An Overview of the Anomalous Soft Photons in Hadron Production

Productions of soft photon with low transverse momenta in high-energy hadron-hadron collisions and $e^+$-$e^-$ annihilations indicate that they are consistently produced in excess of what are predicted by electromagnetic bremsstrahlung when hadrons (mostly mesons) are produced, but they agree with electromagnetic bremsstrahlung predictions in the absence of hadron production. These excess soft photons are called anomalous soft photons. The occurrence of anomalous soft photons in association with hadron production reveals the presence of additional QED soft photon sources in QCD hadron production. Many different models have been proposed to explain the anomalous soft production. We shall examine specifically a quantum field theory of simultaneous meson and soft photon production in QCDxQED in which the meson production arises from the oscillation of color charge densities of the quarks of the underlying vacuum in a flux tube. As a quark carries both a color charge and an electric charge, the oscillation of the color charge densities will be accompanied by the oscillation of electric charge densities, which will in turn lead to the simultaneous production of anomalous soft photons during the meson production process.Comment: 16 pages, 2 figures, invited talk presented at International Conference on the Structure and the Interactions of the Photon including the 20th International Workshop on Photon-Photon Collisions and the International Workshop on High Energy Photon Linear Colliders 20-24 May 2013, Paris, France, to be published in Proceedings of Scienc

Foundation of Hydrodynamics for Systems with Strong Interactions

For a dense and strongly interacting system, such as a nucleus or a strongly-coupled quark-gluon plasma, the foundation of hydrodynamics can be better found in the quantum description of constituents moving in the strong mean fields generated by all other particles. Using the result that the Schroedinger equation and the Klein-Gordon equation can be written in hydrodynamical forms, we find that the probability currents of the many-body system in the mean-field description obey a hydrodynamical equation with stress tensors arising from many contributions: quantum effects, mean-field interactions, and thermal fluctuations. The influence of various contributions to the hydrodynamical motion is expected to vary with the temperature, as the quantum and mean-field stress tensors playing more important roles at low and moderate temperatures.Comment: 10 pages, lecture presented at the Relativistic Fluids Symposium in the IV Mexican Meeting on Mathematical and Experimental Physics, Mexico City, Mexico, July 13-19, 201

Signatures of Quark-Gluon Plasma Phase Transition in High-Energy Nuclear Collisions

In high-energy nuclear collisions, the new phase of the quark-gluon plasma is indicated by an anomalous increase in pressure, an excess of direct photon production, an excess of strangeness production, and an anomalous J/psi suppression. We review these signatures and discuss how recent high-energy heavy-ion experiments at CERN are consistent with the production of the quark-gluon plasma in high-energy Pb+Pb collisions.Comment: 12 pages, 6 figures, in LaTex, invited talk presented at the Third Catania Relativistic Ion Studies on Phase Transitions in Strong Interactions, Acicastello, Italy, May 22-26, 2000, to be published in the Conference proceeding

Quantum Treatment of the Multiple Scattering and Collective Flow in Intensity Interferometry

We apply the path-integral method to study the multiple scattering and collective flow in intensity interferometry in high-energy heavy-ion collisions. We show that the Glauber model and eikonal approximation in an earlier quantum treatment are special examples of the more general path-integral method. The multiple scattering and collective flow lead essentially to an initial source at a shifted momentum, with a multiple collision absorption factor that depends on the pion absorption cross section and a phase factor that depends on the deviations of the in-medium particle momenta from their asymptotic values.Comment: 6 pages, in LaTex, to be published in the Proceedings of the Workshop on Particle Correlations and Femtoscopy, Kromeriz, Czech Republic, August 15-17, 200