Results from the Pierre Auger Observatory

J. R. T. de Mello NetoUniversity of Chicago &

Universidade Federal do Rio de Janeirofor the Pierre Auger Collaboration

Outline• Introduction: the UHECRs• The Pierre Auger Observatory – an hybrid detector• Energy calibration• The model-independent energy spectrum• Hadronic models• Photon fraction limit• Anisotropy studies• Perspectives

– Auger South enhancements– North Site

• Auger contributions in the proceedings of ICRC 07 – Merida, Mexico

S. Swordy

Cosmic rays flux vs. Energy

UHECR • one particle per century per km2

• many interesting questions

• (nearly) uniform power-law spectrum spanning 10 orders of magnitude in E and 32 in flux!

• structures :~ 3 – 5 1015 eV: kneechange of source? new physics? ~ 3 1018 eV: ankletransition galactic – extragalatic?change in composition?

Open questions

• How cosmic rays are accelerated at ?• What are the sources? • How can they propagate along astronomical

distances at such high energies?• Are they substantially deflected by magnetic fields?• Can we do cosmic ray astronomy?• What is the mass composition of cosmic rays?

eV 1019E

Detection techniques

Particles at ground level• large detector arrays (scintillators, water Cerenkov tanks, etc)• detects a small sample of secondary particles (lateral profile)• 100% duty cicle• aperture: area of array (independent of energy)• primary energy and mass composition are model dependent (rely on Monte Carlo simulations based on extrapolations of the hadronic models constrained at low energies by accelerator physics)

ex: AGASA

Detection techniques

Fluorescence of N2 in the atmosphere• calorimetric energy measurement as function of atmospheric depth• only for E > 1017 eV• only for dark nights (10% duty cicle)• requires good knowledge of atmospheric conditions• aperture grows with energy, varies with atmosphere

ex: HiRes

The Auger Observatory: Hybrid design• A large surface detector array

combined with fluorescence detectors results in a unique and powerful design;

• Simultaneous shower measurement allows for transfer of the nearly calorimetric energy calibration from the fluorescence detector to the event gathering power of the surface array.

• A complementary set of mass sensitive shower parameters contributes to the identification of primary composition.

• Different measurement techniques force understanding of systematic uncertainties in each.

Czech Republic

France

Germany

Italy

Netherlands

Poland

Portugal

Slovenia

Spain

United Kingdom

Argentina

Australia

Brasil

Bolivia*

Mexico

USA

Vietnam*

*Associate Countries

~300 PhD scientists from

~70 Institutions and 17 countries

The Pierre Auger Collaboration

Aim: To measure properties of UHECR with unprecedented statistics and precision

1438 deployed 1400 filled 1364 taking data

090707 ~ 85%

All 4 fluorescence buildings complete,each with 6 telescopes

1st 4-fold on 20 May 2007

AIM: 1600 tanks

HYBRID DETECTOR

Pierre Auger South Observatory3000 km2

A surface array station

Communications antenna GPS antenna

Electronicsenclosure Solar panels

Battery box

3 photomultiplier tubes looking into the water collect light left

by the particles

Plastic tank with 12 tons of very pure water

The fluorescence detector

Los Leones telescope

The fluorescence telescope

30 deg x 30 deg view per telescope

20 May 2007 E ~ 1019 eV

First hybrid qudripleevent!

Signal in all four FD detectors and 15 SD stations!

First 4-fold hybrid on 20 May 2007

θ~ 48º, ~ 70 EeV

Flash ADC tracesFlash ADC traces

Lateral density distribution

Typical flash ADC trace

at about 2 km

Detector signal (VEM) vs time (µs)

PMT 1

PMT 2

PMT 3

-0.5 0 0.5 1.0 1.5 2.0 2.5 3.0 µs

18 detectors triggered

Hybrid Event

longitudinal profile

= 79 °

Inclined Events offer additional aperture

Energy spectrum from Auger Observatory

• Based on fluorescence and surface detector data• First model- and mass-independent energy spectrum• Power of the statistics and well-defined exposure of the

surface detector• Hybrid data confirm that SD event trigger is fully efficient

above 3x1018 eV for θ<60o

• Uses energy scale of the fluorescence detector (nearly calorimetric, model independent energy measurement) to calibrate the SD energy.

• SD parameter S1000: interpolated tank signal at 1000 meters from the lateral distribution function• Determined for each SD event• It is proportional to the primary energy

Energy calibration

• Reduced measurement uncertainty (shower fluctuations dominate) • VEM = vertical equivalent muons from self calibration of the tank signal (from ambient muons)

Energy calibration (constant intensity cut)

• How to relate S(1000 m) to E?• It depends on the atmospheric depth --> shower zenith angle, • =0 one atm, =90 36 atm, shower is attenuated depending on

the zenith angle;• Showers with the same energy developing at differente zenith

angles produce different S1000 signals at ground level– The corresponding grammage of atmosphere along the shower

axis (shower age) is different• Choose a reference zenith angle 38° (median of the Auger data set)• Make use of the isotropy of the observed CR flux

• For a fixed I0 find S(1000) at each θ such that I(>S(1000)) = I0

Constant intensity cut

Integral number of events for cos2(θ) for the indicated minimum value of S(1000)

• Derived attenuation curve, CIC(θ), fitted with a quadratic function.• Normalized so that CIC(38°) = 1;

Define energy parameter S38= S(1000)/CIC(θ) for each shower :“the S(1000) it would have produced if it had arrived at 38o zenith angle”

Same value of S1000 at higher zenith angle correspond to a higher energy

S38 (1000) vs. E(FD)

387 hybrid events

Nagano et al, FY used

4 x 1019 eV

Energy calibration

Fractional difference between the SD and FD energy for the hybrid events;

• Small relative dispersion• includes uncertainties in both the FD energy and the SD signal

• S(1000) is intrinsecally a very good energy estimator• Reliable energy measurements when properly calibrated

Summary of systematic uncertainties

Note: Activity on several fronts to reduce these uncertainties

Fluorescence Detector Uncertainties Dominate

• Invisible energy: fraction of the energy carried away by neutrinos and energetic muons (Monte Carlo dependent) • energy determination nearly independent of mass or model assumptions

Energy spectrum from SD < 60°

Calibration unc. 18%FD syst. unc. 22%

5165 km2 sr yr ~ 0.8 full Auger year

Exp Obs>1019.6 132 +/- 9 51

> 1020 30 +/- 2.5 2

Slope = -2.62 ± 0.03

•sharp suppression in the spectrum is seen for the last energy decade•pure power law is rejected with 6σ ( E > 1018.6 eV ) and 4σ ( E > 1019 eV )

Slope = -2.7 ± 0.1

Hybrid Spectrum: clear evidence of the ‘ankle’ at ~ 4 x 1018 eV

- 3.1 ± 0.3

• The agreement between the spectra derived using three diferent methods is good • It is underpinned by the common method of energy calibration based on the FD measurements.

Energy spectra from Auger

Astrophysical models and the Auger spectrum

models assume: an injectionspectral index, an exponential cutoff at an energy of Emax times the charge of the nucleus,and a mass composition at the acceleration site as well as a distribution of sources.

Auger data: sharp suppression in the spectrum with a high confidence level!

Expected GZK effect or a limit in the acceleration process?

Composition from hybrid data

• UHECR: observatories detect induced showers in the atmosphere• Nature of primary: look for diferences in the shower development• Showers from heavier nuclei develop earlier in the atm with smaller

fluctuations– They reach their maximum development higher in the atmosphere

(lower cumulated grammage, Xmax )

• Xmax is increasing with energy (more energetic showers can develop longer before being quenched by atmospheric losses)

Composition from hybrid data

Xmax resolution ~ 20 g/cm2

composition from hybrid data

• The results of all three experiments are compatible within their systematic uncertainties.• The statistical precision of Auger data already exceed that of preceeding experiments ( data taken during construction of the observatory)

test of hadronic models

• Assumption: universality of the eletromagnetic shower evolution• Test: number of muons needed to obtain a self consistent

description of data

Lateral distributionfunction

Longitudinal profile

Universality of the e/m shower component

Sem parameterised as a function of the distance to ground DG = Xdet - Xmax

)eV10,(),( 19, DGSNEDGSS pQGSIIrelEMMC

Predicted signal at 1000 m:

includes e/m signal for muon decays

constant intensity method

Cosmic ray flux isotropic

.sin ),,,()1000(

2

max

constd

dN

relMC NXESS

ev

Result accounting for shower fluctuations and detector resolution

09.0

11.011.045.1)10( 19

eVN rel

expected tank signal at 1019 eV

)10(),38,10()10( 19,max

191938 eVSNXeVSeVS pQGSIIrel

EM

from Auger data:const. intensity method

from Auger hybrid data

VEM 3.2

1.27.15.37)10( 19

38

eVS

Corresponding energy scale: FDEE 3.1

• within current uncertainty of fluorescence detector energy scale• it corresponds to assigning showers a ~ 30% higher energy than done in the fluorescence detector-based Auger shower reconstruction!

test of hadronic models

• two other methods, one using golden hybrid events and another using inclined showers, give consistent results with the constant intensity method ;

• Auger hybrid data: test of hadronic interaction models up to ultra-high energy ( Elab > 1019 eV, )

• The number of muons measured in data is about 1.5 times bigger than that predicted by QGSJET II for proton showers!

• Universality of eletromagnetic shower evolution indicates energy scale compatible with that of fluorescence detectors.

TeV 200~s

Top down models

• acceleration models (astrophysics):• active galactic nuclei, gamma-ray bursts...• not easy to reach > 100 EeV; • photon fractions typically < ~ 1%

• non-acceleration models (particle physics)• UHECR: decay products of high-mass particles (> 1021eV) • super-heavy dark matter (SHDM): from early universe and concentraded on the halo of galaxies and clusters of galaxies• topological defects (TD) produced throughout the universe • UHECR produced as secondary particles (hadronization process) and are most photons and neutrinos, with minority of nucleus• photon fraction typically > ~ 10%• SHDM: CR from our galaxy, photons with a hard energy spectrum• TD: sources distributed in the universe, photons interact with CMB (expect smaller photon fraction)

UHE photons status in 2005

HP: Haverah Park Ave et al.,2000; event rates

A1, A2: AGASA muons @ 1000 m Shinozaki et al., 2002; M. Risse et al., 2005

Models: ZB,SHDM,TD - Gelmini et al. 2005 SHDM' – Ellis et al., 2005

• cosmic ray photon fraction: check nonacceleration models• upper limits so far: surface detectors only !?• needed: cross check by fluorescence technique (Xmax in hybrids)

variables for composition (photons)

Photons: greater time spread and smaller radius of curvature

• Data lying above the dashed line ( the mean of the distribution for photons) are identfied as photon candidates. • No events meet this requirement.

Showers with greater Xmax have a time distribution in the SD which is more spread (geometrical effect)

Energetic muons ( spherical shower front) larger values of Xmax related to smaller values of Rc.

photon limits

A = AgasaHP = Haverah ParkY = Yakutsk

Angular resolution

Surface detector

Hybrid data: better angular resolution, ~ 0.7o @ 68% c.l. in the EeV energy range

Events with E > 10 EeV :6 or more SD stations

Galactic center

• Galactic Center is a “natural” site for cosmic ray acceleration– Supermassive black hole– Dense clusters of stars– Stellar remnants– SNR (?) Sgr A East

• SUGAR excess is consistent with a point source, indicating neutral primaries

• Neutrons would go undeflected, and neutron decay length at 1018 eV is comparable to the distance to the Galactic center (~8.5 kpc)

Chandra

Source at the Galactic center

AGASA

)4.5( 6.413

506

expected

observed

20o scales

1018 – 1018.4 eV

N. Hayashida et al., Astroparticle Phys. 10 (1999) 303

Significance (σ)

• Cuts are a posteriori • Chance probability is not well defined

22% excess

)280,15(),(

Source at Galactic center

J.A. Bellido et al., Astroparticle Phys. 15 (2001) 167

SUGAR

)2.9( 8.11

8.21

expected

observed

85% excess

1018 – 1018.4 eV

5.5o cone)274,22(),(

test of AGASA: obs/exp = 2116/2159.5 R = 0.98 ± 0.02 ± 0.01

NOT CONFIRMED (with 3x more stats)

test of SUGAR: obs/exp = 286/289.7 R = 0.98 ± 0.06 ± 0.01

NOT CONFIRMED (with 10x more stats)

Galactic Center as a point source (σ=1.5°): obs/exp = 53.8/45.8 R = 1.17 ± 0.10 ± 0.01 NO SIGNIFICANT EXCESS

upper limit on the flux of neutrons coming from GC:

Galactic Plane: NO SIGNIFICANT EXCESS

astro-ph/0607382(Astropart. Phys., 2007)

Φs < 0.08 ξ km-2 yr-1 at 95% C.L.Φs < 0.08 ξ km-2 yr-1 at 95% C.L.

5°, top-hat

AGASASUGAR

G.P.

results for the galactic center

(check proceedings ICRC 07 for an update)

Overdensity search (galactic center)

Li, Ma ApJ 272, 317-324 (1983)

significance

All distributionsconsistent withisotropy

1 EeV < E <10 EeV

0.1 EeV < E < 1 EeV

anisotropy searches

• All-sky blind searches for sources: NO EXCESS FOUND• Right-ascension (RA) distribution of the events is remarkably

isotropic!– Upper limit of 1.4% on the first harmonic amplitude (dipole in the RA

modulation)

• Angular coincidences between Auger events and BL Lac objects (as possibly seen by HiRes) was not confirmed;

• Search for clustering (as seen by AGASA), no strong excess was observed

• Scan in angle and energy: hints of clustering at larger energies and intermediate angular scales– Large scale distribution of nearby sources?

– Chance probability of such a signal from an isotropic flux ~ 2% (marginally significant)

Anisotropy studies

For each target: specify a priory probability levels and angular scalesavoids uncertainties from “penalty factors” due to a posteriori probability estimation

Targets: • low energy: Galactic center and AGASA-SUGAR location• high energy: nearby violent extragalactic objects(ICRC 05)

New results are coming out! Stay tuned!

other physics topics to be explored

• Neutrinos• Gamma ray burst detection• Measurement of the primary cosmic ray cross section;• and many others ...

Conclusion e perspectives

• More events > 10 EeV than from AGASA or HiRes • and close to more than their total • AND with superior angular and energy resolution• Auger South: about 90% complete • Detector working very well ( SD: 97% uptime)• First rate physics results: spectrum, composition, anisotropy

and many others

• Auger statistics will totally dominate after another year !!

Future for Auger Collaboration

• Complete Auger-South in ~ 6 months and provide reliable and extensive experimental data for many years

• Commence construction of Auger South upgrades:– HEAT: high elevation FD (to 60°)– AMIGA dense SD array plus muon detectors

• Submit Auger-North proposal within a year

Backup slides

GKZ suppression

• Cosmic rays E = 1020 eV interact with 2.7 K photons

• In the proton frame

• Nuclei

• Proton with less energy, eventually below the cutoff energy EGZK= 5x 1019 eV

Universe is opaque for E > EGZK !

n

pp k0

3

MeVE 300

Photon-pion production

Photon dissociation

x 10 between 1 and 10 EeV

Depends on assumptions about Models, Mass and Spectrum slope

5-fold3-fold

Comparison of Auger and HiResapertures

Linear

logarithmic

The Hybrid Era

AngularResolution

Aperture

Energy

Hybrid SD-only FD-only mono (stereo – low N)

~ 0.2° ~ 1 - 2° ~ 3 - 5°

Flat with energy AND E, A, spectral mass and model (M) free slope and M

dependent

A and M free A and M A and M free dependent

Super-Heavy Dark Matter

Fit to AGASA data (Gelmini et al, 05)• Similar shapes for ZB (Weiler, 1982) e TD (Hill 1983 ) models• signature for exotics

• produced during inflation; Mx ~ 1023 eV, clumped in galactic halo (overdensity ~ 105)• lifetime ~ 1020 y: decay (SUSY-QCD) -> pions -> UHE photons (and neutrinos)• little processing during propagation: decay spectrum at Earth

Spectrum forγSHDM and pSHDM

P: nucleonic component at lower energyPhotons dominate E > 5 x 1019 eV