Aspects Of Heavy Ion Collisions Research Articles

Excited hadron channels in hadronization

The proper treatment of hadronic resonances plays an important role for many aspects of heavy ion collisions. We expect this to be the case also for hadronization, due to the large degeneracies of excited states, and the abundant production of hadrons from their decays. We show how a comprehensive treatment of excited meson states can be incorporated into quark recombination, and in extension, into Hybrid Hadronization. We discuss in detail the quantum mechanics of forming excited states, utilizing the Wigner distribution functions of angular momentum eigenstates of isotropic 3-D harmonic oscillators. We describe how resonance decays can be handled, based on a set of minimal assumptions, by creating an extension of hadron decays in PYTHIA 8. Finally, we present a study of hadron production by jets using PYTHIA and Hybrid Hadronization with excited mesons up to orbital angular momentum L = 4. We find that states up to L = 2 are produced profusely by quark recombination.

Aspects of heavy-ion collisions at the LHC

Three features of relativistic heavy-ion collisions are discussed: (1) Stopping at RHIC and LHC energies in a QCD-based model, (2) Charged-particle production in a relativistic diffusion model (RDM), and (3) Υ suppression in PbPb collisions at the current LHC energy of √sNN = 2.76 TeV.

The Gauge-String Duality and Heavy Ion Collisions

I review at a non-technical level the use of the gauge-string duality to study aspects of heavy ion collisions, with special emphasis on the trailing string calculation of heavy quark energy loss. I include some brief speculations on how variants of the trailing string construction could provide a toy model of black hole formation and evaporation. This essay is an invited contribution to "Forty Years of String Theory" and is aimed at philosophers and historians of science as well as physicists.

Investigation of jet quenching and elliptic flow within a pQCD-based partonic transport model

The partonic transport model BAMPS (a Boltzmann approach to multiparton scatterings) is employed to investigate different aspects of heavy ion collisions within a common framework based on perturbative QCD. This report focuses on the joint investigation of the collective behavior of the created medium and the energy loss of high–pT gluons traversing this medium. To this end the elliptic flow and the nuclear modification factor of gluons in heavy ion collisions at 200 AGeV are simulated with BAMPS.The mechanism for the energy loss of high energy gluons within BAMPS is studied in detail. For this, purely elastic interactions are compared to radiative processes, gg → ggg, that are implemented based on the matrix element by Gunion and Bertsch. The latter are found to be the dominant source of energy loss within the framework employed in this work.

Heavy-ion physics prospects with the ATLAS detector at the LHC

The next great energy frontier in relativistic heavy-ion collisions is quickly approaching with the completion of the large hadron collider and the ATLAS experiment is poised to make important contributions in understanding QCD matter in extreme conditions. While designed for high-pT measurements in high-energy p+p collisions, the detector is well suited to study many aspects of heavy-ion collisions from bulk phenomena to high-pT and heavy-flavor physics. With its large and finely segmented electromagnetic and hadronic calorimeters, the ATLAS detector excels in measurements of photons and jets, observables of great interest at the LHC. In this paper, we highlight the performance of the ATLAS detector for Pb+Pb collisions at the LHC with special emphasis on a key feature of the ATLAS physics program: jet and direct photon measurements.

Recent results on Pb+Pb collisions at 158 AGeV from the WA98 experiment at CERN

We present recent results obtained with the WA98 experiment at CERN SPS. The experiment consists of large acceptance hadron and photon spectrometers which allow to study many aspects of heavy ion collisions. We use event-by-event measurements of charged and neutral particle multiplicity to establish the limit on the prodution of Disoriented Chiral Condensates. We use the Plastic Ball detector together with a set of tracking chambers to study collective flow. The tracking chambers together with the excellent particle identification allow us to study the production of Δ ++. The high resolution photon calorimeter array allows us to study inclusive photon and π 0 spectra and search for excess direct photons.

A Monte Carlo program for nuclear collision geometry

Many of the aspects of heavy ion collisions are closely related to the nuclear geometry. Any Monte Carlo based model in this field, therefore, has to have a part describing the nuclear geometry. The subroutine described here is one attempt to provide that part. The nuclei are described in a way which is consistent with experimental findings. Routines for deformed nuclei are provided.

Role of giant resonance excitation in heavy ion collisions

Abstract In this paper we discuss several aspects of heavy ion collisions involving collective vibrational modes. In our approach the relative motion is treated in a semiclassical approximation, while the intrinsic degrees of freedom are described microscopically within the RPA. The differences with respect to macroscopic models are analyzed in the appendix. First we present some results on the inelastic scattering cross section and we show that the structures observed experimentally can be explained in terms of multiple excitation of the Giant Quadrupole Resonance. After we calculate an adiabatic polarization potential describing the coupling to the collective vibrational modes and show that it produces a strong enhancement of the subbarrier fusion cross section. This enhancement is found to be enough to reproduce the experimental data for symmetric systems, while for asymmetric reactions the coupling to other degrees of freedom, like transfer, is needed. Finally we report some preliminary results on a dynamical calculation of the real and imaginary parts of the polarization potential. We show that at high incident energies ( E A > 20 MeV ) the role of the Giant Quadrupole Resonance becomes dominant.

Contribution of multistep transfers to low-energy elastic and reaction cross sections

Two aspects of heavy-ion collisions at near-barrier energies deviate considerably from the predictions of simple potential models. Fusion cross sections are generally greatly underpredicted, and in a recent analysis of 16O elastic scattering on 208Pb the optical potential had a marked energy dependence. We show that the inclusion of both neutron and proton transfers in addition to inelastic excitation processes within a coupled channels framework can give a consistent description of the data.