Effects of isospin and energy dependences of the nuclear mean field in spallation reactions

In many applications of the intranuclear-cascade (INC) model to spallation reactions, all nucleons in the target are assumed to move in a common potential well. However, the potential depth should depend upon nucleon isospin and energy. The present paper describes the first results obtained after the introduction of these features in the Liége INCL3 model. It is shown that such modifications change cascade particle multiplicities significantly but total particle multiplicities are only slightly altered. Nucleon inclusive cross-sections are not modified significantly, except in the region of the quasi-elastic peaks. In particular, the centroid of the peak in neutron double differential cross-sections relative to proton-induced reactions can be sizeably shifted toward larger energy losses, as is observed experimentally. Implications of these results are discussed.Received: 28 October 2003, Published online: 13 July 2004PACS: 25.40.-h Nucleon-induced reactions - 24.10.-i Nuclear reaction models and methods - 24.10.Lx Monte Carlo simulations (including hadron and parton cascades and string breaking models)     

Properties of hot residual nuclei produced in pA reactions

The predictions for the production of nuclides and particles in proton-induced reactions are important e.g. for the detailed design of spallation neutron sources or accelerator-driven-systems. Computational tools are required that are able to describe quantitatively the two-stage process i.e. intra-nuclear cascade followed by evaporation-fission. The first stage is a highly non-equilibrated process in which incoming proton deposits in hot residual nucleus both excitation energy and angular momentum. The CBUU transport model calculation for few targets, for the proton energy range 0.4-2.0 GeV are presented, with the idea to find global parametrizations for the distributions of charge, mass, excitation energy, angular momentum of hot residual nuclei.Received: 30 September 2002, Published online: 22 October 2003PACS: 24.10.-i Nuclear reaction models and methods - 24.10.Lx Monte Carlo simulations (including hadron and parton cascades and string breaking models)     

高能核碰撞中带电多重数快度与能量和中心度的关系

用强子–弦级联模型JPCIAE及相应的Monte Carlo事例产生器研究相对论性核–核碰撞中带电粒子多重数的赝快度密度对能量和中心度的依赖关系.无需另调任何模型参数的条件下,此模型可以同时较好地描述相对论性pp实验数据及PHOBOS和PHENIX实验组的Au+Au实验数据.本文指出:因〈N_part〉并非严格定义的物理量,致使实验上和理论上确定〈N_part〉有一定任意性,从而使得每参加者核子对的带电粒子赝快度密度随着〈N_part〉的增加可能逐渐增大,也可能逐渐减小,因此用它来区分粒子产生机制是欠妥的.     

Problems with fitting to the power-law distribution

This short communication uses a simple experiment to show that fitting to a power law distribution by using graphical methods based on linear fit on the log-log scale is biased and inaccurate. It shows that using maximum likelihood estimation (MLE) is far more robust. Finally, it presents a new table for performing the Kolmogorov-Smirnov test for goodness-of-fit tailored to power-law distributions in which the power-law exponent is estimated using MLE. The techniques presented here will advance the application of complex network theory by allowing reliable estimation of power-law models from data and further allowing quantitative assessment of goodness-of-fit of proposed power-law models to empirical data.Received: 18 June 2004, Published online: 12 October 2004PACS: 02.50.Ng Distribution theory and Monte Carlo studies - 05.10.Ln Monte Carlo methods - 89.75.-k Complex systems     

Statistical hadronization and hadronic micro-canonical ensemble II

We present a Monte Carlo calculation of the micro-canonical ensemble of the ideal hadron-resonance gas including all known states up to a mass of about 1.8 GeV and full quantum statistics. The micro-canonical average multiplicities of the various hadron species are found to converge to the canonical ones for moderately low values of the total energy, around 8 GeV, thus bearing out previous analyses of hadronic multiplicities in the canonical ensemble. The main numerical computing method is an importance sampling Monte Carlo algorithm using the product of Poisson distributions to generate multi-hadronic channels. It is shown that the use of this multi-Poisson distribution allows for an efficient and fast computation of averages, which can be further improved in the limit of very large clusters. We have also studied the fitness of a previously proposed computing method, based on the Metropolis Monte Carlo algorithm, for event generation in the statistical hadronization model. We find that the use of the multi-Poisson distribution as proposal matrix dramatically improves the computation performance. However, due to the correlation of subsequent samples, this method proves to be generally less robust and effective than the importance sampling method.Received: 9 July 2004, Revised: 21 July 2004, Published online: 9 November 2004     

Production and transport of hadrons generated in nuclear cascades initiated by muons in the rock (exclusive approach)

Monte Carlo calculation of differential distributions of hadrons going into LVD (Large Volume Detector) experimental hall from the rock was performed. Probability of energy transfer into nuclear cascade by muon is taken according to Bezrukov and Bugaev (1981) giving 9.45×10⁻⁶ inelastic muon-nucleus interactions per gram per year at the depth of Gran Sasso. Simulation of hadron cascades in the rock was made using the universal hadron transport code SHIELD. It allowed to calculate transport of hadrons at energy up to 1 TeV providing the exclusive simulation of nuclear reactions in the whole energy range. Differential distributions of neutrons, protons and charged pions are obtained for the roof, walls and floor of the hall separately in absolute units. Total number of hadrons with energy above 15 MeV going into the hall is about 250 particles per m² per year. Number of ingoing neutrons is in good agreement with measurement. The yield of high energy hadrons (>1 GeV) in backward hemisphere is observed. Possible role of K⁰-mesons as a source of background events in LVD is distinguished.     

The CCFM Monte Carlo generator CASCADE Version 2.2.03

The European Physical Journal C - Cascade is a full hadron level Monte Carlo event generator for ep, γp and $p\bar{p}$ and pp processes, which uses the CCFM evolution equation for the initial...     

Cascade particles,nuclear evaporation,and residual nuclei in high energy hadron-nucleus interactions

Based on a Monte Carlo realization of the Dual Parton Model we study the production of target associated particles and of nuclear fragments in high energy hadronnucleus interactions. A formation zone intranuclear cascade of low energy secondaries inside the target nucleus is discussed. We calculate excitation energies of residual nuclei left after the intranuclear cascade process and treat their fürther disintegration by introducing models for the evaporation of protons, neutrons, and light fragments, high energy fission, and by applying a Fermi Break-up model to light nuclear fragments. The results are compared to data on target associated particle production. We fürthermore calculate cross sections for the production of nuclear fragments.     

Comparison of deep-inelastic electron-photon scattering data with the HERWIG and PHOJET Monte Carlo Models

Deep-inelastic electron-photon scattering is studied in the range from 1.2 to 30 GeV using the LEP1 data taken with the ALEPH, L3 and OPAL detectors at centre-of-mass energies close to the mass of the Z boson. Distributions of the measured hadronic final state are corrected to the hadron level and compared to the predictions of the HERWIG and PHOJET Monte Carlo models. For large regions in most of the distributions studied the results of the different experiments agree with one another. However, significant differences are found between the data and the models. Therefore the combined LEP data serve as an important input to improve on the Monte Carlo models. Received: 5 July 2000 / Published online: 15 February 2002     

Monte Carlo methods for yrast spectroscopy

We discuss the details of the recently proposed Monte Carlo method to evaluate the exact energies of yrast levels. Energy levels are evaluated up to J = 18 with small statistical errors using the Metropolis method for the case of ¹⁶⁶Er using the pairing plus quadrupole model within one major shell. We also discuss the evaluation of the probabilities of the Hartree-Fock-Bogoliubov wave functions in the corresponding yrast eigenstates and they are found to be large. The model displays a too strong backbending behaviour not seen experimentally.Received: 29 September 2003, Published online: 24 August 2004PACS: 21.60.-n Nuclear-structure models and methods - 02.70.Ss Quantum Monte Carlo methods - 21.60.Ka Monte Carlo models - 21.10.Re Collective levels     

高能重离子碰撞中正负荷电粒子比单事例起伏研究

用强子和弦级联模型,JPCIAE及相应的Monte Carlo事例产生器,研究相对论性核–核碰撞中有限快度区间内正负荷电粒子比单事例起伏与能量、中心度、共振态衰变及快度间隔的关系.JPCIAE模型能够较好地符合CERN/SPS能区Pb+Pb碰撞的实验结果.本文还用此模型预言了RHIC能区Au+Au碰撞和ALICE能区Pb+Pb碰撞中的正负荷电粒子比单事例起伏.可以看出碰撞能量、中心度、共振态衰变及快度间隔对正负荷电粒子比单事例起伏的影响都不大.     

Effect of Intranuclear Cascades on the Composition and Energy of Fragments Originating from Si( $${p,x}$$ ) and Fe( $${p,x}$$ ) Nuclear Reactions

Physics of Atomic Nuclei - Quantum-mechanical models and the Monte Carlo method are used to study the composition and energies of products of nuclear reactions induced by collisions of fast protons...     

秦山二期堆芯临界计算中核数据的敏感性分析北大核心CSCD

核电软件需要给出计算结果的不确定性,在此基础上才可有效评价核电的安全性。核数据是核电软件堆芯计算不确定性的重要来源之一,而堆芯宏观参数对核数据的敏感性分析是不确定性分析的重要步骤。以秦山二期堆芯为研究对象,对其临界计算结果开展核数据的敏感性分析。首先采用蒙特卡罗程序建立秦山二期首循环计算模型,然后基于中国核数据中心研制的连续能量截面库CENACE V1.0,采用反复裂变几率法计算有效增殖系数对核数据的敏感性系数。通过整理分析秦山二期冷热态、寿期初中末状态的敏感性系数,梳理出核电软件不确定分析中需要关注的重要核素数据。     

Diphoton production at hadron colliders: a fully differential QCD calculation at next-to-next-to-leading order

We consider direct diphoton production in hadron collisions, and we compute the next-to-next-to-leading order QCD radiative corrections at the fully differential level. Our calculation uses the q(T) subtraction formalism, and it is implemented in a parton-level Monte Carlo program. The program allows the user to apply arbitrary kinematical cuts on the final-state photons and the associated jet activity and to compute the corresponding distributions in the form of bin histograms. We present selected numerical results related to Higgs boson searches at the LHC and corresponding results at the Tevatron.     

Exact lattice calculations of dispersion coefficients in the presence of external fields and obstacles

We present a study of the field-dependent dispersion coefficient of point-like particles in various 2D overdamped systems with obstructions (periodic, percolating, and trapping distributions of obstacles). These calculations profit from the synthesis of a newly proposed Monte Carlo algorithm --the first such algorithm that correctly reproduces the free dispersion coefficient in the presence of finite external fields-- and an asymptotically exact calculation technique. The resulting method efficiently produces algebraic and numerical results without the need to actually perform Monte Carlo simulations. When compared to such simulations, our exact method features a negligible computational cost and exponentially small errors. Utilizing the power of this numerical method, we engage in comprehensive parametric analysis of several model systems, revealing very subtle effects that would otherwise be swamped by statistical errors or incur prohibitive computational costs. The unified framework presented here serves as a template for further applications of lattice random-walk models of biased diffusion.Received: 27 July 2004, Published online: 1 October 2004PACS: 87.15.Vv Diffusion - 82.20.Wt Computational modeling; simulation - 05.10.Ln Monte Carlo methods     

Time-dependent intranuclear cascade model

An intranuclear cascade model with explicit consideration of the time coordinate in the Monte Carlo simulation of the development of a cascade particle shower has been considered. Calculations have been performed using a diffuse nuclear boundary without any step approximation of the density distribution. Changes in the properties of the target nucleus during the cascade development have been taken into account. The results of these calculations have been compared with experiment and with the data which had been obtained by means of a time-independent cascade model. The consideration of time improved agreement between experiment and theory particularly for highenergy shower particles; however, for low-energy cascade particles (with grey and black tracks in photoemulsion) a discrepancy remains at T ? 10 GeV.     

High transverse momentum suppression and surface effects in <Emphasis Type="Bold">Cu+Cu</Emphasis> and <Emphasis Type="Bold">Au+Au</Emphasis> collisions within the PQM model

We study parton suppression effects in heavy-ion collisions within the parton quenching model (PQM). After a brief summary of the main features of the model, we present comparisons of calculations for the nuclear modification and the away-side suppression factor to the data in Au+Au and Cu+Cu collisions at  =200 GeV. We discuss properties of light hadron probes and their sensitivity to the medium density within the PQM Monte Carlo framework.     

Hadronic Interactions in the Energy Region of Future Hadron Colliders,Dual Topological Unitarization of Hard and Soft Hadronic Cross Sections

The dual topological unitarization of hard and soft hadronic collisions is formulated as a Monte Carlo event generator for events containing both the soft (low p ?) and hard (jets, minijets) component of hadron production. The parameters of the model are determined from fits to the energy dependence of the total and inelastic hadron cross-sections and from the predictions of the QCD-parton model for the perturbative hard constituent scattering cross sections. The predictions of the model for TeV colliders are presented. Interesting changes of the produced multiparticle system are found when selecting classes of events with and without hard jets or minijets.