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
years, with the assumption of e+ production only in interaction of hadronic Cosmic rays
with interstellar matter challenged by new measurements of CRE spectrum and related
quantities. Indeed, all recent experiments seem to confirm an hardening in the e+,
a feature that is totally in contrast with the all-secondaries hypothesis, even if significant
disagreements are present about the CRE spectral behavior and the possible presence of
spectral features. These disagreements, together with insufficient precision of current
measurements, prevent the identification of the primary e+ sources, with models involving
Dark matter or astrophysical sources like Supernova Remnants (SNRs) and Pulsar
Wind Nebulae (PWNe) all able to explain current data.
The Fermi-LAT contribution to the CRE study was fundamental, with the 2009 measurement
of the e+e- spectrum extended to the 7 MeV – 1 TeV range with a statistics
already exceeding previous results by many order of magnitude; however, LAT results
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
of this Thesis is to proceed in this direction.
This Thesis will first present an extensive review of the CRE models and of current
results, followed by the update of CRE measurement using 4 years data reprocessed with
the improved event reconstruction introduced in 2011. The results obtained, even if not
in complete agreement with the previous measurement, substantially confirm its main
results; in addition, the data analysis performed allows to identify the effects of the main
changes introduced in the event reconstruction.
The LAT collaboration has developed a new event reconstruction process, expected
to be released at the end of 2014, expected to lead to substantial improvements in LAT
performances. In view of an improvement in the e+ e- result using this new event reconstruction,
this Thesis will present a description of the main changes introduced, together
with a study of the effect of the update of the GEANT4 software used for particle simulation.
Finally, I have performed an extensive comparison of flight and simulated data; the results
obtained show the high level of data-simulation agreement reached, which is crucial
for the reduction of systematic uncertainties that dominated previous LAT measurements.