Results from the Pierre Auger Observatory : Results from the Pierre Auger Observatory J. R. T. de Mello Neto
University of Chicago &
Universidade Federal do Rio de Janeiro
for the Pierre Auger Collaboration
Outline : 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
Cosmic rays flux vs. Energy : 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: knee
change of source? new physics?
~ 3 1018 eV: ankle
transition galactic – extragalatic?
change in composition?
Open questions : 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?
Detection techniques : 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 : 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 : 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.
Slide8 : The Pierre Auger Collaboration Aim: To measure properties of UHECR with
unprecedented statistics and precision
Slide9 : 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 Observatory 3000 km2
A surface array station : A surface array station Communications
antenna GPS antenna Electronics
enclosure 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 : The fluorescence detector Los Leones
telescope
The fluorescence telescope : The fluorescence telescope 30 deg x 30 deg view per telescope
Slide13 : 20 May 2007 E ~ 1019 eV First hybrid qudriple
event! Signal in all four FD detectors and 15 SD stations! First 4-fold hybrid on 20 May 2007
Slide14 : θ~ 48º, ~ 70 EeV Flash ADC traces Flash ADC traces -0.5 0 0.5 1.0 1.5 2.0 2.5 3.0 µs 18 detectors triggered
Slide15 : Hybrid Event longitudinal
profile
Slide16 : = 79 ° Inclined Events offer additional aperture
Energy spectrum from Auger Observatory : 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.
Energy calibration : 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) : 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 : 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
Slide21 : S38 (1000) vs. E(FD) 387 hybrid events Nagano et al, FY used 4 x 1019 eV
Energy calibration : 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 : 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° : 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 )
Slide25 : Slope = -2.7 ± 0.1
Slide26 : Hybrid Spectrum: clear evidence
of the ‘ankle’ at ~ 4 x 1018 eV - 3.1 ± 0.3
Slide27 : 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 : Astrophysical models and the Auger spectrum models assume: an injection
spectral 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 : 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 : Composition from hybrid data Xmax resolution ~ 20 g/cm2
composition from hybrid data : 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 : 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 distribution
function Longitudinal profile
Universality of the e/m shower component : Universality of the e/m shower component Sem parameterised as a function of the distance to ground DG = Xdet - Xmax Predicted signal at 1000 m: includes e/m signal for muon decays
constant intensity method : constant intensity method Cosmic ray
flux isotropic Result accounting for shower fluctuations and detector resolution
expected tank signal at 1019 eV : expected tank signal at 1019 eV from Auger data:
const. intensity method from Auger hybrid data Corresponding energy scale: 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 : 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.
Top down models : 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 : 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) : 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 : photon limits A = Agasa
HP = Haverah Park
Y = Yakutsk
Angular resolution : 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 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 : Source at the Galactic center AGASA 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
Source at Galactic center : Source at Galactic center J.A. Bellido et al., Astroparticle Phys. 15 (2001) 167 SUGAR 85% excess 1018 – 1018.4 eV 5.5o cone
Slide45 :
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. 5°, top-hat AGASA SUGAR G.P. results for the galactic center (check proceedings
ICRC 07 for an update)
Overdensity search (galactic center) : Overdensity search (galactic center) Li, Ma ApJ 272, 317-324 (1983) significance All distributions
consistent with
isotropy 1 EeV < E <10 EeV 0.1 EeV < E < 1 EeV
anisotropy searches : 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 : Anisotropy studies For each target: specify a priory probability levels and angular scales
avoids 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 : 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 : 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 : 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 : Backup slides
GKZ suppression : 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 ! Photon-pion production Photon dissociation
Slide55 : x 10 between 1 and 10 EeV
Depends on assumptions
about Models, Mass and
Spectrum slope 5-fold 3-fold Comparison of
Auger and HiRes
apertures Linear logarithmic
The Hybrid Era : The Hybrid Era
Angular
Resolution
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 : 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 for
γSHDM and pSHDM
P: nucleonic component
at lower energy
Photons dominate
E > 5 x 1019 eV