UHE Cosmic Rays and Neutrinos with the Pierre Auger Observatory

Transcription

1 UHE Cosmic Rays and Neutrinos with the Pierre Auger Observatory Gonzalo Parente Bermúdez Universidade de Santiago de Compostela & IGFAE for the Pierre Auger Collaboration Particle Physics and Cosmology PPC 2010 Torino july 2010

2 Overview The Pierre Auger Observatory Recent results from the observatory: Energy spectrum Arrival directions Mass composition Photons Neutrinos Conclusions and Future 2

3 The Pierre Auger Observatory 3

4 The Pierre Auger Southern Observatory: Malargüe, Mendoza (Argentina) 1600 water cherenkov stations 4 fluorescence stations (24 telescopes) ~ 3000 km2 35.5º S, 69.3º W 1400 m a.s.l. (880 g cm-2) 1.5 km triangular grid 4

5 5

6 Pierre Auger Southern Observatory June

7 Auger is a hybrid detector it combines two different techniques by E.Zas Fluorescence telescopes e s nc e c F re o u l t h g li Water Cherenkov stations ~ 10% of events are observed with both techniques 7

8 Hybrid event detected with 4 FD eyes & SD 20 May 2007 E ~ 1019 ev M. Mostafá 8

9 Auger observables Fluorescence Detector (FD) - Light track and arrival times recorded by the telescopes. - Longitudinal shower profile: reconstructed using of fluorescence and Cherenkov yields, lateral distributions, and corrected for atmos. attenuation. - Arrival direction, energy and composition parameters (Xmax). Surface Detector (SD) - Signal and arrival times at the array stations. - S(1000) (signal at 1 km from the core): use lateral distributions. - Arrival direction, energy (calibrated with FD) and composition sensitive parameters (rise time, curvature,...) Hybrid mode - Simultaneous SD & FD events: used to calibrate the energy of SD events, and used in arrival direction and photon fraction studies. - Coincident FD events with at least one SD station: used in composition and spectrum studies. 9

10 Energy reconstruction (fluorescence detector) * Measured fluorescence light vs depth proportional to deion/dx vs X * Shower energy ~ dx (deion/dx) (nearly calorimetric measurement) weakly dependent on hadronic model & composition (~ 5%) from missing energy (muons and neutrinos not seen by the fluorescence detector) de dx dx 10

11 Energy reconstruction (surface detector) Event Footprint on the ground θ ~ 48º & E ~ 7 x 1019 ev Lateral density distribution S(1000) East [km] Energy estimator: S(1000) = signal at 1000 m from shower core How to relate S(1000) to the energy of the UHECR? 11

12 log10 (S/VEM) Energy calibration of S(1000) with hybrids Linear correlation between EFD and S(1000) Extrapolate calibration to events observed with the Surface Detector sigma ~ 20% Minimises dependence on hadronic model and mass composition (~ 5%) Jan 04 Aug hybrid events θ < 60º log10 (EFD/eV) 12

13 Summary of Auger Results Flux: Observation of the knee at 4x10^18 ev and strong suppression above 4x10^19 ev (40 EeV) Arrival directions: Observation of anisotropy above 55 EeV associated with nearby sources < 75 Mpc, on a small angular scale (few deg.) Composition: Observation of change in the shower elongation rate at 2x10^18 ev. UHE photons: limits to the photon fraction in cosmic rays at the highest energies UHE neutrinos: bounds to diffuse fluxes. 13

14 Energy spectrum 14

15 Cosmic Ray Energy Spectrum Particle Data Group

16 Cosmic Ray Energy Spectrum at UHE (θ < 60 ) γ E γ=3.3 Different interpretations: Knee: - transition galactic-extragalactic, - e+e- dep,... γ= σ Suppression: - exhausted sources, - GZK cutoff. Auger combined spectrum: FD (hybrid) + SD Phys. Lett. B,

17 Arrival directions 17

18 Anisotropies Cen A: 12 events (out of 58) within 18 deg. (2.7 expec.) Auger Coll. ICRC 2009, Lodz Correlation with nearby AGNs (< 75 Mpc) for the highest energy events (> 55 EeV) with angular scale of a few degrees Correlate 18 events of 27 (5.7 expected) Correlate 26 events of 58 (12.2 expected) Auger, Science 318 (2007) Astropart. Phys. 29 (2008) Auger Coll. ICRC 2009 (Lodz) 18

19 ... from arrival directions studies The observed correlation is consistent with an extragalactic origin of the highest energy CRs The small angular scale correlation suggests a light composition for the cosmic ray flux... then The highest energy cosmic rays could be protons or light nuclei from nearby extragalactic sources 19

20 Mass composition 20

21 Composition dependent parameter in FD (Xmax) depth at which the shower reach the maximum number of particles Xmax 21

22 Depth of shower maximum (as a function of energy) Auger Coll. Phys. Re. Lett. 104, (2010) 106 g/cm²/decade 24 g/cm²/decade Elongation rate d X max d log E 22

23 Depth of shower maximum (comparison with MC predictions) Average Fluctuations Auger Coll. PRL 104, (2010) Compatible with mixed composition that becames heavier as increasing energy (if hadronic interactions does not change significantly) 23

24 UHE photons 24

25 Determination of the photon fraction Surface Detector Radius of curvature vs Rise time Fluorescence Detector 25

26 Photon fraction in the integral cosmic ray flux TD Possible sources of EeV photons: - GZK process - Production by nuclei in regions of intense star light (galactic center,...) - Top-down models: SHDM, TD, Zburst,... 26

27 UHE neutrinos 27

28 Deep Inelastic Scattering Neutrino Interactions 28

29 Inclined showers & Neutrino search Protons or nuclei Inclined showers induced by protons or nuclei high in the atmosphere are composed (mainly) of muons at ground. Neutrinos... induced by neutrinos low in the atmosphere exhibit a significant electromagnetic component at ground. Search for inclined showers with a significant EM component at ground 29

30 Earth-skimming ν τ ν τ production in astrophysical sources disfavoured Neutrinos interacting in the crust of the Earth however, after travelling over cosmological distances: νe : νµ : ντ ~ 1 : 1 : 1 τ s travel large distances in the Earth without losing too much energy before decaying close to the detector. Sensitivity to ν τ CC channel Small solid angle (few deg.) Dense mass target (Earth crust) Signature: almost horizontal shower with a significant EM content 30

31 Looking for broad signals: Area Over Peak (AOP) FADC trace Signal AOP = Area/Peak Peak value Area Time (ns) Slow & broad signal Large AOP ( > 3) Fast & narrow signal Small AOP (~ 1)

32 Upper limit to the diffuse UHE ν flux p + γ CMB π ν up-going 1Jan04-28 Feb09 (~ 2 yr full Auger) down-going 1 Nov07-28 Feb09 (~0.8 yr full Auger) Auger Coll., PRL 2008, PRD 2009 (up-going), ICRC 2009 Lodz (down-going) 32

33 Conclusions and Future Summary of Auger results: The ankle and high energy suppression of the spectrum Anisotropy at the highest energies Mixed composition becoming heavier with energy Limits to the photon fraction above 2 EeV. Bounds to diffuse neutrino fluxes. - Future: Increase statistics, hadronic interactions studies,... Enhancement to lower energy (SD) + muon counters (AMIGA) Increase fluorescence detector aperture (HEAT) Radio detection of Extensive Air Showers (AERA) - R&D Auger North (Colorado, USA): enhancement to higher energy and full sky coverage. 33

34 THE END 34