Inclusive spectra of secondaries produced on nuclear targets at superhigh energies and with violation of Feynman scaling

Effects of Feynman scaling violation in yields of hadron secondaries inpA and πA collisions that arise when initial energy is increased are considered. There result from the growth of hadron-nucleon cross sections and an expected increase of the average transverse momenta of secondaries. The model of quark-gluon strings is used to calculate the inclusive spectra of secondaries. Interactions with a fixed number of nucleons are calculated, taking account of the growth of the slope parameter in elastichN scattering. Violation of Feynman scaling at superhigh energies turns out to be stronger than the additive quark model predicts it to be.     

Confronting models of cosmic ray interactions with particle physics at LHC energies

Inelastic pp collisions are dominated by soft (low momentum transfer) physics, to which perturbative QCD cannot be fully applied. A deep understanding of both soft and semi-hard processes is crucial for predictions of minimum bias and underlying events of the pp large hadron collider (LHC) now coming on line. Moreover, the interaction of cosmic ray particles entering in the atmosphere is extremely sensitive to these soft processes and consequently cannot be formulated from first principles. Because of this, air shower analyses strongly rely on hadronic interaction models, which extrapolate collider data by several orders of magnitude. A comparative study of Monte Carlo simulations of pp collisions (at the LHC center-of-mass energy ≃14 TeV) using the most popular hadronic interaction models for ultrahigh energy cosmic ray (SIBYLL and QGSJET) and for collider physics (the PYTHIA multiparton model) is presented. The most relevant distributions are studied including the observables from diffractive events with the aim of discriminating between the different models. PACS 13.85.-t; 96.40.-z     

Photon-photon luminosities in relativistic heavy ion collisions at LHC energies

Effective – luminosities are calculated for various realistic hadron collider scenarios. The main characteristics of photon-photon processes at relativistic heavy-ion colliders are established and compared to the corresponding –-luminosities ate ⁺-e ^– — and future photon linear colliders (PLC). Higher order corrections as well as inelastic processes are discussed. It is concluded that feasible high luminosity Ca–Ca collisions at the Large Hadron Collider (LHC) are an interesting option for – physics up to about 100 GeV – CM energy.     

Description of pp collisions at LHC energies

The Monte Carlo version of quark-gluon string model is employed to study the multiplicity, rapidity and pr spectra of particles in pp collisions at energies from √s = 200 GeV to 14 TeV. A good quantitative agreement with the experimental data is found in a broad energy range. It means that the general features of ultrarelativistic pp interactions can be well understood in terms of soft- and hard-Pomeron exchanges. Predictions are made for the top LHC energy √s = 14TeV.     

Parton rearrangement and fast thermalization in heavyion collisions at RHIC and LHC energies

The implications of parton rearrangement processes on the dynamics of ultra-relativistic heavyion collisions have been investigated. A microscopic transport approach, namely the quark gluon string model (QGSM) which has been extended for a locally density-dependent partonic rearrangement and fusion procedure served as the tool for this investigations. The model emulates effectively the dynamics of a strongly coupled quark plasma and final hadronic interactions. Main QGSM results on anisotropic flow components v ₁ and v ₂ at top RHIC energy are compiled. Predictions for the pseudorapidity dependence of directed and elliptic flow in Pb+Pb collisions under LHC conditions are presented.     

Midrapidity production of secondaries in pp collisions at RHIC and LHC energies in the quark–gluon string model

We consider the phenomenological implications of the assumption that baryons are systems of three quarks connected through a gluon string junction. The transfer of baryon number in rapidity space due to the string junction propagation is considered in detail. At high energies this process leads to a significant effect on the net baryon production in hN collisions at midrapidities. The numerical results for midrapidity inclusive densities of different secondaries in the framework of the quark–gluon string model are in reasonable agreement with the experimental data. One universal value, λ≃0.25, for the strangeness suppression parameter correctly describes the yield ratios of Λ/p, Ξ/Λ, and Ω/Ξ. The predictions for pp collisions at LHC energies are also presented. PACS 25.75.Dw     

Saturation of gluon density and soft pp collisions at LHC

We find the relation of the unintegrated gluon distribution at low intrinsic transverse momenta to the inclusive spectrum of the hadrons produced in pp collision at LHC energies in the mid-rapidity region and low hadron transverse momenta. It allows us to study the saturation of the gluon density at low Q ² more carefully and find the saturation scale that does not contradict to both the LHC and HERA data.     

Change of primary cosmic ray mass composition at superhigh energies

The EAS MSU array experimental data are analyzed in relation to the primary cosmic ray composition in the energy range above 10¹⁷–10¹⁸ eV. The problem of the existence of an additional cosmic ray component, which cannot be explained in the framework of traditional mechanism of Galactic cosmic ray production, is considered. The fraction of gamma-quanta in the primary cosmic radiation is evaluated as well.     

Low-redshift cosmic baryon fluid on large scales and She-Leveque universal scaling

We investigate the statistical properties of cosmic baryon fluid in the nonlinear regime, which is crucial for understanding the large-scale structure formation of the Universe. With the hydrodynamic simulation sample of the Universe in the cold dark matter model with a cosmological constant, we show that the intermittency of the velocity field of cosmic baryon fluid at redshift z = 0 in the scale range from the Jeans length to about 16 h(-1) Mpc can be extremely well described by She-Leveque's universal scaling formula. The baryon fluid also possesses the following features: (1) for volume weight statistics, the dissipative structures are dominated by sheets, and (2) the relation between the intensities of fluctuations is hierarchical. These results imply that the evolution of highly evolved cosmic baryon fluid is similar to a fully developed turbulence.     

Identification of baryon resonances in central heavy-ion collisions at energies between 1 and 2 AGeV

The mass distributions of baryon resonances populated in near-central collisions of Au on Au and Ni on Ni are deduced by defolding the p_t spectra of charged pions by a method which does not depend on a specific resonance shape. In addition the mass distributions of resonances are obtained from the invariant masses of (p, π^±) pairs. With both methods the deduced mass distributions are shifted by an average value of −60 MeV/c² relative to the mass distribution of the free Δ(1232) resonance, the distributions descent almost exponentially towards mass values of 2000 MeV/c². The observed differences between (p, π⁻) and (p, π⁺) pairs indicate a contribution of isospin I = 1/2 resonances. The attempt to consistently describe the deduced mass distributions and the reconstructed kinetic energy spectra of the resonances leads to new insights about the freeze out conditions, i.e. to rather low temperatures and large expansion velocities. Received: 26 June 1998 / Revised version: 2 September 1998     

Pseudo-rapidity distributions of charged hadrons in pp and pA collisions at the LHC

In the framework of the Color Glass Condensate, the pseudo-rapidity distributions of charged hadrons in pp and pA collisions at the LHC are studied with the UGD function from the GBW model. With a χ² analysis of the CMS data in pp collisions at √s=0.9, 2.36, 7 TeV, the normalization factor is obtained and the theoretical results are in good agreement with the experimental data. Then, considering the influence of nucleon hard partons transverse distribution on the number of participants in pA collisions by using a Glauber Monte Carlo method, we also give the predictive results for the multiplicity distributions in pPb collisions at √s=4.4 TeV.     

Uncertainties of Drell-Yan production cross section in pp collisions at the LHC

The results of calculations of uncertainties of the Drell-Yan production cross section at the energy √s = 13 TeV are presented. Systematic errors related to uncertainties in the quark and gluon distribution functions, the choice of the QCD factorization scale, and the QCD running coupling constant are considered.     

Universal scaling of kinetic freeze-out parameters across different collision systems at LHC energies

In this study, we perform Tsallis Blast-Wave analysis on the transverse momentum spectra of identified hadrons produced in a wide range of collision systems at the Large Hadron Collider (LHC) including pp, pPb, XeXe, and PbPb collisions. The kinetic freeze-out properties varying with event multiplicity are investigated across these systems. We find that the extracted kinetic freeze-out temperature, radial flow velocity, and non-extensive parameter exhibit a universal scaling behavior for these systems with very different geometric sizes, especially when the independent baryon Tsallis non-extensive parameter is considered. This universality may indicate the existence of a unified partonic evolution stage in different collision systems at the LHC energies.