Quark-gluon String Model Research Articles

Centrality dependence of multistrange baryon production in high-energy heavy-ion collisions

We consider the experimental data on the production of strange \Lambda^{\prime}Λ′s, and multistrange baryons (\XiΞ, \OmegaΩ), and antibaryons, on nuclear targets, at the energy region from SPS up to LHC, in the framework of the Quark-Gluon String Model. One remarkable result of this analysis is the significant dependence on the centrality of the collision of the experimental \overline{\Xi}^+/\overline{\Lambda}Ξ¯+/Λ¯ and \overline{\Omega}^+/\overline{\Lambda}Ω¯+/Λ¯ ratios in heavy-ion collisions, at SPS energies.

Self-consistent description of HERA data at low Q2 and soft hadron production at LHC

Using the analytical expression for transverse momentum dependent (TMD) gluon density in a proton, a self-consistent simultaneous description of low Q2 data on proton structure function F2(x,Q2), reduced cross section for the electron-proton deep inelastic scattering at HERA and soft hadron production in pp collisions at the LHC is achieved in the framework of color dipole approach and modified quark-gluon string model.

Toward the global fit of the TMD gluon density in the proton from the LHC data

We propose a new analytical expression for the transverse-momentum-dependent (TMD, or unintegrated) gluon density in the proton. Essential phenomenological parameters are extracted from the LHC data on inclusive hadron production in $pp$ collisions at low transverse momenta ${p}_{T}\ensuremath{\le}1\text{ }\text{ }\mathrm{GeV}$. The latter are described in the framework of a modified soft quark-gluon string model, where the gluonic state and nonzero transverse momentum of partons inside the proton are taken into account. To determine the parameters important at moderate and large $x$, we use the measurements of inclusive $b$-jet and Higgs boson production at the LHC as well as the latest HERA data on proton structure functions ${F}_{2}^{c}(x,{Q}^{2})$ and ${F}_{2}^{b}(x,{Q}^{2})$ and reduced cross sections ${\ensuremath{\sigma}}_{\mathrm{red}}^{c}(x,{Q}^{2})$ and ${\ensuremath{\sigma}}_{\mathrm{red}}^{b}(x,{Q}^{2})$. The Catani-Ciafaloni-Fiorani-Marchesini evolution equation is applied to extend the initial gluon distribution to the whole kinematical region. We achieve a simultaneous description of all considered processes with ${\ensuremath{\chi}}^{2}/\mathrm{d}.\mathrm{o}.\mathrm{f}.=2.2$, thus moving toward the global fit of the TMD gluon density from collider data. The obtained TMD gluon distribution in a proton is available for public usage and implemented in the tmdlib package and Monte Carlo event generator pegasus.

Quark–Gluon String Model and Its Application to Inelastic $${d}$$C Interactions at a Momentum of 4.2 GeV/$${c}$$ per Nucleon

Quark–Gluon String Model and Its Application to Inelastic $${d}$$C Interactions at a Momentum of 4.2 GeV/$${c}$$ per Nucleon

Multistrange hyperon production on nuclear targets

We consider the experimental data on yields of protons, strange $\Lambda^{\prime}$s, and multistrange baryons ($\Xi$, $\Omega$), and antibaryons production on nuclear targets, and the experimental ratios of multistrange to strange antibaryon production, at the energy region from SPS up to LHC, and compare them to the results of the Quark-Gluon String Model calculations. In the case of heavy nucleus collisions, the experimental dependence of the $\overline{\Xi}^+/\overline{\Lambda}$, and, in particular, of the $\overline{\Omega}^+/\overline{\Lambda}$ ratios, on the centrality of the collision, shows a manifest violation of quark combinatorial rules.

Study of Strongly Intense Quantities and Robust Variances in Multi-Particle Production at LHC Energies

The strongly intense quantities and robust variances in processes of multi-particle production in pp and AA interactions at LHC energies was studied. The Monte Carlo and analytic modelling of these quantities in the framework of a quark-gluon string model were implies. The string fusion effects were also taken into account by implementing of a lattice (grid) in the impact parameter plane. Strongly intensive variable $\Sigma(n_F,\ n_B)$ was calculated for different energies for two values of the width of the observation rapidity windows as a function of the distance between the centres of this windows. Scaled variance $\omega_n$ and robust variance $R_n$ for different energies and for different width of the observation rapidity window was calculated by MC simulations.

Centrality dependence of multistrangeness production in high-energy heavy-ion collisions

We compare the experimental data on yields of protons, strange Λ′s, and multistrange baryons (Ξ, Ω), and antibaryons production on nuclear targets, and the experimental ratios of multistrange to strange antibaryon production, at the energy region from SPS up to LHC, with the corresponding results of the Quark-Gluon String Model calculations. In the case of heavy nucleus collisions, the experimental dependence of the Ξ̅+/Λ̅, and Ω̅+/Λ̅ ratios, on the centrality of the collision, shows a manifest violation of quark combinatorial rules.

Baryon production at LHC experiments: average pt of hyperons versus energy

This paper examines the transverse momentum spectra of baryons in the multiparticle production at modern colliders in the frameworks of Quark–Gluon String Model (QGSM). It discusses: (i) the difference in [Formula: see text] hyperon spectra at proton–antiproton versus proton–proton reactions on previous colliders; (ii) the difference in hyperon spectra between the experiments on colliders of low energies and the results from modern machines; (iii) the growth of average transverse momenta of [Formula: see text] hyperon with the energies of proton–proton collisions up to [Formula: see text] TeV of LHC experiments. This analysis of baryon spectra led to the following conclusions. First, the fragmentation of antidiquark–diquark side of one-pomeron diagram makes the major contribution to baryon production spectra in the asymmetric [Formula: see text] reaction. Second, the average [Formula: see text]’s of hyperons in [Formula: see text] collisions steadily grow with energy in the range from [Formula: see text] GeV to 7 TeV. The additional conclusion is the following: since no dramatic changes have been seen in the characteristics of baryon production, the hadroproduction processes do not cause the “knee” in the cosmic ray proton spectra at the energies between Tevatron collider and LHC.

Prompt atmospheric neutrinos in the quark\u2013gluon string model

We calculate the atmospheric flux of prompt neutrinos, produced in decays of the charmed particles at energies beyond 1 TeV. Cross sections of the D mesons and {Lambda }^{+}_{c} baryons production in pA and pi A collisions are calculated in the phenomenological quark–gluon string model (QGSM) which is updated using recent measurements of cross sections of the charmed meson production in the LHC experiments. A new estimate of the prompt atmospheric neutrino flux is obtained and compared with the limit from the IceCube experiment, and with predictions of other charm production models.

Towards Simulation of Quark and Diquark Fragmentations in the Quark-Gluon String Model (QGSM)

The NA61/SHINE collaboration has presented experimental data on $${{\rho }^{0}}$$, $$\omega $$ and $${{K}^{{0 * }}}$$ meson productions in $${{\pi }^{ - }}{\text{C}}$$ interactions at $$Plab = 158$$ and 350 GeV/c. As shown by the collaboration, the existing Monte Carlo event generators badly describe the data. In this paper a possibility to describe the data is considered in the Quark-Gluon String (QGS) model of Geant4. QGS model was proposed by A.B. Kaidalov and K.A. Ter-Martirosyan. Within the model, A.B. Kaidalov found a behaviour of quark and diquark fragmentation functions for $$z \to 0$$ and $$z \to 1$$, and proposed interpolation formulae for the functions in the whole region of $$z$$. These functions must be a solution of the well-known system of the integral equations. A simplified Monte Carlo estimation of the functions, based on usage of the fragmentation functions at $$z \to 1$$ as the kernel functions of the system, does not reproduce Kaidalov’s results. An improvement of the Monte Carlo simulations is proposed in this paper. It can be implemented in Monte Carlo event generators such as Los Alamos QGSM, QGSJet-II and the Geant4 QGS model. It will improve a description of experimental data in the models, especially, the description of the latest NA61/SHINE Collaboration data. Description of the data is a problem in DPMJet, QGSJet, EPOS and Sibyll models.

FANSY 2.0: A Monte Carlo tool for study of superhigh-energy cosmic-ray interactions

Simulation of meson–proton interactions is considered in the framework of a new phenomenological model (FANSY 2.0 QGSJ) developed on the basis of the traditional quark-gluon string model to simulate hadron interactions in a wide energy range. The model reproduces low-energy accelerator data on the generation of $$\pi ^0$$ mesons, $$\rho ^{+,0}$$ , $$\omega $$ and $$f_2$$ resonances, strange $$K^{*0,+}$$ , $$\bar{K}^{*0}$$ , $${K}^{*0}_2$$ and $$\phi $$ resonances, charmed $$D^{\pm ,0}$$ , $$D^{\pm }_s$$ and $$\bar{D}^0$$ mesons, p, $$\bar{p}$$ and $$\Delta ^{++}$$ baryons, $$\Lambda $$ and $$\bar{\Lambda }$$ hyperons in pion–proton and kaon–proton interactions. The relationship between the quark composition of the most energetic hadrons and the leading effect is discussed. A general agreement between simulated results and experimental data is shown.

Hadroproduction of neutral K*-mesons up to LHC energies

We consider the experimental data on neutral Kstar-meson production on nucleon and nuclear targets. The Quark-Gluon String Model quantitatively describes the inclusive density in the midrapidity region, as well as the initial energy and A dependences of the produced Kstar-mesons.

Examination of Calculations of the Atmospheric Muon and Neutrino Spectra Using New Measurements

The atmospheric muon and neutrino fluxes at energies from 10 GeV to 10 PeV are calculated with the Kimel–Mokhov (KM), SIBYLL 2.1, EPOS LHC, and QGSJET-II hadronic models for known parameterizations of the cosmic ray spectra by Zatsepin--Sokolskaya and Hillas–Gaisser. The calculations with the KM, EPOS LHC, and SIBYLL 2.1 models are agree well with the measurements of the atmospheric muon spectra in IceCube and IceTop experiments. The measurement of high-energy muon spectra indicates the presence of the prompt muon component at energies above 500 TeV, which is well reproduced in calculations with the quark-gluon string model. The calculations of the atmospheric muon neutrino spectrum performed for the KM, EPOS LHC, and SIBYLL 2.1 models give good fit with the measurement data of IceCube, ANTARES, and Super-Kamiokande experiments.

Centrality and rapidity dependences of negative pions in He–C collisions at 4.2 A GeV/c

In the current research paper, we investigated the dependence of [Formula: see text] spectra of [Formula: see text] mesons on centrality of collision and different rapidity [Formula: see text] range. These negative pions are produced in Alpha–Carbon collisions at a momentum of 4.2 A GeV/c. We used Boltzmann and Hagedorn functions for one and two temperature fitting, of transverse momentum spectra obtained from experimental data and Model (Quark Gluon String Model, QGSM) data. By fitting these mathematical functions, we analyzed the change in shape of slopes of [Formula: see text] spectra. The fitting results for spectral temperatures were consistently larger (both in the experiment and QGSM) for the [Formula: see text] spectra of negative pions produced in range of mid-rapidity in comparison with those produced in fragmentation regions of colliding nuclei. It was also observed that extracted spectral temperatures from experimental data have a weak dependence on the collision centrality. The pion spectra can be described nicely by fitting two temperature functions for the experimental [Formula: see text] spectra for whole range and for the interval [Formula: see text]. In the [Formula: see text] range of [Formula: see text], one temperature functions were found sufficient for fitting the experimental [Formula: see text] spectra. The extracted temperatures from experimental data were found more sensitive to the fitting range of [Formula: see text], in contrast with temperatures obtained from QGSM data.

Directed Flow in Microscopic Models in Relativistic A+A Collisions

Evolution of directed flow of charged particles produced in relativistic heavy-ion collisions at energies 4 ≤ s ≤ 19.6 GeV is considered within two microscopic transport models, ultra-relativistic quantum molecular dynamics (UrQMD) and quark-gluon string model (QGSM). In both models, the directed flow of protons changes its sign at midrapidity from antiflow to normal flow with decreasing energy of collisions, whereas the flows of mesons and antiprotons remain antiflow-oriented. For lighter colliding systems, such as Cu+Cu or S+S, changing of the proton directed flow occurs at lower bombarding energies and for more central topologies compared to a heavy Au+Au system. The differences can be explained by dissimilar production zones of different hadrons and by the influence of spectators. Directed flows of most abundant hadronic species at midrapidity are found to be formed within t = 10–12 fm/c after the beginning of nuclear collision. The influence of hard and soft mean-field potentials on the directed flow is also studied.

The atmospheric neutrino flux from decays of charmed particles

We calculate the high-energy component of the atmospheric neutrino flux which arises from decays of the charmed particles. Cross sections of the D mesons and baryons production in pA and πA collisions are calculated within the framework of the quark-gluon string model (QGSM). The recent data on the cross sections of charmed meson production at high energies, obtained in experiments at the LHC, allow an improvement of the QGSM free parameters and new estimate of the prompt atmospheric neutrino flux. The newly-calculated flux of the prompt neutrinos is three times smaller than the flux predicted with the previous version of QGSM. We compare our result with the constraint derived from IceCube experiment as well as with predictions obtained with different charm production models.

Study of azimuthal correlations in the target fragmentation region in p, d, He, C+C, Ta and C+Ne, Cu collisions at momenta of 4.2, 4.5 and 10 A GeV/c

Azimuthal correlations between the same type of particles (protons or pions) in the target fragmentation region was studied in d, He, C+C, Ta (4.2A GeV/c, C+Ne, Cu (4.5A GeV/c) and p+C, Ta (10 GeV/c) interactions. The data were obtained from the SKM-200-GIBS streamer chamber and from the Propane Bubble Chamber (PBL-500) systems utilized at JINR. Study of multiparticle azimuthal correlations offers unique information about space-time evolution of the interactions. Azimuthal correlations were investigated by using correlation function $ C(\Delta\phi) = \mathrm{d} N/\mathrm{d} (\Delta\phi)$ , where $ \Delta\phi$ represents the angle between the sums of transverse momenta vectors for particles emitted in the forward and backward hemispheres. For protons “back-to-back” (“negative”) azimuthal correlations were observed in the above-mentioned interactions. The absolute values of the correlation coefficient $ \vert\xi\vert$ --the slope parameter of $ C(\Delta\phi)$, strongly depend on the mass number of the target ($ A_{T}$) nuclei in the nucleon-nucleus and nucleus-nucleus collisions. Namely, $ \vert\xi\vert$ decreases with increase of $ A_T$ in p+C and p+Ta collisions, while $ \vert\xi\vert$ initially decreases from d+C to C+Ne and then almost does not change with increase of $ A_P$, $ A_T$ in (d+He)Ta, C+Cu and C+Ta collisions. For pions “back-to-back” correlations were obtained for light targets (C, Ne), and “side-by-side” (“positive”) correlations for heavy targets (Cu, Ta). The $ \vert\xi\vert$ insignificantly changes with increase of the momenta per nucleon and almost does not change with increase of $ A_P$ and $ A_T$. Models used for description of the data, the Ultra relativistic Quantum Molecular Dynamic (UrQMD) and Quark-Gluon String Model (QGSM), satisfactorily describe the obtained experimental results.

Determination of the TMD gluon density in a proton using recent LHC data

Unintegrated (or transverse momentum dependent, TMD) parton distributions in a proton are important in high-energy physics. Using the latest LHC data on the hadron production in pp collisions, we determine the parameters of the initial TMD gluon density, derived in the framework of quark-gluon string model at the low scale μ0 ~ 1 − 2 GeV and refine its large-x behavior using data on the tt̅ production at $\sqrt s = 13\,{\rm{TeV}}$. Then, by using the Catani-Ciafaloni-Fiorani-Marchesini (CCFM) evolution equation, we extend the obtained TMD gluon density to the whole kinematic region. We tested the proposed TMD gluon density to the inclusive Higgs production in different decay modes, t-channel single top production at the LHC and to the proton structure functions $F_2^c(x,\,{Q^2})$ and $F_2^b(x,\,{Q^2})$ in a wide region of x and Q2. Good agreement with the latest LHC and HERA data is achieved.

Description of ϕ-meson production in hadronic and nuclear collisions at very high energies

We expose the current experimental and theoretical situation of the interesting case of the production of [Formula: see text] mesons in up to very high energy collisions of hadrons on both nucleon and nuclear targets, and we present a quantitatively good theoretical description of the corresponding experimental data, based on the formalism of the well established Quark–Gluon String Model, that has proved to be valid for a wide energy range. All the available experimental data for [Formula: see text]-meson production in hadron–nucleon collisions on the spectra of secondary [Formula: see text], and on the ratios of [Formula: see text] and [Formula: see text] production cross-sections, as well the corresponding ones for [Formula: see text]-meson production on nuclear targets, are considered. In particular, it is seen that the production of [Formula: see text]-mesons on nuclear targets presents unusually small shadow corrections for the inclusive density in the central rapidity region.

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.