Ultra- high energy cosmic rays

Transcription

1 Ultra- high energy cosmic rays Tiina Suomijärvi Institut de Physique Nucléaire Université Paris Sud, Orsay, IN2P3/CNRS, France Atélier CTA, IAP, Paris, June 2014

2 Outline Pierre Auger Observatory: measurement technique Recent results Ques:ons for future Conclusions

3 The Pierre Auger Observatory Pampa area at 1400m altitude in Argentina Water-Cherenkov Detectors (SD) 1600 in a 1.5 km standard grid 61 in 0.75 km infill grid (~30 km 2 ) Fluorescence Telescopes (FD) 24 in 4 buildings overlooking SD 3 in 1 building overlooking the Infill Muon detectors: AMIGA engineering array phase - 61 aside the Infill stations AERA radio antennas (MHz) 124 in the Infill region (~6 km 2 ) R&D GHz antennas AMBER - MIDAS (2 imaging radio telescopes) EASIER (61 radio sensors)

4 Measurement technique

5 Measurement technique

6 Exposure km 2 sr yr Exposure at the ICRC 2013

7 Energy spectrum Sharp angle at around 7 EeV Suppression above 50 EeV Nature of suppression: propagation (GZK) or acceleration power? Nature of angle: transition galactic/ extra galactic? The Pierre Auger Collaboration, Physics Letters B 685 (2010)

8 Combined energy spectrum 761 events above ev 4 above ev Energy systematic uncertainty FD energy scale 14% absolute calibration 9% fluorescence yield 4% shower reconstruction 6% atmospheric corrections 3-6% invisible energy 6%

9 Composi:on: Xmax and RMS(Xmax) Trend to heavier composition Pointing to sources become difficult (magnetic fields) Are hardonic interaction models correct? The Pierre Auger Collaboration, Physical Review Letters, 104, (2010)

10 Number of muons Horizontal showers: EM component completely attenuated, only muons arrive to ground. Simulations don t reproduce the muon number. ICRC 2013 The total number of muons reaching ground relative to that contained in the reference distribution

11 Large scale anisotropy The phase at lower energies is compatible with the right ascension of the Galactic Center α GC = The anisotropy is found to be very small (% level). Hint for a smooth transition in phase from 270 O below 1 GeV (Galactic origin?) to 90 O above 4 EeV (random phase expected from isotropy).

12 Large scale anisotropy A/S: Gal CRs at EeV, anis due to their escape by diffusion/drift. A/S = antisymm./symm. halo field Gal: Gal CRs are galactic at all energies, anisotropy caused by diffusion due to the turbulent component of the GMF C-G Xgal: Compton-Getting effect for extragal. CRs (motion of our Galaxy wrt the frame of extragal. isotropy,cmb) Upper limits on equatorial dipole: exclusion of models with antisymmetric halo magnetic field >0.25 EeV exclusion of Galactic model at few EeV

13 Point source searches Correlation study of ultra-high energy events with the directions of nearby AGNs of the Véron-Cetty Véron (VCV) catalog: 106 events with energies above ev, out of which 33 (31 %) arrived from a direction of less than 3.1 from a nearby AGN. The Pierre Auger Collaboration, Astroparticle Physics 34 (2010) Excess of events from a region close to Centaurus A 19 events in a 24 o circular window vs 7.6 expected

14 Diffuse photon limit The Pierre Auger Collaboration, Astroparticle Physics 31 (2009) Top-down models highly constrained GZK photons within reach

15 Diffuse neutrino limit The Pierre Auger Collaboration, Advances in High Energy Physics, 2013 (2013) The Pierre Auger Collaboration, Astrophysical Journal Letters, 755 (2012) L4 Integral and differential limits to diffuse fluxes Data from 1 Jan 04 to 31 Dec 12 excluding training samples ICRC 2013

16 Auger results The ankle is clearly seen at ev The cut-off is established (>20σ), E 1/2 = ev The composition gets heavier for increasing energy No primary photons: exclusion of top-down models No photons/neutrons form Galactic sources Neutrino constraints on astrophysical models No large scale anisotropy above 1-2% Exclusion of antisymmetric models of Galactic MF Exclusion of Galactic models above few EeV Hints for Gal-XGal transition from dipole phase Point source anisotropy above 55 EeV (3σ level) Smooth growth of the pp cross section (measured at 57 TeV) Muons put constraints to the hadronic interaction models

17 Astrophysical scenarios Photo-disintegration: Sources accelerate nuclei to a maximum energy Light elements are fragments of heavier nuclei Cut-off: energy loss processes of nuclei (photo-disintegration) Light elements appear at E shifted by m daughter /m parent N-Si nuclei in the sources, no protons Maximum energy: Sources accelerate nuclei to a maximum energy Z Composition in the source similar to the Galactic one Cut-off: Emax reached in the source Composition getting heavier for increasing energy Protons at the ankle are extragalactic, no GZK γ or ν Proton dominance: The all particle flux consists of extragalactic protons The source has a cut-off energy Cut-off: energy loss processes for protons (pion-photoproduction) Ankle due to pair production of protons on CMB New physics to explain heavier composition at UHE

18 Science case The origin of the cut-off: GZK or Emax? The proton component at UHE: what is its fraction? The hadronic interactions: particle physics beyond accelerators? Operate Auger until 2023 with improved detector composition sensitivity : MUONS Discrimination of muons vs EM component in SD will give composition info in the cut-off region increase our knowledge in the ankle region help in disentangling composition and hadronic interactions systematics

19 Conclusions Origin of cosmic rays is still an open question! The Auger observatory has yielded important results but also opened new questions. The Auger upgrade aims to identify primary particles at the highest energies. The gamma observatories have identified and studied a large number of sources. New gamma observatories are coming on-line: CTA, HAWC and LHAASO. The combination of observations of charged particles, gammas and also neutrinos will help to solve the question of the origin of cosmic rays.