Quark-gluon String Model Research Articles

Employing RHIC and LHC data to determine the transverse momentum dependent gluon density in a proton

Transverse momentum dependent (TMD) parton distributions in a proton are important in high energy physics from both theoretical and phenomenological points of view. Using the latest RHIC and LHC data on the inclusive soft hadron production in $pp$ and $AA$ collisions at small transverse momenta, we determine the parameters of the initial TMD gluon density, derived in the framework of quark-gluon string model at the low scale $\mu_0 \sim 1 - 2$ GeV and refine its large-$x$ behaviour using the LHC data on the $t \bar t$ production at $\sqrt s = 13$ TeV. Then, we apply the Catani-Ciafaloni-Fiorani-Marchesini (CCFM) evolution equation to extend the obtained TMD gluon density to the whole kinematical region. In addition, the complementary TMD valence and sea quark distributions are generated. The latter are evaluated in the approximation where the gluon-to-quark splitting occurs at the last evolution step using the TMD gluon-to-quark splitting function. Several phenomenological applications of the proposed TMD quark and gluon densities to the LHC processes are discussed.

Hyperon polarization in heavy-ion collisions and holographic gravitational anomaly

We study the energy dependence of global polarization of $\Lambda$ hyperons in peripheral $Au-Au$ collisions. We combine the calculation of vorticity and strange chemical potential in the framework of kinetic Quark-Gluon String Model with the anomalous mechanism related to axial vortical effect. The earlier found effect of helicity separation implies the quadrupole structure of longitudinal vorticity. We pay special attention to the temperature dependent contribution related to gravitational anomaly and found that the preliminary RHIC data are compatible with its suppression discovered earlier in lattice calculations. The antihyperons polarization is excessing that of hyperons and the difference is more pronounced at smaller energies.

Simulation of AntiMatter–Matter Interactions in Geant4

Cross sections of antiproton and antinucleus interactions with nuclei are calculated using stochastic averaging method. A new implementation of the Quark-Gluon-String Model (QGSM) is proposed for simulation of multi-particle production in antinucleus-nucleus collisions. A combination of the cross sections and the new implementation of QGSM allows experimental data on antiproton and antinucleus interactions with nuclei to be described. The combination is included in the well-known Geant4 simulation toolkit.

Short- and long-range rapidity correlations in the model with a lattice in transverse plane

In the framework of the quark-gluon string model we consider the various fluctuation and correlation observables used in the analysis of the multiparticle production in hadronic interactions at high energy. We express these observables through the fundamental string characteristics and analyze their resulting properties: the dependence on the width of observation window(s), the range of the correlation in rapidity, the intensive or strongly intensive behavior. To take into account the influence of a string fusion processes on the string characteristics and on the behavior of the observables. we use the version of string model with a lattice (grid) in the impact parameter plane. In particular we show that the observable between multiplicities in two acceptance windows separated in rapidity, which is a strongly intensive in the case with independent identical strings, loses this property, when we take into account the string fusion and the formation of strings of a few different types takes place in a collision.

Production of φ Mesons on Nuclear Targets in the Quark–Gluon String Model

Experimental data on the production of φ mesons in proton–nucleus and nucleus–nucleus collisions are considered. These data show unusually small shadowing corrections to the inclusive density for φ-meson production in the midrapidity region. It is found that the results of calculations based on the quark–gluon string model are in qualitative agreement with experimental data on the density of produced φ mesons as a function of both the initial energy ranging from the Collaboration NA49 energy to the LHC high energies and the target atomic number A.

Production of Charmed Particles in the Quark-Gluon String Model and Estimate of Their Contributions to Atmospheric Neutrino Fluxes

An estimate of the flux of prompt atmospheric neutrinos produced in decays of charmed particles is obtained. Cross sections of the production of charmed particles (D, Λ c ) in pA and πA collisions are calculated in the quark-gluon string model (QGSM) for the energy range 1 TeV – 100 PeV. New data on the cross sections of charmed meson production at high energies, obtained in experiments at the Large Hadron Collider, make it possible to refine the values of the free parameters of the QGSM and obtain a preliminary estimate of the prompt atmospheric neutrino flux. A comparison is made with the results of other neutrino flux calculations carried out for other charm production models – the dipole model and SIBYLL 2.3rc1.

Inelastic nuclear screening for different secondaries produced in p+Pb collisions at LHC energy

We calculate the inclusive spectra of secondaries produced in soft (minimum-bias) pPb collisions in the framework of the quark-gluon string model at LHC energy, by taking into account the inelastic screening corrections (percolation effects). The role of these effects is expected to be very large at the very high energies, and they should decrease the spectra more than 2 times in the midrapidity region at ${\sqrt{s}}_{NN}=5\text{ }\text{ }\mathrm{TeV}$.

Production of energetic light fragments in extensions of the CEM and LAQGSM event generators of the Monte Carlo transport code MCNP6

We extend the cascade-exciton model (CEM), and the Los Alamos version of the quark-gluon string model (LAQGSM), event generators of the Monte-Carlo N-particle transport code version 6 (MCNP6), to describe production of energetic light fragments (LF) heavier than 4He from various nuclear reactions induced by particles and nuclei at energies up to about 1 TeV/nucleon. In these models, energetic LF can be produced via Fermi break-up, preequilibrium emission, and coalescence of cascade particles. Initially, we study several variations of the Fermi break-up model and choose the best option for these models. Then, we extend the modified exciton model (MEM) used by these codes to account for a possibility of multiple emission of up to 66 types of particles and LF (up to 28Mg) at the preequilibrium stage of reactions. Then, we expand the coalescence model to allow coalescence of LF from nucleons emitted at the intranuclear cascade stage of reactions and from lighter clusters, up to fragments with mass numbers A < 8, in the case of CEM, and A < 13, in the case of LAQGSM. Next, we modify MCNP6 to allow calculating and outputting spectra of LF and heavier products with arbitrary mass and charge numbers. The improved version of CEM is implemented into MCNP6. Finally, we test the improved versions of CEM, LAQGSM, and MCNP6 on a variety of measured nuclear reactions. The modified codes give an improved description of energetic LF from particle- and nucleus-induced reactions; showing a good agreement with a variety of available experimental data. They have an improved predictive power compared to the previous versions and can be used as reliable tools in simulating applications involving such types of reactions.

The comparison of the calculated atmospheric neutrino spectra with the measurements of IceCube and ANTARES experiments

We calculate the atmospheric neutrino spectra in the energy range of 102 − 107 GeV using the hadronic models QGSJET-II, SIBYLL 2.1 and the parameterizations of cosmic ray spectra by Zatsepin-Sokolskaya, and Hillas-Gaisser supported by experiments. It is shown that rare decay mode of short-lived neutral kaons produce about 30% of the electron neutrino flux and up to 10% of muon neutrinos at energies above 200 TeV. Comparative analysis of our calculations based on the Ƶ(E, h)-function approach and those obtained with use of the new MCEq-method (A. Fedynitch et al.) demonstrates the close agreement of both calculations. The comparison of calculated neutrino spectrum to the experimental data shows that IceCube and ANTARES measurements leave opened window for the prompt neutrino flux contribution obtained with the quark-gluon string model (QGSM).

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.

Hyperons polarization in heavy-ion collisions

We study the structure of vorticity and hydrodynamic helicity fields in peripheral heavy-ion collisions using the kinetic Quark-Gluon Strings Model. The angular momentum which is a source of P-odd observables is preserved within this model with a good accuracy. We observe the formation of specific toroidal structures of vorticity field. Their existence is mirrored in the polarization of hyperons of the percent order. The observed qualitative energy dependence of polarization was predicted earlier and is quantified now.

How many of the scaling trends inppcollisions will be violated atsNN=14 TeV? Predictions from Monte Carlo quark-gluon string model

Multiplicity, rapidity and transverse momentum distributions of hadrons produced both in inelastic and nondiffractive $pp$ collisions at energies from $\sqrt{s} = 200$\,GeV to 14\,TeV are studied within the Monte Carlo quark-gluon string model (QGSM). Good agreement with the available experimental data up to $\sqrt{s} = 13$\,TeV is obtained, and predictions are made for the collisions at top LHC energy $\sqrt{s} = 14$\,TeV. The model indicates that Feynman scaling and extended longitudinal scaling remain valid in the fragmentation regions, whereas strong violation of Feynman scaling is observed at midrapidity. The Koba-Nielsen-Olesen (KNO) scaling in multiplicity distributions is violated at LHC also. The origin of both maintenance and violation of the scaling trends is traced to short range correlations of particles in the strings and interplay between the multistring processes at ultrarelativistic energies.

Femto-vortex sheets and hyperon polarization in heavy-ion collisions

We study the structure of vorticity and hydrodynamic helicity fields in peripheral heavy-ion collisions using the kinetic Quark-Gluon String Model. The angular momentum conservation within this model holds with a good accuracy. We observe the formation of specific toroidal structures of vorticity field (vortex sheets). Their existence is mirrored in the polarization of hyperons of the percent order.

Scaling trends in proton-proton collisions from SPS to LHC in quark-gluon string model

Fulfillment of scaling relations, such as Feynman scaling, extended longitudinal scaling and Koba-Nielsen-Olesen (KNO) scaling, in ultrarelativistic proton-proton collisions are checked within the microscopic quark-gluon string model (QGSM). The model is based on Reggeon Field theory accomplished by string phenomenology. Multiplicity, rapidity and transverse momentum spectra are described quite well in a wide span of the collision energy. Predictions are made for pp collisions at √s = 14 TeV.

Chaotic vortical flows and their manifestations

We study vorticity and hydrodynamic helicity in semi-peripheral heavy-ion collisions using the kinetic model of Quark-Gluon Strings. The angular momentum, which is a source of P-odd observables, is preserved with a good accuracy. We observe formation of the specific toroidal structures of the vorticity field. Their existence, accompanied by the strange chemical potential, is mirrored in the polarization of hyperons of the percent order.

Midrapidity hyperon production in pp and pA collisions from low to LHC energies

The experimental data on p, Lambda, Xi-, Omega-, baryons and the corresponding antibaryons spectra obtained by different collaborations are compared with the results of the calculations performed into the frame of the Quark-Gluon String Model. The contribution of String Junction diffusion and the inelastic screening corrections are accounted for in the theoretical calculations. The predictions of the Quark-Gluon String Model both for pp and pA collisions are extended up to the LHC energies.

Hydrodynamic helicity and strange hyperon polarization in heavy-ion collisions

We study the P-odd effects related to the vorticity of the medium formed in noncentral heavy ion collisions. Using the kinetic Quark-Gluon String Model, we perform numerical simulations of the vorticity and hydrodynamical helicity for various atomic numbers, energies and centralities. We observe vortical structures typically occupying a relatively small fraction of the fireball volume. In the course of numerical simulations a noticeable hydrodynamic helicity was observed manifesting a specific mirror behaviour with respect to the reaction plane. The effect is maximal at the NICA and FAIR energy range.

Centrality dependences of soft and hard components of pt distributions of negative pions in 4He+12C collisions at 4.2A GeV/c

The dependences of the shapes of transverse momentum distributions of the negative pions, produced in minimum bias 4 He +12 C collisions at a momentum of 4.2 GeV/c per nucleon, on collision centrality and fitting range of pt were analyzed systematically. To study the change in slopes (temperatures) of the pt spectra of π- with changing collision centrality and fitting pt range, the pt spectra, extracted from the experimental data and quark–gluon string model (QGSM) calculations, were fitted by the one- and two-temperature Hagedorn and Boltzmann functions. Fitting of the experimental pt distributions of π- in both the whole pt and pt = 0.1–1.2 GeV/c intervals required the two-temperature functions for adequate description of spectra, in agreement with the previous findings for different sets of colliding nuclei and various energies. On the whole, the absolute values of the extracted temperatures were lower in case of fitting range pt = 0.1–0.7 GeV/c as compared to the fitting interval pt = 0.1–1.2 GeV/c. The one-temperature functions were sufficient for fitting satisfactorily the experimental pt distributions of the negative pions in range pt = 0.1–0.7 GeV/c. In contrast to the experimental temperatures, the extracted QGSM temperatures were not sensitive to collision centrality and fitting range of pt. The collision centrality dependences of the temperatures of soft (pt = 0.1–0.5 GeV/c) and hard (pt = 0.5–1.2 GeV/c) components of the experimental pt distributions of the negative pions in 4 He +12 C collisions at 4.2A GeV/c were studied separately. The extracted temperatures of both soft and hard components of pt distributions of π- depended on geometry (size) and degree of overlap of colliding nuclei in peripheral, semicentral and central 4 He +12 C collisions. The temperature of soft pt component of the negative pions was consistently larger in semicentral and central 4 He +12 C collisions than that in peripheral interactions. The temperature of hard pt component of π- in 4 He +12 C collisions decreased consistently with an increase in collision centrality. The physical interpretations of the observed centrality dependences of temperature (T) of soft and hard pt components of the negative pions in 4 He +12 C collisions were given.

Average transverse momenta in hyperon production at p-p collider experiments

The transverse momentum spectra of Λ0 hyperon from LHC experiments (ALICE, ATLAS, CMS in the comparison with earlier experiments are considered from the point of view of Quark-Gluon String Model (QGSM) as examples of typical baryon spectra at very high energies. The LHC data at √s = 0.9 and 7 TeV and STAR data at √s = 200 GeV are fitted with the universal QGSM formula that includes the energy dependent slope as the main parameter. The dependence of average transverse momenta on √s has been obtained with the help of this formula. The asymptotics of the energy dependence of < pt > shows the behavior s0.055. This conclusion is very important for cosmic ray physics. It means that the long debated ”knee” in the cosmic proton spectra at Ep = (2, 5−4) * 1015 eV in laboratory system can not be considered any more as the result of dramatic changes in the dynamics of baryon hadroproduction. In the same time it may indicate the maximal energy of protons that can be produced in our Galaxy (or in other Galaxies).