Ultra-High-Energy Cosmic Rays Ultra-High-Energy Cosmic Rays

Ultra-High-Energy Cosmic Rays Ultra-High-Energy Cosmic Rays

Etienne Parizot

APC & Université Paris 7 (France)

results and perspective

from the Pierre Auger Observatory

Cosmic rays: “CRs”

Cosmic rays: “CRs”



Key subject in astrophysics!



Still very poorly understood

 CRs regulate star formation

 One of the main components of the Galaxy (> 1 eV/cm

)

 CRs control the ionization of the interstellar medium

+ heating + turbulent magnetic field + astro-chemistry!

+ Herschel and price of wheat in England!



Role in Earth climate and species evolution

+ legitimate hopes for significant progress soon

Why?

100 years  40 000 years

photon astronomy CR physics

Year ZERO of CR

astronomy?

Photon astronomy

started millenaries ago

with this instrument:

Cosmic ray physics

started one century ago

with this instrument:

“Spontaneous” discharge!



1901: Wilson notices that discharge is identical on the ground and underground (~7 div/hour)



1910: Theodore Wulf (Jesuit and amateur physicist who builds the best electrometers) works on the top of the Eiffel tower



Rutherford shows that

natural radioactivity (ground and contaminated apparatus) is responsible

6 ions/cm

3.5 ions/cm

(instead of

0.4 ions/cm

expected)

Viktor Hess: 7 August 1912

12h15 : landing close to de Pieskow (Brandenburg)

10h45 : maximum

altitude (5350 m)

0 km 2 km 4 km 6 km 8 km 10 km

0 20 40 60 80

Synthèse des mesures de Hess et de Kolhörster

(1912 - 1914)

Increase of the radiation

Increase of the radiation

2 km 4 km 6 km 8 km 10 km

Synthèse des mesures de Hess et de Kolhörster

(1912 - 1914)

Increase of the radiation Increase of the radiation

« The result of these observations seems to be explained in the easiest way by assuming that an extremely penetrating radiation

enters the atmosphere from above » (V. Hess)

« The result of these observations seems to be explained in the easiest way by assuming that an extremely penetrating radiation

enters the atmosphere from above » (V. Hess)

Then a long story begins…



17 years to recognize that CRs are charged!



1932: Anderson

discovers the positron (predicted in 1930 by Dirac) in a CR track



1936: Neddermeyer and Anderson discover the muon



1947: Powel discovers the pion (predicted in 1936 by Yukawa)

+ strange particles, etc.

Particle production

1 energetic particle 1 energetic particle

many much less energetic particles!

many much less

energetic particles!

CR-induced atmospheric showers

Pierre Auger

discovers atmospheric showers in 1938

CRs with E > 10 eV !!!

astrophysics astrophysics

At the crossroads…

Study of cosmic rays

Study of cosmic rays

1953

CRs are (also)

interesting for themselves!



What are the primaries?



Where do they come from?



How do they get their energy?



What do they reveal about our universe?



Can they be used as tools for astrophysics?



May they be valuable “messengers” from

distant sources?

Fundamental observables

Angular spectrum

Mass spectrum

Energy spectrum

arrival directions composition differential flux

1 2 3

Fundamental observables

Angular spectrum

Mass spectrum

Energy spectrum

arrival directions composition differential flux

1 2 3

Angular distribution

 Isotropic!

( no information about sources)

Interaction with B inhomogeneities



Magnetic inhomogeneities ≈ perturbed field lines

r

~  r

^>>  r

^<< 

Scattering of EPs in

irregular B fields

depends on gyroradius and thus rigidity, and on the energy present at

Scattering of EPs in

irregular B fields

depends on

gyroradius

and thus

rigidity, and

on the energy

present at

Propagation is not rectilinear!



Galactic magnetic field : ~ a few G (10

T)

10

eV 1 pc

10

eV 1 kpc

10

eV

1 Mpc B = 1 G

B

B

Supernova remnant Galactic disk + halo >> galaxy



Gyro-radius (protons):

Propagation is not rectilinear!



Galactic magnetic field : ~ a few G (10

T)

1 pc 1 kpc 1 Gpc

B = 1 G

B

B



Gyro-radius (protons):

in a 1 nanoGauss field!

Fundamental observables

Angular spectrum

Mass spectrum

Energy spectrum

arrival directions composition differential flux

1 2 3

Cosmic-ray composition

10% of He

89% of H 99% of nuclei

1% of electrons

(not neutral!)

CR vs solar system

Composition compatible with a solar-like source, with secondary nuclei…

solar system

Z (charge number)

GCR

re la tiv e a bo n da nc e

CR-induced spallation



Direct spallation:

light projectile  heavy target



Inverse spallation:

heavy projectile  light target

LiBeB nucleo- synthesis

CR

Fruitful composition studies



Secondary/primary ratios  CRs have gone through a grammage of X

= 6–10 g/cm

on average, from their sources to the Earth



Cosmic-ray clocks (radioactive secondaries)

 CRs have spent t

~ 2 10

years on their way



Thus, they propagated in a medium of average density n = X

/ct

~ 0.2 part. cm



Thus, they must have spent most of their time in

the halo!

Galactic cosmic-ray confinement



Magnetic confinement of cosmic rays in a much larger volume than the standard interstellar gas

halo disk

bulge sources?

Fundamental observables

Angular spectrum

Mass spectrum

Energy spectrum

arrival directions composition differential flux

1 2 3

The first wonder of the physical world

The first wonder of the physical world

The first wonder of the physical world

1 part/m

/year

1 /km

/century ! 1 part/m

/s

ankle

knee

non thermal

Limit for satellites

4 CR/cm

/s  1 kg/year

[CR flux] x E ³

[CR flux] x E ³

GZK

ankle

Second knee?

knee

Particle cascades and showers

One

very energetic particle

Many

less energetic particles

 same thing in the Earth atmosphere!

Detector arrays...

John Linsley chasing the

serpents!

Volcano ranch (New-Mexico)

Volcano ranch (New-Mexico)

John Linsley chasing the

serpents!

196

A cosmic ray with an energy 2

larger than 10

eV !!! !!! !!! !!! !!!

The fluorescence technique



Cosmic rays ionize the air (that’s how they were discover!)

 fluorescence light



UV light detectable on dark moonless nights



10

eV shower

 over 100 billion particles!

The Fly’s Eye (Utah)

The Fly’s Eye (Utah)

15

of October, 1991 An event at 3.210

eV

Do even higher-energy CRs exist ?

QuickTime™ and a GIF decompressor are needed to see this picture.

High Resolution Fly’s Eye

12.5km

AGASA

Akeno Giant Air Shower Array

111 Electron Det.

27 Muon Det.

0 4 km

100 km

The Pierre Auger Observatory

Northern site



Participating Countries



Argentina



Australia



Brazil



Czech Republic



France (+ Vietnam)



Germany



Italy



Mexico (+ Bolivia)



Netherlands



Poland



Slovenia

50 Institutions,

400 Scientists

10 000 km

38° South, Argentina, Mendoza, Malargue 1.4 km altitude, 850

g/cm ²

Australia Bolivia

Brasil Czech Republic

France Germany

Italy Poland Mexico Slovenia

Spain United Kingdom

USA Vietnam

The Pierre Auger Observatory

Completion: end of 2007

¡ Bienvenida en la tierra cósmica !

1600 "surface detectors"

(Cherenkov water tank)

One Auger station

PMT

Plastic tank 12 m³ of clean water

Solar pannel Comms antenna

GPS antenna

battery

Diffusive white “liner”

Hexagonal array (1.5 km spacing, 3000 km )

SD deployment

9th July 2007

1438 deployed 1400 filled

1364 taking data

AIM: 1600 tanks

Aerial view of Los Leones fluorescence station

4 times 6 telescopes overlooking the site

Fluorescence detector (FD)

Drum for uniform illumination of each fluorescence camera – part of end to end calibration .

Lidar at each Fluorescence building

E = 5.3 10

eV

E = 4.8 10

eV E = 4.9 10

eV

Independent analyses of

stereo events

1st 4-fold hybrid event!

Time, t

Χ°

R

km

Example Event

A moderate angle event - 762238 Zenith angle ~ 48º, Energy ~ 70 EeV

Lateral density

distribution

Anywhere (18 July 2007) — UHECRs and Auger results (Virtual Institute seminar) — E. Parizot (APC / Univ. Paris 7)

No.4

Theta = 59.9 [degree]

E = 86 [EeV]



SD energy estimator: interpolated signal in a tank at 1000 meters and 38°

Energy reconstruction

Cross-calibration of detectors

FD energy SD energy

estimator

Cross-calibration of detectors

Fractional dispersion of FD/SD energy estimates

Very good

estimator !

“Inter-zenithal calibration”

FD energy SD energy

estimator

S

: signal 1000 m away from the shower axis

 depends on energy AND zenith angle

 constant intensity method relate S

() to the value

“Attenuation curve”

Integral flux above a given value of S

 zenith angle

equal flux  equal energy

Attenuation curve: at a given energy,

lower signal at larger zenith angle

Energy reconstruction

1 Determination of the signal 1000 m away from shower axis

2 Convertion into the signal that would have been measured at a 38° zenith angle

3 Convertion into an FD-equivalent energy

(improvements expected soon…)

Uncertainty on the energy scale

source systematic uncertainty

Fluorescence yield

P, T and humidity effects Calibration

Atmosphere Reconstruction Invisible energy

14%

7%

9.5%

4%

10%

4%

Total: 22%

Energy spectrum

Differential flux

1

Cosmic-ray primary observables

Mass spectrum

Angular spectrum

Composition Arrival direction

2 3

The GZK effect



Greisen (1966) + Zatsepin & Kuz’min (1966)



Energy losses through e

/e

pair and pions production!



Threshold : E

 2 m

c

in the proton rest frame

 p

e

e

Proton rest frame

p  p

“Cosmic frame”

E

> 1 MeV



Threshold : E

 m

c

in the proton rest frame E

> 160 MeV

10^-5 0,0001

0,001 0,01 0,1 1

σκ (barn)

roduction de ions

roduction de aires e⁺/e^-

[cross section] x [inelasticity]

Attenuation length

e

e



Interaction length

Attenuation length

100 1000 10⁴

λ

(Mc)

roton attenuation enth (in CMB)

Attenuation length – horizons

1000 Mpc

100 Mpc

Evolution of the CR energy

10^-11

Flux E×

a

z = 0.01, i.e. D ∼ 60 Mc

"Propagated" spectrum

accumulation

Source spectrum:

E

up to infinity...

GZK cutoff

10^-12 10^-11

10¹⁷ 10¹⁸ 10¹⁹ 10²⁰ 10²¹

Flux E×

a

Enerie (en eV)

z = 0.01 z = 0.1

D 60 Mc≈ D 530 Mc≈

accumulation

pions prod.

pair prod.

accumulation

GZK cutoff

0,1 1 10

Φ (E) × E

2.3

(eV

2



-2

s

-1

sr

-1

)

Sectre roaé

(source uniue au redshift z _s)

z_s = 0.01 z_s = 0.1

z_s = 0.3

z_s = 0.5 z_s=0.65

z_s = 1

10²³ 10²⁴ 10²⁵ 10²⁶

10¹⁷ 10¹⁸ 10¹⁹ 10²⁰ 10²¹

AGASA

Stereo Fly's Eye Akeno 1 km2

distribution uniforme de sources de z=0.001 à z=1

(spectre source en E^-2.5)

Φ (E) ×

E (eV

2



-2

s

-1

sr

-1

)

Uniform source distribution

GZK cutoff

calib. uncert. 10%

FD syst. unc. 22%

5165 km

sr yr ~ 0.8 full Auger year

Slope = -2.62 ± 0.03

calib. uncert. 10%

FD syst. unc. 22%

5165 km

sr yr ~ 0.8 full Auger year

5165 km

sr yr ~ 0.8 full Auger year

Exp. Obs.

>10

eV 132 ± 9 51

> 10

eV 30 ± 2.5 2

calib. uncert. 10%

FD syst. unc. 22%

Slope = -2.62 ± 0.03

significance = 6s

60° ≤  ≤ 80°

inclined events:

29% of the nominal data set

1510 km

sr yr

(> AGASA)

Spectrum facts Spectrum facts

There is an ankle

How to interpret it?

Galactic/Extragalactic transition?

Spectral feature from pair-production energy losses of pure-proton UHECRs?

or

There is a “cut-off”

How to interpret it?

GZK suppression?

Limit of the acceleration process?

or

Energy spectrum

Differential flux

1

Cosmic-ray primary observables

Mass spectrum

Angular spectrum

Composition Arrival direction

2 3

Photo-disintegration of nuclei

2D nuclear scheme

New cross sections

10

10

10

10

10

Φ (E) x E

3

(arb. units) B = 1 nG D = 10 Mc

source in E

secondaries Δθ = 2.5°

4

He

primaries

protons protons

all particles

CNO

12 ≤ Z < 20

20 ≤ Z ≤ 26

E

= 3 10

eV

Individual sources

10

10

UHECR flux (arb. units)

protons only

E

(p) = 3 10

eV

E

(p) = 3 10

eV N(≥10

eV) = 866

Examples of "propagated" spectra

0,1 1 10

17 17,5 18 18,5 19 19,5 20 20,5

Φ(E) ×

3E (10

24 eV

2m

-2s

-1sr

-1)

log10 E (eV) mixed composition

(uniform source distribution) Q(E) ~ E ^{- 2.3}

HiRes 1 (mono) HiRes 2 (mono)

inferred Galactic component

Mixed composition (Allard et al.)

Source spectrum in E ^-2.3

Ankle = gal./extragal. transition

0,1 1 10

17 17,5 18 18,5 19 19,5 20 20,5

Φ(E) ×

3E (10

24 eV

2m

-2s

-1sr

-1)

log10 E (eV) protons only

(uniform source distribution) Q(E) ~ E ^{- 2.6}

HiRes 1 (mono) HiRes 2 (mono)

inferred Galactic components with cut

with low E cut

Pure protons (cf. Berezinsky et al.)

Source spectrum in E ^-2.6

Ankle = "pair production dip"

Are there nuclei among EGCRs?

Composition studies with a FD

Composition studies with a FD

Composition observable: shower maximum Composition observable: shower maximum

+ fluctuations in X smaller for heavier nuclei

Expectations from different hadronic models

Mixed composition (Allard et al.)

650 700 750 800

17,5 18 18,5 19 19,5

Fly's eye Yakutsk

log E (eV)

QGSJet-01

SIBYLL model A

QGSJet-II

< X

max

> (g/cm

2)

Pure protons (cf. Berezinsky et al.)

650 700 750 800

17,5 18 18,5 19 19,5

HiRes Fly's eye Yakutsk QGSJet-01

SIBYLL QGSJet-II

log E (eV) model B

< X

max

> (g/cm

2)

Composition observables

(Galactic/Extragalactic transition)

Shower maximum

measured over 2 decades in E

+ fluctuations in X to be exploited

111 69 25 12 426

326

Comparison with previous studies

Comparison with previous studies

Photon limit



Photon-induced showers look very different

Showers at E = 10

eV, θ = 0º :



Top-down models predict abundant fluxes of UHE photons

SHDM models: decay of super- heavy dark matter accumulated in Galactic halo

TD models: supermassive particle

decay from topological defect

interaction or annihilation

Photon limit



Larger X : photon showers delayed by > 200 g/cm

at 10

eV

LPM effect

Constraints on super-heavy dark matter

models for the source of UHECRs

Super heavy dark matter (SHDM)

models are excluded as UHECR sources!

Auger results (photon limit)

Auger results (photon limit)

Constraints on topological defects models

for the source of UHECRs

Auger results (photon limit) Auger results (photon limit)

Topological defects

(TD) are still possible

UHECR sources

Auger results

Auger results be constrained by

Auger neutrino limits

Fundamental observables

Energy spectrum

Differential flux

1

Mass spectrum

Angular spectrum

Composition Arrival direction

2 3



There is a strong suppression of the UHECR flux in the last observed decade of energy



But what does it mean? GZK or acceleration cut-off?



Can we see “GZK in action”, i.e. a cut-off at lower energy for more distant sources?



Probably soon, once we see individual sources or a

correlation of the highest energy CRs with nearby

matter (i.e. with an upper limit on redshift)!

Interaction with B inhomogeneities



At ultra-high energy, the gyroradius of the particles is larger than the correlation length of the magnetic field

r

>>  r

<< 

Scattering of EPs in

irregular B fields

depends on gyroradius and thus rigidity, and on the energy present at

Scattering of EPs in

irregular B fields

depends on gyroradius and thus rigidity, and on the energy present at

Small random deflections over a correlation length…



E = 10

eV

B = 10 nG L

= 1 Mpc

Diffusive regime



E = 10

eV

B = 10 nG

L

= 1 Mpc



E = 10

eV

B = 10 nG

L

= 1 Mpc



E = 10

eV

B = 10 nG L

= 1 Mpc

“Ballistic” regime

Angular effects of the magnetic field



deflection



angular diffusion



isotropization



diffusion in space

1 10⁴ 2 10⁴ 3 10⁴ 4 10⁴

nb of particles per solid angle

3 Myr

10 Myr

32 Myr E = 10¹⁹ eV

B = 10 nG Lc = 1 Mpc

Deflection of protons

Angular diffusion regime

High-pass filter effect



High energies are less spread out



Nearby sources are less spread out



Different spectra are to be expected

0 1 10⁴ 2 10⁴ 3 10⁴ 4 10⁴

-180 -135 -90 -45 0 45 90 135 180

nb of particles per solid angle

Δθ

3 Myr

10 Myr

32 Myr E = 10¹⁹ eV

B = 10 nG Lc = 1 Mpc

Deflection of protons

0 2 10⁵ 4 10⁵ 6 10⁵

-30 -20 -10 0 10 20 30

nb of particles per solid angle

Δθ

3.2 Mc

100 Mc E = 10²⁰ eV

B = 10 nG Lc = 1 Mpc

Deflection of protons

10 Mpc

32 Mpc

10

eV

10

eV

10⁹ 10¹⁰

Φ(E) x E

3 (arb. units) B = 10 nG D = 10 Mc

a artice sectru

source in E^-2.3

2.5°

5°

10°

10⁹ 10¹⁰

Φ(E) x E

3 (arb. units) B = 1 nG D = 10 Mc

a artice sectru

source in E^-2.3

2.5°

5°

10°

a sky

Individual sources

moderate field strong field

10⁷ 10⁸ 10⁹ 10¹⁰ 10¹¹

10²⁰ 10²¹

Φ(E) x E

3 (arb. units)

E (eV) B = 1 nG

Δθ = 2.5°

a artice sectru

32 Mc

source in E^-2.3

10 Mc

100 Mc

Spectrum of particles within 2.5° of a cluster Individual sources

10⁹ 10¹⁰ 10¹¹

10²⁰ 10²¹

Φ(E) x E

3 (arb. units)

E (eV) D = 10 Mc

Δθ = 2.5°

a artice sectru

1 nG

10 nG

source in E^-2.3

E^-1.6

E^-0.3

Measure of the magnetic field?

Influence of source distance

Auger anisotropy results Auger anisotropy results



Angular resolution of ~1°: good enough!



No large-scale signal (dipole) at any energy above 1 EeV



No significant emission from Galactic center



No signal from BL-Lacs as possibly seen by HiRes

e.g. a < 0.7% for 1 EeV ≤ E ≤ 3 EeV

Results on source correlations Results on source correlations



Nothing can be reported yet



Maybe first indications that proton astronomy will be possible indeed?



Two prescriptions are being tested…



Opening of a new era: the future is bright!

(but statistics should soon be large enough if

EGMF not unexpectedly large)

Some conclusions… (1/3)

1

All 3 “spectral dimensions” must be considered together



Energy spectrum



Angular distribution and diffusion



Mass composition

2

Magnetic fields are important!



Can change the energy spectrum



Can change the composition at low E



Anisotropies



Magnetic horizons

useful constraints on EGMF and GMF!

3

A major question: CR source composition!



Changes a lot the phenomenology of CRs and of the GCR/EGCR transition

4

Individual sources



GZK cutoff not so meaningful/important



Measuring the overall spectrum is the past!



Not only better measurements, but new measurements!



Individual source spectra are astrophysically rich!

Individual cut-offs, distance, low-E depletion, EGMF structure…



 definite predictions for primary observables!



 importance of composition measurement…

Some conclusions… (2/3)

A s t r o n o m y

The ankle is the key!

NB: Auger enhancements

5

Multi-messenger studies



Neutrinos and gamma-rays



in the source



cosmogenic (associated with CR propagation)

6

GZK horizons and high-energy physics



Correlation of high-energy CRs with nearby sources:

another way to detect the GZK effect!



Constraints on the experimental energy scales!



Important goal!

Some conclusions… (3/3)



 bring astroparticle physicist and astrophysicists closer!

Thank you very much!