This thesis describes the study of electrons and positrons in the cosmic radiation. New measurements of the positron fraction at the top of the atmosphere between 200 MeV and 3.0 GeV are presented, together with the electron spectrum up to 20 GeV. The measurement was conducted with the space borne PAMELA experiment from July 2006 to December 2008, that is a period of minimum solar activity and negative solar magnetic field polarity. PAMELA provides the first long term observation of the low energy positron abundance during this particular solar and heliospheric state. The great amount of collected statistics allows to study the variation of the particle intensity at Earth with energy and time, and to investigate effects depending on the particles sign of charge. During approximately 860 days of data collection about 16300 positrons and 178000 electrons were identified. The major sources of background, constituted by cosmic protons and locally produced pions, have been studied. The derived electron spectrum clearly shows the effect of the solar modulation below few GeV. The detected positron fraction has been found to be in accordance with predictions from theoretical models that describe the transport of particles in the heliosphere taking drift effects into account.
Questa tesi descrive lo studio di elettroni e positroni nella radiazione cosmica. Nuove misure della frazione di positroni al top dell’atmosfera tra 200 MeV e 3.0 GeV, nonché lo spettro di elettroni fino a 20 GeV, sono presentati. La misura è stata effettuata con l’esperimento PAMELA da Luglio 2006 a Dicembre 2008, periodo di minima attività solare e polarità negativa. PAMELA fornisce le prime osservazioni a lungo termine della frazione di positroni di bassa energia durante questo particolare stato della eliosfera. La grande statistica collezionata permette di studiare la variazione del flusso di particelle a Terra in funzione dell’energia e del tempo, e di investigare effetti dipendenti dal segno della carica. Durante circa 860 giorni di raccolta dati circa 16000 positroni e 178000 elettroni sono stati identificati. Le maggiore fonte di fondo, costituite da protoni e pioni localmente prodotti, sono state studiate. Lo spettro di elettroni derivato mostra chiaramente l’effetto della modulazione solare sotto qualche GeV. La frazione di positroni è risultata in accordo con le predizioni di modelli teorici che descrivono il trasporto di particelle nell’eliosfera che tengono conto di effetti di drift.
DI FELICE, V. (2010). Low energy electron and positron measurements in space with the PAMELA experiment.
Low energy electron and positron measurements in space with the PAMELA experiment
DI FELICE, VALERIA
2010-04-01
Abstract
This thesis describes the study of electrons and positrons in the cosmic radiation. New measurements of the positron fraction at the top of the atmosphere between 200 MeV and 3.0 GeV are presented, together with the electron spectrum up to 20 GeV. The measurement was conducted with the space borne PAMELA experiment from July 2006 to December 2008, that is a period of minimum solar activity and negative solar magnetic field polarity. PAMELA provides the first long term observation of the low energy positron abundance during this particular solar and heliospheric state. The great amount of collected statistics allows to study the variation of the particle intensity at Earth with energy and time, and to investigate effects depending on the particles sign of charge. During approximately 860 days of data collection about 16300 positrons and 178000 electrons were identified. The major sources of background, constituted by cosmic protons and locally produced pions, have been studied. The derived electron spectrum clearly shows the effect of the solar modulation below few GeV. The detected positron fraction has been found to be in accordance with predictions from theoretical models that describe the transport of particles in the heliosphere taking drift effects into account.File | Dimensione | Formato | |
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