Cosmic Rays at Extreme Energies The Pierre Auger Observatory

Transcript

1 Cosmic Rays at Extreme Energies The Pierre Auger Observatory Ezio Menichetti Dip. di Fisica Sperimentale, Universita di Torino INFN, Sez. di Torino Lecture 1

2 Outline Lecture 1 The High End of the Cosmic Ray Spectrum Lecture 2 Extended Air Showers Detection Lecture 3 The Observatory and its First Results

3 The Cosmic Ray Spectrum

4 Outstanding Issues Acceleration Mechanism GZK Composition Point Sources

5 The Magnetic Mirror Energy exchange Drift Revolution Inhomogeneous B field Spiral trajectories around field lines High gradient regions acting like walls

6 Fermi Mechanism - 2nd Order Scattering by B-field Stochastic process: E β 2 E Expect: Slow, inefficient E= γe( 1 β cosθ) E 4 ' β E2= γe2( 1+ β cosθ2) E θ1, θ 3 2 '

7 Fermi Mechanism - 1st Order As before, scattering by B -field irregularities Momentum gain: Speed=U 1 > Speed=U 2 E 4 R 1 E 3 R β angles δ p p=+ 2 U c head-on acceleration Expect: fast, efficient 1 δ p p= 2 U c tail-on deceleration 2 ( ) δ p p= 2 U U c >0 net gain 1 2 Shock compression ratio

8 A General Argument - I Just a couple of units: 1 pc = 3.2 light yr 1 EeV = ev = 0.16 J To get accelerated: No early escape from the source R Larmor 1 E ZB Source size > = kpc Z 1EeV µ G To get accelerated: Synchrotron loss < energy gain 2 de dt B de dt B (Greisen,1965)

9 A General Argument - II W = B 2 B 4 4π 3 πr γ 3 5 particle Ex ev W B >10 57 erg Such humongous source should be a strong radio emitter (like erg s -1 ) Easy to detect!

10 Simple estimate of max. energy (Hillas): Maximum Energy Emax = ZeβBL β: Plasma speed B: Mag field L: Source size

11 Spectral Index, Time Constant Power law spectrum N( E) E x Fermi 2nd order: x= 1+ τ τ 1 acc esc t acc >10 8 yr! KO Fermi 1st order: R+ 2 x= 2 R 1 t acc ~1 month! OK

12 Compact sources Just meaning: Non electromagnetic acceleration Various mechanisms proposed: Black hole accretion disks Gamma ray bursts Topological defects (monopoles, cosmic strings,..) UHE ν s from decays of high mass particles

13 Cosmic Microwave Background Penzias, Wilson & the Antenna The CMB spectrum (by FIRAS)

14 CMB Photons Peak energy k B T= 0.6 mev Density 400 cm -3 Possible CR interactions: A,A,A A

15 G(reisen),Z(atepsin),K(uz min) + p+ γ( 2.7K) n+ π γ π ( 2.7 ) 0 p+ K p+ 19 E thresh 6 10 ev En.loss 20% /int ( 2.7 ) p+ γ K p+ e + e + 18 E thresh 1 10 ev En.loss 0.1% /int (G, Z&K ) The moral: CR s above threshold bound to lose energy

16 The GZK Cutoff So UHECR s just can t propagate beyond, say, 50 Mpc! Then we should find a suitable source just round the corner. But where?

17 The High End of the CR spectrum ~ x 2 effect ~ 2-3 σ issue..

18 Composition Issues Spectrum Depth of Shower Maximum in Air vs. E Galactic? Extra-Galactic?

19 More on Composition Proton/Iron Discrimination tied to Intra/Extra-Galactic origin

20 Opening a New Window? Effect of Extra-Galactic Magnetic Field on CR trajectories Simulation E = ev E = ev Clearly, around ev a new astronomy is feasible if Cosmic Rays of that energy are actually observed

21 No High E Little deflection from extragalactic mag field B not well known 10-9 G Constant field region: B, size l, var[defl]=σ 2 Assuming random walk through N regions θ ( E) Negligible deflection 1 2 d mrad λ λbe λ :, :, :10 20 Mpc B ng E ev

22 The Known Matter (< 21 Mpc)

23 Anisotropies, Point Sources? AGASA HIRES > 6 Clusters observed Controversial results Issues at stake: Detection Technique Angular Resolution Statistics! No cluster

24 Cosmic Rays Detection Airborne conventional detectors: E<10 14 ev Not suitable to deal with small fluxes E> ev : E(xtensive) A(ir) S(showers) Different techniques: Ground arrays (scintillators, water Cherenkov) Air Cherenkov telescopes Fluorescence detectors

25 EAS - I 10 km

26 EAS - II Data & MCarlo Inelastic σ(p,air) Tevatron LHC

27 Next slides from R.Engel s simulations See for example: R.Engel EAS EAS development Lectures given at ISAPP 2005 Summer School

28 EAS-I

29 EAS-II

30 EAS-III

31 EAS-IV

32 EAS-V

33 EAS - Profiles Longitudinal Lateral

34 EAS - Electron Lateral Distribution

35 EAS - Muons vs Electrons

36 EAS The Movie