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 Università degli studi di Torino and INFN Torino Photo: Steven Saffi, University of Adelaide Observatorio Pierre Auger, Av. S. Martín, Norte 304, 5613 Malargüe, Argentina Full author list http://www.auger.org/archive/authors_icrc_2017.html

The Pierre Auger Observatory Surface detector (SD) • 1500 m array 3000 km 2 – 1600 detectors 1500 m grid E > 3 Eev  750 m array 24 km 2 – 61 detectors 750 m grid E > 0.3 EeV Fluorescence detector (FD)  24 telescopes in 4 building Elevation 0-30 0 E > 1 EeV  3 additional telescopes Elevation 30-60 0 E > 0.1 EeV 2 “The Pierre Auger Cosmic Ray Observatory”, NIM A 798 (2015) 172-213

The hybrid detection E FD ∝ ∫ dE dX dX Duty Cycle ~ 13% Duty Cycle ~100% S ( 1000 )∝ E 3

Four different data sets 1500 m 750 m Θ < 60 º Θ < 55 º E > 3EeV E > 0.3EeV E = A S 38 B E = A S 35 B 1500 m FD + 1 SD stat. 60 < Θ < 80 º E > 1EeV E > 4EeV Calorimetric E = A N 19 B 4

Improvements in the reconstruction of FD events dE ∫ E cal = dX dX Fluorescence photons dE dX ● Improved aerosols estimation (M. Malacari, PoS(ICRC2017) 398) • Telescope-wise optical efficiency • Improved Gaisser-Hillas fit • Improved estimation of the invisible energy 5

Improvements in the invisible energy The invisible energy is carried by muons and neutrinos E = E cal +E inv Updates New estimation from inclined SD showers (previously estimated using vertical showers) Barbosa et al., Astrop.. Phys. 22 (2004) 159. Extension to low energies taking into account the mass composition inferred from Auger X max data Inclined showers are muon dominated 6

Improvements in the longitudinal profile fit At low energy the profile is detected only around the maximum Bias on the GH fit f GH ( E ) E cal = ∫ f GH ( E ) dE Solution: constraint k in the likelihood minimization E cal k = ( dE / dX ) max Only relevant below 10 18 eV! k = (332 ± 13) log 10 ( E cal ) g/cm 2 σ = 29 g / cm 2 k fluctuates in a limited range and is Updates determined through simulations At low energy: k constraint dE / dX measured around the maximum Better pixel selection and determination of shower axis ~-1% in E FD Non biased energy estimate 7

Further improvements LM Updates Telescope-wise measurement of LA optical efficiency Improved estimation of photomultiplier calibration constants for the first years CO Changes affect E FD ~ +1% LL Updates Improved aerosols treatment -Phase function of aerosol scattering -Multiple scattering (M. Malacari, PoS(ICRC2017) 398) Changes affect E FD < +3% 8

Improvements in the reconstruction of FD events FD energy systematic uncertainties unchanged 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% Total FD energy shift below +4% TOTAL 14% V. Verzi, ICRC13 arXiv:1307.5059 9

The zenith angle dependence of the attenuation ● The attenuation depends on the zenith angle ● Model independent Constant Intensity Cut (CIC) to correct for the attenuation S ( 1000 )(θ ,E )= S 38 ( E ) CIC (θ) Updates New parameters CIC (θ)= 1 + a X + b X 2 + c X 3 Data up to Dec 2016 Weather and geomagnetic 2 (θ)− cos 2 ( 38 o ) corrections on S(1000) X (θ)= cos 10

The SD-1500 energy calibration  High quality hybrid events (Jan. 2004 – Dec 2015) E FD = A ^ B S ^ S = S 38 ,S 35 , N 19 Updates New calibration parameters Data up to Dec 2015 Resolution: Including updates on S(1000) and E FD SD–1500 ~ 15% SD-1500 inclined ~ 17% SD-750 ~ 13% FD ~ 7% 11

The SD-1500 vertical spectrum 14 events above 10 20 eV ● Jan. 2004 – Dec. 2016 ● 183332 events for log(E)>18.4 ● Systematic uncertainty on energy 14%  Exposure = 51588 km 2 sr yr  Systematic uncertainty on flux 5.8% (~20% more than for ICRC15) 12

The declination dependence of the spectrum No evidence of declination dependence of the spectrum Compatible with large scale dipole anisotropy published by Auger ( O. Taborda , PoS (ICRC2017) 523 ) 13

The declination dependence of the spectrum No evidence of declination dependence of the spectrum Compatible with large scale dipole anisotropy published by Auger ( O. Taborda , PoS (ICRC2017) 523 ) 14

Different measurements of the flux Energy systematic uncertainty (dominated by the FD energy scale) Δ E/E = 14% Hybrid 11680 events log(E/eV)>18 Exposure: 1946 km 2 sr yr @ 10 19 eV (25% increase wrt 2015) Flux uncertainty: 10% SD-1500 inclined 19602 events log(E/eV) >18.5 SD-1500 vertical SD-750 vertical Exposure: 15121 km 2 sr yr 183332 events 87402 events (38% increase wrt 2015) log(E/eV)>18.4 log(E/eV)>17.5 Exposure: 51588 km 2 sr yr Exposure 228 km 2 sr yr Flux uncertainty: 5% (20% increase wrt 2015) (50% increase wrt 2015) Flux uncertainty: 5.8% Flux uncertainty 14 – 7% @ (0.3 – 3) EeV 15

The combined spectrum Exposure = 67000 km 2 sr yr 16

The combined spectrum E 1/2 = (22.6 ± 0.8 ±4.3) EeV E < E ankle E > E ankle ϕ( E )∝ E −γ 2 [ 1 +( E Δ γ ] − 1 ϕ( E )∝ E −γ 1 E s ) 17

Summary  Improvements in the FD reconstruction  Cumulative FD energy increase below 4%  Full consistency with the 14% systematic uncertainty previously quoted ● Robust determination of the CR spectrum with four independent data sets ● Spectral features measured with unprecedented precision and fully consistent with previous results ● No dependence of the spectrum on declination 18

Thanks a lot for your attention 19

Weather and geomagnetic corrections arXiv:1702.02835 S(1000) depends on the angle between shower direction and geomagnetic field  S(1000) is affected by a modulation due to variable pressure and density  Parametrized the dependence of S(1000) on pressure and density Updates Total effect of corrections ~-2% in flux Weather and geomagnetic effects corrected 20 A. Coleman, PoS (ICRC2017) 326

The calculation of the spectrum 6T5 trigger Exposure calculation Exposure is a purely geometrical calculation Exposure= ∫∫ N cell ( t ) a cell cos ( θ ) dtd Ω =πa cell ∫ N cell ( t ) dt 1 Hexagon = 4.59 km 2 sr Unfolding Calculation of spectrum without the resolution effects Forward folding to calculate the correction factor C(E) unfolded ( E ) =C ( E ) ϕ measured ( E ) ϕ 21 Nucl. Instrum. Methods A 613 (2010) 29-39

ICRC 2017 – ICRC 2015 Vertical 22

The SD-1500 energy estimator ( θ >60 ° ) Muons are the dominant component at ground Example of the reference muon distribution Proton shower, 10EeV, ZA=80 º EM component is largely absorbed The energy estimator N 19 is the normalization of the muon content relative to a reference 2D distribution ρ μ (⃗ r )= N 19 ρ μ , 19 (⃗ r , θ , ϕ) N 19 independent of zenith angle 23 JCAP 08 (2015) 049, arXiv:1503.07786v2

The combined spectral parameters ICRC 2015 ICRC 2017 Parameter Value Parameter Value E ankle 4.8±0.1 (±0.8) EeV E ankle 5.08±0.06 (±0.8) EeV E s 42.1±1.7 (±8) EeV E s 39±2 (±8) EeV γ 1 3.29±0.02 (±0.05) γ 1 3.293±0.002 (±0.05) γ 2 2.6±0.02 (±0.1) γ 2 2.53±0.02 (±0.1) Δγ 3.14±0.2 (±0.4) Δγ 2.5±0.1 (±0.4) E 1/2 24.7±0.1 (-3.4+8.2) E 1/2 22.6±0.8 (±4.3 EeV) 24