HIJING

HIJING
Name	HIJING
Title	HIJING
Author	Xin-Nian Wang, Miklos Gyulassy
Developer	Columbia University, Lawrence Berkeley National Laboratory
Released	1991
Latest release	1.383 (example)
Programming language	Fortran
Operating system	Unix-like, Linux
License	Academic
Genre	Monte Carlo event generator

HIJING

HIJING is a Monte Carlo event generator for high-energy hadronic and nuclear collisions designed to simulate particle production in Quantum Chromodynamics-dominated processes. It models multiparticle production in collisions involving protons, neutrons, nucleuss and heavy ions for experiments at facilities such as the CERN Large Hadron Collider, Brookhaven National Laboratory's Relativistic Heavy Ion Collider, and planned accelerators. The program combines perturbative hard-scattering physics with phenomenological models for soft processes to provide event-by-event final states used in analyses by collaborations like ALICE (A Large Ion Collider Experiment), CMS, ATLAS, STAR, and PHENIX.

Overview

HIJING was developed to bridge descriptions used in parton-based models and string-based fragmentation approaches common in generators such as PYTHIA and FRITIOF. The generator incorporates ideas from Gribov-Regge theory, perturbative Quantum Chromodynamics (pQCD) for hard parton scattering, and nuclear effects like shadowing and multiple scattering drawn from studies at institutions including Columbia University and Lawrence Berkeley National Laboratory. HIJING produces final states containing partons, strings, and hadrons suitable for detector simulation chains employed by experiments like ALICE (A Large Ion Collider Experiment), where comparisons to data from SPS and RHIC were pivotal.

Physics Model and Components

The physics model of HIJING couples pQCD hard scattering kernels similar to those in JETSET/PYTHIA with soft interactions modeled using string excitation akin to Lund (model). Hard subprocess cross sections are computed with matrix elements regulated by a cutoff scale informed by studies at CERN and Fermilab, then matched to parton distribution functions such as CTEQ, MRST, or EPS09 nuclear PDFs. Nuclear modifications include shadowing parametrizations based on fits from groups like Eskola and Paukkunen, and multiple scattering uses Glauber geometry as formulated by R. J. Glauber and applied in analyses by W. Czyż and M. Gyulassy. Hadronization follows string fragmentation scenarios related to work by Andersson and Sjostrand. The model also optionally includes jet quenching mechanisms drawing on energy loss formalisms developed by Baier, Dokshitzer, Gyulassy, and Wang.

Implementation and Code Structure

HIJING is implemented primarily in Fortran 77 with modular subroutines reflecting the separation of hard-scattering, soft-interaction, nuclear-geometry, and fragmentation components. The code interfaces with external libraries and packages such as PYTHIA, JETSET, and parton distribution libraries maintained by collaborations like CTEQ Collaboration and NNPDF. Input steering is handled through card files or driver programs widely used in computing environments at CERN OpenLab and batch systems common at BNL and LBL. Output formats support conversion to common event-description standards used by experiments such as HepMC and legacy formats adopted by GEANT 3 and GEANT4 detector simulation frameworks.

Applications and Use in Research

HIJING has been used extensively in phenomenological studies of particle yields, transverse momentum spectra, collective flow proxies, and jet-medium interactions in analyses conducted by ALICE (A Large Ion Collider Experiment), CMS, ATLAS, STAR, and PHENIX. It serves as a baseline generator for background modeling in searches performed at LHC experiments and for acceptance studies at fixed-target facilities like CERN SPS experiments. The generator has featured in theoretical investigations comparing mechanisms proposed by M. Gyulassy, X.-N. Wang, E. V. Shuryak, and groups working on quark–gluon plasma signatures, and has been cited in interdisciplinary reports from laboratories including Brookhaven National Laboratory and Lawrence Berkeley National Laboratory.

Validation and Performance

Validation of HIJING has proceeded via comparisons to multiplicity distributions, pseudorapidity densities, and identified-hadron spectra measured by experiments at SPS, RHIC, and LHC. Studies benchmarking against generators like PYTHIA, AMPT, and EPOS have highlighted strengths in modeling nuclear effects and limitations in collective-flow reproduction, prompting hybrid approaches combining HIJING initial states with hydrodynamic evolution frameworks developed by groups centered at INT and research teams associated with Duke University and McGill University. Performance profiling typically occurs on HPC clusters operated by NERSC and batch farms at CERN; optimization efforts have included vectorization, parallel event generation, and interfacing with modern C++ analysis stacks used by collaborations like ALICE (A Large Ion Collider Experiment).

Development History and Versions

HIJING was originally released in the early 1990s by developers at Columbia University and Lawrence Berkeley National Laboratory to address emerging heavy-ion programs. Subsequent updates incorporated nuclear PDF options from groups like Eskola (EKS98), energy-loss modules inspired by work of Baier, Dokshitzer, Mueller, and parameters tuned to data from RHIC runs analyzed by STAR and PHENIX. Later maintenance added interfaces to newer PDF sets produced by collaborations such as CTEQ Collaboration and NNPDF, and adapted I/O for evolving experiment frameworks at CERN and BNL. The code remains a reference in heavy-ion phenomenology and continues to influence generator development in projects at institutions including Oak Ridge National Laboratory and university groups worldwide.

Category:Particle physics software