S. Ostapchenko

Bio: S. Ostapchenko is an academic researcher from Frankfurt Institute for Advanced Studies. The author has contributed to research in topics: KASCADE & Cosmic ray. The author has an hindex of 40, co-authored 253 publications receiving 7356 citations. Previous affiliations of S. Ostapchenko include Moscow State University & Karlsruhe Institute of Technology.

Monte Carlo treatment of hadronic interactions in enhanced Pomeron scheme: I. QGSJET-II model

Abstract: The construction of a Monte Carlo generator for high energy hadronic and nuclear collisions is discussed in detail. Interactions are treated in the framework of the Reggeon Field Theory, taking into consideration enhanced Pomeron diagrams which are resummed to all orders in the triple-Pomeron coupling. Soft and “semihard” contributions to the underlying parton dynamics are accounted for within the “semihard Pomeron” approach. The structure of cut enhanced diagrams is analyzed; they are regrouped into a number of subclasses characterized by positively-defined contributions which define partial weights for various “macro-configurations” of hadronic final states. An iterative procedure for a Monte Carlo generation of the structure of final states is described. The model results for hadronic cross sections and for particle production are compared to experimental data.

Quark-Gluon String Model and EAS Simulation Problems at Ultra-High Energies

Abstract: The reliability of model calculations is of considerable significance because at energies above those attained by accelerators only model predictions enable us to extract primary cosmic ray characteristics. Different phenomenological models based on the quark-gluon picture of hadron interactions are of use now as a foundation for experimental data analysis at energies > 10 15 eV. In this paper we consider the present status of quark-gluon string (QGS) model with allowance made for semihard processes and (in the framework of so advanced model) discuss experimental data obtained at energies 10 15 ÷ 10 19 eV. In doing so we assume mass composition following from the diffusion notions of cosmic ray propagation through the Galaxy. Some general problems of EAS simulation and among them the simulation of electron-photon cascades are also discussed.

Detection and imaging of atmospheric radio flashes from cosmic ray air showers

Abstract: The nature of ultrahigh-energy cosmic rays (UHECRs) at energies >10(20) eV remains a mystery. They are likely to be of extragalactic origin, but should be absorbed within approximately 50 Mpc through interactions with the cosmic microwave background. As there are no sufficiently powerful accelerators within this distance from the Galaxy, explanations for UHECRs range from unusual astrophysical sources to exotic string physics. Also unclear is whether UHECRs consist of protons, heavy nuclei, neutrinos or gamma-rays. To resolve these questions, larger detectors with higher duty cycles and which combine multiple detection techniques are needed. Radio emission from UHECRs, on the other hand, is unaffected by attenuation, has a high duty cycle, gives calorimetric measurements and provides high directional accuracy. Here we report the detection of radio flashes from cosmic-ray air showers using low-cost digital radio receivers. We show that the radiation can be understood in terms of the geosynchrotron effect. Our results show that it should be possible to determine the nature and composition of UHECRs with combined radio and particle detectors, and to detect the ultrahigh-energy neutrinos expected from flavour mixing.

QGSJET-II: towards reliable description of very high energy hadronic interactions

Abstract: Since a number of years the QGSJET model has been successfully used by different groups in the field of high energy cosmic rays. Current work is devoted to the first general update of the model. The key improvement is connected to an account for non-linear interaction effects which are of crucial importance for reliable model extrapolation into the ultra-high energy domain. The proposed formalism allows to obtain a consistent description of hadron-hadron cross sections and hadron structure functions and to treat non-linear effects explicitly in individual hadronic and nuclear collisions. Other ameliorations concern the treatment of low mass diffraction, employment of realistic nuclear density profiles, and re-calibration of model parameters using a wider set of accelerator data.

Phd by thesis

Abstract: Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

LOFAR: The LOw-Frequency ARray

Abstract: LOFAR, the LOw-Frequency ARray, is a new-generation radio interferometer constructed in the north of the Netherlands and across europe. Utilizing a novel phased-array design, LOFAR covers the largely unexplored low-frequency range from 10-240 MHz and provides a number of unique observing capabilities. Spreading out from a core located near the village of Exloo in the northeast of the Netherlands, a total of 40 LOFAR stations are nearing completion. A further five stations have been deployed throughout Germany, and one station has been built in each of France, Sweden, and the UK. Digital beam-forming techniques make the LOFAR system agile and allow for rapid repointing of the telescope as well as the potential for multiple simultaneous observations. With its dense core array and long interferometric baselines, LOFAR achieves unparalleled sensitivity and angular resolution in the low-frequency radio regime. The LOFAR facilities are jointly operated by the International LOFAR Telescope (ILT) foundation, as an observatory open to the global astronomical community. LOFAR is one of the first radio observatories to feature automated processing pipelines to deliver fully calibrated science products to its user community. LOFAR's new capabilities, techniques and modus operandi make it an important pathfinder for the Square Kilometre Array (SKA). We give an overview of the LOFAR instrument, its major hardware and software components, and the core science objectives that have driven its design. In addition, we present a selection of new results from the commissioning phase of this new radio observatory.

Monte Carlo methods

Abstract: Bayesian inference often requires integrating some function with respect to a posterior distribution. Monte Carlo methods are sampling algorithms that allow to compute these integrals numerically when they are not analytically tractable. We review here the basic principles and the most common Monte Carlo algorithms, among which rejection sampling, importance sampling and Monte Carlo Markov chain (MCMC) methods. We give intuition on the theoretical justification of the algorithms as well as practical advice, trying to relate both. We discuss the application of Monte Carlo in experimental physics, and point to landmarks in the literature for the curious reader.

Tuning Monte Carlo Generators: The Perugia Tunes

Abstract: We present 9 new tunes of the p{sub perpendicular}-ordered shower and underlying-event model in Pythia 6.4. These 'Perugia' tunes update and supersede the older 'S0' family. The data sets used to constrain the models include hadronic Z{sup 0} decays at LEP, Tevatron min-bias data at 630, 1800, and 1960 GeV, Tevatron Drell-Yan data at 1800 and 1960 GeV, and SPS min-bias data at 200, 546, and 900 GeV. In addition to the central parameter set, called 'Perugia 0', we introduce a set of 8 related 'Perugia variations' that attempt to systematically explore soft, hard, parton density, and color structure variations in the theoretical parameters. Based on these variations, a best-guess prediction of the charged track multiplicity in inelastic, nondiffractive minimum-bias events at the LHC is made. Note that these tunes can only be used with Pythia 6, not with Pythia 8.