ETD system

Electronic theses and dissertations repository


Tesi etd-11272014-220632

Thesis type
Tesi di dottorato di ricerca
Preliminary study on the Cosmic-Ray Electron spectrum measurement using a new event-level analysis of Fermi-LAT
Settore scientifico disciplinare
Corso di studi
tutor Bellazzini, Ronaldo
relatore Baldini, Luca
Parole chiave
  • fermi-LAT
  • cosmic ray electrons
Data inizio appello
Riassunto analitico
The study of Galactic Cosmic Ray Electrons (CREs) saw important developments in recent<br>years, with the assumption of e+ production only in interaction of hadronic Cosmic rays<br>with interstellar matter challenged by new measurements of CRE spectrum and related<br>quantities. Indeed, all recent experiments seem to confirm an hardening in the e+,<br>a feature that is totally in contrast with the all-secondaries hypothesis, even if significant<br>disagreements are present about the CRE spectral behavior and the possible presence of<br>spectral features. These disagreements, together with insufficient precision of current<br>measurements, prevent the identification of the primary e+ sources, with models involving<br>Dark matter or astrophysical sources like Supernova Remnants (SNRs) and Pulsar<br>Wind Nebulae (PWNe) all able to explain current data.<br>The Fermi-LAT contribution to the CRE study was fundamental, with the 2009 measurement<br>of the e+e- spectrum extended to the 7 MeV – 1 TeV range with a statistics<br>already exceeding previous results by many order of magnitude; however, LAT results<br>could be further and significantly refined exploiting the full LAT statistics (at present, almost 6 yr) and the improvements made in LAT event reconstruction since 2009. The aim<br>of this Thesis is to proceed in this direction.<br>This Thesis will first present an extensive review of the CRE models and of current<br>results, followed by the update of CRE measurement using 4 years data reprocessed with<br>the improved event reconstruction introduced in 2011. The results obtained, even if not<br>in complete agreement with the previous measurement, substantially confirm its main<br>results; in addition, the data analysis performed allows to identify the effects of the main<br>changes introduced in the event reconstruction.<br>The LAT collaboration has developed a new event reconstruction process, expected<br>to be released at the end of 2014, expected to lead to substantial improvements in LAT<br>performances. In view of an improvement in the e+ e- result using this new event reconstruction,<br>this Thesis will present a description of the main changes introduced, together<br>with a study of the effect of the update of the GEANT4 software used for particle simulation.<br>Finally, I have performed an extensive comparison of flight and simulated data; the results<br>obtained show the high level of data-simulation agreement reached, which is crucial<br>for the reduction of systematic uncertainties that dominated previous LAT measurements.