Quark-gluon String Model Research Articles

Net-Baryon Production in Nucleus-Nucleus Collisions and Rare QGP Events

The experimental data on net proton and net Λ-hyperon spectra obtained by the NA35 Collaboration, as well as the inclusive densities of Λ and obtained by NA49, NA57, and STAR collaborations, are compared with the predictions of the Quark-Gluon String Model. The contributions of String Junction diffusion, interactions with nuclear clusters, and percolation corrections are accounted for. The level of numerical agreement of the calculations with the experimental data is of about 20-30%. We also consider the experimental ratios of multistrange to strange antibaryon production. The significant differences between the experimental and, especially, values and the QGSM predictions can be interpreted as the signal of the existence of an additional source of multistrange antibaryon production.

Hadroproduction ofφ-mesons in the quark-gluon string model

We consider the experimental data on $\ensuremath{\varphi}$-meson production in hadron-nucleon collisions for a wide energy region. The quark-gluon string model quantitatively describes the spectra of secondary $\ensuremath{\varphi}$, as well as the ratios of $\ensuremath{\varphi}/{\ensuremath{\pi}}^{\ensuremath{-}}$ and $\ensuremath{\varphi}/{K}^{\ensuremath{-}}$ production cross sections.

MCNP6 fragmentation of light nuclei at intermediate energies

Fragmentation reactions induced on light target nuclei by protons and light nuclei of energies around 1GeV/nucleon and below are studied with the latest Los Alamos Monte Carlo transport code MCNP6 and with its cascade-exciton model (CEM) and Los Alamos version of the quark-gluon string model (LAQGSM) event generators, version 03.03, used as stand-alone codes. Such reactions are involved in different applications, like cosmic-ray-induced single event upsets (SEU׳s), radiation protection, and cancer therapy with proton and ion beams, among others; therefore, it is important that MCNP6 simulates them as well as possible. CEM and LAQGSM assume that intermediate-energy fragmentation reactions on light nuclei occur generally in two stages. The first stage is the intranuclear cascade (INC), followed by the second, Fermi breakup disintegration of light excited residual nuclei produced after the INC. Both CEM and LAQGSM account also for coalescence of light fragments (complex particles) up to 4He from energetic nucleons emitted during INC. We investigate the validity and performance of MCNP6, CEM, and LAQGSM in simulating fragmentation reactions at intermediate energies and discuss possible ways of further improving these codes.

Centrality dependence of rapidity spectra of negative pions in 12 C+12 C and 12 C+181 Ta collisions at 4.2 GeV/c per nucleon

The centrality dependences of the experimental rapidity as well as transversemomentumversus rapidity spectra of negative pions were analyzed quantitatively in 12C+12C and 12C+181Ta collisions at 4.2 GeV/c per nucleon using fitting the pion spectra by Gaussian distribution function. The experimental results were compared systematically with the predictions of the Quark-Gluon-String Model (QGSM) adapted to intermediate energies.

Proton and Λ hyperon production in nucleus-nucleus collisions

The experimental data on net proton and net Lambda-hyperon spectra obtained by the NA35 Collaboration, as well as the inclusive densities of Lambda and bar-Lambda obtained by NA49, NA57, and STAR collaborations, are compared with the predictions of the Quark-Gluon String Model. The contributions of String Junction diffusion, interactions with nuclear clusters, and the inelastic screening corrections are accounted for. The level of numerical agreement of the calculations with the experimental data is of about 20-30%. The predictions for LHC are also presented.

Preequilibrium Emission of Light Fragments in Spallation Reactions

The ability to describe production of light fragments (LF) is important for many applications, such as cosmic-ray-induced single event upsets (SEUs), radiation protection, and cancer therapy with proton and heavy-ion beams. The cascade-exciton model (CEM) and the Los Alamos version of the quark-gluon string model (LAQGSM) event generators in the LANL transport code MCNP6, describe quite well the spectra of fragments with sizes up to 4He across a broad range of target masses and incident energies (up to ∼ 5 GeV for CEM and up to ∼ 1 TeV/A for LAQGSM). However, they do not predict the high-energy tails of LF spectra heavier than 4He well. Most LF with energies above several tens of MeV are emitted during the precompound stage of a reaction. The current versions of our event generators do not account for precompound emission of LF larger than 4He. The aim of our work is to generalize the precompound model to include such processes, leading to increased predictive power of LF production. Extending the model in this way provides preliminary results that have much better agreement with experimental data.

MCNP6 Study of Fragmentation Products from 112Sn+112Sn and 124Sn+124Sn at 1 GeV/A

Isotope production cross sections from 112Sn + 112Sn and 124Sn + 124Sn reactions at 1 GeV/nucleon, which were measured recently at GSI using the heavy-ion accelerator SIS18 and the Fragment Separator (FRS), have been analyzed with the latest Los Alamos Monte-Carlo transport code MCNP6 using the LAQGSM03.03 event generator. MCNP6 reproduces reasonably well all the measured cross sections. Comparison of the MCNP6 results with the measured data and with calculations by a modification of the Los Alamos version of the Quark-Gluon String Model allowing for multifragmentation processes in the framework of the Statistical Multifragmentation Model (SMM) by Botvina and coauthors, as realized in the code LAQGSM03.S1, does not suggest unambiguous evidence of a multifragmentation signature.

Proton-proton collisions at ultra-relativistic energies in quark-gluon string model

The microscopic Monte Carlo quark-gluon string model (QGSM) is employed to study particle production in ultrarelativistic proton-proton collisions. The model is based on Reggeon Field theory accomplished by string phenomenology. Various observables, including multiplicity, rapidity and transverse momentum spectra, short-range, long-range and femtoscopy correlations, are described quite well in a wide span of the collision energy. Predictions are made for pp collisions at √ s = 14 TeV.

Cumulative protons in12C fragmentation at intermediate energy

In the FRAGM experiment at heavy ion accelerator complex TWAC-ITEP, the proton yields at an angle 3.5° have been measured in fragmentation of carbon ions at T0 = 0.3, 0.6, 0.95 and 2.0 GeV/nucleon on beryllium target. The data are presented as invariant proton yields on cumulative variable x in the range 0.9 < x < 2.4. Proton spectra cover six orders of invariant cross section magnitude. They have been analyzed in the framework of quark cluster fragmentation model. Fragmentation functions of quarkgluon string model are used. The probabilities of the existence of multi-quark clusters in carbon nuclei are estimated to be 8–12% for six-quark clusters and 0.2–0.6% for ninequark clusters.

Production of Energetic Light Fragments in Spallation Reactions

Different reaction mechanisms contribute to the production of light fragments (LF) from nuclear reactions. Available models cannot accurately predict emission of LF from arbitrary reactions. However, the emission of LF is important for many applications, such as cosmic-ray-induced single event upsets, radiation protection, and cancer therapy with proton and heavy-ion beams, to name just a few. The cascade-exciton model (CEM) and the Los Alamos version of the quark-gluon string model (LAQGSM), as implemented in the CEM03.03 and LAQGSM03.03 event generators used in the Los Alamos transport code MCNP6, describe quite well the spectra of fragments with sizes up to 4He across a broad range of target masses and incident energies. However, they do not predict high-energy tails for LF heavier than 4He. The standard versions of CEM and LAQGSM do not account for preequilibrium emission of LF larger than 4He. The aim of our work is to extend the preequilibrium model to include such processes. We do this by including the emission of fragments heavier than 4He at the preequilibrium stage, and using an improved version of the Fermi Break-up model, providing improved agreement with various experimental data.

Helicity separation 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 strings model, we perform numerical simulations of the vorticity and hydrodynamical helicity for various atomic numbers, energies, and centralities. We observed vortical structures typically occupy the relatively small fraction of the fireball volume. In the course of numerical simulations, the noticeable hydrodynamical helicity was observed to manifest specific mirror behavior with respect to the reaction plane. The effect is maximal at the Nuclotron based Ion Collider fAcility and Facility for Antiproton and Ion Research in Europe energy range.

Manifestation of quark clusters in the emission of cumulative protons in the experiment on the fragmentation of carbon ions

The proton yields at an angle of 3.5° have been measured in the FRAGM experiment on the fragmentation of carbon ions with the energies T0 = 0.6, 0.95, and 2.0 GeV/nucleon on a beryllium target at the heavy-ion accelerator complex TWAC (terawatt accumulator, Institute for Theoretical and Experimental Physics). The data are represented in the form of the dependences of the invariant cross section for proton yield on the cumulative variable x in the range of 0.9 < x < 2.4. This invariant cross section varies within six orders of magnitude. The proton spectra have been analyzed within the theoretical approach of the fragmentation of quark clusters with the fragmentation functions obtained in the quark-gluon string model. The probabilities of the existence of six- and nine-quark clusters in the carbon nuclei are estimated as 8–12 and 0.2–0.6%, respectively. The results are compared to the estimated of quark effects obtained by other methods.

Feynman scaling violation on baryon spectra in pp collisions at LHC and cosmic ray energies

A significant asymmetry in baryon/antibaryon yields in the central region of high energy collisions is observed when the initial state has nonzero baryon charge. This asymmetry is connected with the possibility of baryon charge diffusion in rapidity space. Such a diffusion should decrease the baryon charge in the fragmentation region and translate into the corresponding decrease of the multiplicity of leading baryons. As a result, a new mechanism for Feynman scaling violation in the fragmentation region is obtained. Another numerically more significant reason for the Feynman scaling violation comes from the fact that the average number of cut Pomerons increases with initial energy. We present the quantitative predictions of the Quark-Gluon String Model for the Feynman scaling violation at LHC energies and at even higher energies that can be important for cosmic ray physics.

Features of parameters of gamma-ray families formed from AA-interactions at superhigh energies above 1016 eV

Different lateral and energetic characteristics of gamma-ray families produced in nucleus-nucleus (AA) interactions of primary cosmic rays (PCR) are studied. Primary mass composition analysis performed on the basis of "Pamir" Collaboration X-ray emulsion chambers (XREC) data by using of selection criteria of gamma-ray families originating from AA-interactions above 10 PeV. Experimental data are compared with results of MC0 algorithm based on quark-gluon string model (QGSM). Among seven considered variables, only two lateral parameters, R1E and ρ, are not described by the MC0 model.

Production of secondaries in soft p+Pb collisions at LHC and Alice data

We calculate the inclusive spectra of secondaries produced in soft (minimum bias) p+Pb collisions in the framework of Quark–Gluon String Model at LHC energy, and by taking into account the inelastic screening corrections (percolation effects). The role of these effects is expected to be very large at very high energies, and they should decrease the spectra more than 1.5 times in the midrapidity region and increase them about 1.5 times in the fragmentation region at the energy of LHC.

Nuclear fragmentation study at ITEP heavy ion facility

In an experiment performed at ITEP TWA heavy ion accelerator, the yields of hydrogen (p,d,t) and helium (from 3He to 8He) isotopes at 3.5° from fragmentation of 12C at T0 = 0.2 − 3.2 GeV/nucleon on a Be target have been measured. Momentum spectra of the fragments in the projectile rest frame have been obtained in larger momentum intervals than in the previous experiments with heavy ion beams. The main attention was given to the region of high momentum where fragment velocity exceeds the velocity of the projectile nucleus. The obtained data cover about 6 orders of the differential cross section magnitude. It made possible the observation of a transition from the Gaussian shape of the longitudinal momentum spectra in projectile rest frame, expected for the evaporation mechanism, to the exponential shape, typical for the cumulative (pre-equilibrium) processes. The Feynman x distributions for protons are analyzed in the framework of quark-gluon string model. The probabilities of existence of six-and nine-quark clusters are estimated and compared with the results on two- (three-) nucleon short range correlations in nuclei measured at Jefferson Laboratory.

Forward heavy-flavour production in pp collisions at LHC and intrinsic quark components in protons

The LHC data on the forward heavy-flavour hadron production can be a new unique source for estimation of intrinsic charm and bottom contributions to the proton. For example, we analyze the forward heavy-baryon production, namely Λb-baryon, within the soft QCD quark gluon string model and present the predictions for observables which could be measured at the LHC. We also present some predictions for the D-meson production in pp collisions made within the perturbative QCD including the intrinsic charm in the proton that can be verified at the LHC.

Multiparticle azimuthal correlations of negative pions in nucleus-nucleus collisions

Multiparticle azimuthal correlations of π − mesons have been studied in dC, HeC, CC, CNe, MgMg, (d, He)Ta, CCu, CTa, and OPb collisions at momentum of 4.2, 4.5 GeV/c per nucleon within the standard transverse momentum analysis method of P. Danielewicz and G. Odyniec. The data were obtained by SKM-200-GIBS and Propane Bubble Chamber Collaborations of JINR. The axis has been selected in the phase space and with respect to this axis π − meson correlations were observed. The values of the coefficient of the correlations linearly depend on the mass numbers of projectile (A P ) and target (A T ) nuclei. The Quark-Gluon String Model satisfactorily describes the experimental results.

ROLE OF GLUONS IN SOFT AND SEMI-HARD MULTIPLE HADRON PRODUCTION IN pp COLLISIONS AT LHC

Hadron inclusive spectra in pp collisions are analyzed within the modified quark–gluon string model including both the longitudinal and transverse motion of quarks in the proton in the wide region of initial energies. The self-consistent analysis shows that the experimental data on the inclusive spectra of light hadrons like pions and kaons at ISR energies can be satisfactorily described at transverse momenta not larger than 1–2 GeV /c. We discuss some difficulties to apply this model at energies above the ISR and suggest to include the distribution of gluons in the proton unintegrated over the internal transverse momentum. It leads to an increase in the inclusive spectra of hadrons and allows us to extend the satisfactory description of the data in the central rapidity region at energies higher than ISR.

How much charm can $$\bar P$$ ANDA produce?

We consider the production of charmed baryons and mesons in the proton-antiproton binary reactions at the energies of the future $$\bar P$$ ANDA experiment. To describe these processes in terms of hadronic interaction models, one needs strong couplings of the initial nucleons with the intermediate and final charmed hadrons. Similar couplings enter the models of binary reactions with strange hadrons. For both charmed and strange hadrons we employ the strong couplings and their ratios calculated from QCD light-cone sum rules. In this method finite masses of c and s quarks are taken into account. Employing the Kaidalov’s quark-gluon string model with Regge poles and adjusting the normalization of the amplitudes in this model to the calculated strong couplings, we estimate the production cross-section of charmed hadrons. For $$p\bar p \to \Lambda _c \bar \Lambda _c$$ it can reach several tens of nb at p lab = 15 GeV, whereas the cross-sections of Σ c and D pair production are predicted to be smaller.