Forward-backward Multiplicity Correlations Research Articles

A model dependent study of forward–backward multiplicity correlation in pp collisions at LHC energies

A model dependent study of forward–backward multiplicity correlation in pp collisions at LHC energies

Forward-backward multiplicity correlation and fluctuation in 197Au + 197Au collisions at fixed target Elab = 10A, 20A, 30A and 40A GeV in the UrQMD model

We use the ultra-relativistic quantum molecular dynamics (UrQMD) model to study the multiplicity correlations and fluctuations of charged hadrons emitted in the forward and backward rapidity hemispheres in 197Au + 197Au collisions at four different incident beam energies, namely Elab=10A,20A, 30A and 40A GeV. Dependence of the correlation and fluctuation parameters on the incident beam energy, collision centrality, rapidity gap and rapidity window size are examined. Both short and long-ranged correlations contribute to our UrQMD simulated results. In the framework of the UrQMD model the short-ranged correlations can be interpreted in terms of resonance decays and/or cluster formation. The long-ranged correlations on the other hand, perhaps originate from multiple rescattering suffered by the hadrons and decay of longitudinally stretched strings in the rapidity space. Our simulation based analysis can be used to set a reference base-line for any future experimental study on the forward-backward multiplicity correlation for the colliding system and collision energies involved in the present case.

System scan of the multiplicity correlation between forward and backward rapidities in relativistic heavy-ion collisions using a multi-phase transport model * *Supported in part the National Natural Science Foundation of China (11890710, 11890714, 11875066, 11925502, 11961141003), the Strategic Priority Research Program of CAS (XDB34000000), National Key R&D Program of China (2018YFE0104600, 2016YFE0100900), and Guangdong Major Project of Basic and Applied

A systematic study on forward–backward (FB) multiplicity correlations from large systems to small ones through a multi-phase transport model (AMPT) has been performed and the phenomenon that correlation strength increases with centrality can be explained by taking the distribution of events as the superposition of a series of Gaussian distributions. It is also found that correlations in the plane can imply the shape of the event. Furthermore, long-range correlations originate from the fluctuations associated with the source information. FB correlations allow us to decouple long-range correlations from short-range correlations, and may provide a chance to investigate the α-clustering structure in initial colliding light nuclei as well. It seems the tetrahedron 16O + 16O collision gives a more uniform and symmetrical fireball, that emits the final particles more isotropically or independently in the longitudinal direction, indicating that the forward–backward multiplicity correlation could be used to identify the pattern of α-clustered 16O in future experiments.

System evolution of forward-backward multiplicity correlations in a multiphase transport model

The initial geometry effect on forward-backward multiplicity correlations $C(N_{f},N_{b})$ is studied in relativistic collisions between light nuclei by using a multiphase transport model (AMPT). It is found that tetrahedron $^{16}$O + $^{16}$O gives a more uniform and symmetrical fireball which produces a more isotropic distribution of final particles after the expansion and evolution, and leads to a small $C(N_{f},N_{b})$. Forward-backward multiplicity correlation could be taken as a useful probe to distinguish the pattern of $\alpha$-clustered $^{16}$O in experiments by comparing the neighboring colliding nuclear systems like $^{14}$N + $^{14}$N and $^{19}$F + $^{19}$F.

Forward–backward multiplicity correlation and event-by-event multiplicity fluctuation in nucleus–nucleus collisions at 200A GeV

Correlation among singly charged particles emitted in the forward and backward pseudo-rapidity cones is measured in [Formula: see text]O-Ag/Br and [Formula: see text]S-Ag/Br interactions at an incident energy of [Formula: see text] GeV/nucleon. Event-by-event fluctuations in the charged particle multiplicities and their pseudo-rapidity values are also investigated in terms of some known statistical measures. Evidences of short-ranged particle correlation and cluster formation in the pseudo-rapidity space are found from our analysis. A microscopic transport model based on the Ultra-relativistic Quantum Molecular Dynamics could not match the experimental results. The differences between experimental observation and corresponding simulation could neither be accounted for even when a Bose–Einstein type of correlation effect is implemented into the simulated data.

Study of Forward-Backward Multiplicity Fluctuations and Correlations with Pseudorapidity

Multiplicity fluctuations in two separated pseudorapidity intervals are studied in terms of strongly intensive variables. This work presents results obtained in the MC model with quark-gluon strings as objects extended in pseudorapidity space and acting as particle emitting sources. The string interactions are implemented within the discrete model of local string fusion. Strings of fluctuating length in pseudorapidity are considered in order to estimate the non-critical background of fluctuations. The results on the dependence of strongly intensive observables on the width of acceptance windows, on the pseudorapidity separation between them and on the string density qualitatively describe the available data from the NA61/SHINE and ALICE experiments.

Extraction of multiple parton interactions and color reconnection from forward\u2013backward multiplicity correlations

Forward–backward multiplicity correlations have been studied in electron-positron, proton–proton and more recently in lead-lead collisions. For the proton–proton case, comparison of experimental results to different models reveals an incomplete understanding of the physical phenomenon associated with these correlations. In this work, we present a study of forward–backward multiplicity correlations in proton–proton collisions using the PYTHIA event generator, at LHC energies. A detailed analysis is presented with and without weak decays, splitting data samples into soft and hard QCD processes, and comparing the computed correlations for short and long range pseudorapidity regions. Each of these regions is analyzed accounting for the effects of color reconnection and independent multiple parton interactions. We show that a combination of these effects is required to explain the latest measurements on proton–proton data. Furthermore, is shown that from measurements of multiplicity correlations is possible to extract the average number of multiple parton interactions in the event producing these correlations, and albeit model depending, to predict the strength of these correlations, not yet measured, for higher energy collisions.

Hadronization from color interactions * * Supported in part by National Natural Science Foundation of China (11435004, 11375069), the Ministry of Science and Technology of China (2015CB56901), and the Programme of Introducing Talents of Discipline to Universities (B08033)

A quark coalescence model, based on semi-relativistic molecular dynamics with color interactions among quarks, is presented and applied to pp collisions. A phenomenological potential with two tunable parameters is introduced to describe the color interactions between quarks and antiquarks. The interactions drive the process of hadronization that finally results in different color neutral clusters, which can be identified as hadrons based on some criteria. A Monte Carlo generator PYTHIA is used to generate quarks in the initial state of hadronization, and different values of tunable parameters are used to study the final state distributions and correlations. Baryon-to-meson ratio, transverse momentum spectra, pseudorapidity distributions and forward-backward multiplicity correlations of hadrons produced in the hadronization process, obtained from this model with different parameters, are compared with those from PYTHIA.

Correlations with Fluctuating Strings

We present a semi-analytic approach to forward-backward multiplicity correlations in ultra-relativistic nuclear collisions, based on particle emission from strings with fluctuating end-points. We show that with the constraints from rapidity spectra, one can obtain bounds for the magnitude of the standard measures of the forward-backward fluctuations. The method is generic under the assumption of independent production from sources. For definiteness, we use the wounded quark model for Au+Au and d+Au collisions at the energy of $\sqrt{s_{NN}}=200$ GeV.

Chou-Yang Model for Forward-Backward Multiplicity Correlations at 7 TeV using Generalized Multiplicity Distribution.

The basis of the Chou-Yang model is made up of a stochastic and non-stochastic distribution and has been successful in describing forward-backward multiplicities.[1] This project examines data drawn from CERN’s 7 TeV run where we revist the Chou-Yang model’s components. It also approaches phenomenological descriptions for cluster sizes from forward-backward multiplicaity correlation strength by the E735 collaboration.[6] For the stochastic binomial component, it examines the variance of the charge asymmetry parameter z with regards to fixed total charged multiplicities n. The fitting of the Generalized Multiplicity distribution along with the linear least square fitting of the forward backward multiplicity is analysed. The parameters for the Generalized Multiplicity Distribution is presented along with an investigation on the cluster size r.[3] This serves as an extention to the work done by W.Y Wang’sWeighted GMD model at7TeV, however the nonweighted GMD model is used here.[7]

On the origin of forward–backward multiplicity correlations in pp collisions at ultrarelativistic energies

We study multiplicity correlations of hadrons in forward and backward hemispheres in pp inelastic interactions at energies 200 GeV≤s≤13 TeV within the microscopic quark–gluon string model. The model correctly describes (i) the almost linear dependence of average multiplicity in one hemisphere on the particle multiplicity in other hemisphere in the centre-of-mass frame; (ii) the increase of the slope parameter bcorr with rising collision energy; (iii) the quick falloff of the correlation strength with increase of the midrapidity gap; (iv) saturation of the forward–backward correlations at very high multiplicities. Investigation of the sub-processes on partonic level reveals that these features can be attributed to short-range partonic correlations within a single string and superposition of several sub-processes containing different numbers of soft and hard Pomerons with different mean multiplicities. If the number of Pomerons in the event is fixed, no forward–backward correlations are observed. Predictions are made for the top LHC energy s=13 TeV.

Evidence of forward–backward multiplicity correlation at SPS energy

In this paper, a detailed study of two-particle rapidity correlation has been presented by measuring the dynamical fluctuation variable [Formula: see text] in forward and backward pseudo-rapidity window of shower particles produced in the relativistic heavy ion collision, [Formula: see text]O–AgBr interactions at 60[Formula: see text]AGeV and [Formula: see text]S–AgBr interactions at 200[Formula: see text]AGeV. Variations of [Formula: see text] with rapidity gap between forward and backward zones and with the width of each zone have been studied. For both cases, [Formula: see text] increase with increasing either width of the zone or gap between the zones. Our findings show the presence of strong long-range correlation. Comparison of experimental results with MC-RAND events confirms the present correlation to be dynamical in nature. We have also compared our results with FRITIOF and UrQMD events. Such events also show the presence of correlation, but found to fail to reproduce the experimental results both quantitatively and qualitatively. Strength of correlation is dependent on the centrality of collision for experimental events, it decreases with centrality.

Forward backward multiplicity correlations: a tool to study properties of the proton-proton collisions

Forward-backward multiplicity correlations have been used to study hadron production mechanisms in electron-positron, proton-proton and more recently in leadlead collisions. The experimental results on this correlations and its comparison to different models reveals an incomplete agreement. In this work, we present an study of forward backward multiplicity correlations in proton-proton collisions using PYTHIA event generator, at LHC energies. Detailed analysis is presented in the case of soft and hard QCD processes, incorporating color reconnection model as part of hadronization mechanism and multiple parton interactions effects in the correlations. Our results and its comparison to available experimental data suggest that this kind of correlations are great tools to characterize the events and gives the possibility to disentangle phenomena in hard and soft QCD processes.

Measurement of forward-backward multiplicity correlations in lead-lead, proton-lead, and proton-proton collisions with the ATLAS detector

Two-particle pseudorapidity correlations are measured in $\sqrt{s_{\rm{NN}}}$ = 2.76 TeV Pb+Pb, $\sqrt{s_{\rm{NN}}}$ = 5.02 TeV $p$+Pb, and $\sqrt{s}$ = 13 TeV $pp$ collisions at the LHC, with total integrated luminosities of approximately 7 $\mu\mathrm{b}^{-1}$, 28 $\mathrm{nb}^{-1}$, and 65 $\mathrm{nb}^{-1}$, respectively. The correlation function $C_{\rm N}(\eta_1,\eta_2)$ is measured as a function of event multiplicity using charged particles in the pseudorapidity range $|\eta|<2.4$. The correlation function contains a significant short-range component, which is estimated and subtracted. After removal of the short-range component, the shape of the correlation function is described approximately by $1+\langle{a_1^2}\rangle \eta_1\eta_2$ in all collision systems over the full multiplicity range. The values of $\sqrt{\langle{a_1^2}\rangle}$ are consistent between the opposite-charge pairs and same-charge pairs, and for the three collision systems at similar multiplicity. The values of $\sqrt{\langle{a_1^2}\rangle}$ and the magnitude of the short-range component both follow a power-law dependence on the event multiplicity. The $\eta$ distribution of the short-range component, after symmetrizing the proton and lead directions in $p$+Pb collisions, is found to be smaller than that in $pp$ collisions with comparable multiplicity.

Forward–backward multiplicity correlations in ring like and jet like events in 16O–AgBr interactions at 60 AGeV

We have studied the forward–backward correlations of charged-particle multiplicities in symmetric bins in pseudorapidity space in order to gain insight into the underlying correlations structure of particle production in case of ring-like and jet-like events of 16O–AgBr interactions at 60 AGeV. The variance σc2 of a suitably defined the forward-backward asymmetry variable C has been determined. The experimental results confirm correlations of the produced particles in the forward and the backward pseudorapidity region for both ring-like and jet-like events.

Forward--Backward Multiplicity Correlations at the LHC from Independent Sources

It is argued that the superposition approach, where partons are independently emitted from longitudinally extended sources in the early stage, is fully compatible with the experimental results for the forward-backward multiplicity correlations in Pb+Pb collisions at $\sqrt{s_{NN}}=2.76 \textrm{ TeV}$. The pertinent correlation analysis is based on the PhD Thesis of Ref. [1], which includes an unpublished analysis of data taken by the ALICE Collaboration. Our calculations show that in the experimentally covered pseudorapidity range $\Delta \eta=1.2$, the initial sources in the backward and forward bins are maximally correlated, which complies to the string-like interpretation of the underlying early-stage production mechanism.

Basic features of proton-proton interactions at ultra-relativistic energies and RFT-based quark-gluon string model

Proton-proton collisions at energies from √s = 200 GeV up to √s = 14 TeV are studied within the microscopic quark-gluon string model. The model is based on Gribov’s Reggeon Field Theory accomplished by string phenomenology. Comparison with experimental data shows that QGSM describes well particle yields, rapidity - and transverse momentum spectra, rise of mean 〈 pT 〉 and forward-backward multiplicity correlations. The latter arise in QGSM because of the addition of various processes with different mean multiplicities. The model also indicates fulfillment of extended longitudinal scaling and violation of Koba-Nielsen-Olesen scaling at LHC. The origin of both features is traced to short-range particle correlations in the strings. Predictions are made for √s = 14 TeV.

Forward-backward multiplicity correlations in proton-proton collisions from several GeV to LHC energies

Forward-backward multiplicity correlations in pp collisions at LHC energies are studied with the quark-gluon string model. Comparison with experimental data and with model calculations for lower energies is performed. The model correctly reproduces the linear slope of the correlations, 〈nB (nF )〉 = a + bcorr nF , in the whole energy interval. Positive correlations arise because of mixing of sub-processes with different mean multiplicities. The increase of bcorr with rising collision energy is linked to the increase of the variety of sub-processes going via the soft and hard multi-Pomeron exchanges. For the events with fixed amount of Pomerons the correlation slope bcorr is shown to be essentially zero.

Forward-backward correlations between intensive observables

We demonstrate that the investigations of the forward-backward correlations between intensive observables enable to obtain more clear signal about the initial stage of hadronic interaction, e.g. about the process of string fusion, compared to usual forward-backward multiplicity correlations. As an example, the correlation between mean-event transverse momenta of charged particles in separated rapidity intervals is considered. We performed calculations in the framework of dipole-based Monte Carlo string fusion model. We obtained the dependence of the correlation strength on the collision centrality for different initial energies and colliding systems. It is shown that the dependence reveals the decline of the correlation coefficient for most central Pb-Pb collisions at LHC energy. We compare the results both with the ones obtained in alternative models and with the ones obtained by us using various MC generators.

Forward-backward multiplicity correlations in pp, p + Pb and Pb + Pb collisions with the ATLAS detector

Two-particle pseudorapidity correlations are measured in sNN=2.76 TeV Pb+Pb, sNN=5.02 TeVp+Pb and s=13 TeVpp collisions [ATLAS Collaboration, ATLAS-CONF-2015-051; ATLAS-CONF-2015-020]. Correlation function is measured using charged particles in the pseudorapidity range |η|<2.4 with transverse momentum pT>0.2 GeV, and it is measured as a function of event multiplicity, defined by number of charged particles with |η|<2.5 and pT>0.4 GeV. The correlation function is decomposed into a short-range component (SRC) and a long-range component (LRC). The SRC differs significantly between the opposite-charge pairs and same-charge pairs, and between the three collision systems at similar multiplicity. The LRC is described approximately by 1+〈a12〉η1η2 in all collision systems over the full multiplicity range. The values of 〈a12〉 are consistent between the opposite-charge and same-charge pairs, and are similar for the three collision systems at similar multiplicity. The values of 〈a12〉 and the magnitude of the SRC both follow a power-law dependence on the event multiplicity.