18942639
Femtoscopically Probing the Freeze-out Configuration in Heavy Ion Collisions
Two-particle femtoscopy reveals the space-time substructure of the freeze-out configuration from heavy ion collisions. Detailed fingerprints of bulk collectivity are evident in space-momentum correlations, which have been systematically measured as a function of particle type, three-momentum, and collision conditions. A clear scenario, dominated by hydrodynamic-type flow emerges. Reproducing the strength and features of the femtoscopic signals in models involves important physical quantities like the Equation of State, as well as less fundamental technical details. An interesting approximate "factorization" in the measured systematics suggests that the overall physical freeze-out scale is set by final state chemistry, but the kinematic substructure is largely universal. Referring to previous results from hadron and lepton collisions, we point to the importance of determining whether these "universal" trends persist from the largest to the smallest systems. We review theoretical expectations for heavy ion femtoscopy at the LHC, and point to directions needing further theory and experimental work at RHIC and the LHC.
123768410
TWO-PARTICLE AND MULTI-PARTICLE MEASUREMENTS FOR THE QUARK-GLUON PLASMA
118808591
A soluble statistical model for nuclear fragmentation
The statistical model of Chase and Mekjian, which offers an analytic solution for the canonical ensemble of non-interacting fragments, is investigated for it's thermodynamic behavior. Various properties of the model, which exhibits a first-order phase transition, are studied. The effects of finite particle number are investigated. Three extensions of the model are considered, excluded volume, Coulomb effects and inclusion of isospin degrees of freedom. A formulation of a microcanonical version of the model is also presented.
119498041
Statistical Models of Nuclear Fragmentation
A method is presented that allows exact calculations of fragment multiplicity distributions for a canonical ensemble of non-interacting clusters. Fragmentation properties are shown to depend on only a few parameters. Fragments are shown to be copiously produced above the transition temperature. At this transition temperature, the calculated multiplicity distributions broaden and become strongly super-Poissonian. This behavior is compared to predictions from a percolation model. A corresponding microcanonical formalism is also presented.
122092624
Balance functions: A signal of late-stage hadronization
126055148
Effects of Charge Conservation and Flow on Fluctuations of parity-odd Observables ar RHIC
The observation of fluctuations of parity-odd angular observables at RHIC has been interpreted as a signal of a local parity violation. We show how the observed correlations can be explained by local charge conservation at freeze-out combined with elliptic flow. Calculations from a blast wave model, which overlays thermal emission onto a collective flow profile, are shown to account for the experimentally observed signal.
7071388
Nonperturbative versus perturbative effects in generalized parton distributions
Generalized parton distributions (GPDs) are studied at the hadronic (nonperturbative) scale within different assumptions based on a relativistic constituent quark model. In particular, by means of a meson-cloud model we investigate the role of nonperturbative antiquark degrees of freedom and the valence-quark contribution. A QCD evolution of the obtained GPDs is used to add perturbative effects and to investigate the GPDs' sensitivity to the nonperturbative ingredients of the calculation at larger (experimental) scale.
17088589
Analytic treatment of positronium spin splittings in light-front QED
We study the QED bound-state problem in a light-front Hamiltonian approach. Starting with a bare cutoff QED Hamiltonian H{sub B} with matrix elements between free states of drastically different energies removed, we perform a similarity transformation that removes the matrix elements between free states with energy differences between the bare cutoff {Lambda} and effective cutoff {lambda} ({lambda}{lt}{Lambda}). This generates effective interactions in the renormalized Hamiltonian H{sub R}. These effective interactions are derived to order {alpha} in this work, with {alpha}{lt}1. H{sub R} is renormalized by requiring it to satisfy coupling coherence. A nonrelativistic limit of the theory is taken, and the resulting Hamiltonian is studied using bound-state perturbation theory. The effective cutoff {lambda}{sup 2} is fixed, and the limit 0{l_arrow}m{sup 2}{alpha}{sup 2}{lt}{lambda}{sup 2}{lt}m{sup 2}{alpha}{r_arrow}{infinity} is taken. This upper bound on {lambda}{sup 2} places the effects of low-energy (energy transfer below {lambda}) emission in the effective interactions in the {vert_bar}e{bar e}{r_angle} sector. This lower bound on {lambda}{sup 2} ensures that the nonperturbative scale of interest is not removed by the similarity transformation. As an explicit example of the general formalism introduced, we show that the Hamiltonian renormalized to O({alpha}) reproduces the exact spectrum of spin splittings, with degeneracies dictated by rotationalmore » symmetry, for the ground state through O({alpha}{sup 4}). The entire calculation is performed analytically, and gives the well-known singlet-triplet ground-state spin splitting of positronium, (7)/(6){alpha}{sup 2}Ryd. We discuss the remaining corrections other than the spin splittings and how they can be treated in calculating the spectrum with higher precision. {copyright} {ital 1997} {ital The American Physical Society}« less