Measurement of the Cosmic-ray Proton Spectrum …...Measurement of the Cosmic-ray Proton Spectrum...
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Measurement of the Cosmic-ray Proton Spectrum with the Fermi Large Area Telescope David Green, Liz Hays On Behalf of the Fermi-LAT Collaboration 7th Fermi Symposium Garmisch-Partenkirchen, Germany October 15-20, 2017 We report the measurement of the cosmic-ray proton spectrum between 54 GeV and 9.5 TeV using 7 years of Pass 8 flight data from the Fermi Large Area Telescope (LAT). Our analysis yields a dataset with statistical uncertainty under 1% up to 1 TeV and residual contamination less than 5% from all other cosmic-ray species. We estimate the systematic uncertainties by testing different event selections and different hadronic interaction models for the GEANT4 Monte-Carlo simulations, and we found that they are an order of magnitude larger than the statistical uncertainty. Energy [GeV] 2 10 3 10 4 10 ] -1 sr -2 m -1 s -1 J(E) [GeV × 2.7 E 4 10 CREAM-I (2005) ATIC (2003) AMS-02 (2011-2013) PAMELA (2006-2008) Fermi-LAT (2008-2015) PRELIMINARY Does not include energy uncertainties
Transcript of Measurement of the Cosmic-ray Proton Spectrum …...Measurement of the Cosmic-ray Proton Spectrum...
Measurement of the Cosmic-ray Proton Spectrum with the Fermi Large Area Telescope
David Green, Liz HaysOn Behalf of the Fermi-LAT
Collaboration
7th Fermi SymposiumGarmisch-Partenkirchen, Germany
October 15-20, 2017
We report the measurement of the cosmic-ray proton spectrum between 54 GeV and 9.5 TeV using 7 years of Pass 8 flight data from the Fermi Large Area Telescope (LAT). Our analysis yields a dataset with statistical uncertainty under 1% up to 1 TeV and residual contamination less than 5% from all other cosmic-ray species.We estimate the systematic uncertainties by testing different event selections and different hadronic interaction models for the GEANT4 Monte-Carlo simulations, and we found that they are an order of magnitude larger than the statistical uncertainty.
Energy [GeV]210 310 410
]-1
sr
-2 m
-1 s
-1 J
(E) [
GeV
× 2.
7E
410
CREAM-I (2005)ATIC (2003)AMS-02 (2011-2013)PAMELA (2006-2008)Fermi-LAT (2008-2015)
PRELIMINARY
Does not include energy uncertainties
Event Selection• The proton event selection is defined as:
• Event has to trigger and pass onboard filters• Require event to have reconstructed track• Deposited energy >20 GeV in CAL• Require a well reconstructed track using Pass 8
direction classifier
True Energy [GeV]210 310 410
sr]
2Pr
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Trigger & FilterTrack Found
Energy > 20 GeV
Track Reconstruction
PRELIMINARY
• Use the TKR and the ACD to independently measure the charge of incoming cosmic rays (CR)
• Find a residual contamination from CR helium and nuclei less than 1%
• After final event selection electron contamination is 4% at 50 GeV and decreasing with increasing energy
Fermi Gamma-ray Space Telescope
Systematic Uncertainties
• This study is dominated by systematic uncertainties
• We use two methods to estimate our systematic uncertainties:
• Signal Efficiency• Selecting events with different
path-lengths• Alternative GEANT4 models
• Response uncertainties via alternate hadronic models
• Uncertainty in the energy measurement is still being finalized
True Energy [GeV]210 310
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0.14 StatisticalSignal EfficiencyAlternative GEANT4 ModelsStat + Sys Uncertainties
PRELIMINARY
Does not include energy uncertainties
Fermi Gamma-ray Space Telescope
Cosmic-ray Proton Spectrum
• Using 7 years of LAT flight data, August 4, 2008 to July 30, 2015
• Extends energy of space-based measurement to 9.5 TeV
• Red markers represent statistical uncertainty
• Red shaded region includes systematic uncertainties
• Good agreement with other cosmic-ray measurements
• Allows for additional cosmic-ray proton studies with the LAT
Energy [GeV]210 310 410
]-1
sr
-2 m
-1 s
-1 J
(E) [
GeV
× 2.
7E
410
CREAM-I (2005)ATIC (2003)AMS-02 (2011-2013)PAMELA (2006-2008)Fermi-LAT (2008-2015)
PRELIMINARY
Does not include energy uncertainties
Fermi Gamma-ray Space Telescope
