Contribution of #pi#"o and #eta# Dalitz decays to the dilepton invariant-mass spectrum in 1 A.GeV heavy-ion collisions

The Dalitz-decay contributions of #pi#"0 and #eta# mesons to the di-electron invariant-mass spectrum at 1 A.GeV have been obtained from a systematics of inclusive meson production cross sections measured for the collision systems "1"2C+"n"a"tC and "4"0Ar,"4"0Ca+"n"a"tCa in the bombarding-energy range of 0.8 -2.0 A.GeV. These results are compared with the recently published di-electron mass spectra of the DLS collaboration. Systematic errors and angular-distribution effects are discussed. We conclude that the low-mass part of the DLS data cannot be explained by the Dalitz decays of light neutral mesons only. (orig.)Available from FIZ Karlsruhe / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Investigation of reabsorption effects in subthreshold #pi#"0 production

We present results from our experimental studies of reabsorption effects in sub-threshold #pi#"0 production in the reactions "1"2"9Xe+"1"9"7Au at 44 MeV/u, as well as "3"6Ar+"1"9"7Au and "3"6Ar+"1"2C at 95 MeV/u. From our data we extract information on the #pi#"0 absorption length in nuclear matter. For the #pi#"0 kinetic-energy range #approx =# 5 - 100 MeV the energy-averaged #lambda#_A_B_S and its momentum dependence is obtained, and compared with optical-model calculations. We also show preliminary results from exclusive #pi#"0 emission in coincidence with projectile-like fragments, giving evidence for pion production in very peripheral collisions. (orig.)SIGLEAvailable from TIB Hannover: RO 801(93-25) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Polar and azimuthal distributions of subthreshold #pi#"o"'s: a probe of reaction dynamics and pion final-state interactions

In a measurement during the first TAPS campaign at GANIL (March 1990) we have extended the available experimental systematics of #pi#"0 production cross sections to a very heavy collision system, i.e. characterized by particularly large final-state effects. From these inclusive data, first quantitative results could be extracted on the absorption length of neutral pions in nuclear matter. (orig./HSI)Available from TIB Hannover: RO 801(93-48) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Excitation and decay of two-phonon giant dipole resonances

In heavy ion collisions at near relativistic energies, electromagnetic excitation of the double giant dipole resonance occurs with large cross sections. We summarize the presently available experimental data and discuss related theoretical efforts. Emphasis is paid to the question of anharmonicities and to the damping of the two-phonon states. (orig.)Available from TIB Hannover: RO 801(98-60) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

A large area scintillating fiber detector for relativistic heavy ions

A scintillating fiber detector for relativistic heavy ions with an active area of 50 x 50 cm"2 has been developed and was tested with various ion beams (1#<=#Z#<=#92). A count rates of up to 10"5 particles/s, the position resolution was found to be determined by the fiber width of 1 mm; depending on the nuclear charge of the beam, efficiencies between 89% and 100% and time resolutions between 800 and 200 ps (FWHM) were obtained. (orig.)SIGLEAvailable from TIB Hannover: RO 801(97-60) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Electromagnetic excitation of the two-phonon giant dipole resonance

The nuclear response of "1"3"6Xe and "2"0"8Pb to electromagnetic excitation was studied in peripheral, near-relativistic heavy-ion collisions. Large cross sections were observed for the one-phonon and two-phonon isovector giant dipole resonance. The results, in particular the unexpectedly large strength found for the double giant dipole resonance, are discussed and compared to that of other recent measurements. (orig.)Available from TIB Hannover: RO 801(93-72) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Two-phonon giant dipole resonance in "2"0"8Pb

Excitation of the two-phonon isovector giant dipole resonance was observed in "2"0"8Pb projectiles incident on different target nuclei (C, Sn, Ho, Pb, U) at high energy (640 A.MeV). Evidence is found for a two-step electromagnetic excitation mechanism. An enhancement of 1.33(16) for the excitation cross section is observed relative to the harmonic approximation. Neutron- and #gamma#-decay probabilities are derived as well. (orig.)SIGLEAvailable from TIB Hannover: RO 801(96-27) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Exclusive studies of neutron and charged particle emission in collisions of "1"9"7Au+"1"9"7Au at 400 MeV/nucleon

We present data on collective flow of neutrons in collisions of "1"9"7Au+"1"9"7Au at 400 MeV/nucleon. The azimuthal distribution about the beam axis is investigated with respect to the reaction plane as determined from light charged particles. The 'squeeze-out' of neutrons, perpendicular to the reaction plane, is observed for the first time. Quantitative agreement to a high level of accuracy is found between the behaviour of neutrons and hydrogen ions. (orig.)Accepted for publication by Phys. Rev. Lett.SIGLEAvailable from TIB Hannover: RO 801(93-60) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Energy dependence of collective flow of neutrons and charged particles in "1"9"7Au+"1"9"7Au collisions

Our contribution focusses on one particular aspect of collective flow of nuclear matter: the so-called ''squeeze-out'', i.e. the preferential emission of mid-rapidity particles perpendicular to the reaction plane. The data were taken for the system "1"9"7Au + "1"9"7Au at 400, 600 and 800 MeV/u. We cover two topics, the comparison of neutrons and protons, and the bombarding energy dependence of the neutrons' squeeze-out. (orig.)Available from TIB Hannover: RO 801(94-02) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Invariant mass spectrum and #alpha# - n correlation function studied in the fragmentation of "6He on a carbon target

Momentum distributions and invariant mass spectra from the breakup of "6He ions with an energy of 250 MeV/u interacting with a carbon target have been studied. The data were used to extract information about the reaction mechanism which is influenced by the structure of "6He. It is found that the dominant reaction mechanism is a two-step process: knock out of one neutron followed by the decay of the "5He resonance. The shape of the (#alpha#+n) two-body invariant mass spectrum is interpreted as mainly reflecting the "5He ground state which is a J "#pi# =3/2"- resonance. However, no evidence for correlations between #alpha# particles and neutrons is observed in the momentum widths of the distributions. It is demonstrated that a combined analysis of the two-body invariant mass spectrum and an appropriate correlation function may be used to determine the properties of the intermediate resonance. (orig.)Available from TIB Hannover: RO 801(97-61) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman