Lorenzo Perrone for the Pierre Auger Collaboration Università del Salento and INFN Lecce (Italy)

Results from the

Pierre Auger Observatory

Lorenzo Perrone for the Pierre Auger Collaboration Università del Salento and INFN Lecce (Italy)

106° Congresso Società Italiana di Fisica 2020 September 14-18 2020

Image:

S.Saffi

PRD 2020 arXiv 2008.06486 PRL 2020 arXiv 2008.06488

Ankle

Transition galactic to

extra-galactic cosmic rays

Energy spectrum Arrival directions Composition

Search for photon and neutrinos as primary cosmic rays

Hadronic physics

“GZK”

End of the spectrum

GZK

Particle Data Group

The physics case at the highest energies

Auger/TA

LHC 14 TeV

Ankle

Greisen Zatsepin Kuz'min effect (1966):

Interaction with the cosmic microwave background (CMB)

nuclei: photo-disintegration and

pair production on CMB (RB IR) protons:

End to the cosmic ray spectrum

“horizon” (p and nuclei) ~ 100 Mpc ( ~10²⁰ eV )

propagation scenario propagation scenario

Composition at the highest energies and the detection of cosmogenic neutrino and/or photons is of key importance

source scenario source scenario

We may be observing the end of cosmic ray accelerators “fuel”.

^E_max ^{Z B R}

]

^{E  7 1019 eV}

an array of 1660 Cherenkov stations on a 1.5 km hexagonal grid (~ 3000 km²)

4+1 buildings overlooking the array (24+3 telescopes)

The Pierre Auger Observatory

- Dense array (24km

²

) plus muon detectors → UMD - 3 further high elevation FD telescopes → HEAT

Radio detector

153 Radio Antenna

→ AERA

3000 km

²

Fluorescence detector Surface detector

Low energy extensions

500 members, 17 countries

1.5 km

1.5 km 1.5 km

1.5 km

Camera:

440 PMTs

Aperture of the pixels: 1.5°

Fluorescence detector

Surface detector

Energy estimator Longitudinal profile

FD - calorimetric measurement - duty cycle 15%

Use the energy scale provided by FD to calibrate the entire SD data sample

Density of particles at the ground SD - duty cycle ~ 100%

The Hybrid paradigm

Energy scale uncertainty

Calibration with the FD energy scale

Auger Collaboration PRD 2020 arXiv 2008.06486

Energy resolution

SD: < 20% (zenith < 60° and E > 2.5 EeV)

Important to account for resolution effects in the SD-based spectra

Hybrid: 7-8 % Hybrid (zenith < 60°) [ICRC 2019]

Auger Collaboration PRD 2020 arXiv 2008.06486

Data sample:

215030 events

1/1/2004 – 31/8/2018

Exposure:

60400 km

²

sr y

Steepening at ~ 5 10

¹⁹

eV confirmed Ankle at ~ 5 10

¹⁸

eV confirmed

New feature at ~ 10

¹⁹

eV identified

No evidence of dependence on declination

Systematic uncertainty

Auger Collaboration PRL 2020 arXiv 2008.06488 SD1500, zenith < 60°

Five measurements same energy scale Fluxes in agreement within systematic

uncertainies

Combined energy spectrum

More than 3 orders of magnitude in energy

Second knee observed ICRC 2019

ICRC 2019

The Auger combined spectrum

→ non constant composition

increase of the mean mass above and below ~ 2 EeV

→ interpretation depends on hadronic interaction models

→ lack of data above 30 EeV

FD Syst uncertainty ~ 10 g cm^-2 (20 g cm^-2 at the lowest energies)

FD Xmax resolution: 15 (25, 40) g cm^-2 at E > 10¹⁹ eV (E~ 10^17.8 eV, E~ 10^17.2 eV)

ICRC 2019

ICRC 2019

Chemical composition

- Model-independent trend in <lnA>

- Pure composition excluded below and around the ankle - QGSJETII04 is in tension with data

Unphysical region

ICRC 2019

<lnA> and variance for testing the interaction models

How well hadronic models match data?

PRL 117, 192001 (2016)

PRL 117, 192001 (2016)

Hybrid events ~ 10

¹⁹

eV, 0°< zenith 60°

Observed longitudinal profile from FD is reproduced by simulations

Measured signal at the ground differ for data and simulations

R

_had

and R

_E

Scaling factors to match data

Evidence of muon excess 1.3< R_had<1.6

Insensitive to energy scale uncertainty R_E~1

Measurement of muon density and impact on models

Zenith < 45°

Data/Sims ~ 1.38 (1.50) for EPOS-LHC (QGSJETII-04)

Models in tension with data on a wide energy range

Eur. Phys J. C (2020) 80:751: first direct measurement of muon number with UMD at Auger

EPOS-LHC

Photon showers develop deeper in the atmosphere and have less muons

steeper LDF longer rise-time

FD → →

deeper Xmax

SD → →

steeper LDF and longer rise-time signals

Higher fraction of muons (hadrons) flattens the LDF

Muons are produced higher in the atmosphere and arrive within a shorter time

Photon signature

Search for photons

Upper limits on diffuse photon flux

Auger is the most sensitive to photons in the EeV region

Strictest limits at E> 1 EeV

- Top-down model strongly disfavored

- CR proton dominated scenario (also the most pessimistic cases) disfavoured

11 candidates > 10 EeV (SD) 3 candidates > 1 EeV (Hybrid)

Preliminary upper limits also above 0.2 EeV presented at ICRC 2019 Targeted search

In coincidence of known sources

including CenA and the Galactic Center [UL following HESS Observation]

NO Candidates found

Search for neutrinos

hadron

Neutrino-like

Sensitivity to different channels

JCAP 10 (2019) 022

Upper limits set assuming dN/dE = k E^-2

→ k ～ 4.4 x 10^-9 GeV cm^-2 s^-1 sr^-1 [0.1 – 25] EeV

Heavy constraints on models assuming sources of CR accelerating only protons with strong evolution in z

Point-like sources

also in coincidence with observations by other experiments

For example the recent TXS 0506+056

Coincidence with GW

For example GW170817

NO Candidates found

Upper limits on the diffuse neutrino flux

See also E. De Vito at this conference

NO Candidates found

Large Scale anisotropy at the highest energies

E > 8 EeV

Exposure=76800 km²sr y

Inhomogeneus large scale distribution of sources

Diffusion in extra-galactic magnetic field by close sources Interpretation

3D dipole → Science 315 (2017) 1266

Astrophys. J. 891 (2020) 142

Large scale anisotropy confirmed 15% more data

3D dipole 6.5%^+0.013_-0.09 → 6.6%^+0.012_-0.08

Modulation 2.6 10

^-8

→ 1.9 10

^-9

(6 )

Study of the energy evolution of the dipole equatorial component and phase

Amplitude increases from 1% to 10% above few EeV

Phase shifts from GC to the opposite at the highest energies

Transition to extragalaction origin above few EeV

Indication of anisotropy at intermediate scale

Likelihood test for anisotropy with astrophysical catalogs

Directional exposure and relative weight of sources taken into account.

Attenuation according to JCAP04 (2017) 38.

TS=2log[L( ,f

_ani

)/L(f

_ani

=0)]

Test statistics (TS): likelihood ratio

f_ani and  ( search radius) free parameters Method: sky model as the sum of an isotropic fraction plus the anisotropic component from selected sources f_ani

The Astrophysical Journal Letters, 853:L29 (2018) and ICRC 2019

Scan in energy 32< E < 80 EeV

2157 events between 1/1/2004 and 31/8/2018

Search for overdensities

Centaurus A region

:

most significant excess at 28° and E = 37 EeV

Combined fit of Auger data (spectrum and X

_max

simultaneously) vs astrophysical scenarios

Auger Collaboration PRL 2020 arXiv 2008.06488

energy density in CR above the ankle (5.66  0.03 10^53 erg Mpc^-3 this constraints the luminosity density for classes of extragalactic

sources accelerating only protons → disfavoured

uniformely distributed sources accelerating nuclei [rigidity dependent] → favoured

indication that the new feature at 10¹⁹ eV may be due to the interplay of He and CNO components

(individual nearby source not favored, spectrum flat in

declination )

additional component required below 5 10¹⁸ eV (possibly a tail from galactic CR)

Auger upgrade program: Auger Prime

3.8 m² (1 cm thick) scintillators on each of the main array station

Scintillators sensitive to the electromagnetic content of the shower

Moreover

- Upgraded and faster electronics - Extension of the dynamic range - Cross check with underground buried UMD detectors

Scenario 2: photo-disintegration

Scenario 1 : maximum rigidity

➡ 12 upgraded stations (Engineering Array) since 2016 with new electronics, higher sampling, large dynamic range

➡ the SSD preproduction array: 77 stations (since March 2019-old electronic 1 PMT missing)

➡ 752 SSD stations already deployed (1500 in total)

➡ Underground Muon detector

➡ The largest radio detector (3000 km²)

➡ 12 upgraded stations (Engineering Array) since 2016 with new electronics, higher sampling, large dynamic range

➡ the SSD preproduction array: 77 stations (since March 2019-old electronic 1 PMT missing)

➡ 752 SSD stations already deployed (1500 in total)

➡ Underground Muon detector

➡ The largest radio detector (3000 km²)

quarantine

Deployment restarted now with reduced resources

2019 2020

Preliminary results “preproduction array”

77 SD stations equipped with SSD (120 km²) old electronic

SD more sensitive to the muonic part, taking over for inclined showers

This translates into the measurement of the LDF

ICRC 2019

SSD

SD

Summary and perspectives

Combined measurements, ankle observed at about 5 10¹⁸ eV, new feature at ~ 10¹⁹ eV, suppression at E > 4 10¹⁹ eV), its nature still not fully understood

Spectrum

Composition

heavier with increasing energy (interpretation is model dependent).

Astronomy

Indication of a possible anisotropy at intermediate scale and evidence of dipole at large scale (and E > 8 EeV)

- need composition data E> 40 EeV to better understand the suppression - better understanding of hadronic interaction models

Models

Mismatch data models for muon content

Neutrals

flux photon limits above 1 EeV (top-down models disfavored, standard astrophysical sources expected). Absence of cosmogenic neutrinos disfavor pure proton composition

Uniformely distributed sources accelerating nuclei (rigity based scenario) favoured

AugerPrime

Auger as a interdisciplinary facility: Elves observation

7 (2020) e2019EA000582

Auger: education…...

37 students, 16 from South America

and outreach

BACKUP SLIDES

Auger and Telescope Array Auger and Telescope Array

TA

Auger

Auger ~3000 km

²

, TA ~ 700 km

²

- Auger and TA are complementary

Overlapping region

Exposure (Time  Area)

AUGER vs Telescope Array

We are observing the sky from different Hemispheres but the spectrum is not changing with declination

Auger Collaboration PRD 2020 arXiv 2008.06486

In agreement at the ankle within energy scale sys. uncert.

Difference at the highest energies→ Auger (TA) would need +10% (-10%) per decade above 10

¹⁹

eV to match

Joint Auger-TA working group working on tracking possible detector

systematics

No indication of dependence on declination

Compatible with the dipole

anisotropy observed at E > 8 EeV

Telescope Array hot spot (δ~ - 44°) is outside the common declination band

AUGER vs Telescope Array

Auger Collaboration PRD 2020 arXiv 2008.06486

Apparently the two measurements differ different hadronic models except for Sibyll.

different methods

Auger data folded with TA acceptance are in perfect agreement with TA data at the level of few g/cm² (much less than systematic uncertainty)

pre-LHC models

Joint Working Group (arXiv:1503.07540)

Telescope Array Collaboration, APP 64 (2015) 49 Auger; Phys. Rev. D 90, 122005 (2014)

Confirmed by more recent analysis

AUGER vs Telescope Array

Lower energy [45718(stat)+19/-25(syst)] mb Higher energy [48616(stat)+19/-25(syst)] mb

Sys uncertainty: method, models, helium contamination

Auger Collaboration @ ICRC 2015

p-air cross-section p-air cross-section

Telescope Array 1505.01860