Multiparticle Production Mechanisms Research Articles

Normalized factorial moments of spatial distributions of particles in high multiplicity events: A Toy model study

In ultra-relativistic heavy-ion collisions a strongly interacting complex system of quarks and gluons is formed. The nature of the system so created and the mechanism of multi-particle production in these collisions may be revealed by studying the normalized factorial moments (Fq) as function of various parameters. Fq moments are observed to be sensitive to the presence of dynamical fluctuations. Further, the resilience of these moments, studied using Toy model events, shows their robustness against the uniform efficiency in the data measurements.

Oscillations in Modified Combinants of Hadronic Multiplicity Distributions

Oscillations in modified combinants (C_jCjs) have been of interest to multiparticle production mechanisms since the 1990s [1]. Recently, there has been a discussion on how these oscillations can be reproduced by compounding a binomial distribution with a negative binomial distribution [2,3]. In this work, we explore a stochastic branching model based on a simple interaction term \lambda\overline{\psi}\phi\psiλψ¯ϕψ for partons and propose a hadronization scheme to arrive at the final multiplicity distribution. We study the effects that compounding our model with a binomial distribution has on C_jCjs and explore its physical implications. We find that there is a significant difference in the oscillations in C_jCjs between high energy pp and p\bar{p}pp‾ scattering that our model can reproduce.

Multiplicity fluctuations in the Glauber Monte Carlo approach

We discuss multiplicity fluctuations of charged particles produced in nuclear collisions measured event-by-event by the NA49 experiment at CERN SPS within the Glauber Monte Carlo approach. We use the concepts of wounded nucleons and wounded quarks in the mechanism of multiparticle production to characterize multiplicity fluctuations expressed by the scaled variance of multiplicity distribution. Although Wounded Nucleon Model correctly reproduce the centrality dependence of the average multiplicity in Pb+Pb collisions, it completely fails in description of corresponding centrality dependence of scaled variance of multiplicity distribution. Using subnucleonic degrees of freedom, i.e. wounded quarks within Wounded Quark Model, it is possible to describe quite well the multiplicity distribution of charged particles produced in proton+proton interactions. However, the Wounded Quark Model with parameters describing multiplicity distribution of particles produced in proton+proton interactions substantially exceeds the average multiplicity of charged particles produced in Pb+Pb collisions. To obtain values of average multiplicities close to those experimentally measured in Pb+Pb collisions, the concept of shadowed quark sources is implemented. Wounded Quark Model with implemented shadowing source scenario reproduces the centrality dependence of scaled variance of multiplicity distribution of charged particles produced in Pb+Pb collisions in the range from the most central to mid-peripheral interactions.

A Look at Multiplicity Distributions via Modified Combinants

The experimentally measured multiplicity distributions exhibit, after a closer inspection, the peculiarly enhanced void probability and the oscillatory behavior of modified combinants. We show that both these features can be used as additional sources of information, not yet fully explored, on the mechanism of multiparticle production. We provide their theoretical understanding within the class of compound distributions.

Intriguing properties of multiplicity distributions

Multiplicity distributions exhibit, after closer inspection, peculiarly enhanced void probability and oscillatory behavior of the modified combinants. We discuss the possible sources of these oscillations and their impact on our understanding of the multiparticle production mechanism. Theoretical understanding of both phenomena within the class of compound distributions is presented.

Intriguing feature of multiplicity distributions

Multiplicity distributions, P(N), provide valuable information on the mechanism of the production process. We argue that the observed P(N) contain more information (located in the small N region) than expected and used so far. We demonstrate that it can be retrieved by analysing specific combinations of the experimentally measured values of P(N) which we call modified combinants, Cj, and which show distinct oscillatory behavior, not observed in the usual phenomenological forms of the P(N) used to fit data. We discuss the possible sources of these oscillations and their impact on our understanding of the multiparticle production mechanism.

Thermal radiation and entanglement in proton-proton collisions at energies available at the CERN Large Hadron Collider

The origin of the apparent thermalization in high-energy collisions is investigated using the data of the ATLAS and CMS Collaborations at the LHC. For this purpose, we analyze the transverse momentum distributions in the following proton-proton collision processes, all at $\sqrt{s} = 13$ TeV: i) inclusive inelastic $pp$ collisions; ii) single- and double-diffractive Drell-Yan production $pp \to \mu^+ \mu^- X$; and iii) Higgs boson production. We confirm the relation between the effective temperature and the hard scattering scale observed at lower energies, and find that it extends even to the Higgs boson production process. In addition we find that the thermal component disappears in diffractive events (even though many charged hadrons are still produced). We discuss the implications of our study for the mechanism of multi-particle production -- in particular, we test the hypothesis about the link between quantum entanglement and thermalization in high-energy collisions.

<i>PP</i> and <i>P<span style='text-decoration:overline;'>P</span></i> Multi-Particles Production Investigation Based on CCNN Black-Box Approach

The multiplicity distribution (P(nch)) of charged particles produced in a high energy collision is a key quantity to understand the mechanism of multiparticle production. This paper describes the novel application of an artificial neural network (ANN) black-box modeling approach based on the cascade correlation (CC) algorithm formulated to calculate and predict multiplicity distribution of proton-proton (antiproton) (PP and PP ) inelastic interactions full phase space at a wide range of center-mass of energy . In addition, the formulated cascade correlation neural network (CCNN) model is used to empirically calculate the average multiplicity distribution nch> as a function of . The CCNN model was designed based on available experimental data for = 30.4 GeV, 44.5 GeV, 52.6 GeV, 62.2 GeV, 200 GeV, 300 GeV, 540 GeV, 900 GeV, 1000 GeV, 1800 GeV, and 7 TeV. Our obtained empirical results for P(nch), as well as nch> for (PP and PP) collisions are compared with the corresponding theoretical ones which obtained from other models. This comparison shows a good agreement with the available experimental data (up to 7 TeV) and other theoretical ones. At full large hadron collider (LHC) energy ( = 14 TeV) we have predicted P(nch) and nch> which also, show a good agreement with different theoretical models.

The Application of the Genetic Algorithm-Back Propagation Neural Network Algorithm in the High-Energy Physics

Multiparticle production mechanism is one of the most phenomena that the high-energy physics concerns. In this work, the evolutionary genetic algorithm (GA) is used to optimize the parameters of the back-propagation neural networks (BPNN). The hybrid evolutionary-neuro model (GA-BPNN) was trained to simulate the rapidity distribution 1/N(dN/dY) of positive and negative pions p-Au, p-Ag and p-Xe for p-Ar, p-Xe interactions at lab momentum Plab =100 GeV/c. Also, for total charged, positive and negative pions for interactions at Plab = 200 GeV/c. Finally, total charged particles for p- Pb collision at center-of-mass energy sqrt(s) = 5.02 TeV are simulated. An efficient ANN network with different connection parameters (weights and biases) have been designed by the GA to calculate and predict the rapidity distribution as a function of the lab momentum Plab, mass number (A) and the number of particles per unit solid angle (Y). Our simulated results have been compared with the experimental data and the matching has been clearly found. It is indicated that the developed GA-BPNN model for rapidity distribution was more successful.

From soft photon study at Nuclotron and U-70 to NICA

Experimental and theoretical studies of direct photon production in hadronic collisions essentially expand our insights in multiparticle production mechanisms. These photons are useful probes to investigate nuclear matter at all stages of the interaction. Soft photons play a particular role in these studies. Until now we have no explanation for the experimentally observed excess of soft photons. These photons have low transverse momenta \( p_{T} < 0.1\) GeV/c, \( \vert x\vert < 0.01\) . In this domain their yield exceeds the theoretical estimates by 5-8 times. The registration of soft photons at Nuclotron (LHEP, JINR) has been carried out by the electromagnetic calorimeter built by the SVD-2 Collaboration. Soft photon electromagnetic calorimeter was tested at U-70, IHEP (Protvino). For the first time the soft photon yield at interactions of 3.5A GeV/c per nucleon deuterium and lithium beams has been measured. The obtained energy spectra confirm the increased yield of soft photons with their energy less than 50MeV (in the laboratory system) in comparison with theoretical predictions and agree with previous experiments at high-energy interactions. It is planned to continue soft photon study at the future accelerator complex NICA with heavy-ion beams.

Measurement of the TeV atmospheric muon charge ratio with the full OPERA data set

The OPERA detector, designed to search for νμ→ντ oscillations in direct appearance mode, is located in the underground Gran Sasso laboratory, a privileged location to study TeV-scale cosmic rays. Given the large rock depth and the detector's wide acceptance, the apparatus was used to measure the atmospheric muon charge ratio in the TeV energy region. The muon charge ratio, defined as the number of positive over negative charged muons, provides an understanding of the mechanism of multiparticle production in the atmosphere in kinematic regions not accessible to accelerators, as well as information on the primary cosmic ray composition. We present the results obtained with the full statistics collected by OPERA from 2008 to 2012. The combination of two data sets with opposite magnet polarities allows minimizing systematic uncertainties and reaching an accurate determination of the muon charge ratio. Relevant parameters on the composition of primary cosmic rays and the associated kaon production in the forward fragmentation region are obtained.

Initial state geometry and fluctuations in deformed and asymmetric nuclear collisions in the IP-Glasma framework

Abstract The IP-Glasma model of initial conditions based on the ab initio color glass condensate framework successfully explains most of the bulk features of the global data for various systems like p+p, p+A and A+A over a wide range of energies. We employ this framework to study deformed U+U collisions, asymmetric Cu+Au collisions and the effect of deformation in Au+Au collisions at RHIC. A combined study of these heavy ion systems with varying initial geometries can provide a unique opportunity to determine the origin of different sources of fluctuations that affect global observables like multiplicity and flow. We study the sensitivity of multiplicity, eccentricity and their event-by-event distributions to the details of initial state geometry. Results are compared to a two-component MC-Glauber model implementation that includes Negative-Binomial multiplicity fluctuations. We argue that the measurements of global observables for these systems at RHIC can constrain the mechanism of multi-particle production.

Finite formation time of hadrons: the QGP signatures

In order to investigate the possible emergence of guark-gluon plasma, it is necessary to understand the properties of multiparticle production mechanisms in a more simple case than in relativistic collisions of heavy ions. The purpose of this article is to discuss some problems of the role of zone formation effectwhich are under active investigation nowadays. The formation length of hadron from particle-nucleus collision is derived and compared with those from relativistic ion collisions.

Erratum: SOFT RIDGE IN PROTON–PROTON COLLISIONS

It is shown that the soft mechanism of multiparticle production by Lund hadronic strings formed by colliding constituent degrees of freedom generates a shape of angular correlations similar to the ridge structure observed in the pp collisions at 7 TeV at the LHC.

SOFT RIDGE IN PROTON–PROTON COLLISIONS

It is shown that the soft mechanism of multiparticle production by Lund hadronic strings formed by colliding constituent degrees of freedom generates a shape of angular correlations similar to the ridge structure observed in the pp collisions at 7 TeV at the LHC.

Strong longitudinal color-field effects inppcollisions at energies available at the CERN Large Hadron Collider

We study the effect of strong longitudinal color fields (SCF) in p+p reactions up to Large Hadron Collider energies in the framework of the HIJING/BBbar v2.0 model that combines (collinear factorized) pQCD multiple minijet production with soft longitudinal string excitation and hadronization. The default vacuum string tension, kappa0 = 1 GeV/fm, is replaced by an effective power law energy dependent string tension, that increases monotonically with center-of-mass energy. The exponent 0.06 is found sufficient to reproduce well the energy dependence of multiparticle observables in RHIC, Tevatron, as well as recent LHC data. This exponent is found to be only half of that predicted by the Color Glass Saturation model, lambda(CGC)=0.115, where gluon fusion multiparticle production mechanisms are assumed. In HIJING/BBbar v2.0, the rapid growth of central-rapidity density with energy is due to the interplay of copious minijet production and increasing SCF contributions. The large (strange)baryon-to-meson ratios measured at Tevatron energies are well described. A significant enhancement of these ratios is predicted up to the highest LHC energy (14 TeV). The effect of JJbar loops and SCF on baryon-anti-baryon asymmetry and its relation to baryon number transport is also discussed.

Modeling the jet quenching, thermal resonance production and hydrodynamical flow in relativistic heavy ion collisions

Physical observables in relativistic heavy ion collisions are determined by various multi-particle production mechanisms. The simultaneous model treatment of different collective nuclear effects at high energies (such as a hard multi-parton fragmentation in hot QCD-matter, thermal resonance production, hydrodynamical flows, etc.) is actually a rather complicated task. We discuss the simulation of the above effects by means of the Monte-Carlo model HYDJET++.

Erraticity analysis of particle production in32S−Ag/Brinteraction at200AGeV/c

Spatial fluctuations as well as event-to-event fluctuations of charged particles produced in central ${}^{32}\mathrm{S}\ensuremath{-}\mathrm{A}\mathrm{g}/\mathrm{B}\mathrm{r}$ interactions at $200A\mathrm{G}\mathrm{e}\mathrm{V}/c$ are investigated by using a new technique called erraticity analysis. A general scaling law between the erraticity moments and number of phase-space intervals is observed, and the values of erraticity parameters are obtained. These parameters can serve a very useful purpose for model calculations of the multiparticle production mechanism in high-energy heavy-ion collisions that takes into account possible sources of fluctuations.

Interconnection phenomena in W pair production at DELPHI

Interactions between the products of the hadronic decays of different Ws in WW pair events can occur at several stages: from the colour rearrangement between the quarks coming from the primary branching, to the gluon exchange during the parton cascade, to the mixing of identical pions due to Bose-Einstein correlations. Besides the intrinsic interest of their study related to the understanding of the multiparticle production mechanisms, these phenomena can affect the ultimate accuracy in the W mass measurement by LEP 2. The status of the DELPHI experimental analysis on interconnection effects between W pairs hadronically decaying is reviewed in this paper.

Interconnection phenomena in WW events at LEP2

Interactions between the products of the hadronic decays of different Ws in WW pair events can occur at several stages: from the colour rearrangement between the quarks coming from the primary branching, to the gluon exchange during the the parton cascade, to the mixing of identical pions due to BoseEinstein correlations. Besides the intrinsic interest of their study related to the understanding of the multiparticle production mechanisms, these phenomena can affect the ultimate accuracy in the W mass measurement by LEP 2. The status of the experimental analysis on interconnection effects between W pairs decaying hadronically is reviewed in this paper. For what is related to Bose-Einstein interference, only the results from ALEPH and DELPHI are presented, being L3 and OPAL discussed in another contribution to this conference.