Highlights of BCPL achievements in 2003
Since January 2000 up to now BCPL has received 64 project proposals has accepted 61 projects for
EU support from the beginning of yr. 2000. So far, more than 100 researchers visited BCPL.
Although, we did not receive additional financing from the EU to cover the excess demand, we did
accommodate more visitors, than our first contract planned. We did not run out of EU financing by
saving on the expenses of the user meetings held at ECT* in Trento Italy, and taking advantage of
our new IBM machine with increased power.
In year 2003/04 we hosted researchers for 20 projects, spreading over particle, high and low energy
nuclear, atomic, plasma and molecular physics, and extending to related fields in astrophysics as
well as abstract statistical physics problems. Two projects were extended and one postponed to the
beginning of year 2004, so these are reported in a brief additional report. Most projects belong to
BCPL’s core activity of reaction modeling in different areas of physics.
PARTICLE PHYSICS
The project "High-pT Meson Production in pA and AA Collision" led by Dr. Gabor Papp, et al.
(project 36) has performed a tedious task, namely the inclusion of intrinsic transverse momentum
of the partons into the NLO pQCD calculation. This way we were able repeat our earlier LO
calculations and include multiscattering into the theoretical frame containing transverse degrees of
freedom [1]. Furthermore, we managed to determine the strength of the nuclear multiscattering and
reproduce the Cronin effect at RHIC energies. These calculations yielded a solid basis to perform a
d+Au calculations at RHIC energies [2]. The latest PHENIX data on pion production at midrapidity were successfully reproduced. Using the GLV-formalism for non-abelian jet-quenching the
project could determine the nuclear modification factor for any value of opacity at any value of
centrality. Scanning the available experimental data one could determine the detected opacity
values and its impact parameter dependence [3]. These calculations led to a better understanding of
formation of hot dense matter in ultra relativistic heavy ion collision and naturally serve a
topographic picture for the collision.
[1] Nuclear Reaction Mechanisms and the Cronin Effect, G.G. Barnaföldi, P.Lévai,G. Papp, G. Fai,
(Rev. of the Univ. of Milano Ricerca Scientifica ed Educatione Permanente p. 549, nuclth/0307062))
[2] Pion Production in d+Au Collision at RHIC Energies, P. Lévai, G.G. Barnaföldi, G. Papp, G.
Fai, (submitted to Nuclear Physics) nucl-th/0306019
[3] Jet Tomography Studies in Au+Au Collision at RHIC Energies, G.G. Barnaföldi, P. Levai, G.
Papp, G.Fai and M. Gyulassy (accepted for publication in Eur. J. of Phys. Direct, nucl-th/0311343)
In the project “Three-body initial states in charmonium dissociation” (project no. 46) from Sylesian
University, Czech Republic, led by P. Lichard, the main goal of the whole project was to take the
formation of the rho resonance into consideration. This leads to the reactions with three hadrons in the
initial state, e.g., pi pi J/psi. The main objective of the two-week stay in Bergen in May 2003 was to
develop and test a computer program for calculating the rate of such reactions in a thermalized hadron
gas.
In Bergen it was realized that it will be convenient to have a universal computer program that can
be used not only for calculating the mean free path of charmonium in a hadron gas, but also the
reaction rates of other processes. The specification of the process under consideration is performed
by introducing the parameters of the incoming and outgoing particles and by supplying the
subroutine that calculates the reaction amplitude squared. The code was successfully tested on the
example of the dilepton production from the three-pion annihilation in a thermalized hadron gas,
where the results had already been obtained by a different program and published.
The project "The knot solitions", led by Egor Babaev (project 50), used the BCPL facilities for the
critically important study of checking applicability of knotted solitons and fractional vortices
concepts for models of two-gap superconductors (equivalent to the two-Higgs doublet model in
High Energy Physics) and to standard model for neutron stars. The results were published in three
articles: [1] E. Babaev "Phase diagram of planar $U(1)\times U(1)$ superconductor, Condensation
of vortices with fractional flux and a non-superconducting superfluid state" to appear in Nucl. Phys.
B [2] E. Babaev "Vortices carrying an arbitrary fraction of magnetic flux quantum, neutral
superfluidity and knotted solitons in two-gap Ginzburg-Landau model" to appear in Physica C. In
these articles we show that U(1)xU(1) system allows for the knot solitons and quasi-neutral quasisuperfluid state. Furthermore [3] E. Babaev "Andreev-Bashkin effect and possible knot solitons in
neutron stars" astro-ph/0211345 submitted to Phys. Rev. D, where we show that in this system,
besides ordinary vortices of the S^1\to S^1 map, (meta)stable finite-length knotted solitons are also
allowed, characterized by a non-trivial Hopf invariant.
HIGH ENERGY SUBATOMIC REACTIONS
Project 44 addressed these reactions with microscopic transport models, while 29, 54 and 57 used
continuum or CFD approaches to evaluate the collective effects in these reactions. Project 29 was
actually an important methodical advance, which introduced the use of different modules in a
reaction model and established an exact physical interface among the modules. This enables later to
create more involved modular reaction models, which can take advantage of GRID computing.
The projects, no. 44, led by F. Puelhofer, Marburg, simulated heavy ion collisions by the UrQMD
model. This project performed a comprehensive analysis of a large number of observables, which
enables us to make a complex assessment of the experimental observations. The equilibration is
studied numerically by a Monte-Carlo simulation, taking into account several strangeness conserving transitions. Due to conceptual problems in the program final results could not be
obtained during the stay in Bergen in September 2003. The preliminary results show no sign of a
volume dependence of relative strangeness. The project is being continued at our home institute.
Project 54 on “Dynamical coupling of microscopic models to relativistic hydrodynamics for heavy
ion collisions” by H. Stoecker, Frankfurt, Germany, extended an existing (3+1)-dim.
hydrodynamical model coupled to chiral fields by introducing finite baryon densities into the
model. We experienced some problems due to compiler differences which were solved with the
excellent help of the local support. To achieve our physical goal, we implemented a higher
dimensional interpolation routine, which had to take into account the physical break off edge in the
pressure function. A lot of effort and computational time went into this objective since the available
numerical routine shows problems for very small densities especially when introducing large
thermal fluctuations for the chiral fields.
In project 57, on “Investigation of models for cosmic ray, air-shower simulation” by the same
group, a wealth of presently used high and low energy hadron interaction models for cosmic ray
simulations were analysed and the resulting lateral distribution functions were compared. The
project showed that the slope as well as the signal at 1000 m distance from the shower axis depend
on both the high and low energy hadronic model used. The models are confronted with available
hadron-nucleus data from accelerator experiments.
LOW & INTERMEDIATE ENERGY SUBATOMIC REACTIONS and ASTROPHYSICS
Project 34 worked on important parts of reaction models, on Meson-Nucleon Scattering (KFKI,
Budapest, by G. Wolf). Wolf developed the model and found a relatively good fit to the experimental
pi-nucleon and p-nucleon exclusive meson production data, except some pi-nucleon channels with
three outgoing pions. This preliminary fit was used to parametrize a qmd-model, i.e. the resonance
properties of the transport model. This enables the transport model to describe at least the pp and pinucleon collisions. With this transport model we calculated three-pion production in pi-nucleus
collisions. In this channel there is a hope to see the effect of rho-a1 meson mixing. We reported this
work in a conference in Valencia, June, 2003. Zetenyi investigated the production of phi-meson in
proton-nucleus collisions close to the threshold energy. This study has been done using a transport
model of relativistic nuclear collisions and the code was run on the supercomputer facility of BCPL.
The main aim was to study the effect of phi-meson in-medium broadening. It was found that the
dependence of the phi production cross section on the target nucleus size is considerably affected by
the phi-meson broadening. This work resulted in a publication accepted in Phys. Rev. C.
Project 53 on “Eta meson production reactions” by Teresa Peña aimed to (1) investigate the validity
of the most used approximations for the energy of the exchanged pion in the pion re-scattering
diagram (for neutral pion production). (2) To use the supercomputer in order to complete these
time-consuming calculations. (3) Interaction and exchange with other groups.
The planned calculations on meson production from NN scattering were finalized.The calculation
employs a physical model for nucleons and pions, with a pseudo-vector couppling for the pi-N
vertex, the chiral perturbation theory pi N - pi N re-scattering amplitude and the realistic Bonn
potential for the NN interaction in the final state. It was verified that: 1. The DWBA amplitude
dominates over the stretched boxes amplitude; 2. The choice of energy for the pion propagator is
not very decisive; 3. The cross section is dramatically suppressed if the approximation for the
energy in the propagator is consistently also implemented for the re-scattering vertex.
In Project 49, "Transmutation of Spent Fuel" by Danas Ridikas et al., the main goal of the project
was to optimize the transmutation scenario of the spent fuel originating from the RBMK type
nuclear reactors. Two different transmutation systems were considered: the high temperature
reactor (HTR) with a coated particle fuel, operating in a once-through cycle, and the fusion-fission
hybrid system, based on the molten salt fuel with reprocessing and feeding on-online. In addition to
the performance of the above systems, a detailed analysis of different data libraries, namely ENDF,
JEF and JENDL, was supposed to be done. Most of the previewed tasks were successfully initiated
and nearly terminated. The preliminary results will be reported in the international conference on
data for nuclear waste transmutation this autumn in Germany
ATOMIC PHYSICS
Project 39, “Asymptotic Behavior of Self-Avoiding Walks” by Zuzana Limpouchová: This project
studied the asymptotic behavior of long self-avoiding walks. These studies are time consuming
even on parallel computers. We improved our simulation technique and were able to perform
simulations up to chain lengths of 20 000 lattice units. The obtained results were applied in
subsequent simulations of block-copolymer micelles.
Project 51, “Molecular dynamics in intense fields” led by McCann, achieved discretization of angle
and orientation dimension using Lagrange mesh functions, and calculated eigenvalues and
eigenvectors for the Mathieu differential equation. The project was the simulation of intense-laser
interactions with matter using parallel computing methods to discretize and solve the associated
partial differential equations. The project is the study of time-dependent calculations of static and
dynamic intense-field ionization in molecules. One of the important tasks in this project was the
modeling of the arbitrary orientation of the molecular axis. In this context, we encounter a
nonlinear equation for the angular variable similar to the Mathieu equation.
In the project “Simulation software for laser-produced plasmas” (project no 52) led by Jiri Limpouch
Czech Technical University in Prague, Czech Republic, simulations of intense short-pulse interaction
using kinetic plasma simulation were performed, with a PIC code in order to get better understanding
of fast electron acceleration under moderate laser intensities.
The PIC code was parallelized so that it uses MPI instead of old PVM library, that ish not
implemented in new REGATTA computer of BCPL. The upgrade was succesfull and the test showed
that new version works as well as the old one. Linear growth of code perfomance was obtained up to
maximum number of processors used (64). We have used it for simulations of laser target interactions
and valuable results on absortion efficiency and fast electron distribution were obtained. The results
will be presented on international conference and published in a scientific journal.
ASTROPHYSICS
In project 58 "Vacuum energy and compact objects" led by Z. Stuchlik of Silesian University,
Opava, Czech Republic: Wide variety of recent cosmological tests, especially measurements of
high-redshift supernovae, indicate that nonzero repulsive cosmological constant, or an analogous
notion of quintessence, has to be invoked to explain the present Universe. It is very impoortant to
understand the role of an effective cosmological constant in various astrophysical situations. The
Opava research group working on relativistic astrophysics currently develops efficient numerical
codes enabling study of the role of the vacuum energy in active galactic nuclei and its influence on
fluctuations of cosmic microwave background due to Rees-Sciama effect. Recently, the influence of
the vacuum energy on compact objects is being studied. The parallel computing provided by
BCPL/Parallab is especially well suited for models of both compact objects and cosmic microwave
background influenced by the vacuum energy.
Project 61, “Microscopic Black Holes and High Temperature Matter” by R.G. Daghigh: The goal of
the project is to study black holes and, also, exotic compact stars such as quark stars and neutron stars.
The current research is focusing on understanding the possible observable signals of primordial
microscopic black holes that can be measured either with the current gamma ray observatories such as
MILAGRO or the neutrino "telescopes" such as IceCube or AMANDA. The relativistic viscous fluid
equations describing the outflow of high temperature matter created via Hawking radiation from
microscopic black holes and the equation of state will to be improved. Cascade simulations of the
spherically expanding matter around microscopic black holes will be carried out. The next stage of
this program will apply these methods and techniques to study similar phenomena in compact stars, in
particular quark stars and strongly magnetized (magnetars) pulsars.
STATISTICAL PHYSICS
Project 45 by Z. Neda, of Cluj, Romania: “Statistical physics approach to clusterization phenomena
in sociological systems”. The aim of the project was to study a spin-glass type frustrated model for
coalition formation in sociological systems. The project paricipants mannaged to make some
preliminary studies on relatively small system (N<100). For very small systems (N<10) an exact
enumeration study was also possible. For larger systems we implemented both the simulating
annealing and the extremal optimization algorithms. We found an interesting geometrical phasetransition in the ground state. The results suggest that a globally coupled large system with +/interactions between the elements, has two marginal behavior. When the + links number dominate
over the - links number in the optimal situation the system will clusterize in a single large cluster.
When the - links number is bigger, the systems splits in as many clusters as many elements there are in
the system. This transition resembles the one obtained in percolation type of problems, and gives a hint
that the model can be used effectively to study the so-called "social-percolation" problem too. For
large system sizes we encountered several technical difficulties in running the code. The present
results does not allow thus to precisely determine the critical point of the system and to study the
critical behavior of the observed transition. We are planning now to reconsider our Monte Carlo
optimization, and during a next visit to improve our data. The transition observed by us is novel, and
has not been reported elsewhere. We are confident that in a second visit the remained problems will
also be clarified.
The project “Event by Event Fluctuations in Heavy Ion Collisions” (project no. 35) led by S.
Mrowczynski, of Soltan Institute, Warsaw, has addressed the question of how collective
fluctuations may develop based on microscopic transport theoretical approaches: HIJING,
FRITIOF and UrQMD. Many thousands of nucleon-nucleon and heavy ion collision events were
generated in Bergen, which will be further analyzed statistically in Warsaw and Kielce in the near
future.
Project 56, on “Statistical hadron formation” by A. Keranen, studied a statistical model, of
fundamental interest and wide applicability.
CONCLUSIONS
The selected projects give a taste of the variability of BCPL's research projects. Most projects were
fully successful and achieved their goal. A few projects plan for a continuation.
We are preparing for the FP6 applications now. We plan to apply as an individual RI for providing
Transnational Access just as before but for more users (40 man-months per year). In addition we
participate in several I3, RI-network applications.
Highlights of BCPL achievements in 2004
A few BCPL projects were completed in year 2004.
Project 59 on "Systematic Studies on Nuclear Effects in High-pT Pion Production" led by G. Papp,
made calculations on the pion production in relativistic proton-nucleus (pA) and nucleus-nucleus
(AA) collisions at intermediate-high transverse momentum (pT) region and compared the results to
existing experiments. The systematic study included collective phenomena, like multiscattering,
shadowing inside the nucleus and induced jet energy loss. A perturbative Quantum
Chromodynamics (pQCD) improved parton model was applied in leading (LO) and, next-toleading order (NLO) and we managed to reproduce the Cronin effect in pA collisions. Using the
Gyulassi-Levai-Vitev (GLV) formalism for the jet energy loss we performed a detailed "jettomography" analysis of the hot dense matter in AuAu collisions at mid-rapidity and compared the
results to the most recent RHIC data. Furthermore, we have started to analyse new experimental
data at larger rapidities to explore the possible role of the proposed Color Glass Condensate
scenario.
The goal of Project 60, "Meson-nucleon scattering" led by Gy. Wolf was to develop a model
capable to describe 2- and 3-pion production besides rho, omega, phi and kaon production in pnucleon and pi-nucleon collisions. This model includes 25 baryon resonances. The resonance
parameters are fitted to the experimental meson production data: i.e pp and pn to all possible
outgoing channels including 1 to 3 mesons in the final states and similarly for pi p and pi n
incoming channels. A further aim was to write a transport code in C++ language.
Project 55 led by V.K. Magas, aimed for the calculation of HBT radii in simulations of Heavy Ion
Reactions. The plan is to use a modular simulation model, which is able to describe adequately
All stages of the reaction. Significant advance was achieved during the stay in Bergen.