arXiv subjects

Paolo Saracco

Publications and source records attributed to Paolo Saracco.

At least 73 records · Page 4Linked to original sources

arXiv2015

Old age and super-solar metallicity in a massive z~1.4 early-type galaxy from VLT/X-Shooter spectroscopy

We present the first estimate of age, stellar metallicity and chemical abundance ratios, for an individual early-type galaxy at high-redshift (z = 1.426) in the COSMOS field. Our analysis is based on observations obtained with the X-Shooter instrument at the VLT, which cover the visual and near infrared spectrum at high (R >5000) spectral resolution. We measure the values of several spectral absorptions tracing chemical species, in particular Magnesium and Iron, besides determining the age-sensitive D4000 break. We compare the measured indices to stellar population models, finding good agreement. We find that our target is an old (t > 3 Gyr), high-metallicity ([Z/H] > 0.5) galaxy which formed its stars at z_{form} > 5 within a short time scale ~0.1 Gyr, as testified by the strong [α/Fe] ratio ( > 0.4), and has passively evolved in the first > 3-4 Gyr of its life. We have verified that this result is robust against the choice and number of fitted spectral features, and stellar population model. The result of an old age and high-metallicity has important implications for galaxy formation and evolution confirming an early and rapid formation of the most massive galaxies in the Universe.

astro-ph.GA↗

arXiv2015

Functorial Constructions for Non-associative Algebras with Applications to Quasi-bialgebras

The aim of this paper is to establish a contravariant adjunction between the category of quasi-bialgebras and a suitable full subcategory of dual quasi-bialgebras, adapting the notion of finite dual to this framework. Various functorial constructions involving non-associative algebras and non-coassociative coalgebras are then carried out. Several examples illustrating our methods are expounded as well.

math.QA↗

arXiv2015

Investigation of Geant4 Simulation of Electron Backscattering

A test of Geant4 simulation of electron backscattering recently published in this journal prompted further investigation into the causes of the observed behaviour. An interplay between features of geometry and physics algorithms implemented in Geant4 is found to significantly affect the accuracy of backscattering simulation in some physics configurations.

physics.comp-ph↗

arXiv2015

Validation Test of Geant4 Simulation of Electron Backscattering

Backscattering is a sensitive probe of the accuracy of electron scattering algorithms implemented in Monte Carlo codes. The capability of the Geant4 toolkit to describe realistically the fraction of electrons backscattered from a target volume is extensively and quantitatively evaluated in comparison with experimental data retrieved from the literature. The validation test covers the energy range between approximately 100 eV and 20 MeV, and concerns a wide set of target elements. Multiple and single electron scattering models implemented in Geant4, as well as preassembled selections of physics models distributed within Geant4, are analyzed with statistical methods. The evaluations concern Geant4 versions from 9.1 to 10.1. Significant evolutions are observed over the range of Geant4 versions, not always in the direction of better compatibility with experiment. Goodness-of-fit tests complemented by categorical analysis tests identify a configuration based on Geant4 Urban multiple scattering model in Geant4 version 9.1 and a configuration based on single Coulomb scattering in Geant4 10.0 as the physics options best reproducing experimental data above a few tens of keV. At lower energies only single scattering demonstrates some capability to reproduce data down to a few keV. Recommended preassembled physics configurations appear incapable of describing electron backscattering compatible with experiment. With the support of statistical methods, a correlation is established between the validation of Geant4-based simulation of backscattering and of energy deposition.

physics.comp-ph↗

arXiv2014

Geant4 and beyond: recent progress in precision physics modeling

This extended abstract briefly summarizes ongoing research activity on the evaluation and experimental validation of physics methods for photon and electron transport. The analysis includes physics models currently implemented in Geant4 as well as modeling methods used in other Monte Carlo codes, or not yet considered in general purpose Monte Carlo simulation systems. The validation of simulation models is performed with the support of rigorous statistical methods, which involve goodness-of-fit tests followed by categorical analysis. All results are quantitative, and are fully documented.

physics.comp-ph↗

arXiv2014

LBT-LUCIFER spectroscopy: kinematics of a compact early type galaxy at z\simeq1.4

We present a high signal to noise (S/N$>$10) medium resolution (R=2000) LBT-LUCIFER spectrum of the early-type galaxy (ETG) S2F1-142 at $z\simeq1.4$. By means of the CaT line at $8662$ Å, we measured its redshift $z=1.386\pm 0.001$ and we estimated its velocity dispersion $σ_{v}=340 ^{-60}_{+120}$ km/s. Its corresponding virial mass is 3.9$\times10^{11}$ M$_\odot$, compatible with the stellar mass estimates obtained assuming Initial Mass Functions (IMFs) less dwarf rich than the Salpeter one. S2F1-142 is a compact galaxy with $R_{e}$=3.1$\pm$0.2 kpc, i.e., an effective radius more than three times smaller than the average $R_{e}$ of early-type galaxies with the same mass in the local universe. At the same time, we found local and high redshift galaxies with a similar mass content and similar effective radius confirming that it is fully consistent with the already available measures of $R_{e}$ and $σ_{v}$ both in the local and in the distant universe. Considering the distribution of $R_{e}$ and $σ_{v}$ as a function of the stellar mass content of ETGs, both in the local and in the distant universe, we noticed that the measured velocity dispersions of the more compact galaxies are on average slightly lower than expected on the basis of their compactness and the virial theorem, suggesting that {\it i)} their dark matter content is lower than in the more diffuse galaxies and/or {\it ii)} their luminosity profiles are steeper than in the more diffuse galaxies and/or {\it iii)} their larger compactness is an apparent effect caused by the overestimate of their stellar mass content (due to bottom lighter IMF and/or systematic affecting the stellar mass estimates).

astro-ph.GA↗

arXiv2014

Theoretical grounds for the propagation of uncertainties in Monte Carlo particle transport

We introduce a theoretical framework for the calculation of uncertainties affecting observables produced by Monte Carlo particle transport, which derive from uncertainties in physical parameters input into simulation. The theoretical developments are complemented by a heuristic application, which illustrates the method of calculation in a streamlined simulation environment.

physics.data-an↗

arXiv2014

Validation of Compton Scattering Monte Carlo Simulation Models

Several models for the Monte Carlo simulation of Compton scattering on electrons are quantitatively evaluated with respect to a large collection of experimental data retrieved from the literature. Some of these models are currently implemented in general purpose Monte Carlo systems; some have been implemented and evaluated for possible use in Monte Carlo particle transport for the first time in this study. Here we present first and preliminary results concerning total and differential Compton scattering cross sections.

physics.comp-ph↗

arXiv2013

Negative Improvements, Relative Validity and Elusive Goodness

Various issues related to the complexity of apprais- ing the capabilities of physics models implemented in Monte Carlo simulation codes and the evolution of the functional quality the associated software are considered, such as the dependence on the experimental environment where the software operates and its sensitivity to detector characteristics. The concept of software validity as relative to the environment is illustrated by means of a real-life experimental test case. Methods and techniques to mitigate the risk of deteriorating the quality of the software are critically discussed: they concern various disciplines of the software development process. Quantitative validation of physics models is advocated as a method to appraise their capabilities objectively and to monitor the evolution of their associated software behavior.

physics.comp-ph↗

arXiv2013

Physics Methods for the Simulation of Photoionisation

Several physics methods for the simulation of the photoelectric effect are quantitatively evaluated with respect to a large collection of experimental data retrieved from the literature. They include theoretical and empirical calculations of total and partial cross sections, and calculations of the photoelectron angular distribution. Some of these models are currently implemented in general purpose Monte Carlo systems; some have been implemented and evaluated for possible use in Monte Carlo particle transport for the first time in this study.

physics.comp-ph↗

arXiv2013

An exact framework for uncertainty quantification in Monte Carlo simulation

In the context of Monte Carlo (MC) simulation of particle transport Uncertainty Quantification (UQ) addresses the issue of predicting non statistical errors affecting the physical results, i.e. errors deriving mainly from uncertainties in the physics data and/or in the model they embed. In the case of a single uncertainty a simple analytical relation exists among its the Probability Density Function (PDF) and the corresponding PDF for the output of the simulation: this allows a complete statistical analysis of the results of the simulation. We examine the extension of this result to the multi-variate case, when more than one of the physical input parameters are affected by uncertainties: a typical scenario is the prediction of the dependence of the simulation on input cross section tabulations.

physics.comp-ph↗

arXiv2013

Validation of Geant4 simulation of electron energy deposition

Geant4-based simulations of the energy deposited by electrons in various materials are quantitatively compared to high precision calorimetric measurements taken at Sandia Laboratories. The experimental data concern electron beams of energy between a few tens of keV and 1 MeV at various incidence angles. Two experimental scenarios are evaluated: the longitudinal energy deposition pattern in a finely segmented detector, and the total energy deposited in a larger size calorimeter. The simulations are produced with Geant4 versions from 9.1 to 9.6; they involve models of electron-photon interactions in the standard and low energy electromagnetic packages, and various implementations of electron multiple scattering. Significant differences in compatibility with experimental data are observed in the longitudinal energy deposition patterns produced by the examined Geant4 versions, while the total deposited energy exhibits smaller variations across the various Geant4 versions, with the exception Geant4 9.4. The validation analysis, based on statistical methods, shows that the best compatibility between simulation and experimental energy deposition profiles is achieved using electromagnetic models based on the EEDL and EPDL evaluated data libraries with Geant4 9.1. The results document the accuracy achievable in the simulation of the energy deposited by low energy electrons with Geant4; they provide guidance for application in similar experimental scenarios and for improving Geant4.

physics.comp-ph↗

arXiv2012

Photon elastic scattering simulation: validation and improvements to Geant4

Several models for the simulation of photon elastic scattering are quantitatively evaluated with respect to a large collection of experimental data retrieved from the literature. They include models based on the form factor approximation, on S-matrix calculations and on analytical parameterizations; they exploit publicly available data libraries and tabulations of theoretical calculations. Some of these models are currently implemented in general purpose Monte Carlo systems; some have been implemented and evaluated for the first time in this paper for possible use in Monte Carlo particle transport. The analysis mainly concerns the energy range between 5 keV and a few MeV. The validation process identifies the newly implemented model based on second order S-matrix calculations as the one best reproducing experimental measurements. The validation results show that, along with Rayleigh scattering, additional processes, not yet implemented in Geant4 nor in other major Monte Carlo systems, should be taken into account to realistically describe photon elastic scattering with matter above 1 MeV. Evaluations of the computational performance of the various simulation algorithms are reported along with the analysis of their physics capabilities.

physics.comp-ph↗

arXiv2011

Validation of proton ionization cross section generators for Monte Carlo particle transport

Three software systems, ERCS08, ISICS 2011 and Šmit's code, that implement theoretical calculations of inner shell ionization cross sections by proton impact, are validated with respect to experimental data. The accuracy of the cross sections they generate is quantitatively estimated and inter-compared through statistical methods. Updates and extensions of a cross section data library relevant to PIXE simulation with Geant4 are discussed.

physics.comp-ph↗

arXiv2011

Ionization cross sections for low energy electron transport

Two models for the calculation of ionization cross sections by electron impact on atoms, the Binary-Encouter-Bethe and the Deutsch-Maerk models, have been implemented; they are intended to extend and improve Geant4 simulation capabilities in the energy range below 1 keV. The physics features of the implementation of the models are described, and their differences with respect to the original formulations are discussed. Results of the verification with respect to the original theoretical sources and of extensive validation with respect to experimental data are reported. The validation process also concerns the ionization cross sections included in the Evaluated Electron Data Library used by Geant4 for low energy electron transport. Among the three cross section options, the Deutsch-Maerk model is identified as the most accurate at reproducing experimental data over the energy range subject to test.

physics.comp-ph↗

arXiv2011

Evaluation of atomic electron binding energies for Monte Carlo particle transport

A survey of atomic binding energies used by general purpose Monte Carlo systems is reported. Various compilations of these parameters have been evaluated; their accuracy is estimated with respect to experimental data. Their effects on physics quantities relevant to Monte Carlo particle transport are highlighted: X-ray fluorescence emission, electron and proton ionization cross sections, and Doppler broadening in Compton scattering. The effects due to different binding energies are quantified with respect to experimental data. The results of the analysis provide quantitative ground for the selection of binding energies to optimize the accuracy of Monte Carlo simulation in experimental use cases. Recommendations on software design dealing with these parameters and on the improvement of data libraries for Monte Carlo simulation are discussed.

physics.comp-ph↗

arXiv2010

Quantifying the Unknown

The issue of how epistemic uncertainties affect the outcome of Monte Carlo simulation is discussed by means of a concrete use case: the simulation of the longitudinal energy deposition profile of low energy protons. A variety of electromagnetic and hadronic physics models is investigated, and their effects are analyzed. Possible systematic effects are highlighted. The results identify requirements for experimental measurements capable of reducing epistemic uncertainties in the simulation.

physics.comp-ph↗

arXiv2010

New techniques in Monte Carlo simulation: experience with a prototype of generic programming application to Geant4 physics processes

An investigation is in progress to evaluate extensively and quantitatively the possible benefits and drawbacks of new programming paradigms in a Monte Carlo simulation environment, namely in the domain of physics modeling. The prototype design and extensive benchmarks, including a variety of rigorous quantitative metrics, are presented. The results of this research project allow the evaluation of new software techniques for their possible adoption in Monte Carlo simulation on objective, quantitative ground.

physics.comp-ph↗