Multiparticle Production Research Articles

Chaos in multiparticle production in 16O–AgBr interactions at 60 A GeV and its target excitation dependence

Chaos in multiparticle production in 16O–AgBr interactions at 60 A GeV and its target excitation dependence

The Equation of State and Multiparticle Production

The Equation of State and Multiparticle Production

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.

Baryon-number — flavor separation in the topological expansion of QCD

Gauge invariance of QCD dictates the presence of string junctions in the wave functions of baryons. In high-energy inclusive processes, these baryon junctions have been predicted to induce the separation of the flows of baryon number and flavor. In this paper we describe this phenomenon using the analog-gas model of multiparticle production proposed long time ago by Feynman and Wilson and adapted here to accommodate the topological expansion in QCD. In this framework, duality arguments suggest the existence of two degenerate junction-antijunction glueball Regge trajectories of opposite C\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\mathcal{C} $$\\end{document}-parity with intercept close to 1/2. The corresponding results for the energy and rapidity dependence of baryon stopping are in reasonably good agreement with recent experimental findings from STAR and ALICE experiments. We show that accounting for correlations between the fragmenting strings further improves agreement with the data, and outline additional experimental tests of our picture at the existing (RHIC, LHC, JLab) and future (EIC) facilities.

The U-Matrix geometrical model for multi-particle production in high-energy hadronic collisions

Inspired by the picture portraying the KNO scaling violation as an extension of the geometrical scaling violation, the current study proposes a phenomenological model for multi-particle production in hadron collisions based on the geometrical approach and using the U-Matrix unitarization scheme of the scattering amplitude. The model has been fine-tuned and all parameters have been derived from optimal fits to various hadronic multiplicity distributions data in p + pp¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ p\\left(\\overline{p}\\right) $$\\end{document} collisions across a broad range of energies. The results have revealed that our model furnishes a reasonable description of diverse multiplicity distributions at various energies. Besides, they have demonstrated a pronounced violation of the geometrical scaling, which eventually resulted in a significant violation of the KNO scaling. The study has also analyzed the higher-order moments of the multiplicity distribution. We have observed an unexpected overestimation of the fluctuations and correlations between final state particles with increasing energy, particularly above LHC energy. It is claimed that this overestimation is due to statistical fluctuations embedded in the U-matrix scheme. The findings of this study have shed light on the key role of the U-matrix scheme in the impact of collision geometry on multi-particle production processes at high energy.

Sibyll[formula omitted]

In the last decade, an increasing number of datasets have revealed a consistent discrepancy between the number of muons measured in ultra-high-energy extensive air showers (EAS) and the numbers predicted by simulations. This gap persists despite incorporating Large Hadron Collider (LHC) data into the tuning of current hadronic interaction models, leading to the phenomenon often termed the “muon puzzle”. To gain a deeper understanding of the potential origins of this muon puzzle, we have developed Sibyll★, a series of phenomenologically modified versions of Sibyll 2.3d. In these models, we have increased muon production by altering ρ0, baryon–antibaryon pair, or kaon production in hadronic multiparticle production processes. These variants remain within bounds from provided by accelerator measurements, including those from the LHC and fixed-target experiments, notably NA49 and NA61, showing a level of consistency comparable to Sibyll 2.3d. Our findings show that these modifications can increase the muon count in EAS by up to 35%, while minimally affecting the depth of shower maximum (Xmax) and other shower variables. Additionally, we assess the impact of these modifications on various observables, including inclusive muon and neutrino fluxes and the multiplicities of muon bundles in deep underground and water/ice Cherenkov detectors. We aim for at least one of these model variants to offer a more accurate representation of EAS data at the highest energies, thereby enhancing the quality of Monte Carlo predictions used in training neural networks. This improvement is crucial for achieving more reliable data analyses and interpretations.

Measurement of the Sensitivity of Two-Particle Correlations in pp Collisions to the Presence of Hard Scatterings.

A key open question in the study of multiparticle production in high-energy pp collisions is the relationship between the "ridge"-i.e., the observed azimuthal correlations between particles in the underlying event that extend over all rapidities-and hard or semihard scattering processes. In particular, it is not known whether jets or their soft fragments are correlated with particles in the underlying event. To address this question, two-particle correlations are measured in pp collisions at sqrt[s]=13 TeV using data collected by the ATLAS experiment at the LHC, with an integrated luminosity of 15.8 pb^{-1}, in two different configurations. In the first case, charged particles associated with jets are excluded from the correlation analysis, while in the second case, correlations are measured between particles within jets and charged particles from the underlying event. Second-order flow coefficients, v_{2}, are presented as a function of event multiplicity and transverse momentum. These measurements show that excluding particles associated with jets does not affect the measured correlations. Moreover, particles associated with jets do not exhibit any significant azimuthal correlations with the underlying event, ruling out hard processes contributing to the ridge.

Study of multiplicity fluctuations in terms of strongly intensive quantity in forward-backward zone

A completely new study of forward-backward multiplicity fluctuation of produced pions in nuclear emulsion detector has been carried out by the method of strongly intensive quantity ΣFB for 16O-AgBr, 28Si-AgBr and 32S-AgBr interactions at 4.5 AGeV/c. Experimental analysis has been compared using MC-RAND events and UrQMD simulated events. UrQMD model could not reproduce the experimental results. Outcome of this analysis supports the presence of dynamical fluctuations in multiparticle production at 4.5 AGeV/c. The results on strongly intensive fluctuation measures at a lower energy show much larger fluctuations in comparison to the higher energy data studied so far.

An outlook to centrality dependence of event-by-event fluctuations of maximum pseudo-rapidity gap

A detailed study of centrality dependence of event-by-event fluctuations of maximum pseudo-rapidity gap of the produced particles has been carried out in terms of the scaled variance ω for 22Ne-emulsion interactions at 4.1 AGeV/c and 28Si-emulsion interactions at 4.5 AGeV/c. Depending on the values of the total charges or sum of the charges of non interacting projectile fragments, event samples were classified into three different centrality classes. Presence of centrality dependence of event-by-event fluctuations of maximum pseudo-rapidity gap is reflected in the multiparticle production process from this analysis. The event-by-event fluctuations are found to increase with decreasing centrality of collisions. Experimental analysis has been compared with the results obtained from the analysis of Monte Carlo simulated (MC-RAND) events in order to extract dynamical fluctuations. The difference between the experimental and simulated values of event-by-event fluctuations establishes the existence of true dynamical correlation among the produced particles.

Some Non-Obvious Consequences of Non-Extensiveness of Entropy

Non-additive (or non-extensive) entropies have long been intensively studied and used in various fields of scientific research. This was due to the desire to describe the commonly observed quasi-power rather than the exponential nature of various distributions of the variables of interest when considered in the full available space of their variability. In this work we will concentrate on the example of high energy multiparticle production processes and will limit ourselves to only one form of non-extensive entropy, namely the Tsallis entropy. We will discuss some points not yet fully clarified and present some non-obvious consequences of non-extensiveness of entropy when applied to production processes.

Suppression exponent for multiparticle production in λϕ4 theory

We compute the probability of producing n particles from few colliding particles in the unbroken (3 + 1)-dimensional λϕ4 theory. To this end we numerically implement semiclassical method of singular solutions which works at n ≫ 1 in the weakly coupled regime λ ≪ 1. For the first time, we obtain reliable results in the region of exceptionally large final-state multiplicities n ≫ λ−1 where the probability decreases exponentially with n, mathcal{P}left(textrm{few}to nright)sim exp left{{f}_{infty}left(varepsilon right)nright} , and its slope f∞ < 0 depends on the mean kinetic energy ε of produced particles. In the opposite case n ≪ λ−1 our data match well-known tree-level result, and they interpolate between the two limits at n ~ λ−1. Overall, this proves exponential suppression of the multiparticle production probability at n ≫ 1 and arbitrary ε in the unbroken theory. Using numerical solutions, we critically analyze the mechanism for multiple Higgs boson production suggested in the literature. Application of our technique to the scalar theory with spontaneously broken symmetry can eradicate (or confirm) it in the nearest future.

Probing Hadronic Interactions with Cosmic Rays

High-energy cosmic rays interact in the Earth’s atmosphere and produce extensive air showers (EASs) which can be measured with large detector arrays at the ground. The interpretation of these measurements relies on models of the EAS development which represents a challenge as well as an opportunity to test quantum chromodynamics (QCD) under extreme conditions. The EAS development is driven by hadron-ion collisions under low momentum transfer in the non-perturbative regime of QCD. Under these conditions, hadron production cannot be described using first principles and these interactions cannot be probed with existing collider experiments. Thus, accurate measurements of the EAS development provide a unique probe of multi-particle production in hadronic interactions.

К выводу в рамках статистики Тсаллиса релятивистского кинетического уравнения для разреженной идеальной газовой системы высокоэнергетических частиц

In this work we discuss the nonextensive kinetic theory for anomalous gas q-systems in a general relativistic framework. By including nonextensive effects in the collision term of the relativistic equation (violating Boltzmann molecular chaos hypothesis) and in a modified 4-vector expression for the q-entropy flux it is shown that the entropic Tsallis formalism preserves a local form of the relativistic H-theorem according to which the entropy growth in any point of space-time is never negative. It is shown that the local collision equilibrium (the zero-point entropy source term) is described by a generalized version of the Yuttner relativistic distribution. Using this distribution, the particle number, energy and entropy densities and the thermal equation of state for a relativistic q-gas of identical particles in the equilibrium state are determined explicitly. The results are reduced to the standard ones in the extensive limit, thus showing that the nonex-tensive entropic scheme can be consistent with the space-time ideas contained in the general rela-tivistic theory. The constructed kinetic equation is designed to describe a wide range of phenomena in as-trophysics, cosmology and high-energy physics, in particular, multiparticle production processes in relativistic collisions.

Investigation of dynamical pseudorapidity fluctuations using strongly intensive quantities on event-by-event basis in nucleus–nucleus interactions at CERN SPS energies

The event-by-event pseudorapidity and multiplicity fluctuations have been investigated for relativistic charged particles produced in [Formula: see text]O–AgBr at 60[Formula: see text]A[Formula: see text]GeV/c and 200[Formula: see text]A[Formula: see text]GeV/c, and [Formula: see text]S–AgBr at 200[Formula: see text]A[Formula: see text]GeV/c. The strongly intensive measures ([Formula: see text], [Formula: see text] and [Formula: see text]) have been studied to unravel the underlying dynamics of multiparticle production. The multiplicity and pseudorapidity dependence of these fluctuation measures has been investigated and significant deviations from the expected reference values of independent particle production model have been observed, implying the presence of genuine dynamical fluctuations and correlations in these interactions. These deviations are due to the correlated particle production and not the modifications in single-particle spectrum. The hadronic rescatterings present within the framework of a multi-phase transport (AMPT) model are found to have no significant impact on the behavior of these observables. Both default and string melting AMPT generally show the same qualitative behavior as that of the experimental data. However, the string melting AMPT exhibits slightly better quantitative agreement with the experimental results.

Multiparticle production in proton–nucleus collisions beyond eikonal accuracy

We study the effects on multigluon production at mid-rapidity in the Color Glass Condensate of the non-eikonal corrections that stem from relaxing the shockwave approximation and giving the target a finite size. We extend previous works performed in the dilute-dilute approximation suitable for proton–proton collisions, to the dilute-dense one applicable to proton–nucleus. We employ the McLerran–Venugopalan model for the projectile averages. For the target averages, we use the Golec-Biernat–Wüsthoff model and restrict to the leading contributions in overlap area that allow a factorization of ensembles of Wilson lines into products of dipoles. We make the connection with the jet quenching formalism and compare with previous results in the literature, providing a parametrization of the so-called decorated dipoles. We show that the non-eikonal effects on single inclusive particle production, contrary to what happens in jet quenching, are only sizable, of a few percent, for modest energies sqrt{s_{NN}}le 100 GeV and central rapidities. On the other hand, we find that the effects on double inclusive gluon production are larger for the same kinematics. We show that, as found previously in the dilute-dilute situation, non-eikonal corrections break the accidental symmetry in the CGC, allowing for the existence of non-vanishing odd azimuthal harmonics.

Unitarity in multi-Higgs production using the Schwinger–Dyson equation

In spontaneously broken scalar theories, perturbative and semi-classical calculations show that multi-particle production grows rapidly with the number of scalar particles at sufficiently high energies. According to recent computations, for λn ≫ 1, where n is the multiplicity and λ is the self-coupling, the amplitude grows exponentially with the energy, resulting in a divergent propagator and predicting the violation of perturbative unitarity. In this paper, in the scalar theory the self-consistent Schwinger–Dyson equation is solved in the spectral representation and the transition rate is calculated. We find an amplitude growing quadratically with the energy which leads to an asymptotically decreasing propagator.

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.

Multi-particle production in proton-nucleus collisions in the Color Glass Condensate

We compute multi-gluon production in the Color Glass Condensate approach in dilute-dense collisions, pA. We include the contributions that are leading in the overlap area of the collision but keep all orders in the expansion in the number of colors. We use a form of the Lipatov vertices that leads to the Wigner function approach for the projectile previously employed, that we generalise to take into account quantum correlations in the projectile wave function. We compute four gluon correlations and we find that the second order four particle cumulant is negative, so a sensible second Fourier azimuthal coefficient can be defined.

Jet rapidity distributions and jet-jet correlation functions

Multi-particle production studies have always been an important tool in the effort to study the properties of the strong force already from the fifties of the previous century. As the center-of-mass energy of present day hadron colliders and in particular the Large Hadron Collider (LHC) has increased enormously over the years and the focus currently is on the study of multi-jet final states, it would be instructive to see whether the early days phenomenological models applied some 50–60 years ago to describe multi-particle production have anything to offer in the study of multi-jet final states as well as whether they offer predictions different from the QCD based ones. In this paper, we will consider events with two jets well separated in rapidity with similar transverse momenta whereas a number of mini-jets or jets is to be found in between these two bounding jets. Such configurations are relevant for the high energy scattering limit of QCD. We fix the final jet multiplicity to take particular values and we report on a first comparison between the predictions of the old multiperipheral Chew-Pignotti model applied for final state jets and those of BFKL. We compare single jet rapidity distributions as well as jet-jet rapidity correlations.

Multiplicity dependence of charged-particle jet production in pp collisions at mathbf {sqrt{s}}=mathbf {13~TeV}

The multiplicity dependence of jet production in pp collisions at the centre-of-mass energy of sqrt{s} = 13 {mathrm {TeV}} is studied for the first time. Jets are reconstructed from charged particles using the anti-k_mathrm {T} algorithm with resolution parameters R varying from 0.2 to 0.7. The jets are measured in the pseudorapidity range |eta _{mathrm{jet}}|< 0.9-R and in the transverse momentum range 5<p_mathrm {T,jet}^{mathrm{ch}}<140 {mathrm {GeV}}/c. The multiplicity intervals are categorised by the ALICE forward detector V0. The p_{mathrm T} differential cross section of charged-particle jets are compared to leading order (LO) and next-to-leading order (NLO) perturbative quantum chromodynamics (pQCD) calculations. It is found that the data are better described by the NLO calculation, although the NLO prediction overestimates the jet cross section below 20 {mathrm {GeV}}/c. The cross section ratios for different R are also measured and compared to model calculations. These measurements provide insights into the angular dependence of jet fragmentation. The jet yield increases with increasing self-normalised charged-particle multiplicity. This increase shows only a weak dependence on jet transverse momentum and resolution parameter at the highest multiplicity. While such behaviour is qualitatively described by the present version of PYTHIA, quantitative description may require implementing new mechanisms for multi-particle production in hadronic collisions.