly due to two-neutron transfer to weakly bound states of the final nucleus.Comment: 20 pages, 5 figures. Nuclear Physics A792 (2007) 2-1

Investigation of the 6He cluster structures

The 4He+2n and t+t clustering of the 6He ground state were investigated by means of the transfer reaction 6He(p,t)4He at 25 MeV/nucleon. The experiment was performed in inverse kinematics at GANIL with the SPEG spectrometer coupled to the MUST array. Experimental data for the transfer reaction were analyzed by a DWBA calculation including the two neutrons and the triton transfer. The couplings to the 6He --> 4He + 2n breakup channels were taken into account with a polarization potential deduced from a coupled-discretized-continuum channels analysis of the 6He+1H elastic scattering measured at the same time. The influence on the calculations of the 4He+t exit potential and of the triton sequential transfer is discussed. The final calculation gives a spectroscopic factor close to one for the 4He+2n configuration as expected. The spectroscopic factor obtained for the t+t configuration is much smaller than the theoretical predictions.Comment: 10 pages, 11 figures, accepted in PR

Structure of unbound neutron-rich 9^{9}He studied using single-neutron transfer

The 8He(d,p) reaction was studied in inverse kinematics at 15.4A MeV using the MUST2 Si-CsI array in order to shed light on the level structure of 9He. The well known 16O(d,p)17O reaction, performed here in reverse kinematics, was used as a test to validate the experimental methods. The 9He missing mass spectrum was deduced from the kinetic energies and emission angles of the recoiling protons. Several structures were observed above the neutron-emission threshold and the angular distributions were used to deduce the multipolarity of the transitions. This work confirms that the ground state of 9He is located very close to the neutron threshold of 8He and supports the occurrence of parity inversion in 9He.Comment: Exp\'erience GANIL/SPIRAL1/MUST

A Phase transition in acoustic propagation in 2D random liquid media

Acoustic wave propagation in liquid media containing many parallel air-filled cylinders is considered. A self-consistent method is used to compute rigorously the propagation, incorporating all orders of multiple scattering. It is shown that under proper conditions, multiple scattering leads to a peculiar phase transition in acoustic propagation. When the phase transition occurs, a collective behavior of the cylinders appears and the acoustic waves are confined in a region of space in the neighborhood of the transmission source. A novel phase diagram is used to describe such phase transition. Originally submitted on April 6, 99.Comment: 5 pages, 5 color figure

Gamma-Ray Spectroscopy of Λ16^{16}_\LambdaO and Λ15^{15}_\LambdaN Hypernuclei via the 16^{16}O(K−,π−)(K^-, \pi^-) reaction

he bound-state level structures of the $^{16}_{\Lambda}$O and $^{15}_{\Lambda}$N hypernuclei were studied by $\gamma$-ray spectroscopy using a germanium detector array (Hyperball) via the $^{16}$O ($K^-, \pi^- \gamma$) reaction. A level scheme for $^{16}_{\Lambda}$O was determined from the observation of three $\gamma$-ray transitions from the doublet of states ($2^-$,$1^-$) at $\sim 6.7$ MeV to the ground-state doublet ($1^-$,$0^-$). The $^{15}_{\Lambda}$N hypernuclei were produced via proton emission from unbound states in $^{16}_{\Lambda}$O . Three $\gamma$ -rays were observed and the lifetime of the $1/2^+;1$ state in $^{15}_{\Lambda}$N was measured by the Doppler shift attenuation method. By comparing the experimental results with shell-model calculations, the spin-dependence of the $\Lambda N$ interaction is discussed. In particular, the measured $^{16}_{\Lambda}$O ground-state doublet spacing of 26.4 $\pm$ 1.6 $\pm$ 0.5 keV determines a small but nonzero strength of the $\Lambda N$ tensor interaction.Comment: 22 pages, 17 figure

Tensor analyzing powers for 7 Li induced transfer breakup reactions

The T20 analyzing powers have been measured for the 12Sn(7Li ,8Be2a) 119In and 120Sn (7Li ,6Li*a+d) 121Sn transfer breakup reactions, using a 70 MeV beam. The data exhibit excellent agreement with the results of coupled reaction channels calculations, providing an important test of these calculations when applied to the transfer breakup reaction mechanism

Effects of finite width of excited states on heavy-ion sub-barrier fusion reactions

We discuss the effects of coupling of the relative motion to nuclear collective excitations which have a finite lifetime on heavy-ion fusion reactions at energies near and below the Coulomb barrier. Both spreading and escape widths are explicitly taken into account in the exit doorway model. The coupled-channels equations are numerically solved to show that the finite resonance width always hinders fusion cross sections at subbarrier energies irrespective of the relative importance between the spreading and the escape widths. We also show that the structure of fusion barrier distribution is smeared due to the spreading of the strength of the doorway state.Comment: 13 pages, 3 figures, Submitted to Physical Review

First Measurement of A_N at sqrt(s)=200 GeV in Polarized Proton-Proton Elastic Scattering at RHIC

We report on the first measurement of the single spin analyzing power (A_N) at sqrt(s)=200GeV, obtained by the pp2pp experiment using polarized proton beams at the Relativistic Heavy Ion Collider (RHIC). Data points were measured in the four momentum transfer t range 0.01 < |t| < 0.03 (GeV/c)^2. Our result, averaged over the whole t-interval is about one standard deviation above the calculation, which uses interference between electromagnetic spin-flip amplitude and hadronic non-flip amplitude, the source of A_N. The difference could be explained by an additional contribution of a hadronic spin-flip amplitude to A_N.Comment: 13 pages, 5 figures. New values of polarization errors. Final version submitted to Phys. Lett.

Double Spin Asymmetries A_NN and A_SS at sqrt{s}=200 GeV in Polarized Proton-Proton Elastic Scattering at RHIC

We present the first measurements of the double spin asymmetries A_NN and A_SS at sqrt{s}=200 GeV, obtained by the pp2pp experiment using polarized proton beams at the Relativistic Heavy Ion Collider (RHIC). The data were collected in the four momentum transfer t range 0.01<|t|<0.03 (GeV/c)^2. The measured asymmetries, which are consistent with zero, allow us to estimate upper limits on the double helicity-flip amplitudes phi_2 and phi_4 at small t as well as on the difference Delta(sigma_T) between the total cross sections for transversely polarized protons with antiparallel or parallel spin orientations.Comment: 13 pages with 3 figures. Final version accepted by Phys. Lett.