The Cosmic Ray energy spectrum measured by the Pierre Auger - - PowerPoint PPT Presentation
The Cosmic Ray energy spectrum measured by the Pierre Auger Observatory PoS (ICRC2017) 486 Francesco Fenu for the Auger Collaboration Universit degli studi di Torino and INFN Torino Photo: Steven Saffi, University of Adelaide Observatorio
Università degli studi di Torino and INFN Torino Observatorio Pierre Auger, Av. S. Martín, Norte 304, 5613 Malargüe, Argentina Full author list http://www.auger.org/archive/authors_icrc_2017.html
Photo: Steven Saffi, University of Adelaide
PoS (ICRC2017) 486
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3000 km2 – 1600 detectors 1500 m grid E > 3 Eev
750 m array
24 km2 – 61 detectors 750 m grid E > 0.3 EeV
24 telescopes in 4 building
Elevation 0-300 E > 1 EeV
3 additional telescopes
Elevation 30-600 E > 0.1 EeV
“The Pierre Auger Cosmic Ray Observatory”, NIM A 798 (2015) 172-213
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EFD∝∫ dE dX dX
S(1000)∝E Duty Cycle ~ 13% Duty Cycle ~100%
4 1500 m Θ < 60º E > 3EeV E = A S38
B
1500 m 60 < Θ < 80º E > 4EeV E = A N19
B
750 m Θ < 55º E > 0.3EeV E = A S35
B
FD + 1 SD stat. E > 1EeV Calorimetric
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Fluorescence photons
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The invisible energy is carried by muons and neutrinos New estimation from inclined SD showers (previously estimated using vertical showers) Extension to low energies taking into account the mass composition inferred from Auger Xmax data
Inclined showers are muon dominated
Barbosa et al., Astrop.. Phys. 22 (2004) 159.
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At low energy the profile is detected only around the maximum Bias on the GH fit fGH ( E )
Ecal=∫ f GH(E)dE
Solution: constraint k in the likelihood minimization
k= Ecal (dE/dX)max
k fluctuates in a limited range and is determined through simulations dE / dX measured around the maximum Non biased energy estimate Only relevant below 1018 eV! k = (332 ± 13) log10 ( Ecal ) g/cm2 σ = 29 g / cm2
At low energy: k constraint Better pixel selection and determination
8 Improved aerosols treatment
scattering
(M. Malacari, PoS(ICRC2017) 398)
Telescope-wise measurement of
Improved estimation of photomultiplier calibration constants for the first years Changes affect EFD < +3%
Changes affect EFD ~ +1%
LA CO LM LL
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Fluorescence yield 3.6% Atmosphere 3.4% ÷ 6.2% FD calibration 9.9% FD profile rec. 6.5% ÷ 5.6% Invisible energy 3% ÷ 1.5% Other contrib. ≈ 5%
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S (1000)(θ ,E )=S38(E)CIC (θ)
New parameters Data up to Dec 2016 Weather and geomagnetic corrections on S(1000)
CIC (θ)=1+a X+b X2+c X3 X (θ)=cos
2(θ)−cos 2(38
zenith angle
Constant Intensity Cut (CIC) to correct for the attenuation
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High quality hybrid events
New calibration parameters Data up to Dec 2015 Including updates on S(1000) and EFD
^ S=S38 ,S35, N19 E FD=A ^ S
B
Resolution: SD–1500 ~ 15% SD-1500 inclined ~ 17% SD-750 ~ 13% FD ~ 7%
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Exposure = 51588 km2 sr yr
(~20% more than for ICRC15)
14 events above 1020 eV
Systematic uncertainty on flux 5.8%
13 No evidence of declination dependence of the spectrum Compatible with large scale dipole anisotropy published by Auger
( O. Taborda , PoS (ICRC2017) 523 )
14 No evidence of declination dependence of the spectrum Compatible with large scale dipole anisotropy published by Auger
( O. Taborda , PoS (ICRC2017) 523 )
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SD-1500 vertical 183332 events log(E/eV)>18.4 Exposure: 51588 km2 sr yr (20% increase wrt 2015) Flux uncertainty: 5.8%
SD-750 vertical 87402 events log(E/eV)>17.5 Exposure 228 km2 sr yr (50% increase wrt 2015) Flux uncertainty 14 – 7% @ (0.3 – 3) EeV SD-1500 inclined 19602 events log(E/eV) >18.5 Exposure: 15121 km2 sr yr (38% increase wrt 2015) Flux uncertainty: 5% Hybrid 11680 events log(E/eV)>18 Exposure: 1946 km2 sr yr @ 1019 eV (25% increase wrt 2015) Flux uncertainty: 10% Energy systematic uncertainty (dominated by the FD energy scale)
ΔE/E = 14%
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E< Eankle
Δ γ] −1
E> Eankle
E1/2 = (22.6±0.8±4.3) EeV
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Improvements in the FD reconstruction Cumulative FD energy increase below 4% Full consistency with the 14% systematic uncertainty previously
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S(1000) is affected by a modulation due to
variable pressure and density
Parametrized the dependence of S(1000) on
pressure and density Total effect of corrections ~-2% in flux
Weather and geomagnetic effects corrected S(1000) depends on the angle between shower direction and geomagnetic field
arXiv:1702.02835
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Exposure calculation Exposure is a purely geometrical calculation Unfolding Calculation of spectrum without the resolution effects Forward folding to calculate the correction factor C(E)
1 Hexagon = 4.59 km2 sr
Exposure=∫∫ N cell(t )acellcos (θ)dtd Ω=πacell∫ N cell (t )dt 6T5 trigger
ϕ
unfolded (E )=C (E) ϕ measured ( E )
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23 Muons are the dominant component at ground EM component is largely absorbed The energy estimator N19 is the normalization of the muon content relative to a reference 2D distribution N19 independent of zenith angle
Example of the reference muon distribution Proton shower, 10EeV, ZA=80º
JCAP 08 (2015) 049, arXiv:1503.07786v2
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Parameter Value Eankle 4.8±0.1 (±0.8) EeV Es 42.1±1.7 (±8) EeV γ1 3.29±0.02 (±0.05) γ2 2.6±0.02 (±0.1) Δγ 3.14±0.2 (±0.4) E1/2 24.7±0.1 (-3.4+8.2) Parameter Value Eankle 5.08±0.06 (±0.8) EeV Es 39±2 (±8) EeV γ1 3.293±0.002 (±0.05) γ2 2.53±0.02 (±0.1) Δγ 2.5±0.1 (±0.4) E1/2 22.6±0.8 (±4.3 EeV)