Ruben Conceição for the Pierre Auger Collaboration TAM, Venice, March 7 th 2013 The Pierre Auger Observatory Results on the highest energies

Ultra High Energy Cosmic Rays Cosmic ray spectrum R. Conceição 2

Ultra High Energy Cosmic Rays Cosmic ray spectrum ? Tevatron (p-p) LHC (p-p) R. Conceição 2

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 R. Conceição 2

Pierre Auger Observatory Located in the Pampa Amarilla, Mendoza, Argentina Altitude: 1400 m a.s.l. ~ 60 km R. Conceição 3

Pierre Auger Observatory 4 Fluorescence Detectors (FD) 6 x 4 Fluorescence Telescopes ~ 1600 Surface Detector (SD) Stations 1.5 km spacing 3000 km 2 Data taking since 2004 Installation completed in 2008 ~ 60 km Low energy extension Aim to E ≈ eV AMIGA – Denser array plus muon detectors HEAT – 3 additional FD telescopes with a high elevation FoV 3

Surface Detector Station Water Cherenkov Tank – Measure charged particles at ground – 100% Duty cycle – SD station Plastic Tank Reflective tyvek liner 12 m 3 purified water 3 PMTs (9 inches) R. Conceição 4 PMT µ e

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 R. Conceição 5 Need to monitor the atmosphere…

Atmospheric monitoring R. Conceição 6 Opportunity to study the atmosphere!

Event Reconstruction Surface 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) X max R. Conceição 7

Event Reconstruction Surface 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) X max R. Conceição 7  Increase accuracy on the energy and direction measurements  Allow complementary shower description

Energy Calibration of the SD 8 SD FD S38 is the equivalent signal of S(1000) of a shower with θ= 38 o Calibration Systematic Uncertainties: - 7% at eV - 15% at 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

RESULTS ON UHECRS Energy Spectrum Mass Composition Hadronic Interactions Search for photons and neutrinos R. Conceição

RESULTS ON UHECRS Energy Spectrum Mass Composition Hadronic Interactions Search for photons and neutrinos R. Conceição

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 R. Conceição 10 SD F. Salamida, ICRC2011

Combined Energy Spectrum (FD+SD) R. Conceição 11

Combined Energy Spectrum R. Conceição 11 Ankle region clearly observed – Very high statistics Galatic to extragalatic transition? Astrophysical interpretation depends: – Primary composition – Sources distribution –...

Combined Energy Spectrum R. Conceição 12 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

Combined Energy Spectrum R. Conceição 12 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

Combined Energy Spectrum R. Conceição 12 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,

Combined Energy Spectrum R. Conceição 12

RESULTS ON UHECRS Energy Spectrum Mass Composition Hadronic Interactions Search for photons and neutrinos R. Conceição

Composition Variables The moments of the X max distribution (mean and RMS) are sensitive to primary composition As the iron showers spend more energy their mean X max and shower to shower flutuations are smaller R. Conceição 13

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) R. Conceição 14 Early StageLate Stage

Analysis procedure Apply quality cuts to reconstructed events – Atmospheric monitoring – Good geometrical reconstruction – X max in the FoV – … Apply anti-bias cuts (X low ; X up ) – Select geometries that allow to observe the full X max distribution – Cuts derived from data – MC based analyses give the same results < E < eV R. Conceição 15

Resolution of the reconstructed X max The detector resolution for X max 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 R. Conceição 16

Moments of the X max distribution As energy increases data seems to favour a heavier composition Break of the elongation rate around log(E/eV) = The interpretation in terms of mass composition depends on the hadronic interaction models R. Conceição Tevatron Auger 17 D. Garcia-Pinto, ICRC

Moments of the X max distribution Same Data (X max ) 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 R. Conceição LHC Tevatron Auger 17

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, X μ max, is sensitive to the primary mass composition X μ max is correlated with X max (e.m.) R. Conceição 18 D. Garcia-Gamez, ICRC2011

Asymmetry of the Signal Rise Time Azimuthal asymmetry in the SD signal is correlated with X max – Early vs. late – The angle of maximum asymmetry, Θ max, is sensitive to the primary mass composition Use the asymmetry of the rise times signal Statistical method (no event-by- event determination) R. Conceição 19 D. Garcia-Pinto, ICRC2011

Meaurements of Shower Development SD statistics allow us to reach higher energies Compatible results within systematic uncertainties Indication of heavier composition at higher energies? R. Conceição 20 FD SD D. Garcia-Pinto, ICRC2011

Meaurements of Shower Development SD statistics allow us to reach higher energies Compatible results within systematic uncertainties Indication of heavier composition at higher energies? R. Conceição 21 FD SD

Interpreting the data in terms of mass composition evolution R. Conceição 22 Mean RMS All the models indicate intermediate masses at the highest energies with a small dispersion in ln(A) JCAP 1302 (2013) 026 Fe N He p ln(A)

RESULTS ON UHECRS Energy Spectrum Mass Composition Hadronic Interactions Search for photons and neutrinos R. Conceição

Cross-section measurement Measurement of the proton-air cross section at sqrt(s)=57 TeV The exponential tail of the X max 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 R. Conceição 23

p-air & p-p cross section at Auger 24 Using standard Glauber formalism R. Ulrich, ICRC2011 Phys. Rev. Lett. 109, (2012)

Muon Measurements Strategies R. Conceição 25 Direct Estimation Vertical Events Jumping Mehtod Smoothing Method Inclined Events Fit normalization Indirect Estimation Hybrid Events Shower Universality Top-down analysis

Muon Measurements Strategies Jump Method – Count Peaks (Muons) Smoothing Method – Obtain smooth function trace (e.m. signal) 25 Direct Estimation Vertical Events Jumping Mehtod Smoothing Method Inclined Events Fit normalization Indirect Estimation Hybrid Events Shower Universality Top-down analysis

Muon Measurements Strategies Ground signal from inclined showers is muon dominated – Fit footprint at ground using MC prediction 26 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 – Shower Universality S μ ( Xmax, S(1000)) Parameters have some model dependence 27 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 28 Direct Estimation Vertical Events Jumping Mehtod Smoothing Method Inclined Events Fit normalization Indirect Estimation Hybrid Events Shower Universality Top-down Analysis

Results on the number of muons Showers 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) R. Conceição 29 R. Engel, UHECR2012 None of these provide an easy solution by itself

Number of muons at E = 10 EeV Results presented with respect to QGSJet-II proton (E = eV) Different methods present similar results Muon signal attenuates faster in simulations than in data – Muon energy spectra? R. Conceição 30 A. Yushkov, UHECR2012 EPOS1.99 Iron Showers

RESULTS ON UHECRS Energy Spectrum Mass Composition Hadronic Interactions Search for photons and neutrinos R. Conceição

Measurement of photons and neutrinos Photons R. Conceição 31 Neutrinos FD: search for events with deep X max Look for almost horizontal showers Experimental signature: “Young showers”, i.e. mostly with e.m. particles SD: search based on signal time structure

Limits on photons and neutrinos Photons No neutrino/photon observed yet Top-down scenarios disfavoured GZK photons/neutrinos within reach in the next years – Optimistic scenarios (proton primaries) Neutrinos R. Conceição 32 Y.Guardincerri, ICRC2011 Astropart. Phys., 35, 660 (2012) M. Settimo, ICRC2011 V. Scherini, UHECR2012

Summary Spectrum – Ankle clearly observed around (6 X eV) – Flux suppression established at (6 X 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 R. Conceição 33

Future R. Conceição 34 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?

END R. Conceição

BACKUP R. Conceição

X max distributions X max distributions for different bins of energy As the energy increases the distributions became narrower P. Facal, ICRC2011

Xmax R. Conceição 52

Elongation Rate R. Conceição 53

Constraining Hadronic Interaction Models R. Conceição 54 E = eV