The density of gluons produced in the central rapidity region of a heavy-ion collision is poorly known. We investigate the influence of the effects of quantum coherence on the transverse momentum distribution of photons and gluons radiated by a quark propagating through nuclear matter. We describe the case where the radiation time substantially exceeds the nuclear radius (the relevant case for RHIC and LHC energies), which is different from what is known as the Landau-Pomeranchuk-Migdal effect corresponding to an infinite medium. We find suppression of the radiation spectrum at small transverse photon(gluon) momentum $k_T,$ but enhancement for $k_T>1\mathrm{}\mathrm{GeV}.$ Any nuclear effects vanish for $k_T>~10\mathrm{GeV}.$ Our results also allow us to calculate the $k_T$-dependent nuclear effects in prompt photon, light, and heavy (Drell-Yan) dilepton and hadron production.

We have carried out simulations of the hadronization of a hot, ideal but effectively massive quark-gluon gas into color-neutral clusters in the framework of the semiclassical SU(3) chromodielectric model. We have studied the possible quark-gluon compositions of clusters as well as the final mass distribution and spectra, aiming to obtain insight into relations between hadronic spectral properties and the confinement mechanism in this model.

Some questions arising in the application of the thermal model to hadron production in heavy ion collisions are studied. We do so by applying the thermal model of hadron production to particle yields calculated by the microscopic transport model RQMD (version 2.3). We study the bias of incomplete information about the final hadronic state on the extraction of thermal parameters. It is found that the subset of particles measured typically in the experiments looks more thermal than the complete set of stable particles. The hadrons which show the largest deviations from thermal behavior in RQMD (version 2.3) are the multistrange baryons and antibaryons. We also looked at the influence of rapidity cuts on the extraction of thermal parameters and found that they lead to different thermal parameters and larger disagreement between the RQMD yields and the thermal model.

A new type of pion interferometry formula is derived, in which not only the correlator but also the pion multiplicity is taken into consideration. The method to obtain information about the initial emission probability of unsymmetrized bosons is given.

We reexamine the production of $J/\psi$ and other charmonium states for a variety of target-projectile choices at the CERN Super Proton Synchrotron, in particular for the interesting comparison between S+U at $200\hspace{0.5em}\mathrm{GeV}/c$ and Pb+Pb at $158\hspace{0.5em}\mathrm{GeV}/c$ as observed in the experiments NA38 and NA50, respectively. For this study we use a newly constructed cascade code LUCIFER II, which yields acceptable descriptions of both hard and soft processes, specifically Drell-Yan and meson production. This code divides the ion-ion collision into an initial phase involving hard interactions of the original nucleons and no soft energy loss, followed after the meson formation time by a “normal” low energy cascade among the secondary particles. The modeling of the charmonium states differs from that of earlier workers in its unified treatment of the hidden charm meson spectrum, which is introduced from the outset as a set of coupled states $\{\psi ,{\chi }^i,{\psi }^{\prime }\}.$ The result is a description of the NA38 and NA50 data in terms of a conventional, hadronic picture. The apparently anomalous suppression found in the most massive Pb+Pb system arises in the present simulation from three sources: destruction in the initial nucleon-nucleon cascade phase, use of coupled channels to exploit the larger breakup in the less bound ${\chi }^i$ and ${\psi }^{\prime }$ states, and comover interaction in the final low energy phase.

Attention is drawn to the role played by the size of the system in the thermodynamic analysis of particle yields in relativistic heavy ion collisions at SIS energies. This manifests itself in the nonlinear dependence of $K^{+}$ and $K^{-}$ yields in $\mathrm{AA}$ collisions at $(1\mathrm{}–2)A\hspace{0.5em}\mathrm{GeV}$ on the number of participants. It is shown that this dependence can be quantitatively well described in terms of a thermal model with a canonical strangeness conservation. The measured particle multiplicity ratios $({\pi }^{+}/p,{\pi }^{-}/{\pi }^{+},d/p,K^{+}/{\pi }^{+},$ and $K^{+}{/K}^{-}$ but not $\eta /{\pi }^0)$ in central Au-Au and Ni-Ni collisions at $(0.8\mathrm{}–2.0)A\hspace{0.5em}\mathrm{GeV}$ are also explained in the context of a thermal model with a common freeze-out temperature and chemical potential. Including the concept of collective flow a consistent picture of particle energy distributions is derived with the flow velocity being strongly impact-parameter dependent.

We derive the relativistic quantum transport equation for the pion distribution function based on an effective Lagrangian of the QHD-II model. The closed-time-path Green’s function technique and the semiclassical, quasiparticle, and Born approximations are employed in the derivation. Both the mean field and collision term are derived from the same Lagrangian and presented analytically. The dynamical equation for the pions is consistent with that for the nucleons and Δ’s which we developed before. Thus, we obtain a relativistic transport model which describes the hadronic matter with N, $\Delta ,$ and $\pi$ degrees of freedom simultaneously. Within this approach, we investigate the medium effects on the pion dispersion relation as well as the pion absorption and pion production channels in cold nuclear matter. In contrast to the results of the nonrelativistic model, the pion dispersion relation becomes harder at low momenta and softer at high momenta as compared to the free one, which is mainly caused by the relativistic kinetics. The theoretically predicted free $\pi \overrightarrow{N}\Delta$ cross section is in agreement with the experimental data. Medium effects on the $\pi \overrightarrow{N}\Delta$ cross section and momentum-dependent $\Delta$-decay width are shown to be substantial.

We calculate the rate for the two-photon decay of the η and ${\mathrm{\eta }}^{\prime }$ mesons in a relativistic quark model which includes a model of confinement. [In the absence of the confinement model, our model reduces to the SU(3)-flavor Nambu–Jona-Lasinio model supplemented by the ’t Hooft interaction.] Since we have studied singlet-octet mixing for the η and ${\mathrm{\eta }}^{\prime }$ in a previous work, we do not have any adjustable parameters in our calculations. The decay of the η may be calculated with or without a confinement model for a fixed set of parameters. In the absence of confinement, the width ${\Gamma }_{\overrightarrow{\eta }\gamma \gamma }$ is overestimated by a factor of 3 in our analysis. However, inclusion of confinement then yields an excellent fit to the data for ${\Gamma }_{\overrightarrow{\eta }\gamma \gamma }$ and a value of ${\Gamma }_{{\eta }^{\prime }\to \gamma \gamma }$ which is about 25% too small. While it is possible to fit ${\Gamma }_{\overrightarrow{\eta }\gamma \gamma }$ without a confinement model, using modified values of the parameters, it is clear that a model of confinement is needed if we are to describe the properties of both the η and ${\mathrm{\eta }}^{\prime }$ in calculations of the type considered here.

Quark-antiquark bound states are considered using a relativistic equal-time (ET) equation for two spin-1/2 particles that includes negative-energy components of wave functions. In the limit where either particle’s mass tends to infinity, the ET equation reduces to the one-body Dirac equation. The use of a scalar confining interaction in the ET equation is found to produce imaginary eigenvalues for the bound-state energy, similar to the findings based on the Salpeter equation. Retardation effects predict a modified static interaction in which couplings to doubly negative components of the wave function vanish. This modified static interaction eliminates the imaginary eigenvalues. However, the modified analysis can produce abnormal solutions with a large relative momentum between the quark and antiquark when used with a scalar confining interaction. Anomalous negative-energy components of wave functions result when a timelike vector confining interaction is used for equal-mass quarks. In the one-body limit, the Klein instability occurs with timelike vector confinement. For stability without regard to the type of confinement, the negative-energy components of wave functions should be omitted.

We study the finite quark mass effects of the low-energy QCD using the improved ladder Schwinger-Dyson and Bethe-Salpeter equations which are derived in the manner consistent with the vector and axial-vector Ward-Takahashi identities. The nonperturbative mass-independent renormalization allows us to calculate the quark condensate for a nonzero quark mass. We explicitly show that the partial conservation of axial-vector current relation holds. The key ingredients are the Cornwall-Jackiw-Tomboulis effective action, the generalized Noether current, and the introduction of the regularization function to the Lagrangian. Reasonable values of the pion mass, the pion decay constant, and the quark condensate are obtained with a rather large ${\Lambda }_{\mathrm{QCD}}.$ The pion mass square and the pion decay constant are almost proportional to the current quark mass up to the strange quark mass region. It suggests that the chiral perturbation is applicable up to the strange quark mass region. We study the validity of the approximation often used in solving the Bethe-Salpeter equations too.

We calculate differential cross sections and the spin transfer coefficient $D_{\mathrm{nn}}$ in the $\overrightarrow{p}+\overrightarrow{\alpha }\overrightarrow{p}+\alpha +{\pi }^0$ reaction for proton bombarding energies from 1 to 10 GeV and ${\pi }^0-p$ invariant masses spanning the region of the $N^{*}\mathrm{}\left(1440\right)\mathrm{}$ Roper resonance. Two processes—$\Delta$ excitation in the $\alpha$ particle and Roper excitation in the proton—are included in an effective reaction model which was shown previously to reproduce existing inclusive spectra. The present calculations demonstrate that these two contributions can be clearly distinguished via $D_{\mathrm{nn}},$ even under kinematic conditions where cross sections alone exhibit no clear peak structure due to the excitation of the Roper resonance.

The electromagnetic form factors $G_E{(q}^2),\hspace{0.5em}{G}_M{(q}^2),$ and $G_Q{(q}^2),$ charge radii, magnetic and quadrupole moments, and decay widths of the light vector mesons ${\rho }^{+}{,K}^{*+},$ and $K^{*0}$ are calculated in a Lorentz-covariant, Dyson-Schwinger-equation-based model using algebraic quark propagators that incorporate confinement, asymptotic freedom, and dynamical chiral symmetry breaking, and vector-meson Bethe-Salpeter amplitudes closely related to the pseudoscalar amplitudes obtained from phenomenological studies of $\pi$ and K mesons. Calculated static properties of vector mesons include the charge radii and magnetic moments $〈r_{\rho +}^2{〉}^{1/2}=0.61\mathrm{}\hspace{0.5em}\mathrm{fm},\hspace{0.5em}〈r_{K^{*+}}^2{〉}^{1/2}=0.54\mathrm{}\hspace{0.5em}\mathrm{fm},$ and $〈r_{K^{*0}}^2〉=-0.048\hspace{0.5em}{\mathrm{fm}}^2$ and ${\mu }_{\rho +}=2.69,\hspace{0.5em}{\mu }_{K^{*+}}=2.37,$ and ${\mu }_{K^{*0}}=-\mathrm{0.40.}$ The calculated static limits of the $\rho$-meson form factors are similar to those obtained from light-front quantum mechanical calculations, but begin to differ above $q^2=1\mathrm{}\hspace{0.5em}{\mathrm{GeV}}^2$ due to the dynamical evolution of the quark propagators in our approach.

We demonstrate that the restoration of chiral symmetry at finite T in a class of confining Dyson-Schwinger equation (DSE) models of QCD is a mean field transition, and that an accurate determination of the critical exponents using the chiral and thermal susceptibilities requires very small values of the current-quark mass: ${\log }_{10}{(m/m}_u)\lesssim -5.$ Other classes of DSE models characterized by qualitatively different interactions also exhibit a mean field transition. Incipient in this observation is the suggestion that mean field exponents are a result of the gap equation’s fermion substructure and not of the interaction.

We study the short-range nucleon-nucleon interaction in a nonrelativistic chiral constituent quark model by diagonalizing a Hamiltonian containing linear confinement and a Goldstone boson exchange interaction between quarks. A finite six-quark basis obtained from single particle cluster model states was previously used. Here we show that the configurations which appear naturally through the use of molecular orbitals, instead of cluster model states, are much more efficient in lowering the six-quark energy.

Approximate two-fermion interactions and Bethe-Salpeter equations for hadron spectra are obtained by making a Fock space expansion of the quantum chromodynamics (QCD) mass eigenstate. Following a partial wave decomposition, we perform an average over quartic gluon vertices and a root mean square (rms) average over cubic vertices. The expansions in terms of quark and gluon configurations are truncated. Equations for the gluon eigenvalues and eigenvectors are derived and approximate solutions are obtained analytically. Using values for the QCD coupling constant and the quark rest masses obtained from a relativistic two- and three-constituent quark model as starting values, the resulting algebraic eigenvalue equations for the mesons and the light baryons are then solved using a multiscale expansion in harmonic oscillator eigenfunctions. Through an approximate but analytic treatment we demonstrate that, at large distances our formalism gives rise to an effective two fermion potential exhibiting linear confinement. That is, we do not introduce any phenomenological confinement interaction. With minor adjustments of the quark rest masses, our results compare favorably with the results of the phenomenological two- and three-constituent quark models and with experiment.

Spatial parity nonconservation (PNC) has been studied in the compound-nuclear states of ${}^{134}\mathrm{Cs}$ by measuring the helicity dependence of the neutron total cross section. Transmission measurements on a thick ${}^{133}\mathrm{Cs}$ target were performed by the time-of-flight method at the Manuel Lujan Neutron Scattering Center with a longitudinally polarized neutron beam in the energy range from 5 to 400 eV. A total of 28 new p-wave resonances were found, their neutron widths determined, and the PNC longitudinal asymmetries of the resonance cross sections measured. The value obtained for the root-mean-square PNC element ${M=(0.06\mathrm{}}_{-0.02}^{+0.25\mathrm{}})$ meV in ${}^{133}\mathrm{Cs}$ is the smallest among all targets studied. This value corresponds to a weak spreading width ${\Gamma }_w{=(0.006\mathrm{}}_{-0.003}^{+0.154\mathrm{}})\times {10}^{-7}$ eV.

Cross sections for the disintegration of the deuteron via neutral-current (NCD) and charged-current (CCD) interactions with reactor antineutrinos $({\overline{\nu }}_e\overrightarrow{d}{\overline{\nu }}_e\mathrm{pn}$ and ${\overline{\nu }}_e\overrightarrow{d}{e}^{+}nn)$ are measured to be $6.08\pm 0.77\times {10}^{-45}\hspace{0.5em}{\mathrm{cm}}^2$ and $9.83\pm 2.04\times {10}^{-45}\hspace{0.5em}{\mathrm{cm}}^2$ per neutrino, respectively, in excellent agreement with current calculations. Since the experimental NCD value depends upon the CCD value, if we use the theoretical value for the CCD reaction, we obtain the improved value of $5.98\pm 0.54\times {10}^{-45}$ for the NCD cross section. The neutral-current reaction allows a unique measurement of the isovector–axial vector coupling constant in the hadronic weak interaction, $\beta .$ In the standard model, this constant is predicted to be exactly 1, independent of the Weinberg angle. We measure a value of ${\beta }^2=1.01\mathrm{}\pm \mathrm{0.16.}$ Using the above improved value for the NCD cross section, ${\beta }^2$ becomes $0.99\pm \mathrm{0.10.}$

The strength of the ${5/2}^{+}$ resonance of the reaction ${}^{36}\mathrm{Ar}(p,\gamma {)}^{37}\mathrm{K}$ at $E_p=918\mathrm{}\hspace{0.5em}\mathrm{keV}$ was measured absolutely: $\omega \gamma =(258\mathrm{}\pm 24)\hspace{0.5em}\mathrm{meV}.$ The new result is consistent with previous results. This resonance was used in several experiments as a calibration standard. Therefore we discuss our experimental uncertainties in detail which is important for the reliability of previous experiments and our new result.

The isotope shift of an optical transition $(\lambda =534.93\mathrm{}\hspace{0.5em}\mathrm{nm})$ in ${\mathrm{Ce}}^{+}$ for radioactive ${}^{144}\mathrm{Ce}$ has been measured by collinear laser-ion-beam spectroscopy as well as those of stable isotopes. The change in mean-square nuclear charge radius determined from the isotope shift is $\delta 〈r^2{〉}^{142,144}=0.232\mathrm{}\left(20\right)\mathrm{}\hspace{0.5em}{\mathrm{fm}}^2,$ and compared with the values from the reduced $E2\mathrm{}$ transition probability and the theoretical predictions.

The pseudorapidity distribution of shower particles produced in nuclear emulsions in heavy ion induced interactions have been studied at high energies. The thermalized cylinder picture is successful in the description of the pseudorapidity distribution of shower particles in the accelerator energy regions available at present. The calculated results are in agreement with the experimental data of $3.7A,14.6A,60A,$ and $200A$ GeV O-AgBr, $14.6A$ GeV Si-AgBr, $200A$ GeV S-AgBr, and $10.6A$ GeV Au-Em (emulsion) interactions.