Recent results from the Pierre Auger Observatory Pham

Recent results from the Pierre Auger Observatory Pham Ngoc Diep for the Pierre Auger Observatory Vinh 10/2011

Cosmic rays ü charged particles, extremely high energies ~1020 e. V=16 Joules! ü power law spectrum ~ E-2. 7 Galactic: DSA in young SNR shells Ultra High Energy Cosmic Ray (UHECR, E>1018 e. V): - Extragalactic (GZK horizon ~75 Mpc) - protons or iron (other nuclei break up) - Photoproduction threshold on CMB: GZK cut-off Main topics: - Accurate measurement of the high end of the energy spectrum; - Nature of the primaries; - Identification of possible sources; - Acceleration mechanism; x = 2. 7 x = 3. 0 x = 2. 7 2

UHECRs observed from the extensive air showers (EAS) Methods: sampling the particle density on ground (surface detector); and detecting the fluorescence light (fluorescence detector). In both cases: timing gives the direction and intensity gives the energy. 3

Pierre Auger Observatory (PAO) The PAO is the first large hybrid detector ever built: it combines the strengths of Surface Detector Array & Air Fluorescence Detectors Located in Mendoza, Argentina PAO collaboration: 19 countries VATLY/Vietnam is an associate member 1660 surface detectors covering ~3000 km 2 4 fluorescence stations 4

SURFACE DETECTOR (SD) Solar panel and electronic box GPS antenna Comm antenna Three 9” PM Tubes White light diffusing liner De-ionized water Battery box Plastic tank Giant detector arrays of the PAO are made of water Cherenkov counters. They are located on a triangular grid having a 1. 5 km mesh size (10 m 2 area each, duty cycle of 100%). One > 1020 e. V shower involves 15 to 20 detectors. Typical angular and energy 5 resolutions are 1° and 20%.

ENERGY MEASUREMENT IN THE SURFACE DETECTOR relies on the dependence of the measured signals on the distance to the shower axis (so-called Lateral Distribution Function, LDF). S [VEM] Surface array view S(1000) D [m] 6

Fluorescence Detector (FD) 11 m 2 mirror UV-Filter 300 -400 nm camera 440 PMTs Four stations of six eyes each, each eye covering a field of view of 30°× 28° with a mirror focusing on an array of 22× 20 pixels (photomultiplier tubes), each having 1. 5° aperture. They measure the induced fluorescence 7 of nitrogen molecules (near UV). Duty cycle is about 13%.

FD SHOWER GEOMETRY RECONSTRUCTION The pixel pattern defines the shower detector plane, the time distribution along the track locates the shower within 8 this plane.

ENERGY MEASUREMENT BY THE FD Light collected at the pixels → converted to energy deposit The calorimetric energy → fitting a Gaisser–Hillas function to the reconstructed energy deposit profile and integrating it. Xmax → calculated Total energy, E, obtained by correcting for the ‘‘invisible energy’’ (neutrinos and high energy muons). Fluorescence yield 14. 0% Reconstruction 10. 0% Missing energy 8. 0% Absolute calibration 9. 5% Wavelength dependence 3. 0% Total uncertainty 22. 0% 9

ENERGY CALIBRATION FOR THE ARRAY Calibration is obtained from subset of high quality hybrid events (detected by both FD and SD): shower geometry from FD, 2 < 2. 5 for the longitudinal profile fit, depth of maximum in the field of view. a=1. 49± 0. 06(stat) ± 0. 12(syst) b=1. 08± 0. 01(stat) ± 0. 04(syst) S 38: An energy estimator for each event (independent of ), the S(1000) that EAS would have produced had they arrived at the median zenith angle of 38 o. 10

The Auger energy spectrum Spectrum obtained from hybrid and surface detector is combined Highest statistics available Ninc: the number of cosmic rays with energy E incident on a surface element d. A, within a solid angle dΩ and time dt. Nsel(E): the number of detected events passing the quality cuts in the energy bin centered around E and having width E. (E): the energy-dependent exposure 20905 km 2 sr yr. A clear suppression is observed at E > 4 1019 e. V. The hypothesis of a single power law is rejected with a significance greater than 6 sd. The data are consistent with GZK cut-off. 11

Measurement of the Depth of Maximum of EAS, Xmax Data: hybrid events, E> 1018 e. V, rejecting time periods with cloud coverage and events with a light emission angle towards the FD <20 o. The energy and shower maximum can be reliably measured only if Xmax is in the field of view of the telescopes (covering from 1. 5 to 30 o in elevation), require good Xmax uncertainty. After all cuts: 3754 events are selected for the Xmax analysis. Simulation proton iron 12

Measurement of the Depth of Maximum of EAS, Xmax increasing average mass of the primary particles Interpretation in terms of a simple mixture not straight forward 13

14

ANISOTROPY Situation as at November 2007: Science and Astroparticle Physics Compare the direction in the sky where UHECRs having E> 56 Ee. V come from with a VCV catalogue of nearby (<75 Mpc) galaxies within 3. 1°; 18 events among 27 correlate with the selected AGN: 67%. Cen A 27 events 15

Current status June 2011: 84 events having E > 55 Ee. V 5° of smoothing Comparison with Swift-BAT AGN density map Correlation with VCV sources has fallen from (69 ± 12%) to (33 ± 5%) 16

Update on Centaurus A Largest departure now at 24 o : 19 observed/ 7. 6 expected 17

18

Summary Selected results obtained by the PAO have been presented: Energy spectrum is measured with highest statistics ever, confirming the suppression of the energy spectrum, consistent with the GZK cut-off. Intriguing trend in Xmax distributions for energies up to 30 Ee. V Arrival directions correlate with matter in the nearby universe above 55 Ee. V, there is an excess of arrival directions towards the celestial position of Cen A. p-Air cross section at cm energy of s=57 Te. V much beyond LHC energy And many more … Thank you for your attention! 19

Back up … 20

Exposure calculation dΩ = sinθ dθ dφ and Ω : differential and total solid angles θ and φ : zenith and azimuth angles d. S = dx×dy : the horizontal surface element The final selection efficiency ε includes the efficiencies of the various steps of: - the analysis: the trigger, reconstruction and selection efficiencies. - the evolution of the detector during the time period T. ε calculated taking into account for: the growth of the array, hardware failures. The data taking of the fluorescence detector is influenced by weather effects such as storms or rainfall. The sensitive area has been calculated from the total area of the hexagons active every second. 21

ANISOTROPY A key element of the anisotropy study is the probability P for a set of N events from an isotropic flux to contain k or more events at a maximum angular distance from any member of a collection of candidate point sources. P is given by the cumulative binomial distribution P= where the parameter p is the fraction of the sky (weighted by the exposure) defined by the regions at angular separation less than from the selected sources. Exploration and confirmation Using data: 1 January 2004 and 26 May 2006 Scan for the minimum of P in the three-dimensional parameter space defined by maximum angular separations , maximumred shifts zmax, and energy thresholds Eth. The lower limit for the scan in corresponds to the angular resolution of the surface array. A minimum of P for the parameters: = 3. 1°, zmax = 0. 018 (Dmax ≤ 75 Mpc), Eth = 56 Ee. V. 22

23

Back up Rms(Xmax) vs E (going from pure Proton to pure Iron) 24