Charged Hadron Multiplicity Distributions Research Articles

Effects of saturation and fluctuating hotspots for flow observables in ultrarelativistic heavy-ion collisions

We investigate the effects of saturation dynamics on midrapidity flow observables by adding fluctuating hotspots into the novel Monte Carlo EKRT (MC-EKRT) event generator for high-energy nuclear collisions. We demonstrate that the intensity of the saturation effects significantly affects the ratio between the flow coefficients v3 and v2 at the LHC. Adding a hotspot substructure to the nucleons enhances the saturation effects and improves the agreement with the measured data. We show that the collision-energy dependence of the flow coefficients obtained using the MC-EKRT initial states with hotspots is improved in comparison with the earlier event-by-event EKRT model. In addition, we present the results for the charged hadron multiplicity distribution in Pb+Pb collisions at the LHC, and show that the minijet multiplicity originating fluctuations of the saturation scale included in MC-EKRT, as well as the presence of hotspots, are necessary for describing the measured large-multiplicity tail in the distribution. Published by the American Physical Society 2024

Koba-Nielsen-Olesen-like scaling within a jet in proton-proton collisions at LHC energies

We study the multiplicity distributions of events with hard jets in proton-proton collisions at LHC energies using PYTHIA 8 Monte-Carlo simulations. We demonstrate that the charged-hadron multiplicity distributions scale with jet momentum. This suggests that the Koba--Nielsen--Olesen (KNO) scaling holds within a jet. The in-jet scaling is fulfilled without multiple-parton interactions (MPI), but breaks down in case MPI is present without color reconnection. Our findings imply that KNO scaling is violated by parton shower or multiple-parton interactions in higher-energy collisions.

Multiplicity and pseudo-rapidity density distributions of charged particles produced in pp, pA and AA collisions at RHIC & LHC energies

Multiplicity and pseudorapidity (η) density (dN ch/dη) distributions of charged hadrons provide key information towards understanding the particle production mechanisms and initial conditions of high-energy heavy-ion collisions. However, detector constraints limit the η-range across which charged particle measurements can be carried out. Extrapolating the measured distributions to large η-range by parameterizing measured distributions and by using calculations from event generators, we characterize the production of charged particles over the full kinematic range. In the present study, we use three different anstze to obtain quantitative descriptions of the shape of pseudorapidity distributions of charged hadrons produced in pp, p–A, and A–A collisions for beam energies () ranging from a few GeV to a few TeV corresponding to RHIC and LHC energies. We study the limiting fragmentation behavior in these collisions and report evidence for participant-scaling violations in high-energy collisions at the TeV scale. We additionally examine measured pseudorapidity distributions to constrain models describing initial conditions of particle production. We predict the centrality dependence of charged particle multiplicity distributions at FAIR and NICA energies and give an estimation of charged particle multiplicity at η = 0 for the proposed HE-LHC and FCC energies.

Probing the Neutron Skin with Ultrarelativistic Isobaric Collisions.

Particle production in ultrarelativistic heavy ion collisions depends on the details of the nucleon density distributions in the colliding nuclei. We demonstrate that the charged hadron multiplicity distributions in isobaric collisions at ultrarelativistic energies provide a novel approach to determine the poorly known neutron density distributions and thus the neutron skin thickness in finite nuclei, which can in turn put stringent constraints on the nuclear symmetry energy.

Numerical solutions to Giovannini’s parton branching equation up to TeV energies at the LHC

The full Giovannini parton branching equation is integrated numerically using the fourth-order Runge-Kutta method. Using a simple hadronization model, a charged-hadron multiplicity distribution is obtained. This model is then fitted to various experimental data up to the TeV scale to study how the Giovannini parameters vary with collision energy and type. The model is able to describe hadronic collisions up to the TeV scale and reveals the emergence of gluonic activity as the center-of-mass energy increases. A prediction is made for [Formula: see text].

Multiphase transport model predictions of isobaric collisions with nuclear structure from density functional theory

Isobaric $^{96}_{44}$Ru+$^{96}_{44}$Ru and $^{96}_{40}$Zr+$^{96}_{40}$Zr collisions were performed at the Relativistic Heavy Ion Collider in 2018. Using the "a multi-phase transport" model with nuclear structures calculated by the density functional theory (DFT), we make predictions for the charged hadron multiplicity distributions and elliptic azimuthal anisotropies in these collisions. Emphases are put on the relative differences between the two collision systems that can decisively discriminate DFT nuclear distributions from the commonly used Woods-Saxon densities.

Pseudorapidity distributions of charged hadrons in proton-lead collisions at sqrt{s_{mathrm{NN}}}=5.02 and 8.16 TeV

The pseudorapidity distributions of charged hadrons in proton-lead collisions at nucleon-nucleon center-of-mass energies sqrt{s_{mathrm{NN}}}=5.02 and 8.16 TeV are presented. The measurements are based on data samples collected by the CMS experiment at the LHC. The number of primary charged hadrons produced in non-single-diffractive proton-lead collisions is determined in the pseudorapidity range |ηlab| < 2.4. The charged-hadron multiplicity distributions are compared to the predictions from theoretical calculations and Monte Carlo event generators. In the center-of-mass pseudorapidity range |ηcm| < 0.5, the average charged-hadron multiplicity densities 〈dNch/dηcm〉|ηcm| < 0.5 are 17.31 ± 0.01 (stat) ± 0.59 (syst) and 20.10 ± 0.01 (stat) ± 0.85(syst) at sqrt{s_{mathrm{NN}}}=5.02 and 8.16 TeV, respectively. The particle densities per participant nucleon are compared to similar measurements in proton-proton, proton-nucleus, and nucleus-nucleus collisions.

Multifractal characteristics of multiparticle production in heavy-ion collisions at SPS energies

Entropy, dimensions and other multifractal characteristics of multiplicity distributions of relativistic charged hadrons produced in ion–ion collisions at SPS energies are investigated. The analysis of the experimental data is carried out in terms of phase space bin-size dependence of multiplicity distributions following the Takagi’s approach. Yet another method is also followed to study the multifractality which, is not related to the bin-width and (or) the detector resolution, rather involves multiplicity distribution of charged particles in full phase space in terms of information entropy and its generalization, Rényi’s order-[Formula: see text] information entropy. The findings reveal the presence of multifractal structure — a remarkable property of the fluctuations. Nearly constant values of multifractal specific heat “[Formula: see text]” estimated by the two different methods of analysis followed indicate that the parameter “[Formula: see text]” may be used as a universal characteristic of the particle production in high energy collisions. The results obtained from the analysis of the experimental data agree well with the predictions of Monte Carlo model AMPT.

More Results from the Opera Experiment at the Gran Sasso Underground Lab

The OPERA experiment reached its main goal by proving the appearance of [Formula: see text] in the CNGS [Formula: see text] beam. Five [Formula: see text] candidates fulfilling the analysis defined in the proposal were detected with a S/B ratio of about ten allowing to reject the null hypothesis at 5.1[Formula: see text]. The search has been extended by loosening the selection criteria in order to obtain a statistically enhanced, lower purity, signal sample. One such interesting neutrino interaction with a double vertex topology having a high probability of being a [Formula: see text] interaction with charm production is reported. Based on the enlarged data sample the estimation of [Formula: see text][Formula: see text] in appearance mode is presented. The search for [Formula: see text] interactions has been extended over the full data set with a more than twofold increase in statistics with respect to published data. The analysis of the [Formula: see text] channel is updated and the implications of the electron neutrino sample in the framework of the 3+1 neutrino model is discussed. An analysis of [Formula: see text] interactions in the framework of the sterile neutrino model has also been performed. Finally, the results of the study of charged hadron multiplicity distributions is presented.

Charged Hadron Multiplicity Distribution at Relativistic Heavy-Ion Colliders

The present paper reviews facts and problems concerning charge hadron production in high energy collisions. Main emphasis is laid on the qualitative and quantitative description of general characteristics and properties observed for charged hadrons produced in such high energy collisions. Various features of available experimental data, for example, the variations of charged hadron multiplicity and pseudorapidity density with the mass number of colliding nuclei, center-of-mass energies, and the collision centrality obtained from heavy-ion collider experiments, are interpreted in the context of various theoretical concepts and their implications. Finally, several important scaling features observed in the measurements mainly at RHIC and LHC experiments are highlighted in the view of these models to draw some insight regarding the particle production mechanism in heavy-ion collisions.

CGC predictions for [formula omitted] collisions at the LHC and signature of QCD saturation

We present various predictions for the upcoming p+Pb collisions at S=5 TeV within the color glass condensate (CGC) formalism, including single inclusive charged hadron production, single inclusive prompt photon production, direct photon production, charged hadron multiplicity distribution and photon–hadron azimuthal correlations. Using the running-coupling Balitsky–Kovchegov evolution equation for calculating various observables, we show that the main source of uncertainties is due to less constrained initial nuclear saturation scale. This gives rise to rather large theoretical uncertainties for nuclear modification factor RpA at the LHC. Nevertheless, we propose a simple scheme in which one can still test the main dynamics of the CGC/saturation in p+A collisions at the LHC.

Particle Production in pA Collisions and QCD Saturation

The forthcoming LHC measurements in proton-nucleus (pA) collisions at forward rapidities can discriminate between the color glass condensate (CGC) and alternative approaches including standard collinear factorization one. We report some of our recent predictions based on gluon saturation/CGC formalism for pA collisions at the LHC including the charged hadron multiplicity distribution, the nuclear modification factor for single inclusive hadron and prompt photon production, and the azimuthal angle correlation of the semi-inclusive hadron-photon production.

Two-component model in quantum statistical framework compared with multiplicity distributions in proton–proton collisions at energies up to [formula omitted

Proton–proton collisions at new high energies (s=2.36 and 7 TeV) at LHC resulted into greater mean multiplicities (〈n〉) of charged particles in the mid-rapidity region than estimated ones by different models and event generators. Another significant observation in multiplicity data is the change in slope in the distribution of primary charged hadrons in symmetric pseudorapidity interval |η|<2.4. The change is most prominent with data at s=7 TeV. These new observations merit further studies. We consider a two-component model of particle production to analyze multiplicity distributions of charged hadrons from proton–proton collisions at centre-of-mass energies s=0.9, 2.36 and 7 TeV in symmetric pseudorapidity intervals |η| of increasing width around the centre-of-mass pseudorapidity ηcm=0. The model, based on Quantum Statistical (QS) formalism, describes multiplicity distribution by convolution of a Negative Binomial Distribution (NBD), representing a chaotic component, and a Poisson Distribution (PD), representing a coherent component of particle productions. The behaviour of characteristic parameters of the model is followed by the LHC data, while a scaling law, involving information entropy in quantum statistical viewpoint and derived as a function of chaotic multiplicity obtained from the two-component model, is not obeyed by the data, satisfactorily. An attempt to match the measured multiplicity distributions and suggested convolutions with values of characteristic parameters extracted from the data confirms disagreement between the data and the model.

Multiplicity distributions of charged hadrons at AGS, SPS and RHIC

It is found that Collective Flow Model (CFM) which can successfully analyze charged particle distributions at AGS and lower SPS (less than 20 GeV/n), fails to analyze that of RHIC. The tail of distribution of charged particle at RHIC has a jump away from the collective model calculation as the energy increase. Thermalization Component Model (TCM) is presented basing on collective flow to study the multiplicity distributions at RHIC in this paper. It is realized that the limitation of phase space of collective flow can denote that of thermalization region. By comparing the contributions of particle productions from thermalization region at different energies and different centrality, we can deep our study on the feature of collective movement at RHIC.

Measurements of hadron production at CMS

First results on hadron production using the 0.9, 2.36 and 7 TeV data are presented. The topics covered include spectra and multiplicity distributions of charged hadrons, spectra of strange hadrons, angular and Bose-Einstein correlations of charged particles. This is just the beginning of a successful physics program at the LHC, with possible future discoveries.

Charged particle multiplicities in pp interactions at $ \sqrt {s} = 0.9 $ , 2.36, and 7 TeV

Measurements of primary charged hadron multiplicity distributions are presented for non-single-diffractive events in proton-proton collisions at centre-of-mass energies of sqrt(s) = 0.9, 2.36, and 7 TeV, in five pseudorapidity ranges from |eta|<0.5 to |eta|<2.4. The data were collected with the minimum-bias trigger of the CMS experiment during the LHC commissioning runs in 2009 and the 7 TeV run in 2010. The multiplicity distribution at sqrt(s) = 0.9 TeV is in agreement with previous measurements. At higher energies the increase of the mean multiplicity with sqrt(s) is underestimated by most event generators. The average transverse momentum as a function of the multiplicity is also presented. The measurement of higher-order moments of the multiplicity distribution confirms the violation of Koba-Nielsen-Olesen scaling that has been observed at lower energies.

Analysis of charged hadron multiplicity distributions at RHIC**Supported by Excellent Youth Foundation of Hubei Scientific Committee(2006ABB036), Education Commission of Hubei Province of China (Z20081302) and Natural Science Foundation of China Three Gorges University (2003C02)

It is demonstrated that with Heinz's collective flow model charged particle distributions at AGS and lower SPS energies (less than 20 GeV/n), can successfully be analyzed, but that the model fails for the RHIC data. Heinz's model calculation underestimates the tails of the charged particle distributions from RHIC, the discrepancy becoming bigger as the energy increases. To study the multiplicity distributions at RHIC we develop the so-called ''Thermalization Component Model'', which is based on Heinz's collective flow model. It is realized that the limitation of phase space of collective flow can be reflected in that of the thermalization region. By comparing the contributions of particle production from the thermalization regions at different energies and different centralities, we can deepen our understanding of the features of collective motion at RHIC.

Thermalization component model of multiplicity distributions of charged hadrons measured at BNL (ENNlab=2−11.6GeV), at CERN (ENNlab=20−200GeV), and at BNL (sNN=19.6−200GeV)

We find that a collective flow model can successfully be used to analyze charged particle distributions at AGS and lower SPS (${E}_{\mathit{NN}}^{\mathrm{lab}}$ less than 20 GeV in the laboratory frame) but fails at RHIC. The tail of the distribution of charged particles at RHIC has a jump from the collective flow model calculation as the energy increases. In this paper a thermalization component model is presented based on collective flow to study the multiplicity distributions at RHIC. It is realized that the region of phase space of collective flow can reflect that of the thermalization region. By comparing the contributions of particle production from the thermalization region at different energies and different centralities, we can deepen our study on collective movement at RHIC.

Modified negative binomial description of the multiplicity distributions in lepton-nucleon scattering

It is shown that charged hadron multiplicity distributions in lepton-nucleon scattering are fairly well described by the modified negative binomial distribution in the energy range from 3–4 to ⋍ 220 GeV. The energy behaviour of the parameter k is similar to the dependence observed for e + e − annihilation.

Multifractal structure of multiplicity distributions in particle collisions at high energies.

Experimental data on the bin size dependence of charged hadron multiplicity distributions in proton-antiproton collisions and electron-positron annihilation are analyzed in terms of multifractals. Linear relations are found between 〈nlnn〉/〈n〉 and ln〈n〉, and also between ln〈${\mathit{n}}^{\mathit{q}}$〉 and ln〈n〉 for q=2,3,4,..., where n is the multiplicity in a single bin of the (pseudo) rapidity space and 〈 〉 stands for the event average. Generalized dimensions ${\mathit{D}}_{\mathit{q}}$ for q=0,1,2, . . . are determined from the slopes. Our result suggests a power law of the form 〈${\mathit{n}}^{\mathit{q}}$〉=c(〈n〉/${\mathit{n}}_{0}$${)}_{\mathit{q}}^{\mathit{b}}$.