arXiv subjects

Todor Stanev

Publications and source records attributed to Todor Stanev.

At least 19 recordsLinked to original sources

arXiv2019

Hadronic interaction model Sibyll 2.3d and extensive air showers

We present a new version of the hadron interaction event generator Sibyll. While the core ideas of the model have been preserved, the new version handles the production of baryon pairs and leading particles in a new way. In addition, production of charmed hadrons is included. Updates to the model are informed by high-precision measurements of the total and inelastic cross sections with the forward detectors at the LHC that constrain the extrapolation to ultra-high energy. Minimum-bias measurements of particle spectra and multiplicities support the tuning of fragmentation parameters. This paper demonstrates the impact of these changes on air shower observables such as $X_{\rm max}$ and $N_\mu$, drawing comparisons with other contemporary cosmic ray interaction models.

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arXiv2018

The hadronic interaction model Sibyll-2.3c and inclusive lepton fluxes

Muons and neutrinos from cosmic ray interactions in the atmosphere originate from decays of mesons in air-showers. Sibyll-2.3c aims to give a precise description of hadronic interactions in the relevant phase space for conventional and prompt leptons in light of new accelerator data, including that from the LHC. Sibyll is designed primarily as an event generator for use in simulation of extensive air showers. Because it has been tuned for forward physics as well as the central region, it can also be used to calculate inclusive fluxes. The purpose of this paper is to describe the use of Sibyll-2.3c for calculation of fluxes of atmospheric leptons.

hep-ph↗

arXiv2017

Data-driven model of the cosmic-ray flux and mass composition from 10 GeV to $10^{11}$ GeV

We present a new parametrization of the cosmic-ray flux and its mass composition over an energy range from 10 GeV to $10^{11}$ GeV. Our approach is data-driven and relies on theoretical assumptions as little as possible. We combine measurements of the flux of individual elements from high-precision satellites and balloon experiments with indirect measurements of mass groups from the leading air shower experiments. To our knowledge, we provide the first fit of this kind that consistently takes both statistical and systematic uncertainties into account. The uncertainty on the energy scales of individual experiments is handled explicitly in our mathematical approach. Part of our results is a common energy scale and adjustment factors for the energy scales of the participating experiments. Our fit has a reduced $\chi^2$-value of 0.5, showing that experimental data are in good agreement, if systematic uncertainties are considered. Our model may serve as a world-average of the measured fluxes for individual elements from proton to iron from 10 GeV to $10^{11}$ GeV. It is useful as an input for simulations or theoretical computations based on cosmic rays. The experimental uncertainties of the input data are captured in a covariance matrix, which can be propagated into derived quantities.

astro-ph.HE↗

arXiv2017

The hadronic interaction model SIBYLL 2.3c and Feynman scaling

The Monte Carlo model Sibyll has been designed for efficient simulation of hadronic multiparticle production up to the highest energies as needed for interpreting cosmic ray measurements. For more than 15 years, version 2.1 of Sibyll has been one of the standard models for air shower simulation. Motivated by data of LHC and fixed-target experiments and a better understanding of the phenomenology of hadronic interactions, we have developed an improved version of this model, version 2.3, which has been released in 2016. In this contribution we present a revised version of this model, called Sibyll 2.3c, that is further improved by adjusting particle production spectra to match the expectation of Feynman scaling in the fragmentation region. After a brief introduction to the changes implemented in Sibyll 2.3 and 2.3c with respect to Sibyll 2.1, the current predictions of the model for the depth of shower maximum, the number of muons at ground, and the energy spectrum of muons in extensive air showers are presented.

hep-ph↗

arXiv2016

The Nature and Origin of Ultra-High Energy Cosmic Ray Particles

We outline two concepts to explain Ultra High Energy Cosmic Rays (UHECRs), one based on radio galaxies and their relativistic jets and terminal hot spots, and one based on relativistic Super-Novae (SNe) or Gamma Ray Bursts (GRBs) in starburst galaxies, one matching the arrival direction data in the South (the radio galaxy Cen A) and one in the North (the starburst galaxy M82). Ubiquitous neutrino emission follows accompanied by compact TeV photon emission, detectable more easily if the direction is towards Earth. The ejection of UHECRs is last. We have observed particles up to ZeV, neutrinos up to PeV, photons up to TeV, 30 - 300 Hz GW events, and hope to detect soon of order Hz to mHz GW events. Energy turnover in single low frequency GW events may be of order 10^63 erg. How can we further test these concepts? First of all by associating individual UHECR events, or directional groups of events, with chemical composition in both the Telescope Array (TA) Coll. and the Auger Coll. data. Second by identifying more TeV to PeV neutrinos with recent SMBH mergers. Third by detecting the order < mHz GW events of SMBH binaries, and identifying the galaxies host to the stellar BH mergers and their GW events in the range up to 300 Hz. Fourth by finally detecting the formation of the first generation of SMBHs and their mergers, surely a spectacular discovery.

astro-ph.HE↗

arXiv2015

A new version of the event generator Sibyll

The event generator Sibyll can be used for the simulation of hadronic multiparticle production up to the highest cosmic ray energies. It is optimized for providing an economic description of those aspects of the expected hadronic final states that are needed for the calculation of air showers and atmospheric lepton fluxes. New measurements from fixed target and collider experiments, in particular those at LHC, allow us to test the predictive power of the model version 2.1, which was released more than 10 years ago, and also to identify shortcomings. Based on a detailed comparison of the model predictions with the new data we revisit model assumptions and approximations to obtain an improved version of the interaction model. In addition a phenomenological model for the production of charm particles is implemented as needed for the calculation of prompt lepton fluxes in the energy range of the astrophysical neutrinos recently discovered by IceCube. After giving an overview of the new ideas implemented in Sibyll and discussing how they lead to an improved description of accelerator data, predictions for air showers and atmospheric lepton fluxes are presented.

hep-ph↗

arXiv2015

Calculation of conventional and prompt lepton fluxes at very high energy

An efficient method for calculating inclusive conventional and prompt atmospheric leptons fluxes is presented. The coupled cascade equations are solved numerically by formulating them as matrix equation. The presented approach is very flexible and allows the use of different hadronic interaction models, realistic parametrizations of the primary cosmic-ray flux and the Earth's atmosphere, and a detailed treatment of particle interactions and decays. The power of the developed method is illustrated by calculating lepton flux predictions for a number of different scenarios.

hep-ph↗

arXiv2015

Charm production in SIBYLL

SIBYLL 2.1 is an event generator for hadron interactions at the highest energies. It is commonly used to analyze and interpret extensive air shower measurements. In light of the first detection of PeV neutrinos by the IceCube collaboration the inclusive fluxes of muons and neutrinos in the atmosphere have become very important. Predicting these fluxes requires understanding of the hadronic production of charmed particles since these contribute significantly to the fluxes at high energy through their prompt decay. We will present an updated version of SIBYLL that has been tuned to describe LHC data and extended to include the production of charmed hadrons.

hep-ph↗

arXiv2014

Cosmic PeV Neutrinos and the Sources of Ultrahigh Energy Protons

The IceCube experiment recently detected the first flux of high-energy neutrinos in excess of atmospheric backgrounds. We examine whether these neutrinos originate from within the same extragalactic sources as ultrahigh-energy cosmic rays. Starting from rather general assumptions about spectra and flavors, we find that producing a neutrino flux at the requisite level through pion photoproduction leads to a flux of protons well below the cosmic-ray data at ~10^18 eV, where the composition is light, unless pions/muons cool before decaying. This suggests a dominant class of accelerator that allows for cosmic rays to escape without significant neutrino yields.

astro-ph.HE↗

arXiv2014

Cosmic backgrounds due to the formation of the first generation of supermassive black holes

The statistics of black holes and their masses strongly suggests that their mass distribution has a cutoff towards lower masses near $3 \times 10^{6}$ M$_{\odot}$. This is consistent with a classical formation mechanism from the agglomeration of the first massive stars in the universe. However, when the masses of the stars approach $10^{6}$ M$_{\odot}$, the stars become unstable and collapse, possibly forming the first generation of cosmological black holes. Here we speculate that the claimed detection of an isotropic radio background may constitute evidence of the formation of these first supermassive black holes, since their data are compatible in spectrum and intensity with synchrotron emission from the remnants. The model proposed fulfills all observational conditions for the background, in terms of single-source strength, number of sources, far-infrared and gamma-ray emission. The observed high energy neutrino flux is consistent with our calculations in flux and spectrum. The proposal described in this paper may also explain the early formation and growth of massive bulge-less disk galaxies as derived from the massive, gaseous shell formed during the explosion prior to the formation of a supermassive black hole.

astro-ph.CO↗

arXiv2013

The Galactic Wind Haze and its $γ$-spectrum

We study the possibility that the gamma ray emission in the Fermi bubbles observed is produced by cosmic ray electrons with a spectrum similar to Galactic cosmic rays. We argue that the cosmic ray electrons steepen near 1 TeV from $E^{-3}$ to about $E^{-4.2}$, and are partially secondaries derived from the knee-feature of normal cosmic rays. We speculate that the observed feature at $\sim 130$ GeV could essentially be due to inverse Compton emission off a pair-production peak on top of a turn-off in the $γ$ ray spectrum at $\sim 130$ GeV. It suggests that the knee of normal cosmic rays is the same everywhere in the Galaxy. A consequence could be that all supernovae contributing give the same cosmic ray spectrum, with the knee feature given by common stellar properties; in fact, this is consistent with the supernova theory proposed by Bisnovatyi-Kogan (1970), a magneto-rotational mechanism, if massive stars converge to common properties in terms of rotation and magnetic fields just before they explode.

astro-ph.HE↗

arXiv2013

Cosmic Ray Energy Spectrum from Measurements of Air Showers

This review focuses on high-energy cosmic rays in the PeV energy range and above. Of particular interest is the knee of the spectrum around 3 PeV and the transition from cosmic rays of Galactic origin to particles from extra-galactic sources. Our goal is to establish a baseline spectrum from 10^14 to 10^20 eV by combining the results of many measurements at different energies. In combination with measurements of the nuclear composition of the primaries, the shape of the energy spectrum places constraints on the number and spectra of sources that may contribute to the observed spectrum.

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arXiv2012

Ultrahigh Energy Cosmic Rays: Review of the Current Situation

We describe the current situation of the data on the highest energy particles in the Universe - the ultrahigh energy cosmic rays. The new results in the field come from the Telescope Array experiment in Utah, U.S.A. For this reason we concentrate on the results from this experiments and compare them to the measurements of the other two recent experiments, the High Resolution Fly's Eye and the Southern Auger Observatory

astro-ph.HE↗

arXiv2012

The Centaurus A Ultrahigh-Energy Cosmic Ray Excess and the Local Extragalactic Magnetic Field

The ultrahigh-energy cosmic-ray anisotropies discovered by the Pierre Auger Observatory give the potential to finally address both the particles' origins and properties of the nearby extragalactic magnetic field (EGMF). We examine the implications of the excess of ~ 10^20 eV events around the nearby radio galaxy Centaurus A. We find that, if Cen A is the source of these cosmic rays, the angular distribution of events constrains the EGMF strength within several Mpc of the Milky Way to > 20 nG for an assumed primary proton composition. Our conclusions suggest that either the observed excess is a statistical anomaly or the local EGMF is stronger then conventionally thought. We discuss the implications of this field, including UHECR scattering from more distant sources, time delays from transient sources, and the possibility of using magnetic lensing signatures to attain tighter constraints.

astro-ph.HE↗

arXiv2012

Neutrinos and cosmic rays

In this paper we review the status of the search for high-energy neutrinos from outside the solar system and discuss the implications for the origin and propagation of cosmic rays. Connections between neutrinos and gamma-rays are also discussed.

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arXiv2011

Predicted power in ultra high energy cosmic rays from active galaxies

Context: As more and more data are collected by cosmic ray experiments such as the Pierre Auger Observatory and Telescope Array (TA), the search for the sources of the Ultra High Energy Cosmic Rays (UHECR) continues. Already we have some hints about the sources or type of sources involved and more work is required to confirm any of this. Aims: We intend to predict the UHECR fluxes and the maximal energies of particles from two complete samples of nearby active galaxies, selected at radio and far-infrared frequencies. Also, we investigate the magnetic scattering of the UHECR path in the intervening cosmic space. Methods: We propose here a new method of searching for the sources of the UHECR in three steps, first we model the activity of the type of sources and get the flux of UHECR and a maximal energy for particle acceleration, then we model the interaction and angle deflection in the intergalactic space and finally we simulate the distribution of the cosmic rays events that can be statistically compared with future data of the cosmic rays observatories. Results: We analyzed two classes of sources, gamma ray bursts (GRBs) and Radio Galaxies (RGs). Ordering by the UHECR flux, few RGs are viable candidates, as for GRB many sources are viable candidates, requiring less scattering of the particles along their path to Earth to interpret the presently observed sky distribution. Most of the flux from RGs comes from the Southern sky, and most of the flux of particles from GRB comes from the North, although the differences are so small as to require large statistics to confirm this. The intergalactic and Galactic magnetic fields may help to distinguish the two extreme cases, also pure protons from heavy nuclei at the same energy. As a consequence flat spectrum radio sources such as 3C279 should confirm the production of UHECR in this class of sources through energetic neutrinos.

astro-ph.HE↗

arXiv2011

Sibyll with charm

The cosmic ray interaction event generator Sibyll is widely used in extensive air shower simulations for cosmic ray and neutrino experiments. Charmed particle production has been added to the Monte Carlo with a phenomenological, non-perturbative model that properly accounts for charm production in the forward direction. As prompt decays of charm can become a significant background for neutrino detection, proper simulation of charmed particles is very important. We compare charmed meson and baryon production to accelerator data.

astro-ph.HE↗

arXiv2011

Ultrahigh Energy Cosmic Rays

This is a review of the most resent results from the investigation of the Ultrahigh Energy Cosmic Rays, particles of energy exceeding 10$^{18}$ eV. After a general introduction to the topic and a brief review of the lower energy cosmic rays and the detection methods, the two most recent experiments, the High Resolution Fly's Eye (HiRes) and the Southern Auger Observatory are described. We then concentrate on the results from these two experiments on the cosmic ray energy spectrum, the chemical composition of these cosmic rays and on the searches for their sources. We conclude with a brief analysis of the controversies in these results and the projects in development and construction that can help solve the remaining problems with these particles.

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