the pierre auger observatory results on the highest energies

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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Cosmic ray spectrum

?

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

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Cosmic ray spectrum

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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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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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• 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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• Protons– Photo-pion production

• Irons– Photo-dissociation

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– Sources running out of power

D. Allard, 1111.3290

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RESULTS ON UHECRS


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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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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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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


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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


• 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


• 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


• 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


• 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


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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

the pierre auger observatory results on the highest energies

Documents

invisible energy

fluorescence telescopes

shower directionenergy

shower geometryenergy

kmlow energy extensionaim

ev fd energy systematics

fluorescence yield

fluorescence photons