High-energy Nucleus-nucleus Collisions Research Articles

Wavelet Analysis of Shower Track Distribution in High-Energy Nucleus-Nucleus Collisions

A continuous wavelet analysis is performed for pattern recognition of charged particle emission data in28Si-Ag/Br interaction at 14.5A GeV and in32S-Ag/Br interaction at 200A GeV. Making use of the event-wise local maxima present in the scalograms, we try to identify the collective behavior in multiparticle production, if there is any. For the first time, the wavelet results are compared with a model prediction based on the ultrarelativistic quantum molecular dynamics (UrQMD), where we adopt a charge reassignment algorithm to modify the UrQMD events to mimic the Bose-Einstein type of correlation among identical mesons—a feature known to be the most dominating factor responsible for local cluster formation. Statistically significant deviations between the experiment and the simulation are interpreted in terms of nontrivial dynamics of multiparticle production.

The compressed baryonic matter experiment at FAIR

Abstract The Compressed Baryonic Matter (CBM) experiment will be one of the major scientific pillars of the future Facility for Antiproton and Ion Research (FAIR) in Darmstadt. The goal of the CBM research program is to explore the QCD phase diagram in the region of high baryon densities using high-energy nucleus-nucleus collisions. This includes the study of the equation-of-state of nuclear matter at high densities, and the search for the deconfinement and chiral phase transitions. The CBM detector is designed to measure both bulk observables with large acceptance and rare diagnostic probes such as charmed particles and vector mesons decaying into lepton pairs.

Glauber-model analysis of total reaction cross sections for Ne, Mg, Si, and S isotopes with Skyrme-Hartree-Fock densities

A systematic analysis is made on the total reaction cross sections for Ne, Mg, Si, and S isotopes. The high-energy nucleus-nucleus collision is described based on the Glauber model. Using the Skyrme-Hartree-Fock method in the three-dimensional grid-space representation, we determine the nuclear density distribution for a wide range of nuclei self-consistently without assuming any spatial symmetry. The calculated total reaction cross sections consistently agree with the recent cross section data on Ne$+^{12}$C collision at 240$A$\,MeV, which makes it possible to discuss the radius and deformation of the isotopes. The total reaction cross sections for Mg$+^{12}$C, Si$+^{12}$C and S$+^{12}$C cases are predicted for future measurements. We also find that the high-energy cross section data for O, Ne, and Mg isotopes on a $^{12}$C target at around 1000\,$A$MeV can not be reproduced consistently with the corresponding data at 240\,$A$MeV.

Monte-Carlo Simulation of Hard Probes in Heavy-Ion Collisions

Results from the Modular Algorithm for Relativistic Treatment of heavy IoN Interactions (MARTINI) are presented. This comprehensive event generator for the hard and penetrating probes in high energy nucleus-nucleus collisions employs a time evolution model for the soft background, PYTHIA 8.1 and the McGill-AMY parton evolution scheme including radiative as well as elastic processes. It generates full event configurations in the high pT region, taking into account thermal QCD and QED effects as well as effects of the evolving medium.

The quark-gluon medium (micro- and macro-QCD)

The properties of the quark-gluon medium observed in high energy nucleus-nucleus collisions are discussed. The main experimental facts about these collisions are briefly described and compared with data about proton-proton collisions. Both microscopic and macroscopic approaches to their description are reviewed. The chromodynamics of the quark-gluon medium at high energies is mainly considered. The energy loss of partons moving in this medium is treated. The principal conclusion is that the medium possesses some collective properties which are crucial for understanding the experimental observations.

The Compressed Baryonic Matter experiment at FAIR

The Compressed Baryonic Matter (CBM) experiment will be one of the major scientific pillars of the future Facility for Antiproton and Ion Research (FAIR) in Darmstadt. The goal of the CBM research program is to explore the QCD phase diagram in the region of high baryon densities using high-energy nucleus-nucleus collisions. This includes the study of the equation-of-state of nuclear matter at high densities, and the search for the deconfinement and chiral phase transitions. The CBM detector is designed to measure both bulk observables with large acceptance and rare diagnostic probes such as charmed particles and vector mesons decaying into lepton pairs. The layout and the physics performance of the proposed CBM experimental facility will be discussed.

MONTE-CARLO SIMULATION OF HEAVY-ION COLLISIONS

Results from the Modular Algorithm for Relativistic Treatment of heavy IoN Interactions (MARTINI) are presented. This comprehensive event generator for the hard and penetrating probes in high energy nucleus-nucleus collisions employs a time evolution model for the soft background, PYTHIA 8.1 and the McGill-AMY parton evolution scheme including radiative as well as elastic processes. It generates full event configurations in the high pT region, allowing to perform the same processing as with experimental data, such as multi-particle correlation analyses and full jet reconstruction.

VHMPID detector for the ALICE experiment upgrade at LHC

Results from high energy nucleus-nucleus collisions at RHIC have shown the importance of particle identification in a very large momentum range, in particular for protons. The ALICE experiment has unique capabilities to identify particles; however its momentum coverage for track-by-track identification should be extended to meet new physics challenges at LHC. The Very High Momentum Charged Particle Identification (VHMPID) detector represents a possible upgrade of the ALICE experimental apparatus. It has been conceived to extend proton identification on a track-by-track basis up to p = 30 GeV/c . The VHMPID is a Ring Imaging Cherenkov with C4F10 gaseous radiator coupled to a CsI based photon detector. The focusing properties of a spherical mirror are exploited to focus Cherenkov photons on the photon detector. The detector layout and the expected performance will be discussed. First results from beam tests of a prototype of 60 × 40 cm 2 will be also presented.

Inclusive electron spectrum from heavy-flavour decays in proton-proton collisions at [formula omitted] measured with ALICE at LHC

We present the status of the analysis on heavy-flavour production in proton-proton collisions at s = 7 TeV via a measurement of their semileptonic decay spectrum at mid-rapidity. An important goal of QCD studies at the LHC is a precise understanding of the heavy-quark production cross section at the high energy frontier in terms of the pQCD framework. Furthermore, heavy quarks are an excellent probe of the hot matter produced in high energy nucleus-nucleus collisions. Establishing precision measurements in proton-proton collisions is a very important baseline for the interpretation of their behaviour in the Quark Gluon Plasma. We present first measurements of the inclusive spectrum of single electrons, using the excellent particle identification capabilities of the ALICE experiment. The subtraction of a cocktail describing photonic and other background sources, as well as an analysis of impact parameter distributions relative to the interaction vertex, are ongoing and will allow the isolation of electrons from heavy-flavour hadron decays.

Full jet tomography of high-energy nuclear collisions

Parton energy loss in the hot QCD medium will manifest itself not only in the leading hadron spectra but also in the reconstructed jet productions in high-energy nucleus-nucleus collisions. In this paper we report on recent theoretical efforts in studying full jet observables in relativistic heavy-ion collisions by discussing the modifications of jet shapes, inclusive jet cross section and the vector boson accompanied jet production in the presence of the QGP-induced jet quenching.

Exclusive glueball production in high-energy nucleus-nucleus collisions

The cross sections for the glueball candidates production in quasi-real photon-photon collisions and on central diffraction processes, i.e. double Pomeron exchange, in heavy ion interactions at RHIC and LHC are computed. The rates for these distinct production channels are compared and they may be a fruitful approach to the investigation of glueballs.

Entropy and specific heat as a measure of fluctuations in multiparticle production in relativistic nuclear collisions

An analysis to disentangle information about the occurrence of dynamical fluctuations in multiparticle production in high energy nucleus-nucleus collisions has been carried out in terms of fractal moments and entropy for the experimental and simulated data using FRITIOF, UrQMD and HIJING generators. Although there is a possibility to thermodynamically interpret the final state of multiparticle production by calculating the values of specific heat, c, using Gq- and Fq-moments. However, both these moments give markedly different values of c. The constancy observed in the values of specific heats calculated from either Gq- or Fq-moments is in accord with the predictions of constant specific heat approximation. Variations of multifractal and factorial moments and various other parameters calculated from these moments predict the presence of non-statistical fluctuations in high energy nuclear collisions.

Three-Particle Coincidence of the Long Range Pseudorapidity Correlation in High Energy Nucleus-Nucleus Collisions

We report the first three-particle coincidence measurement in pseudorapidity (Δη) between a high transverse momentum (p⊥) trigger particle and two lower p⊥ associated particles within azimuth |Δϕ|<0.7 in square root of s(NN)=200 GeV d+Au and Au+Au collisions. Charge ordering properties are exploited to separate the jetlike component and the ridge (long range Δη correlation). The results indicate that the correlation of ridge particles are uniform not only with respect to the trigger particle but also between themselves event by event in our measured Δη. In addition, the production of the ridge appears to be uncorrelated to the presence of the narrow jetlike component.

Rayleigh-like distribution of particle transverse momenta in collisions at high energies

The transverse momentum distributions of final-state particles produced in collisions at high energies are studied by using a two-component Rayleigh-like distribution. This representation is based on Liu's multisource ideal gas model which describes protons and fragments in high energy nucleus-nucleus collisions. The calculated results are in good agreement with the experimental data of Au-Au, Cu-Cu, d-Au, and pp collisions at the relativistic heavy ion collider energies. The experimental particle momentum distributions of p-Be collisions at 6.4, 12.3, and 17.5 GeV/c, as well as Au-Au collisions at 1.5 AGeV are well described by a model based on a single Rayleigh-like distribution of particle transverse momenta.

Jet Tomography of High-Energy Nucleus-Nucleus Collisions at Next-to-Leading Order

We demonstrate that jet observables are highly sensitive to the characteristics of the vacuum and the in-medium QCD parton showers and propose techniques that exploit this sensitivity to constrain the mechanism of quark and gluon energy loss in strongly interacting plasmas. As a first example, we calculate the inclusive jet cross section in high-energy nucleus-nucleus collisions to O(alpha(s)(3)). Theoretical predictions for the medium-induced jet broadening and the suppression of the jet production rate due to cold and hot nuclear matter effects in Au+Au and Cu+Cu reactions at RHIC are presented.

MARTINI: An event generator for relativistic heavy-ion collisions

We introduce the modular algorithm for relativistic treatment of heavy ion interactions (MARTINI), a comprehensive event generator for the hard and penetrating probes in high-energy nucleus-nucleus collisions. Its main components are a time-evolution model for the soft background, PYTHIA 8.1, and the McGill-Arnold, Moore, and Yaffe (AMY) parton-evolution scheme, including radiative as well as elastic processes. This allows us to generate full event configurations in the high ${p}_{T}$ region that take into account thermal quantum chromodynamic (QCD) and quantum electrodynamic (QED) effects as well as effects of the evolving medium. We present results for the neutral pion nuclear modification factor in $\mathrm{Au}+\mathrm{Au}$ collisions at the BNL Relativistic Heavy Ion Collider as a function of ${p}_{T}$ for different centralities and also as a function of the angle with respect to the reaction plane for noncentral collisions. Furthermore, we study the production of high-transverse-momentum photons, incorporating a complete set of photon-production channels.

Understanding saturation and AA collisions with an eA collider

The initial conditions in high energy nucleus-nucleus collisions are determined by the small momentum fraction part of the nuclear wavefunction. This is the regime of gluon saturation and the most direct way to experimentally study it would be deep inelastic scattering at a high energy electron ion collider (EIC). This talk discusses some of the connections between physics at the EIC and the initial stage of relativistic heavy ion collisions. We argue that measurements at an EIC will provide detailed high-precision information about the parameters for the initial conditions, transverse geometry and longitudinal correlations that will be crucial in understanding the initial stage of a heavy ion collision.

Jet quenching in QCD matter: from RHIC to LHC

The current experimental and theoretical status of hadron and jet production at large transverse momentum in high-energy nucleus-nucleus collisions is summarised. The most important RHIC results are compared to theoretical parton energy loss predictions providing direct information on the (thermo)dynamical properties of hot and dense QCD matter. Prospects for the LHC are also outlined.

Classical initial conditions in high energy nucleus-nucleus collisions

An iterative proceedure is proposed to compute the classical gauge field produced in the collision of two heavy nuclei. The leading order is obtained by linearizing the Yang-Mills equations in the light-cone gauge, and provides a simple formula for gluon production in nucleus-nucleus collisions. At this order k t –factorization breaks down.

On the mechanisms of cumulative-proton production in high-energy hadron-nucleus and nucleus-nucleus collisions

The importance of studying processes involving cumulative-proton production stems from their direct relation to the formation of multiquark configurations, so-called fluctons, in a nucleus owing to nucleondensity fluctuations in which two or more nucleons occur at a distance shorter than 1 fm from one another. According to [1], multiquark configurations may arise in two different physics patterns. The first, caused by a fluctuation of the target-nucleus density, is referred to as a cold model, while the second, associated with nuclear-matter compression occurring under the effect of an incident hadron or a projectile nucleus and leading to the formation of dense quark bags, is called a hot model. It should be noted that, in early interpretations, the production of cumulative protons was related to the Fermi momenta of nucleons. However, the calculations that took into account the Fermi momentum of nucleons [2] showed that the spectrum of fast ( p> 500 MeV/c) cumulative protons cannot be described in this way. In the present study, we examine new features of the process of cumulative-proton production—in particular, we analyze the behavior of the mean multiplicity of cumulative protons as a function of the charge and mass numbers of the target nucleus. Previously, our group studied [3–5] cumulativeproton production in π −12 С, pС, 4 НеС, СС, 16 Op, and p 20 Ne collisions at primary energies in the range 3–300 GeV and, on the basis of a vast statistical data sample, confirmed the universal regularity that the slope parameter of inclusive cross sections for cumulative protons in the cumulative number β is independent of the primary energy and mass of the incident particle or nucleus. It was shown that the fraction of events involving cumulative-proton production on a carbon nucleus is sensitive to the