Coherent Compton scattering on light nuclei in the $\Delta$-resonance region is studied in the impulse approximation and is shown to be a sensitive probe of the in-medium properties of the $\Delta$ resonance. The elementary amplitude on a single nucleon is calculated from the unitary K-matrix approach developed previously. Modifications of the properties of the $\Delta$ resonance due to the nuclear medium are accounted for through the self-energy operator of the $\Delta ,$ calculated from the one-pion loop. The dominant medium effects such as the Pauli blocking, mean-field modification of the nucleon and $\Delta$ masses, and particle-hole excitations in the pion propagator are consistently included in nuclear matter.

Particle yields and fluctuations are studied in a general framework based on a cycle class picture in a Feynman path integral approach. Various cases such as the disoriented chiral condensate distribution, a negative binomial distribution, partially coherent state emission, and field emission from Lorentzian line shapes are discussed. Generalizations based on these important specific cases are developed. Connections of the cycle class picture with other approaches based on combinants, cumulants, hierarchical models, and clan variables are presented for the specific and general cases. A relation to a Feynman-Wilson gas and to the Ginzburg-Landau model are discussed.

We discuss the problem of observing spontaneous parity and $\mathrm{CP}$ violation in collision systems. We discuss and propose observables which may be used in heavy-ion collisions to observe such violations, as well as event-by-event methods to analyze the data. Finally, we discuss simple Monte Carlo models of these $\mathrm{CP}$-violating effects which we have used to develop our techniques and from which we derive rough estimates of sensitivities to signals that may be seen at the relativistic heavy-ion collider.

The axial charge in the weak nucleon axial vector current has been precisely determined by measuring the alignment correlation terms in the $\beta$-ray angular distributions of the purely spin aligned mirror pair nuclei ${}^{12}\mathrm{B}{(I}^{\pi }{=1\mathrm{}}^{+}{,T}_{1/2}=20.2\mathrm{}\hspace{0.5em}\mathrm{ms})$ and ${}^{12}\mathrm{N}{(I}^{\pi }{=1\mathrm{}}^{+}{,T}_{1/2}=11.0\mathrm{}\hspace{0.5em}\mathrm{ms}).\mathrm{}$ The axial charge was determined to be $y=4.96\mathrm{}\pm 0.09$ $(\mathrm{stat}.\mathrm{})\pm 0.05$ $(\mathrm{syst}.\mathrm{})$ at a 90% confidence level. The previously obtained data in the year 1996 was reanalyzed to be added to the present result. The combined result is $y=4.90\mathrm{}\pm 0.10$ at a 90% confidence level. The axial charge is enhanced as much as $(72\mathrm{}\pm 4)\%$ from the impulse approximation model calculated value $y_{\mathrm{IA}}=\mathrm{2.85.}\mathrm{}$ Calculations using the impulse approximation with the soft-$\pi$ contribution $y_{\mathrm{th}}=4.15\mathrm{}$ explain the data quite well but not completely. If we introduce the in-medium mass renormalization the unexplained part of the experimental result corresponds to an in nuclear-medium nucleon mass reduction of $(16\mathrm{}\pm 4)\%$ at a 90% confidence level relative to the free nucleon mass, at the place where the decaying nucleon resides.

The gap equation for the fermion in nuclear medium is obtained in a two-flavor gauged Nambu–Jona-Lasino (NJL) model using the Schwinger-Dyson (SD) equations. The gap equation is solved with a quenched truncation. Compared to the four-fermion interaction, the one-gluon-exchange interaction accounts for considerable contributions (about $15-50\%)$ to dynamically generated fermion mass. With incorporation of gluonic contributions into a scheme where there is only four-fermion interaction, the four-fermion coupling constant is made density dependent. Impacts of the density-dependent four-fermion (DDFF) coupling constants on quantities, such as the fermion mass and the chiral order parameter as well as masses of mesons (σ,π), are estimated. The DDFF coupling constants lead to less density dependence of hadron masses and the larger critical density of chiral symmetry restoration than those from the pure four-fermion interaction. The calculated quantities are somehow dependent on the confinement scale ${\Lambda }_{\mathrm{QCD}}.$ However, the range of ${\Lambda }_{\mathrm{QCD}}$ in the present parametrization can be determined by the saturation property of the gluonic contribution in the medium and it turns out quite small.

An eikonal model has been used to assess the relationship between calculated strengths for first forbidden $\beta$ decay and calculated cross sections for $\mathrm{}(p,n)\mathrm{}$ charge exchange reactions. It is found that these are proportional for strong transitions, suggesting that hadronic charge exchange reactions may be useful in determining the spin-dipole matrix elements for astrophysically interesting leptonic processes.

In a recent paper the systematics for the yield of beam velocity α particles from a number of weakly bound light nuclei have been explored. In this paper the α particle yields are continuously referred to as arising from breakup. We caution that these experimental cross sections on which the analysis in the paper is based do not reflect breakup alone, but include yield from at least three different reaction processes.

The transfer/breakup designation was meant to be inclusive of several processes leading to breakup of the projectile. While it would be interesting to separate these various reaction channels, the information required to do so is often not available. This should not be allowed to obscure the observation that the sum of these direct processes appears to follow a systematic trend.

The relative cross sections for scattering of neutrons by protons have been measured at $E_n=10\mathrm{}\hspace{0.5em}\mathrm{MeV}$ for center-of-mass neutron scattering angles from $60°$ to 180°. Absolute differential cross section values were obtained by normalizing the angle-integrated relative angular distribution to the $n-p$ total cross section. The angular distribution exhibits a backward enhancement consistent with an exchange component of the $n-p$ interaction at this energy. The relative shape of the angular distribution is in good agreement with the prediction of the charge-dependent Bonn and Nijmegen potential models and with the Arndt phase-shift analysis. Better agreement is found with the evaluated nuclear data files (ENDF)/B-V than with the ENDF/B-VI evaluation.

Levels in the neutron-rich, odd-mass ${}^{107}\mathrm{Ru}$ nucleus have been reinvestigated with Gammasphere by measuring high-fold, prompt coincidence events following spontaneous fission of ${}^{252}\mathrm{Cf}.$ The ground state band has been extended up to $\frac{27}{2}ħ.$ The structure associated with the $h_{11/2}$ excitation has been confirmed and extended to higher spin. The $h_{11/2}$ band head has been established to lie at 301.8 keV. These results clear up differences between our earlier work and results from another experiment published recently. A new collective band based on a ${9/2}^{-}$ level has been identified for the first time. Some distinct features of the level scheme are discussed.

We analyze low-energy hyperon-nucleon scattering using an effective field theory in next-to-leading order. By fitting experimental cross sections for laboratory hyperon momenta below $200\hspace{0.5em}\mathrm{MeV}/c$ and using information from the hypertriton we determine 12 contact-interaction coefficients. Based on these we discuss the low-density expansion of hyperon mass shifts in the nuclear medium.

We calculate in baryon chiral perturbation theory the relativistic ${1/M}^2$ corrections to the leading order two-pion exchange diagrams. We give explicit expressions for the corresponding one-loop $\mathrm{NN}$ amplitudes in momentum space. The resulting isovector central and isoscalar spin-spin and tensor $\mathrm{NN}$ amplitudes involve nonstatic terms proportional to the squared nucleon center-of-mass momentum $p^2.$ From the two-pion exchange box diagrams we obtain an isoscalar quadratic spin-orbit $\mathrm{NN}$ amplitude. We give also analytical expressions for the corresponding $\mathrm{NN}$ potentials in coordinate space. The diagrammatic results presented here make the chiral $\mathrm{NN}$ potential complete at next-to-next-to-next-to-leading order.

We calculate the inelastic scattering cross sections to populate one- and two-phonon states in heavy ion collisions with both Coulomb and nuclear excitations. Starting from a microscopic approach based on random-phase approximation, we go beyond it in order to treat anharmonicities and nonlinear terms in the exciting field. These anharmonicities and nonlinearities are shown to have important effects on the cross sections both in the low energy part of the spectrum and in the energy region of the double giant quadrupole resonance. By properly introducing an optical potential, the inelastic cross section is calculated semiclassically by integrating the excitation probability over all impact parameters. A satisfactory agreement with the experimental results is obtained.

We discuss the measurement of polarized photons arising from radiative muon capture. The spectrum of left circularly polarized photons or equivalently the circular polarization of the photons emitted in radiative muon capture on hydrogen is quite sensitive to the strength of the induced pseudoscalar coupling constant $g_P.$ A measurement of either of these quantities, although very difficult, might be sufficient to resolve the present puzzle resulting from the disagreement between the theoretical prediction for $g_P$ and the results of a recent experiment. This sensitivity results from the absence of left-handed radiation from the muon line and from the fact that the leading parts of the radiation from the hadronic lines, as determined from the chiral power counting rules of heavy-baryon chiral perturbation theory, all contain pion poles.

X rays from the cascade of antiprotonic atoms have been studied by the PS209 Collaboration at LEAR of CERN. In this publication the strong interaction widths and shifts for calcium isotopes are presented. The isotopes ${}^{40}\mathrm{Ca}{,}^{42}\mathrm{Ca}{,}^{43}\mathrm{Ca}{,}^{44}\mathrm{Ca},$ and ${}^{48}\mathrm{Ca}$ have been investigated. The measured widths are compared with results from Hartree-Fock-Bogoliubov calculations. As a ${\mathrm{CaCO}}_3$ target had been used for the measurement also the lowest antiprotonic transition of ${}^{16}\mathrm{O}$ could be observed.

Previous calculations of the equation of state of symmetric nuclear matter, with the inclusion of the three-hole-line contribution, are extended to densities up to about six times the saturation value. The calculations are performed for the Argone $v_{14}$ and the Argonne $v_{18}$ two-nucleon potentials, and a larger set of partial waves is included. Evidence for the convergence of the Bethe-Brueckner-Goldstone expansion, even at relatively high density, is presented. The contribution to the equation of state of the three-hole-line diagrams, within the continuous choice of the single-particle potential, turns out to be almost negligible, except at the highest densities.

The application of a recently proposed procedure for discretizing the continuum to collision processes involving weakly bound nuclei is studied. In particular, the coupling to breakup states in the collision of ${d+}^{208}\mathrm{Pb}$ at 50 MeV is discussed. For illustrative purposes, only the s-wave component of the bound state of the deuteron is considered, and the study is restricted to the case of nuclear s-wave breakup. The continuum discretization procedure provides a basis of transformed harmonic oscillator wave functions to accomplish the necessary calculations. Appropriate convergence of the elastic and breakup cross sections with increasing dimension of the basis is reported. In addition, it is shown that the results obtained converge to those of a standard continuum discretized coupled channels calculation, with the advantage that the convergence of the method is determined by only one parameter, namely the dimension of the basis.

A thorough analysis of all stages of heavy ion fusion reaction leading to the formation of a heavy evaporation residue has been performed. The main goal of the analysis was to gain better understanding of the whole process and to find out what factors and quantities, in particular, bring major uncertainty into the calculated cross sections, how reliable the calculation of the cross sections of superheavy element formation may be and what additional theoretical and experimental studies should be made in this field.

Beams of protons and pions of $5.9\hspace{0.5em}\mathrm{GeV}/c$ were incident on a C target. Neutrons emitted into the backward hemisphere, in the laboratory system, were detected in (triple) coincidence with two emerging particles of tranverse momenta $p_t>0.6\mathrm{}\hspace{0.5em}\mathrm{GeV}/c.\mathrm{}$ We determined that for $(46.5\mathrm{}\pm 3.7)\%$ of the proton-induced events and for $(40.8\mathrm{}\pm 4.5)\%$ of the pion-induced events with the two high-$p_t$ particles, there is also at least one backward emitted neutron with momentum greater than $0.32\hspace{0.5em}\mathrm{GeV}/c.\mathrm{}$ This observation is in sharp contrast to a well- established universal pattern from a large variety of earlier inclusive measurements with hadrons, electrons, photons, neutrinos, and antineutrinos where the probability for backward nucleon emission was in the 5 to $10\%$ range. We present also a measurement of the momentum spectra for the backward going neutrons. The spectra have the same universal shape observed in the inclusive reactions. We speculate that the enhanced backward neutron emission in this semi-inclusive region could be an indication for a strong dependence of the cross section on the squared total center-of-mass energy (s) and for the importance of short-range nucleon-nucleon correlations.

The minimal standard electroweak model can be tested by allowing all the solar neutrino fluxes, with undistorted energy spectra, to be free parameters in fitting the measured solar neutrino event rates, subject only to the condition that the total observed luminosity of the Sun be produced by nuclear fusion. The rates of the five experiments prior to SNO (chlorine, Kamiokande, SAGE, GALLEX, Super-Kamiokande) cannot be fit by an arbitrary choice of undistorted neutrino fluxes at the level of $2.5\sigma$ (formally 99% C.L.). Considering just SNO and Super-Kamiokande, the discrepancy is at the $3.3\sigma$ level ${(10\mathrm{}}^{-3}\hspace{0.5em}\mathrm{C}.\mathrm{L}.\mathrm{}).\mathrm{}$ If all six experiments are fit simultaneously, the formal discrepancy increases to $4\sigma$ $(7\mathrm{}\times {10}^{-5}\hspace{0.5em}\mathrm{C}.\mathrm{L}.\mathrm{}).\mathrm{}$ If the relative scaling in temperature of the nuclear reactions that produce ${}^7\mathrm{Be}$ and ${}^8\mathrm{B}$ neutrinos is taken into account, the formal discrepancy is at the $7.4\sigma$ level.