MEASUREMENTS OF COSMIC RAYS WITH PRIMARY ENERGIES UP TO 1020 eV Recent results from the Pierre Auger Observatory Danilo Zavrtanik Pierre Auger Collaboration University of Nova Gorica Slovenia I will talk mainly about: P. Auger Observatory, Progress in the observatory construction. Performance of the detectors now in operation. The quality of the data. Results. But let me start with a brief overview about UHECR Institut fur Hochenegiephysik Austrian Academy of Sciences Wien, May 25, 2010 1

OUTLINE Brief overview of UHECR P. Auger Observatory Conclusions Experimental method Results Spectrum Composition Photon flux Arrival direction Conclusions 2

WHY STUDY UHECRs? Measured spectrum extends to E > 1020 eV Where and how are cosmic rays accelerated to these energies No known astrophysical sources seem able to produce such enormous energies Chemical composition unknown The high energy end of the spectrum probes physics at energies out of reach of any man made accelerator Possible new physics 3

WHY STUDY UHECRs? Accesible to experiment Astronomy with charged Energy spectrum Chemical composition Arrival directions Astronomy with charged particles? Problems Very low rates call for giant observatory Protons and nuclei are charged and therefore deflected by galactic and intergalactic magnetic fields  1 particle/km2/century or a few particles/km2/millenium 4

POSSIBLE SOURCES Bottom – Up (Astrophysical Acceleration Mechanisms) Shock acceleration in extended objects or catastrophic events Acceleration in strong fields associated with accretion disks and compact rotating galaxies Collision of galaxies NGC4038 and NGC4039 as seen by Hubble Space Telescope

LIMITS TO ACCELERATION Hillas plot No good candidates for ZeV accelerators in the known Universe!

Models do not reproduce the measured flux which is too high ! POSSIBLE SOURCES Top - Down Models Exotic Mechanisms Decay of topological deffects Relic monopoles Etc. New Physics Supersymmetric particles Strongly interacting neutrinos Decay of massive new long lived particles Violation of LI Models do not reproduce the measured flux which is too high !

PROPAGATION All known particles except neutrinos undergo interactions with Cosmic Microwave Background Example: p + 2.7K  p + 0  n + + For energy > 5 x 1019 p N Δ+ γ2.7K p

Greisen-Zatsepin-Kuzmin Cut-off Size of the observable Universe PROPAGATION Greisen-Zatsepin-Kuzmin Cut-off (Greisen ‘66, Zatsepin & Kuzmin ’66) Particles > 5 x 1019 eV must be < 50 Mpc away Size of the observable Universe ~ 4.000 MPc Cut-off in the spectrum or UHECR comes from our neighbourhood or New physics at work

MAGNETIC FIELD DEFLECTION Above 100 EeV Df < 20 - larger than experimental resolution! A window to CR astronomy ?

EXPERIMENTAL TECHNIQUE Measurement of extensive air showers Calorimetry Calorimeter – atmosphere Read out Fluorescence detectors Particle detector array

EXPERIMENTS PRESENT PAST Yakutsk, Russia Volcano Ranch, USA Scintillators, Atmospheric Čerenkov PAST Volcano Ranch, USA Scintillators Haverah Park, UK Water Čerenkov SUGAR, Australia Fly’s Eye, USA Atmospheric Fluorescence AGASA, Japan Scintillators, muon detectors HiRes, USA P. Auger, Argentina Hybrid: Atmospheric Fluorescence, Water Čerenkov Telescope Array Atmospheric Fluorescence, Scintillator Array FUTURE AirWatch: OWL – JEM/EUSO - TUS Atmospheric Fluorescence

PIERRE AUGER OBSERVATORY A cosmic ray observatory designed for a high statistics study of The Highest Energy Cosmic Rays (1019 - 1021 eV) using Two Large Air Shower Detectors Mendoza, Argentina (observatory fully operational) Colorado, USA (design and proposal in preparation) The objective of the Pierre Auger Observatory is to make a full sky, high statistics, study of cosmic rays at the highest energies. The Auger Observatory will consist of sites – one in each hemisphere at mid latitude – so as to have full sky coverage. The southern site of the Auger Observatory is located in the province of Mendoza, Argentina near the city of Malargüe. The northern site will be in south east Colorado.

~ 450 physicist from ~ 100 institutions P. AUGER COLLABORATION Argentina Australia Bolivia Brazil Croatia Czech Republic France Germany Italy Mexico Netherlands Poland The Observatory is being built by an eclectic mix of high energy physicists, low energy physicists, cosmic ray physics and a few astronomers from 63 institutions in 17 countries. The Auger collaboration is unique among large international science projects in that there is no dominant country or institution – indeed a true partnership. The only cosmic ray experiment of a size of a High energy physics collaboration. Portugal Slovenia Spain UK USA Vietnam ~ 450 physicist from ~ 100 institutions 18 countries 14

SOUTHERN OBSERVATORY HYBRID DETECTOR SD FD World largest array ~ 1.600 surface detectors with 1.5 km spacing FD 4 fluorescence buildings with 6 telescopes each World largest array 3.000 km2 area 1 Auger year = 30 AGASA years (SD) Here is a summary of construction progress. The blue area shows the areas where detector stations have been installed. Over half of the array has been deployed. Three fluorescence enclosures and their 18 telescopes are in operation. The fourth fluorescence enclosure is under construction. As you see the Observatory is still very much work in progress. We have been taking data while construction continues. 15

Event timing and direction determination SURFACE DETECTOR ARRAY Event timing and direction determination Shower timing Shower angle Particle density Shower energy Muon number Measure of Pulse rise time primary mass 16

WATER ČERENKOV DETECTOR 17

FLUORESCENCE DETECTOR Shower ~ 90% electromagnetic Ionization of nitrogen measured directly Calorimetric energy measurement Measure of shower development 18

FLUORESCENCE DETECTOR Fluorescence telescopes: Number of telescopes: 24 Mirrors: 3.6 m x 3.6 m with field of view 30º x 30º, each telescope is equipped with 440 photomultipliers. May 3, 2009

HYBRID OPERATION May 3, 2009

SPECTRUM

ENERGY MEASUREMENT Fluorescence detector Surface detector array Measure light intensity along the track and integrate. Nearly calorimetric, model and mass independent. Surface detector array Particle density S at fixed distance to the shower core is related to the shower energy via simulations. S(1000)‏ Signal Size [VEM] Distance to shower core [m] 23

ENERGY DETERMINATION Energy scale is determined from data Aperture is determined by geometry of surface detector array. Hybrid data is used to establsh conection between S(1000) and shower energy as measured by FD Correction for elevation angle relies on measured data only (CIC). Energy scale is free of simulations. hybrid events Here is a plot of S(1000) – corrected for zenith angle - vs. hybrid reconstructed fluorescence energy from which the energy converter can be obtained. Note that the systematic error grows when extrapolating this rule to 100 EeV! Our rapidly increasing data set and reduced systematic uncertainties will be able to dramatically improve the precision of the energy scale. Ground parameter Energy from FD 24

ENERGY SPECTRUM (< 600) Spectral index changes from 2.69 ± 0.02 ± 0.06 to 4.2 ± 0.4 ± 0.1. Comparison of spectrum to unbroken power law (TP test): 6 σ. Confirms observation of similar suppression in HiRes data. Consistent with longstanding prediction by Greisen and Zatsepin-Kuzmin (GZK) that cosmic ray flux is attenuated above ~ 6×1019 eV due to interaction with CMB Implications if GZK: cosmic rays above ~ 6×1019 eV originate within 100 Mpc. This slide shows a comparison of the Auger spectrum with that of AGASA and HiRes 1 (mono). The Auger points are about 25% below those of AGASA and slightly lower ~ 10% than HiRes. 25

SYSTEMATIC ERRORS Systematic uncertainties in the air fluorescence yield currently dominate but efforts to reduce this error are underway. This slide shows a comparison of the Auger spectrum with that of AGASA and HiRes 1 (mono). The Auger points are about 25% below those of AGASA and slightly lower ~ 10% than HiRes. 26

INCLINED EVENT This slide shows a comparison of the Auger spectrum with that of AGASA and HiRes 1 (mono). The Auger points are about 25% below those of AGASA and slightly lower ~ 10% than HiRes. 28

INCLINED SHOWERS This slide shows a comparison of the Auger spectrum with that of AGASA and HiRes 1 (mono). The Auger points are about 25% below those of AGASA and slightly lower ~ 10% than HiRes. 29

SPECTRUM - INCLINED EVENTS This slide shows a comparison of the Auger spectrum with that of AGASA and HiRes 1 (mono). The Auger points are about 25% below those of AGASA and slightly lower ~ 10% than HiRes. 30

SPECTRUM COMPARISON This slide shows a comparison of the Auger spectrum with that of AGASA and HiRes 1 (mono). The Auger points are about 25% below those of AGASA and slightly lower ~ 10% than HiRes. 31

CHEMICAL COMPOSITION

CHEMICAL COMPOSITION Speed of air shower development depends on the mass of the primary: a heavier nucleus induces earlier shower development. FDs measure the height of the shower maximum directly, but intrinsic fluctuations in the depth of shower maximum are large, so an identification of the primary on an event-by-event basis is not possible. Signal rise time in SD analysis is in progress Study mean height of shower maximum for a large data sample. Elongation rate (mean shower maximum vs. energy) indicates the dominant chemical component, but we have to compare to simulations to interpret the data (strong model dependence!). 33

CHEMICAL COMPOSITION Too early for conclusions! Signal rise time in SD analysis is in progress Proton primaries determined by patterns in sky distribution – new interactions to explain composition measurements Heavy primaries determined by patterns in sky distribution – new source models to explain heavy dominance. Too early for conclusions! 34

PHOTON FLUX

TOP – DOWN MODELS DISFAVORED ! PHOTON FLUX TOP – DOWN MODELS DISFAVORED !

ARRIVAL DIRECTIONS

ARRIVAL DIRECTIONS Here is the raw distribution of arrival directions for the data set on the sky in galactic coordinates. Note the over sampling in the southern hemisphere where the detector is located and the hole in the north The V-C catalog is likely to be incomplete near the Galactic plane also the Galactic magnetic field is stronger in the disk. Out of the 7 events out of the correlation, 5 are within 12º of the Galactic Plane. Cutting on the Galactic Plane (|b|<12º) the minimum reads : P = 2x10-10 at E=57 EeV, z=0.017 and  =3.2º, with 19 of of 21 events in correlation where 5 are expected Short article published in Science 318 (2007) 938-943. Long article published in Astroparticle physic 29 (2008) 188. 38

ARRIVAL DIRECTIONS Acceleration sites Can we say something about the sources? They are not in the Milky Way They are likely astrophysical AGN are plausible acceleration sites More data are needed to identify the sources and their characteristics Here is the raw distribution of arrival directions for the data set on the sky in galactic coordinates. Note the over sampling in the southern hemisphere where the detector is located and the hole in the north 39

CORRELATIONS WITH AGNs Here is the raw distribution of arrival directions for the data set on the sky in galactic coordinates. Note the over sampling in the southern hemisphere where the detector is located and the hole in the north 40

CORRELATIONS WITH AGNs Here is the raw distribution of arrival directions for the data set on the sky in galactic coordinates. Note the over sampling in the southern hemisphere where the detector is located and the hole in the north Signal strength for AGN correlations is not as strong as the first data suggested. Probability psignal of correlating with an AGN appears to settle on a value around 0.4 - the null hypothesis corresponds to p0 = 0.21 Results still shows good correlation with matter. Several events close to Centaurus A. 41

FUTURE Much more statistics needed. Full sky coverage. AUGER NORTH ~ 20.000 km2 Design report finished Needs more work 42

AUGER NORTH Needs more work SIZE OF SLOVENIA 43

FUTURE - EXPOSURE Needs more work 44

CONCLUSIONS Pierre Auger Observatory Physics Results Exposure is now 17,000 km2 sr yr. Current SD statistics: >106 events above 1017 eV. Detector systematics are understood and being reduced. Physics Results Energy spectrum Statistically significant change in spectral index near GZK region. Mass composition Hybrid elongation rate sugests mass mixture. Arrival direction anisotropy New data do not favor previous claims of correlations with local AGNs Still good evidence for correlations with mass distribution Needs more work 45

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