Presentation on theme: "Results from the Pierre Auger Observatory"— Presentation transcript:
1 Results from the Pierre Auger Observatory J. R. T. de Mello NetoUniversity of Chicago &Universidade Federal do Rio de Janeirofor the Pierre Auger Collaboration
2 Outline Introduction: the UHECRs The Pierre Auger Observatory – an hybrid detectorEnergy calibrationThe model-independent energy spectrumHadronic modelsPhoton fraction limitAnisotropy studiesPerspectivesAuger South enhancementsNorth SiteAuger contributions in the proceedings of ICRC 07 – Merida, Mexico
3 Cosmic rays flux vs. Energy (nearly) uniform power-law spectrum spanning 10 orders of magnitude in E and 32 in flux!structures :~ 3 – eV: kneechange of source? new physics?~ eV: ankletransition galactic – extragalatic?change in composition?UHECRone particle per century per km2many interesting questionsS. Swordy
4 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?
5 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 cicleaperture: 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
6 Detection techniques Fluorescence of N2 in the atmosphere calorimetric energy measurement as function of atmospheric depthonly for E > 1017 eVonly for dark nights (10% duty cicle)requires good knowledge of atmospheric conditionsaperture grows with energy, varies with atmosphereex: HiRes
7 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.
8 The Pierre Auger Collaboration Czech RepublicFranceGermanyItalyNetherlandsPolandPortugalSloveniaSpainUnited KingdomArgentinaAustraliaBrasilBolivia*MexicoUSAVietnam**Associate Countries~300 PhD scientists from~70 Institutions and 17 countriesAim: To measure properties of UHECR withunprecedented statistics and precision
9 Pierre Auger South Observatory 3000 km21438 deployed1400 filled1364 taking data~ 85%All 4 fluorescencebuildings complete,each with 6 telescopes1st 4-fold on 20 May 2007AIM: 1600 tanksHYBRID DETECTOR
10 A surface array station CommunicationsantennaGPS antennaElectronicsenclosureSolar panelsBattery box3 photomultiplier tubes looking into the water collect light left by the particlesPlastic tank with 12 tons of very pure water
12 The fluorescence telescope 30 deg x 30 deg view per telescope
13 First 4-fold hybrid on 20 May 2007 First hybrid qudripleevent!Signal in all four FD detectors and 15 SD stations!20 May E ~ 1019 eV
14 θ~ 48º, ~ 70 EeV Typical flash ADC trace at about 2 km 18 detectors triggeredTypical flash ADC traceat about 2 kmDetector signal (VEM) vs time (µs)PMT 1PMT 2PMT 3Now I would like to show you the observatory in action.Here is an event of fairly high energy – about 70 EeV - at a moderate zenith angle of 48 degrees. Note that an EeV corresponds to 1 x 10^18 eV.)At the left are the flash ADC traces of the detector stations that participated in the event. The horizontal axis is in nanoseconds while the vertical axis is in vertical equivalent muons. The three colors are the response to the three PMTs. As you see the signal goes out to 3 mircoseconds.Here is the pattern of hits on the array with the size of the dot proportional to the log of the signal in the tank. The red arrow showed the reconstructed direction and core position.The last frame shows the lateral distribution of detector signals from the core position.Lateral density distributionFlash ADC tracesFlash ADC tracesµs
17 Energy spectrum from Auger Observatory Based on fluorescence and surface detector dataFirst model- and mass-independent energy spectrumPower of the statistics and well-defined exposure of the surface detectorHybrid data confirm that SD event trigger is fully efficient above 3x1018 eV for θ<60oUses energy scale of the fluorescence detector (nearly calorimetric, model independent energy measurement) to calibrate the SD energy.
18 Energy calibrationSD parameter S1000: interpolated tank signal at 1000 meters from the lateral distribution functionDetermined for each SD eventIt is proportional to the primary energyReduced measurement uncertainty (shower fluctuations dominate)VEM = vertical equivalent muons from self calibration of the tank signal (from ambient muons)
19 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, = 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 levelThe corresponding grammage of atmosphere along the shower axis (shower age) is differentChoose a reference zenith angle 38° (median of the Auger data set)Make use of the isotropy of the observed CR fluxFor a fixed I0 find S(1000) at each θ such that I(>S(1000)) = I0All these steps have been taken by Auger!!!
20 Constant intensity cut Integral number of events for cos2(θ) for the indicated minimum value of S(1000)Same value of S1000 at higher zenithangle correspond to a higher energyDerived 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”
21 S38 (1000) vs. E(FD) 4 x 1019 eV Nagano et al, FY used 387 hybrid events
22 Energy calibrationFractional difference between the SD and FD energy for the hybrid events;Small relative dispersionincludes uncertainties in both the FD energy and the SD signalS(1000) is intrinsecally a very good energy estimatorReliable energy measurements when properly calibrated
23 Summary of systematic uncertainties Note: Activity on several fronts to reduce these uncertaintiesFluorescence Detector Uncertainties DominateInvisible energy: fraction of the energy carried away by neutrinos and energetic muons (Monte Carlo dependent)energy determination nearly independent of mass or model assumptions
24 Energy spectrum from SD < 60° Exp Obs> /> /Slope = ± 0.03Calibration unc. 18%FD syst. unc. 22%5165 km2 sr yr ~ 0.8 full Auger yearsharp suppression in the spectrum is seen for the last energy decadepure power law is rejected with 6σ ( E > eV ) and 4σ ( E > 1019 eV )
26 Hybrid Spectrum: clear evidence of the ‘ankle’ at ~ 4 x 1018 eV - 3.1 ± 0.3
27 Energy spectra from Auger The agreement between the spectra derived using three diferent methods is goodIt is underpinned by the common method of energy calibration based on the FD measurements.
28 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?
29 Composition from hybrid data UHECR: observatories detect induced showers in the atmosphereNature of primary: look for diferences in the shower developmentShowers from heavier nuclei develop earlier in the atm with smaller fluctuationsThey 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)
30 Composition from hybrid data Xmax resolution ~ 20 g/cm2
31 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)
32 test of hadronic models Lateral distributionfunctionLongitudinal profileAssumption: universality of the eletromagnetic shower evolutionTest: number of muons needed to obtain a self consistent description of data
33 Universality of the e/m shower component Sem parameterised as a function of the distance to ground DG = Xdet - XmaxPredicted signal at 1000 m:includes e/m signal for muon decays
34 constant intensity method Cosmic rayflux isotropicResult accounting for shower fluctuations and detector resolution
35 expected tank signal at 1019 eV from Auger hybrid datafrom Auger data:const. intensity methodCorresponding energy scale:within current uncertainty of fluorescence detector energy scaleit corresponds to assigning showers a ~ 30% higher energy than done in the fluorescence detector-based Auger shower reconstruction!
36 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.
37 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 galaxiestopological defects (TD) produced throughout the universeUHECR produced as secondary particles (hadronization process) and are most photons and neutrinos, with minority of nucleusphoton fraction typically > ~ 10%SHDM: CR from our galaxy, photons with a hard energy spectrumTD: sources distributed in the universe, photons interact with CMB(expect smaller photon fraction)
38 UHE photons status in 2005HP: Haverah Park Ave et al.,2000; event ratesA1, A2: AGASA 1000 m Shinozaki et al., 2002; M. Risse et al., 2005Models: ZB,SHDM,TD - Gelmini et al SHDM' – Ellis et al., 2005cosmic ray photon fraction: check nonacceleration modelsupper limits so far: surface detectors only !?needed: cross check by fluorescence technique (Xmax in hybrids)
39 variables for composition (photons) 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.Photons: greater time spread and smaller radius of curvatureData lying above the dashed line( the mean of the distribution for photons)are identfied as photon candidates.No events meet this requirement.
41 Angular resolution Surface detector Hybrid data: better angular resolution, ~ 0.7o@ 68% c.l. in the EeVenergy rangeEvents with E > 10 EeV :6 or more SD stationsAll these steps have been taken by Auger!!!
42 Galactic centerGalactic Center is a “natural” site for cosmic ray accelerationSupermassive black holeDense clusters of starsStellar remnantsSNR (?) Sgr A EastSUGAR excess is consistent with a point source, indicating neutral primariesNeutrons would go undeflected, and neutron decay length at 1018 eV is comparable to the distance to the Galactic center (~8.5 kpc)Chandra
43 Source at the Galactic center AGASASignificance (σ)20o scales1018 – eV22% excessCuts are a posterioriChance probability is not well definedN. Hayashida et al., Astroparticle Phys. 10 (1999) 303
44 Source at Galactic center SUGAR5.5o cone1018 – eV85% excessJ.A. Bellido et al., Astroparticle Phys. 15 (2001) 167
45 results for the galactic center test of AGASA: obs/exp = 2116/2159.5R = 0.98 ± 0.02 ± 0.01NOT CONFIRMED (with 3x more stats)test of SUGAR: obs/exp = 286/289.7R = 0.98 ± 0.06 ± 0.01NOT CONFIRMED (with 10x more stats)Galactic Center as a point source (σ=1.5°):obs/exp = 53.8/45.8R = 1.17 ± 0.10 ± 0.01NO SIGNIFICANT EXCESSupper limit on the flux of neutrons coming from GC:Galactic Plane: NO SIGNIFICANT EXCESSAGASA5°, top-hatSUGARG.P.astro-ph/(Astropart. Phys., 2007)(check proceedingsICRC 07 for an update)Φs < 0.08 ξ km-2 yr-1 at 95% C.L.
46 Overdensity search (galactic center) 1 EeV < E <10 EeV0.1 EeV < E < 1 EeVsignificanceLi, Ma ApJ 272, (1983)All distributionsconsistent withisotropy
47 anisotropy searchesAll-sky blind searches for sources: NO EXCESS FOUNDRight-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 observedScan in angle and energy: hints of clustering at larger energies and intermediate angular scalesLarge scale distribution of nearby sources?Chance probability of such a signal from an isotropic flux ~ 2% (marginally significant)
48 Anisotropy studies New results are coming out! Stay tuned! For each target: specify a priory probability levels and angular scalesavoids uncertainties from “penalty factors” due to a posteriori probability estimationTargets:low energy: Galactic center and AGASA-SUGAR locationhigh energy: nearby violent extragalactic objects(ICRC 05)New results are coming out! Stay tuned!
49 other physics topics to be explored NeutrinosGamma ray burst detectionMeasurement of the primary cosmic ray cross section;and many others ...
50 Conclusion e perspectives More events > 10 EeV than from AGASA or HiResand close to more than their totalAND with superior angular and energy resolutionAuger South: about 90% completeDetector working very well ( SD: 97% uptime)First rate physics results: spectrum, composition, anisotropy and many othersAuger statistics will totally dominate after another year !!
51 Future for Auger Collaboration Complete Auger-South in ~ 6 months and provide reliable and extensive experimental data for many yearsCommence construction of Auger South upgrades:HEAT: high elevation FD (to 60°)AMIGA dense SD array plus muon detectorsSubmit Auger-North proposal within a year
53 GKZ suppression Universe is opaque for E > EGZK ! EGZK= 5x 1019 eV Cosmic rays E = 1020 eV interact with 2.7 K photonsIn the proton frameNucleiProton with less energy, eventually below the cutoff energyEGZK= 5x 1019 eVPhoton-pion productionPhoton dissociationUniverse is opaque for E > EGZK !
55 Comparison ofAuger and HiResapertures3-fold5-foldLinearx 10 between 1 and 10 EeVDepends on assumptionsabout Models, Mass andSpectrum slopelogarithmic
56 The Hybrid Era Hybrid SD-only FD-only Angular Resolution Aperture EnergyHybrid SD-only FD-onlymono(stereo – low N)~ 0.2° ~ 1 - 2° ~ 3 - 5°Flat with energy AND E, A, spectralmass and model (M) free slope and MdependentA and M free A and M A and M free
57 Super-Heavy Dark Matter produced during inflation; Mx ~ 1023 eV, clumped in galactic halo (overdensity ~ 105)lifetime ~ y: decay (SUSY-QCD) -> pions -> UHE photons (and neutrinos)little processing during propagation: decay spectrum at EarthSimilar shapes for ZB (Weiler, 1982) e TD (Hill 1983 ) modelssignature for exoticsFit to AGASA data (Gelmini et al, 05)Spectrum forγSHDM and pSHDMP: nucleonic componentat lower energyPhotons dominateE > 5 x 1019 eV