T. Aumann

Hypernuclear spectroscopy of products from Li-6 projectiles on a carbon target at 2 A GeV

Abstract A novel experiment, aiming at demonstrating the feasibility of hypernuclear spectroscopy with heavy ion beams, was conducted. Using the invariant mass method, the spectroscopy of hypernuclear products of 6Li projectiles on a carbon target at 2 A GeV was performed. Signals of the Λ-hyperon and H Λ 3 and H Λ 4 hypernuclei were observed for final states of p + π − , He 3 + π − and He 4 + π − , respectively, with significance values of 6.7, 4.7 and 4.9σ. By analyzing the proper decay time from secondary vertex distribution with the unbinned maximum likelihood fitting method, their lifetime values were deduced to be 262 − 43 + 56 ± 45 ps for Λ, 183 − 32 + 42 ± 37 ps for H Λ 3 , and 140 − 33 + 48 ± 35 ps for H Λ 4 .

Quasifree (

We study (p,2p )a nd (p,pn) reactions at proton energies in the range of 100 MeV–1 GeV. Our purpose is to explore the most sensitive observables in unpolarized reactions with inverse kinematics involving radioactive nuclei. We formulate a model based on the eikonal theory to describe total cross sections and momentum distributions of the recoiled residual nucleus. The model is similar to the one adopted for knockout reactions with heavy ions. We show that momentum distributions are sensitive to the angular momentum of the ejected nucleon which can be used as an spectroscopic tool. The total cross sections are sensitive to the nucleon separation energies and to multiple scattering effects. Our calculations also indicate that a beam energy around 500 MeV/nucleon has a smaller dependence on the anisotropy of the nucleon-nucleon elastic scattering.

p,2p

The A/Z dependence of projectile fragmentation at relativistic energies has been studied with the ALADIN forward spectrometer at SIS. A stable beam of (124)Sn and radioactive beams of (124)La and (107)Sn at 600 MeV per nucleon have been used in order to explore a wide range of isotopic compositions. Chemical freeze-out temperatures are found to be nearly invariant with respect to the A/Z of the produced spectator sources, consistent with predictions for expanded systems. Small Coulomb effects (DeltaT approximately 0.6 MeV) appear for residue production near the onset of multifragmentation.

) and (

Directed and elliptic flows of neutrons and light charged particles were measured for the reaction 197Au+197Au at 400 MeV/nucleon incident energy within the ASY-EOS experimental campaign at the GSI laboratory. The detection system consisted of the Large Area Neutron Detector LAND, combined with parts of the CHIMERA multidetector, of the ALADIN Time-of-flight Wall, and of the Washington-University Microball detector. The latter three arrays were used for the event characterization and reaction-plane reconstruction. In addition, an array of triple telescopes, KRATTA, was used for complementary measurements of the isotopic composition and flows of light charged particles. From the comparison of the elliptic flow ratio of neutrons with respect to charged particles with UrQMD predictions, a value \gamma = 0.72 \pm 0.19 is obtained for the power-law coefficient describing the density dependence of the potential part in the parametrization of the symmetry energy. It represents a new and more stringent constraint for the regime of supra-saturation density and confirms, with a considerably smaller uncertainty, the moderately soft to linear density dependence deduced from the earlier FOPI-LAND data. The densities probed are shown to reach beyond twice saturation.

p,pn

The electric dipole (E1) response of exotic nuclei, with a focus on the soft E1 excitation of halo nuclei and the pygmy dipole resonance (PDR) of neutron-skin nuclei, is reviewed here from an experimental point of view. Since the discovery of halo nuclei in the late 1980s, the particular dipole response of these loosely bound nuclei located at the neutron-drip line resulting in an extraordinary enhancement of the electric dipole strength at low excitation energies (soft E1 excitation) has been one of the phenomena under intense investigation both in experiments and in nuclear theories. We discuss how such phenomena have been recognized as a unique feature of halo nuclei and how it is applied to probe the halo structure in a quantitative way. Another intriguing feature of the E1 response of neutron-rich nuclei is the PDR in neutron-skin nuclei, which is viewed as a dipole vibration of excess neutrons against a core nucleus and which appears in the low-energy part of the E1 strength function below the giant dipole resonance. The status of the experimental evidence for such a redistribution of dipole strength for neutron-rich nuclei compared to stable ones is reviewed. The relation of the dipole response to the symmetry energy in the equation of state of asymmetric nuclear matter and to the neutron-skin thickness is also briefly discussed. Finally, we outline some perspectives for future experimental investigations toward heavier and more neutron-rich systems. The experimental results reviewed here have been accumulated over the last two decades at fragmentation facilities worldwide at GANIL, GSI, MSU and RIKEN.

) reactions with unstable nuclei

The unbound nucleus ^{26}O has been investigated using invariant-mass spectroscopy following one-proton removal reaction from a ^{27}F beam at 201  MeV/nucleon. The decay products, ^{24}O and two neutrons, were detected in coincidence using the newly commissioned SAMURAI spectrometer at the RIKEN Radioactive Isotope Beam Factory. The ^{26}O ground-state resonance was found to lie only 18±3(stat)±4(syst)  keV above threshold. In addition, a higher lying level, which is most likely the first 2^{+} state, was observed for the first time at 1.28_{-0.08}^{+0.11}  MeV above threshold. Comparison with theoretical predictions suggests that three-nucleon forces, pf-shell intruder configurations, and the continuum are key elements to understanding the structure of the most neutron-rich oxygen isotopes beyond the drip line.

Isotopic dependence of the nuclear caloric curve

This work presents a direct measurement of the

Results of the ASY-EOS experiment at GSI : the symmetry energy at suprasaturation density

^{96}

The electric dipole response of exotic nuclei

Ru(

Nucleus

p, \gamma