Heavy Ion Jet Interaction Generator Research Articles

Upper limit on the chiral magnetic effect in isobar collisions at the Relativistic Heavy-Ion Collider

The chiral magnetic effect (CME) is a phenomenon that arises from the QCD anomaly in the presence of an external magnetic field. The experimental search for its evidence has been one of the key goals of the physics program of the Relativistic Heavy-Ion Collider. The STAR Collaboration has previously presented the results of a blind analysis of isobar collisions (Ru4496+Ru4496, Zr4096+Zr4096) in the search for the CME. The isobar ratio (Y) of CME-sensitive observable, charge separation scaled by elliptic anisotropy, is close to but systematically larger than the inverse multiplicity ratio, the naive background baseline. This indicates the potential existence of a CME signal and the presence of remaining nonflow background due to two- and three-particle correlations, which are different between the isobars. In this postblind analysis, we estimate the contributions from those nonflow correlations as a background baseline to Y, utilizing the isobar data as well as Heavy Ion Jet Interaction Generator simulations. This baseline is found consistent with the isobar ratio measurement, and an upper limit of 10% at 95% confidence level is extracted for the CME fraction in the charge separation measurement in isobar collisions at sNN=200 GeV. Published by the American Physical Society 2024

Two- and three-particle nonflow contributions to the chiral magnetic effect measurement by spectator and participant planes in relativistic heavy ion collisions

Correlation measurements with respect to the spectator and participant planes in relativistic heavy ion collisions were proposed to extract the chiral magnetic effect (CME) from background dominated azimuthal correlators. This paper investigates the effects of two- and three-particle nonflow correlations on the extracted CME signal fraction, $f_{\text{CME}}$. It is found, guided by a multiphase transport (AMPT) model and the heavy ion jet interaction generator (HIJING) together with experimental data, that the nonflow effects amount to approximately $(4\pm5)$% and $(-5\pm3)$% without and with pseudorapidity gaps, respectively, in 20-50% centrality Au+Au collisions at $\sqrt{s_{\text{NN}}}= 200 \text{ GeV}$.

Initial nuclear effects in the improved HIJING code and the production of charged pions, kaons and (anti)protons at STAR BES

The improved Heavy Ion Jet Interaction Generator (HIJING) code is introduced to explore possible initial nuclear effects on the bulk observables of charged pions, kaons and (anti)protons observed in Au+Au collisions at sNN=7.7, 11.5, 19.6, 27 and 39 GeV. The standard HIJING code is extended by (i) different baryon production mechanisms, and (ii) Regge collective cascade recipe. We find that the centrality dependence of the identified particle multiplicity dN/dy at mid-rapidity is quite sensitive to Regge cascading. The overall contribution of baryon production mechanism is shown to enhance the centrality dependence of the mixed particle ratios, K±/π± and p±/π± at <Npart><200 (which corresponds to 20%−100% centrality), especially at higher collision energy. It turns out that the bulk data are shown to be more consistent with HIJING (plus a suitable hadron rescattering code) employing both an advanced popcorn baryon production mechanism and Regge initial scatterings.

Study of diffusion coefficients of identified particles at energies available at BNL Relativistic Heavy Ion Collider

Using event-by-event fluctuations, we study the diffusion parameters of net-charge, net-pion, net-kaon, and net-proton in the heavy-ion jet interaction generator (HIJING), and ultra-relativistic quantum molecular dynamics (UrQMD) models at different collision energies \sqsn available at BNL Relativistic Heavy Ion Collider (RHIC). The diffusion parameter ($\sigma$) of net-charge and identified particles are estimated in rapidity space at various \sqsn. It is observed that, the $\sigma$ values are independent of collision energies but emphasises the particle-species dependence of diffusion coefficient in the QGP medium. The present work on particle-species dependence of diffusion coefficient provides a baseline for comparison with the experimental data.

Effects of popcorn mechanisms in p + p and Pb + Pb collisions at CERN SPS energies within the HIJING code

We have investigated the influence of different baryon production mechanisms on the rapidity distributions (dn/dy) and transverse mass (mT) spectra of π±, k± and p± in p + p and Pb + Pb collisions at the CERN super proton synchrotron (SPS) energies by utilizing the heavy ion jet interaction generator (HIJING) code incorporated with a modern version of PYTHIA (version 6.4). Predictions are compared using the simple and advanced popcorn mechanisms, denoted as HIJING/SP and HIJING/AP, respectively, with different model parameters. It is found that HIJING/AP/set4 (that includes the suppression of first rank baryons) better describes the yields of π±, k± and in p + p interactions at SPS energies. We have also validated the HIJING/AP/set5 (that includes set4 and string tension with value of , where k0 = 1 GeV/fm is the default string tension) by reproducing the identified hadron rapidity distributions and mT-spectra in both peripheral (33%–43%) and central (0%–5(7)%) Pb + Pb collisions at different SPS energies.

Fluctuations of identified particle yields using the νdyn variable at energies available at the BNL Relativistic Heavy Ion Collider

We study the fluctuations of net-charge, net-pion, net-kaon and net-proton using $D$-measure and $\nu_{dyn}$ variables in heavy-ion jet interaction generator (HIJING), ultra-relativistic quantum molecular dynamics (UrQMD), and hadron resonance gas (HRG) model at different collision energies \sqsn. It has been observed that, the values of $D$ strongly dependent on $\Delta \eta$ in HIJING and UrQMD models and independent in HRG model. The diffusion coefficients ($\sigma$) of identified particles are estimated at various \sqsn. It is observed that, the $\sigma$ values are independent of collision energies but emphasizes the particle species dependence of diffusion coefficient in the QGP medium. This study provides a realistic baseline for comparison with the experimental data.

Data structure in the HIJING 2.0 Monte Carlo program

The Heavy-Ion Jet Interaction Generator (HIJING) Monte Carlo model was developed to simulate hadron production in proton–proton, proton–nucleus and nucleus–nucleus collisions. It has been updated recently with the latest parton distributions functions (PDFs) and new set of the parameters in the two-component mini-jet model that controls total [Formula: see text] cross-section and the central pseudorapidity density. We will discuss these new elements in the HIJING 2.0 model, derive the two-component model from the eikonal formalism of hadron–hadron collisions and review the hadron spectra and multiplicity distributions as compared to recent experimental data at the LHC energies. We will review in particular the data structure of the Monte Carlo program and discuss future improvements.

Fluctuations of collective flows for event-by-event hydrodynamic evolution sources

Through investigating the space-time evolution of the hydrodynamic particle-emitting sources with the fluctuating initial conditions generated by Heavy Ion Jet Interaction Generator (HIJING), we discussed the space-time and velocity evolution of quark gluon plasma (QGP). In order to detect the event-by-event inhomogeneity of the sources, we examine the distribution of the error-inverse-weighted fluctuations, between the two-pion Bose-Einstein correlation functions of single events. We find that the distribution becomes wide for the fluctuating initial sources with velocity v = 0, which means the sources evolution faster than nonzero initial conditions. We also discussed the elliptic flow effect, velocity and temperature evolution in Heavy Ion Reactions, and get the same results.

Observation of universality for high pT distribution at LHC energies

We have studied the distributions of the yield of primary charged particles produced in the asymmetric [Formula: see text]–[Formula: see text] collisions at [Formula: see text] for the three pseudorapidity regions: [Formula: see text] and [Formula: see text] and the transverse momentum range of [Formula: see text]. Heavy ion jet interaction generator (HIJING) and Ultra relativistic quantum molecular dynamics (UrQMD) models are used to produce simulated data and the results are compared with the CMS and ATLAS data. The comparison of models and data shows the existence of high [Formula: see text] area with boundary values that depend upon pseudorapidity ([Formula: see text]). At high [Formula: see text] values, the behavior of the distributions shows some universality, which does not depend upon the models. The reason of the universality could be the string dynamics for the parton hadronization at high [Formula: see text] values.

Conserved charge fluctuations using the D measure in heavy-ion collisions

We study the net-charge fluctuations, $D$-measure variable, in high energy heavy-ion collisions in heavy-ion jet interaction generator (HIJING), ultrarelativistic quantum molecular dynamics (UrQMD) and hadron resonance gas (HRG) models for various center-of-mass energies (\sqsn). The effect of kinematic acceptance and resonance decay, in the pseudorapidity acceptance interval ($\Delta\eta$) and lower transverse momentum ($p_{T}^{min}$) threshold, on fluctuation measures are discussed. A strong dependence of $D$ with the $\Delta\eta$ in HIJING and UrQMD models is observed as opposed to results obtained from the HRG model. The dissipation of fluctuation signal is estimated by fitting the $D$-measure as a function of the $\Delta\eta$. An extrapolated function for higher $\Delta\eta$ values at lower \sqsn is different from the results obtained from models. Particle species dependence of $D$ and the effect of the $p_T^{min}$ selection threshold are discussed in HIJING and HRG models. The comparison of $D$, at midrapidity, of net-charge fluctuations at various \sqsn obtained from the models with the data from the ALICE experiment is discussed. The results from the present work as a function of $\Delta\eta$ and \sqsn will provide a baseline for comparison to experimental measurements.

Production of D-mesons in p + p and p + Pb collisions at LHC energies

We present theoretical model comparison with published ALICE results for [Formula: see text]-mesons ([Formula: see text], [Formula: see text] and [Formula: see text]) in [Formula: see text] collisions at [Formula: see text] = 7 TeV and [Formula: see text] collisions at [Formula: see text][Formula: see text]TeV. Event generator Heavy-Ion Jet Interaction Generator (HIJING), transport calculation of AMPT and calculations from Next-to-Leading Order (NLO)(MNR) and Fixed-Order Next-to-Leading-Logarithmic (FONLL) have been used for this study. We found that HIJING and AMPT model predictions are matching with published [Formula: see text]-meson cross-sections in [Formula: see text] collisions, while both under predict the same in [Formula: see text] collisions. Attempts were made to explain the [Formula: see text] data using NLO-pQCD(MNR), FONLL and other above mentioned models.

Kinematic constraints on interacting nucleons in Pb + Pb collisions atsNN=2.76TeV within the HIJING code

The kinematic constrains on interacting nucleons in Large Hadron Collider (LHC) heavy-ion collisions are investigated in the framework of the Heavy Ion Jet Interaction Generator (HIJING) code incorporated with a collective cascade recipe. The latter is used to implement energy-momentum conservation constrains on both primary and secondary interacting nucleons. It is found that the energy-momentum conservation constrains on the interacting nucleons affect the whole charged particle pseudo-rapidity density distribution $(\frac{dN_{ch}}{d\eta})$, at different centralities (from central (0-5\%) to peripheral (70-80\%) collisions), in Pb+Pb collisions at $\sqrt{s_{NN}} =2.76$ TeV. In particular, the kinematic constrains on interacting nucleons are shown to reduce $(\frac{dN_{ch}}{d\eta})$ yield at mid-pseudorapidity $(\lvert\eta\rvert<2)$ in all centrality intervals, which is consistent with the LHC data. In addition, the model predicts an enhancement of the hadron production at $\lvert\eta\rvert>8$, which could be checked in future ALICE Zero Degree calorimeter. Such an enhancement is found to be mainly due to the interactions of protons at the spectator parts of the collision. This indicates that the kinematic constrains are important for a correct geometrical treatment of Pb+Pb collisions at LHC energies.

Interpretation of charged-particle spectra inp+pandp+Pbcollisions at energies available at the CERN Large Hadron Collider using an improved hijing code with a collective cascade

We supplement the Heavy Ion Jet Interaction Generator (hijing) code with a collective cascade recipe and updated Martin-Stirling-Thorne-Watt (MSTW2009) parton distribution functions (PDFs) to describe nonsingle diffractive (NSD) $p+p$ and Pb collisions at CERN Large Hadron Collider energies. The collective cascade, developed in the space of an impact parameter, is used to induce nuclear modification of nucleons, that are involved in primary interactions, inside the dense nuclear medium. It is found that the improved hijing (Imhijing) code (that with MSTW2009 PDFs) reproduces rather well the pseudorapidity density, the multiplicity, and the transverse momentum distributions of charged particles within the pseudorapidity interval $|{\ensuremath{\eta}}_{\mathrm{c}.\mathrm{m}.\mathrm{system}}|&lt;2.4$ in NSD $p+p$ collisions at $\sqrt{{s}_{\mathrm{NN}}}=0.9$, 2.36, and 7 TeV. The Imhijing with collective cascade calculations is also shown to be a good fit to the pseudorapidity density (in the laboratory system) and transverse momentum $({p}_{T})$ dependence of the nuclear modification of charged particles in NSD $p+\mathrm{Pb}$ collisions at $\sqrt{{s}_{\mathrm{NN}}}=5.02\phantom{\rule{4pt}{0ex}}\mathrm{TeV}$. The effects of the collective cascade are clearly seen in the target $(3&lt;{\ensuremath{\eta}}_{\mathrm{lab}}&lt;4)$ and central (within $|{\ensuremath{\eta}}_{\mathrm{c}.\mathrm{m}.\mathrm{system}}|&lt;0.3$ at $1&lt;{p}_{T}&lt;8\phantom{\rule{0.28em}{0ex}}\mathrm{GeV}/\phantom{\rule{0.0pt}{0ex}}c)$ interaction regions when studying the pseudorapidity density and transverse momentum dependence of the nuclear modification factor of the charged particles, respectively.

Source function extracted from single-event HBT correlation functions of hydrodynamical sources

We investigate the single-event two-pion correlation functions for the hydrodynamic particle-emitting sources with the fluctuating initial conditions generated by the Heavy Ion Jet Interaction Generator (HIJING). Using a three-dimension fast Fourier transform (FFT), we further extract the source functions from the single-event correlation functions. It is found that the inhomogeneity of the hydrodynamic sources with the fluctuating initial conditions lead to event-by-event fluctuations of the correlation functions and source functions.

Hadron production inp+p,p+Pb, andPb+Pbcollisions with the hijing 2.0 model at energies available at the CERN Large Hadron Collider

The Heavy-Ion Jet Interaction Generator (hijing) Monte Carlo model is updated with the latest parton distributions functions and a new set of the parameters in the two-component minijet model that controls the total $p+p$ cross section and the central pseudorapity density. We study hadron spectra and multiplicity distributions using the hijing$2.0$ model and compare to recent experimental data from $p+p$ collisions at the Large Hadron Collider (LHC) energies. We also give predictions of hadron production in $p+p$, $p+\text{Pb}$, and $\text{Pb}+\text{Pb}$ collisions at the full LHC energy.

Multiphase transport model for relativistic heavy ion collisions

We describe in detail how the different components of a multiphase transport (AMPT) model that uses the heavy ion jet interaction generator (HIJING) for generating the initial conditions, Zhang's parton cascade (ZPC) for modeling partonic scatterings, the Lund string fragmentation model or a quark coalescence model for hadronization, and a relativistic transport (ART) model for treating hadronic scatterings are improved and combined to give a coherent description of the dynamics of relativistic heavy ion collisions. We also explain the way parameters in the model are determined and discuss the sensitivity of predicted results to physical input in the model. Comparisons of these results to experimental data, mainly from heavy ion collisions at the BNL Relativistic Heavy Ion Collider, are then made in order to extract information on the properties of the hot dense matter formed in these collisions.

Multiphase transport model for relativistic nuclear collisions

To study heavy ion collisions at energies available from the Relativistic Heavy Ion Collider (RHIC), we have developed a multiphase transport model that includes both initial partonic and final hadronic interactions. Specifically, the Zhang's parton cascade (ZPC) model, which uses as input the parton distribution from the heavy ion jet interaction generator (HIJING) model, is extended to include the quark-gluon--to--hadronic-matter transition and also final-state hadronic interactions based on a relativistic transport (ART) model. Predictions of the model for central Au on Au collisions at RHIC are reported.