High-spin states in the doubly-odd $Z=77$ nucleus ${}^{188}\mathrm{I}\mathrm{r}$ were populated in the ${}^{186}\mathrm{W}\left({}^7\mathrm{L}\mathrm{i},5n\right)$ reaction at $52\mathrm{MeV}$. Two nearly degenerate $\Delta I=1$ sequences with the same parity were established. Both bands have been assigned the $\pi h_{9∕2}\otimes \nu i_{13∕2}$ configuration, based on the systematic behavior of these excitations in the $\mathrm{Ir}$ nuclei and on the measured values for the $B\left(M1\right)∕B\left(E2\right)$ ratios, and they are suggested as candidates for a chiral doublet.

With the view to study complete and incomplete fusion in heavy ion induced reactions, experiments have been carried out for measuring excitation functions for several reactions in the system ${}^{16}\mathrm{O}+{}^{169}\mathrm{Tm}$ at energies near the Coulomb barrier to well above it, using an activation technique. The measured excitation functions have been compared with those calculated theoretically using three different computer codes viz., ALICE-91, CASCADE and PACE2. The enhancement of experimentally measured cross sections for alpha emission channels over their theoretical prediction has been attributed to the fact that these residues are formed not only by complete fusion but also through incomplete fusion. In order to separate out the relative contributions of complete and incomplete fusion, the recoil range distributions of eight residues produced in the interaction of ${}^{16}\mathrm{O}$ with ${}^{169}\mathrm{Tm}$ at $\approx 87\mathrm{MeV}$ have been measured. The recoil range distributions indicate significant contributions from incomplete fusion at $\approx 87\mathrm{MeV}$ for some of the channels.

We report inclusive photon measurements about midrapidity $(\mid y\mid <0.5)$ from ${}^{197}\mathrm{Au}+{}^{197}\mathrm{Au}$ collisions at $\sqrt{s_{NN}}=130\mathrm{GeV}$ at RHIC. Photon pair conversions were reconstructed from electron and positron tracks measured with the Time Projection Chamber (TPC) of the STAR experiment. With this method, an energy resolution of $\Delta E∕E\approx 2\%$ at $0.5\mathrm{GeV}$ has been achieved. Reconstructed photons have also been used to measure the transverse momentum $\left(p_t\right)$ spectra of ${\pi }^0$ mesons about midrapidity $(\mid y\mid <1)$ via the ${\pi }^0\to \gamma \gamma$ decay channel. The fractional contribution of the ${\pi }^0\to \gamma \gamma$ decay to the inclusive photon spectrum decreases by $20\%\pm 5\%$ between $p_t=1.65\mathrm{GeV}∕c$ and $p_t=2.4\mathrm{GeV}∕c$ in the most central events, indicating that relative to ${\pi }^0\to \gamma \gamma$ decay the contribution of other photon sources is substantially increasing.

We investigate alternatives to the standard formalism used for the study of relativistic Coulomb excitation of the giant dipole resonance in nuclei. The idea is to obtain reasonable results for the probabilities of excitation and cross sections to the one-phonon and two-phonon levels avoiding the substantial complexity of the treatments exploited so far. This is achieved for the relevant range of partial waves up to bombarding energies of at least $5\mathrm{GeV}$ per nucleon. The transfer of energy to the center of mass of the excited nuclei is also investigated.

A significant drop of the vector meson masses in nuclear matter is observed in a chiral SU(3) model due to the effects of the baryon Dirac sea. This is taken into account through the summation of baryonic tadpole diagrams in the relativistic Hartree approximation. The appreciable decrease of the in-medium vector meson masses is due to the vacuum polarization effects from the nucleon sector and is not observed in the mean field approximation.

We study the anomalous decays ${\pi }^0,\eta \to \gamma \gamma$ in the framework of the three–flavor Nambu–Jona-Lasinio (NJL) model at finite temperature. The similarities and differences between these results and those obtained at zero temperature and finite density are discussed. In both cases the lifetimes of these mesons decrease significantly at the critical point, although this might not be sufficient to observe enhancement of these decays in heavy-ion collisions.

Excited levels in ${}^{69}\mathrm{As}$ were studied using the ${}^{40}\mathrm{Ca}({}^{32}\mathrm{S},3p){}^{69}\mathrm{As}$ reaction at 95 and 105 MeV beam energy. Gamma rays were detected with the EUROBALL spectrometer operated in conjunction with the Neutron Wall and the charged-particle detector array EUCLIDES. New level sequences with positive and negative parity were identified from $3p\text{−}\gamma \gamma$ and $\gamma \gamma \gamma$ coincidences. Spins were assigned to many of the levels on the basis of directional correlations of oriented states measurements. The previously observed positive-parity band was extended to spin $45∕2^{+}$ and it was found to exhibit a crossing with another configuration identified up to spin $53∕2^{+}$. Three negative-parity bands were observed for the first time up to spins $(43∕2^{-}),39∕2^{-}$, and $(41∕2^{-})$. The previously known band was extended to spin $(49∕2^{-})$. No evidence for superdeformation was found, despite very high counting statistics. Configurations were assigned to each of the observed bands through comparisons to the cranked Nilsson-Strutinsky calculations.

The Coulomb breakup of one-neutron halo nuclei is studied within the postform distorted-wave Born approximation (DWBA) theory. A method of evaluation of the DWBA breakup amplitude in momentum space is presented. The theory is applied to the Coulomb breakup of the ${}^{11}\mathrm{Be}$ and ${}^{19}\mathrm{C}$ halo nuclei on ${}^{208}\mathrm{Pb}$ at the beam energy of $\sim 70\mathrm{MeV}∕\text{nucleon}$. Calculations for relative energy spectra are compared with available experimental data. Good agreement in shape is found for low relative energies. Comparison with the results obtained using a local momentum approximation to the DWBA amplitude shows that the effects of this additional approximation are substantial. The DWBA calculations are also compared to those of an adiabatic breakup theory. The two theories lead to significantly different results.

A mechanism that uses the environment to increase the probability of the nuclear reaction when a beam of accelerated nuclei collides with a target nucleus implanted in condensed matter is suggested. The effect considered is exponentially large for low collision energies. For $t+p$ collision the mechanism becomes effective when the energy of the projectile tritium is below $1\mathrm{KeV}$ per nucleon. The gain in probability of the nuclear reaction is due to a redistribution of energy and momentum of the projectile in several “preliminary” elastic collisions with the target nucleus and the environmental nuclei in such a way that the final inelastic projectile-target collision takes place with larger relative velocity, which is accompanied by the corresponding decrease of the center of mass energy. This increase of the relative velocity exponentially increases the penetration through the Coulomb barrier.

We report on the rapidity and centrality dependence of proton and antiproton transverse mass distributions from ${}^{197}\mathrm{Au}+{}^{197}\mathrm{Au}$ collisions at $\sqrt{s_{NN}}=130\mathrm{GeV}$ as measured by the STAR experiment at the Relativistic Heavy Ion Collider (RHIC). Our results are from the rapidity and transverse momentum range of $\mid y\mid <0.5$ and $0.35<p_t<1.00\mathrm{GeV}∕c$. For both protons and antiprotons, transverse mass distributions become more convex from peripheral to central collisions demonstrating characteristics of collective expansion. The measured rapidity distributions and the mean transverse momenta versus rapidity are flat within $\mid y\mid <0.5$. Comparisons of our data with results from model calculations indicate that in order to obtain a consistent picture of the proton (antiproton) yields and transverse mass distributions the possibility of prehadronic collective expansion may have to be taken into account.

The first results are reported on $({}^6\mathrm{He},{}^8\mathrm{Be})$ two-proton pick-up reactions on ${}^{12}\mathrm{C}$, ${}^{16}\mathrm{O}$, and ${}^{19}\mathrm{F}$ nuclei. The measurements were done with an $18\mathrm{MeV}$ beam on ${}^6\mathrm{LiF}$, ${}^7\mathrm{LiF}$, ${}^6\mathrm{Li}_2\mathrm{C}{\mathrm{O}}_3$, and ${}^{12}\mathrm{C}$ targets. The measured angular distributions for the ${}^{12}\mathrm{C}({}^6\mathrm{He},{}^8\mathrm{Be}){}^{10}\mathrm{Be}$ (g.s.) and ${}^{12}\mathrm{C}({}^6\mathrm{He},{}^8\mathrm{Be}){}^{10}\mathrm{Be}^{*}\left(3.37\mathrm{MeV}\right)$ reactions show a clear signature of a direct process. Although the contributions from the ${}^6\mathrm{Li}({}^6\mathrm{He},{}^8\mathrm{Be}){}^4\mathrm{H}$ reaction were observed, no clear extraction of the ${}^4\mathrm{H}$ data was possible.

We propose a model independent method which allows us to distinguish between shadow and edge or surface effects in the angular distributions of heavy-ion elastic scattering, showing regular patterns of marked oscillations. The method is illustrated with a few experimental results where this undulatory behavior is present.

We explore the connection between pentaquarks and dibaryons composed of three diquarks in the framework of the diquark model. With the available experimental data on $H$ we estimate the Pauli blocking and annihilation effects and constrain the $P=-\text{pentaquark}SU{\left(3\right)}_F$ singlet mass. Using the ${\Theta }^{+}$ pentaquark mass, we estimate $P=-\text{dibaryon}\text{mass}$

States near the ${}^{23}\mathrm{Na}+p$ threshold in ${}^{24}\mathrm{Mg}$ were investigated using the ${}^{23}\mathrm{Na}({}^3\mathrm{He},d){}^{24}\mathrm{Mg}$ reaction over the angular range of $5°⩽{\theta }_{\mathrm{lab}}⩽35°$ at $E\left({}^3\mathrm{He}\right)=20\mathrm{MeV}$. Spectroscopic factors were extracted for states corresponding to resonances in the ${}^{23}\mathrm{Na}(p,\gamma ){}^{24}\mathrm{Mg}$ and ${}^{23}\mathrm{Na}(p,\alpha ){}^{20}\mathrm{Ne}$ reactions. We find that one state, corresponding to a previously unobserved resonance at $E_{\mathrm{c.m.}}=138\mathrm{keV}$, may make a significant contribution to the rates of both reactions at low temperatures. Another state, corresponding to a possible resonance at $E_{\mathrm{c.m.}}=37\mathrm{keV}$ may make a small contribution to the ${}^{23}\mathrm{Na}(p,\alpha ){}^{20}\mathrm{Ne}$ reaction. New rates for the ${}^{23}\mathrm{Na}(p,\gamma ){}^{24}\mathrm{Mg}$ and ${}^{23}\mathrm{Na}(p,\alpha ){}^{20}\mathrm{Ne}$ reactions are presented and the astrophysical implications are discussed.

High-spin excited states have been identified for the first time in the $N=Z+1$ nucleus ${}^{89}\mathrm{Ru}$ with the reaction ${}^{54}\mathrm{Fe}({}^{40}\mathrm{Ca},\alpha n\gamma )$ at 130 MeV, using the GASP array, the ISIS Silicon array, and the $n$-Ring detector system. The observed structure is discussed within systematics of the $N=45$ isotones and is compared with shell model calculations.

We have searched for the nuclear excitation by electronic transition (NEET) of the isomeric level at 76 eV in ${}^{235}\mathrm{U}$ in a plasma induced by a YAG laser with an energy of 1 Joule and a full width at half maximum time distribution of 5 ns, operating at an intensity of ${10}^{13}\text{W}{\mathrm{cm}}^{-2}$. We present a thorough description of the experimental conditions and analysis of our data. In this experimental situation we do not detect any excitation of the isomeric level, a result that is at variance with a previously reported one. An upper limit of $6\times {10}^{-6}$ per atom and per second averaged over the laser-pulse width has been set on the nuclear excitation rate. This value is compared with results obtained in previous experimental and theoretical works.

Reactions induced by radioactive ${}^{6,8}\mathrm{He}$ beams from the SPIRAL facility were studied on ${}^{63,65}\mathrm{Cu}$ and ${}^{188,190,192}\mathrm{Os}$ targets and compared to reactions with the stable ${}^4\mathrm{He}$ projectiles from the Mumbai Pelletron. Partial residue cross sections for fusion and neutron transfer obtained from the measured intensities of characteristic in-beam $\gamma$ rays for the ${}^6\mathrm{He}+{}^{63,65}\mathrm{Cu}$ systems are presented. Coincidence measurements of heavy reaction products, identified by their characteristic $\gamma$ rays, with projectilelike charged particles, provide direct evidence for a large transfer cross section with Borromean nuclei ${}^6\mathrm{He}$ at 19.5 and 30 MeV and ${}^8\mathrm{He}$ at 27 MeV. Reaction cross sections were also obtained from measured elastic angular distributions for ${}^{6,8}\mathrm{He}+\mathrm{Cu}$ systems. Cross sections for fusion and direct reactions with ${}^{4,6}\mathrm{He}$ beams on heavier targets of ${}^{188,192}\mathrm{Os}$ at 30 MeV are also presented. The present work underlines the need to distinguish between various reaction mechanisms leading to the same products before drawing conclusions about the effect of weak binding on the fusion process. The feasibility of extracting small cross sections from inclusive in-beam $\gamma$-ray measurements for reaction studies near the Coulomb barrier with low intensity isotope separation on-line beams is highlighted.

Multiplicity distributions of intermediate mass fragments (IMFs) seen in intermediate energy heavy ion collisions have been of great interest in the last ten years. The distributions of single intermediate sized elements are close to Poissonian and have been subjected to widely different physical interpretations. We calculate the multiplicity distributions in a thermodynamic model whose physical basis is equal populations in phase space, which implies equilibrium statistics. We found distributions of a single element are to a good approximation Poissonian, and this result is attributed to the small emission probability of a given IMF among all the possible channels. We also found significant deviation from a Poisson distribution for a range of IMFs, and suggest strong correlations as an explanation. The systematics of the multiplicity distributions are explored in both one-component and two-component models. In the one-component model, sudden changes for the multiplicity distributions are found at the phase transition region. In the two-component model, the multiplicity distributions have more subtleties. Results from the current model are compared with available data, and good agreements are found. New signals for the multiparticle correlations are also suggested.

We present STAR measurements of charged hadron production as a function of centrality in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{NN}}=130\mathrm{GeV}$. The measurements cover a phase space region of $0.2<p_T<6.0\mathrm{GeV}∕c$ in transverse momentum and $-1<\eta <1$ in pseudorapidity. Inclusive transverse momentum distributions of charged hadrons in the pseudorapidity region $0.5<\mid \eta \mid <1$ are reported and compared to our previously published results for $\mid \eta \mid <0.5$. No significant difference is seen for inclusive $p_T$ distributions of charged hadrons in these two pseudorapidity bins. We measured $dN∕d\eta$ distributions and truncated mean $p_T$ in a region of $p_T>p_T^{\text{cut}}$, and studied the results in the framework of participant and binary scaling. No clear evidence is observed for participant scaling of charged hadron yield in the measured $p_T$ region. The relative importance of hard scattering processes is investigated through binary scaling fraction of particle production.

A method is developed for treating the effect of the neutron-proton mass difference in isospin-violating nuclear forces. Previous treatments utilized an awkward subtraction scheme to generate these forces. A field redefinition is used to remove that mass difference from the free Lagrangian (and hence from asymptotic nucleon states) and replace its effect by effective interactions. Previous calculations of static class II charge-independence-breaking and class III charge-symmetry-breaking potentials are verified using the new scheme, which is also used to calculate class IV nuclear forces. Two-body forces of the latter type are found to be identical to previously obtained results. A three-body force is also found. Problems involving Galilean invariance with class IV one-pion-exchange forces are identified and resolved.