Ruben Conceição

for the Pierre Auger Collaboration

TAM, Venice, March 7th 2013

The Pierre Auger ObservatoryResults on the highest energies

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Ultra High Energy Cosmic Rays

Cosmic ray spectrum

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Ultra High Energy Cosmic Rays

Cosmic ray spectrum

?

Tevatron (p-p) LHC (p-p)

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Ultra High Energy Cosmic Rays

Cosmic ray spectrum

?

Tevatron (p-p) LHC (p-p)

• UHECRs• Where/how are they produced?• What is the flux composition?• How do they interact?

• Study Hadronic interactions at sqrt(s) ~ 100 TeV

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Pierre Auger Observatory

• Located in the Pampa Amarilla, Mendoza, Argentina• Altitude: 1400 m a.s.l.

~ 60 km

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Pierre Auger Observatory

• 4 Fluorescence Detectors (FD)• 6 x 4 Fluorescence Telescopes

• ~ 1600 Surface Detector (SD) Stations• 1.5 km spacing• 3000 km2

Data taking since 2004Installation completed in 2008

~ 60 km

Low energy extension• Aim to E ≈ 1017 eV• AMIGA

– Denser array plus muon detectors

• HEAT– 3 additional FD

telescopes with a high elevation FoV

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Surface Detector Station

• Water Cherenkov Tank– Measure charged

particles at ground– 100% Duty cycle

– SD station• Plastic Tank • Reflective tyvek liner• 12 m3 purified water • 3 PMTs (9 inches)

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PMT µ e

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Fluorescence Detector• Operates in moonless nights

– Duty cycle ~13%• Collects the fluorescence photons

to reconstruct the energy deposit longitudinal profile

• 6 Telescopes each with 30° x 30° FoV• Camera composed by 440 PMTs

5Need to monitor the atmosphere…

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Atmospheric monitoring

6Opportunity to study the atmosphere!

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Event ReconstructionSurface Detector

• Lateral Distribution (LDF)• Tank hit time gives shower

direction• Energy is obtained using the

signal measured at 1000 meters from the shower core S(1000)

Fluorescence Detector

• Longitudinal Profile• Evolution seen in camera gives the

shower geometry• Energy is calculated by integrating

the longitudinal profile (calorimetric measurement)

Xmax

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Event ReconstructionSurface Detector

• Lateral Distribution (LDF)• Tank hit time gives shower

direction• Energy is obtained using the

signal measured at 1000 meters from the shower core S(1000)

Fluorescence Detector

• Longitudinal Profile• Evolution seen in camera gives the

shower geometry• Energy is calculated by integrating

the longitudinal profile (calorimetric measurement)

Xmax

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Increase accuracy on the energy and direction measurements

Allow complementary shower description

Energy Calibration of the SD

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SD

FD

S38 is the equivalent signal of S(1000) of a shower with θ= 38o

Calibration Systematic Uncertainties: - 7% at 1019 eV- 15% at 1020 eV

FD Energy Systematics:- Fluorescence yield 14%- FD abs calib 9.5%- Invisible Energy 4%- Reconstruction 8%- Atmospheric Effects 8%- TOTAL: 22%

R. Pesce, ICRC2011

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RESULTS ON UHECRS

• Energy Spectrum• Mass Composition• Hadronic Interactions• Search for photons and neutrinos

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RESULTS ON UHECRS

• Energy Spectrum• Mass Composition• Hadronic Interactions• Search for photons and neutrinos

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Energy spectrum

• SD has a higher exposure ( ~20905 km2 sr yr) allowing to reach higher energies

• Energy resolution is around 15%– Unfolding method to correct for bin-to-bin migration

• FD (Hybrid) can reach lower energies but exposure is MC based• Good agreement between FD and SD

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SD

F. Salamida, ICRC2011

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Combined Energy Spectrum (FD+SD)

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Combined Energy Spectrum

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• Ankle region clearly observed– Very high statistics

• Galatic to extragalatic transition?• Astrophysical interpretation

depends:– Primary composition– Sources distribution– ...

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Combined Energy Spectrum

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• Auger data shows a flux suppression at the highest energies– Cutoff significance > 20 σ

• This feature is compatible with:– GZK cuttoff

• Greisen, Zatsepin, Kuz'min (1966)

• Cosmic ray interaction with CMB

– Sources running out of power

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Combined Energy Spectrum

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• Auger data shows a flux suppression at the highest energies– Cutoff significance > 20 σ

• This feature is compatible with:– GZK cuttoff

• Greisen, Zatsepin, Kuz'min (1966)

• Cosmic ray interaction with CMB

• Protons– Photo-pion production

• Irons– Photo-dissociation

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Combined Energy Spectrum

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• Auger data shows a flux suppression at the highest energies– Cutoff significance > 20 σ

• This feature is compatible with:– GZK cuttoff

• Greisen, Zatsepin, Kuz'min (1966)

• Cosmic ray interaction with CMB

– Sources running out of power

D. Allard, 1111.3290

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Combined Energy Spectrum

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RESULTS ON UHECRS

• Energy Spectrum• Mass Composition• Hadronic Interactions• Search for photons and neutrinos

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Composition Variables

• The moments of the Xmax distribution (mean and RMS) are sensitive to primary composition

• As the iron showers spend more energy their mean Xmax and shower to shower flutuations are smaller

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Analysis procedure

• Shower reconstruction accounts for different types of light and propagation– Fluorescence light: isotropic

emission– Cherenkov light: beamed emission– Cherenkov scattering

• Rayleigh• Mie (aerosols)

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Early

Sta

ge

Late

Sta

ge

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Analysis procedure

• Apply quality cuts to reconstructed events– Atmospheric monitoring– Good geometrical reconstruction– Xmax in the FoV– …

• Apply anti-bias cuts (Xlow ; Xup)– Select geometries that allow to observe the

full Xmax distribution– Cuts derived from data– MC based analyses give the same results

1018.1 < E < 1018.2 eV

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Resolution of the reconstructed Xmax

• The detector resolution for Xmax has been estimated from MC simulations to be 20 g cm-2

• Stereo Events (events seen by 2 FDs) can be used to check MC performance

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Moments of the Xmax distribution

• As energy increases data seems to favour a heavier composition

• Break of the elongation rate around log(E/eV) = 18.38• The interpretation in terms of mass composition

depends on the hadronic interaction models

Tevatron

Auger

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D. Garcia-Pinto, ICRC2011

- 0.17+ 0.07

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Moments of the Xmax distribution

• Same Data (Xmax)• New hadronic interaction models with LHC constraints• Spread between models diminishes • The interpretation depends of hadronic interaction

physics at energy above the LHC– E.g.: These results can be mimic with a change in the cross-

section without violating the Froissart bound

LHC

Tevatron

Auger

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Muon Production Depth

• SD Events• Inclined shower events

– θ in [55:65]– Mostly Muons

• Use arrival time to reconstruct production depth

• The maximum of the muon production profile, Xμ

max, is sensitive to the primary mass composition

• Xμmax is correlated with Xmax

(e.m.)

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D. Garcia-Gamez, ICRC2011

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Asymmetry of the Signal Rise Time

• Azimuthal asymmetry in the SD signal is correlated with Xmax

– Early vs. late– The angle of maximum asymmetry, Θmax, is

sensitive to the primary mass composition• Use the asymmetry of the rise times

signal• Statistical method (no event-by-event

determination)

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D. Garcia-Pinto, ICRC2011

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Meaurements of Shower Development• SD statistics allow us to

reach higher energies• Compatible results within

systematic uncertainties• Indication of heavier

composition at higher energies?

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FD

FD

SD

SD

D. Garcia-Pinto, ICRC2011

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Meaurements of Shower Development• SD statistics allow us to

reach higher energies• Compatible results within

systematic uncertainties• Indication of heavier

composition at higher energies?

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FD

FD

SD

SD

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Interpreting the data in terms of mass composition evolution

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Mean RMS

All the models indicate intermediate masses at the highest energies with a small dispersion in ln(A)

JCAP

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2 (2

013)

026

Fe

N

He

p 0.0

0.7

2.6

4.0

ln(A)

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RESULTS ON UHECRS

• Energy Spectrum• Mass Composition• Hadronic Interactions• Search for photons and neutrinos

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Cross-section measurement• Measurement of the

proton-air cross section at sqrt(s)=57 TeV

• The exponential tail of the Xmax distribution is sensitive to the primary cross-section

• Deepest events are proton dominated– Except for small fraction of

photons which can be estimated from data

• Apply fiducial cuts to get unbiased tail

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p-air & p-p cross section at Auger

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Using standard Glauber formalism

R. Ulrich, ICRC2011Phys. Rev. Lett. 109, 062002 (2012)

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Muon Measurements Strategies

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Direct Estimation

Vertical Events

Jumping Mehtod

Smoothing Method

Inclined Events

Fit normalization

Indirect Estimation

HybridEvents

Shower Universality

Top-down analysis

Muon Measurements Strategies

• Jump Method– Count Peaks (Muons)

• Smoothing Method– Obtain smooth function trace

(e.m. signal)

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Direct Estimation

Vertical Events

Jumping Mehtod

Smoothing Method

Inclined Events

Fit normalization

Indirect Estimation

HybridEvents

Shower Universality

Top-down analysis

Muon Measurements Strategies

• Ground signal from inclined showers is muon dominated– Fit footprint at ground using MC

prediction

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Direct Estimation

Vertical Events

Jumping Mehtod

Smoothing Method

Inclined Events

Fit normalization

Indirect Estimation

HybridEvents

Shower Universality

Top-down analysis

Muon Measurements Strategies

• Use Hybrid Events– Shower Universality

• Sμ( Xmax, S(1000))• Parameters have some model

dependence

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Direct Estimation

Vertical Events

Jumping Mehtod

Smoothing Method

Inclined Events

Fit normalization

Indirect Estimation

Hybrid Events

Shower Universality

Top-down Analysis

Muon Measurements Strategies

• Use Hybrid Events– Fit longitudinal

profile with MC– Compare expected

signal at ground

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Direct Estimation

Vertical Events

Jumping Mehtod

Smoothing Method

Inclined Events

Fit normalization

Indirect Estimation

Hybrid Events

Shower Universality

Top-down Analysis

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Results on the number of muonsShowers up to 60°

zenith angle

• Models systematically bellow data even for iron primaries– Energy scale uncertainty (22%)– Mixed composition – Hadronic interaction models

Inclined Shower(Muon dominated)

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R. Engel, UHECR2012

None of these provide an easy solution by itself

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Number of muons at E = 10 EeV

• Results presented with respect to QGSJet-II proton (E = 1019 eV)• Different methods present similar results• Muon signal attenuates faster in simulations than in data

– Muon energy spectra?

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A. Yushkov, UHECR2012

EPOS1.99 Iron Showers

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RESULTS ON UHECRS

• Energy Spectrum• Mass Composition• Hadronic Interactions• Search for photons and neutrinos

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Measurement of photons and neutrinosPh

oton

s

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Neu

trin

os

FD: search for events with deep Xmax

Look for almost horizontal showersExperimental signature: “Young showers”, i.e. mostly with e.m. particles

SD: search based on signal time structure

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Limits on photons and neutrinosPhotons

• No neutrino/photon observed yet• Top-down scenarios disfavoured• GZK photons/neutrinos within reach in the next years

– Optimistic scenarios (proton primaries)

Neutrinos

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Y.Guardincerri, ICRC2011Astropart. Phys., 35, 660 (2012)

M. Settimo, ICRC2011V. Scherini, UHECR2012

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Summary• Spectrum

– Ankle clearly observed around (6 X 1018 eV)– Flux suppression established at (6 X 1019 eV)

• Composition– Indication of light(heavier) composition at lower(higher) energies– Complex mass composition scenario (interpretation depends of

hadronic interactions)• Hadronic Interactions

– Proton-Air cross section measured at √s = 57 TeV– Models predict fewer muons than observed

• Energy scale, composition, hadronic interaction models?

• Photons and Neutrinos– Observation Limits were set– Top-down models disfavored

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Future

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• Accumulate Statistics– Huge observatory running smoothly

• Build a consistent picture of the shower– Multivariate Analyses

• Independent measurement of the e.m. and muonic shower component at ground– Muon detectors upgrade?

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END

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BACKUP

Xmax distributions

• Xmax distributions for different bins of energy

• As the energy increases the distributions became narrower

P. Facal, ICRC2011

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Xmax

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Elongation Rate

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Constraining Hadronic Interaction Models

E = 1019 eV