Cosmic rays:Cosmic rays:a walk across the Universea walk across the Universe

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Cosmic rays:

Cosmic rays:

a walk across the Universe a walk across the Universe

Lorenzo Perrone Lorenzo Perrone

Dipartimento di Matematica e Fisica Dipartimento di Matematica e Fisica Universit

Università à del Salento e INFN Lecce del Salento e INFN Lecce

Using particle physics to understand and image the Earth

ISAPP

Ferrara 2-12 July 2018

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First day:

History, nature, sources and propagation of Cosmic Rays Composition and energy spectrum

Second day:

Observation and overview of detection techniques

The case of ultra-high energy cosmic rays: focus on the Pierre Auger Observatory Second day:

Observation and overview of detection techniques

The case of ultra-high energy cosmic rays: focus on the Pierre Auger Observatory

OUTLOOK

Reading code:

slides marked with a red and bold T have technical content

Using particle physics to understand and image the Earth

ISAPP

Ferrara 2-12 July 2018

(3)

The energy spectrum of high energy cosmic rays

1 particle cm-2s-1

1 particle m-2y-1

1 particle km-2century-1

Direct measurement:

Direct measurement:

satellites (AMS), satellites (AMS), balloons (CREAM) balloons (CREAM)

Ground array Ground array ~ km~ km22 Kascade-Grande, Icetop Kascade-Grande, Icetop High-altitude ground array,

High-altitude ground array,

~0.01 km

~0.01 km22 ARGO-YBJ, ARGO-YBJ, Tibet ASg

Tibet ASg

Ground/Hybrid array Ground/Hybrid array Auger

Auger 3000 km3000 km22 TA

TA 700 km700 km22

courtesy of R. Engel

“knee”

“ankle”

Above LHC energy

(4)

Direct search in space

- Spectrum - Composition (B/C ratio etc..) - Dark matter

Alpha Magnetic Spectrometer (AMS-02) FERMI Gamma ray Space telescope

Gamma ray sky above 1 GeV

Beautiful instruments, precision physics.

Limited by their size (cannot cover the highest energies)

(5)

What cosmic rays do when they enter the

terrestrial atmosphere?

(6)
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Indirect Measurement of Cosmic Rays

Indirect Measurement of Cosmic Rays

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Cosmic Rays in the atmosphere Cosmic Rays in the atmosphere

Vertical flux of cosmic rays in the atmosphere with E > 1 GeV

Data points for measurements of negative muons

Muons dominate the flux of cosmic rays at sea level

~ 1-2 muons/cm

2

/min

produced at ~15 km

lose about 2 GeV along their path

<E> at ground ~ 4 GeV

angular distribution ∝ cos

2

(9)

S h ow

er A xi s

Particle Shower

ARGO: a ground array at the highest altitude

Detector of “extensive showers” of particles

generated in the Cosmic Ray (protons, He nuclei, e, , ...) interactions with nuclei of terrestrial atmosphere.

Detector: RPC

N u m b e r o f Fi re d S tr ip s

(x1,t1) (xi,ti)

Sho we

r Fr ont

Tibet @ 4300 m asl

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The Imaging Air Cherenkov Detection The Imaging Air Cherenkov Detection

technique:concept technique:concept

Each telescope observes the shower from different points of view.

Multiple telescopes observation provides a more accurate reconstruction of the shower arrival direction

Several experiments successfully operating MAGIC (Canarie islands) VERITAS (Arizona)

HESS (Namibia)

(11)

Neutrinos: elusive but everywhere Neutrinos: elusive but everywhere

Each body is hit every second by

- 100000 billions neutrinos coming from the Sun

- 50 billions neutrions from terrestrial radioactivity

- from 10 a 100 billions neutrinos from all nuclear plants all over the world

- 10 million relic neutrinos from the Big Bang - 1000 atmospheric neutrinos originating from the interaction of CR with the atmosphere

Moreover

The human body has about 20 mg of (radiocative) 40K

Asa consequence it emits about 340 milions neutrinos per day!

+ neutrino from sources

+ cosmogenic neutrinos

(12)

CHARGE CURRENT INTERACTION

* large volume (1-10 km3)

* well shielded site (underground, underwater/ice)

* high sensitivity at high energy

* good capability to discriminate the background

* precise particle tracking for pointing purposes

Neutrinos from sources : detection concept Neutrinos from sources : detection concept

Background:

• atmospheric 

• atmospheric 

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Heitler cascade EAS model Heitler cascade EAS model

T

(15)

Electron Bremsstrahlung Electron Bremsstrahlung

Critical energy for different materials

Infrared divergence

Complete screening of atomic nuclei for high energy electrons

T T

(16)

Pair production Pair production

Complete screening of atomic nuclei for Bremsstrahlung and Compton scattering negligible (Approximation A of cascade theory)

T T

(17)

Electromagnetic cascade Electromagnetic cascade

T

(18)

Hadronic cascade Hadronic cascade

T

(19)

CR induced showers CR induced showers

Hadrons Muons Electrons Neutrons

Monte Carlo Simulations

(20)

Key observables (proton cascade) Key observables (proton cascade)

Primary energy ∝ number of charged particle at the shower maximum

Muon number ∝primary energy

Depth of shower maximum

∝ln(primary energy)

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Nuclear primaries: superposition model Nuclear primaries: superposition model

A nucleus with mass number A and total energy E

0

is taken to be A individual single nucleons each with energy E

0

/A and each acting individually

Depth of shower maximum sensitive to the mass of primary particle

Heavier nuclei have more muons

(22)

E = 10

E = 10

1919

eV, zenith =0 eV, zenith =0

Xmax as indicator of mass composition Xmax as indicator of mass composition

Atmospheric depth of shower maximum correlated with primary type

(Example: proton showers develop deeper than iron , X

max,pr

> X

max,Fe

)

(23)

Muon number

Muon number

(24)

Ankle

Transition galactic to extra- galactic cosmic rays

Energy spectrum Arrival directions Composition

Search for photon and neutrinos as primary cosmic rays

Hadronic physics

“GZK”

End of the spectrum

GZK

Particle Data Group

The physics case at the highest energies

Auger/TA

LHC 14 TeV

Ankle

(25)

The Pierre Auger Observatory

Ultra-high energy cosmic rays (10

17

-10

21

) eV

Flusso ad E>10

19.5

eV molto basso 1 particella/(km2 sr secolo)

Large size

3000 km2 (Pampa Argentina)

30 events/y @ Auger

(26)

an array of 1660 Cherenkov stations on a 1.5 km hexagonal grid (~ 3000 km2)

4+1 buildings overlooking the array (24+3 telescopes)

The Pierre Auger Observatory

- Dense array (24km

2

) plus muon detectors → AMIGA - 3 further high elevation FD telescopes → HEAT

Radio detector

153 Radio Antenna

→ AERA

3000 km

2

Fluorescence detector Surface detector

Low energy extensions

500 members, 17 countries

(27)

1.5 km

1.5 km 1.5 km

1.5 km

Camera: 440 PMTs

Aperture of the pixels: 1.5°

Fluorescence detector

Surface detector

Pierre Auger

Observatory

(28)

Not always straight

environmental conditions….

(29)
(30)
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Energy estimator

Longitudinal profile

FD - calorimetric measurement - duty cycle 15%

Density of particles at the ground SD - duty cycle ~ 100%

“In order to make further progress, particularly in the field of cosmic rays, it will be necessary to apply all our resources and apparatus simultaneously and side-by-side.”

Use the energy scale provided by FD to calibrate the entire SD data sample

V.H.Hess, Nobel Lecture, December 1936

The Hybrid paradigm

(34)

Search for neutrinos with AUGER Search for neutrinos with AUGER

Important for neutrino detection: observable only if almost horizontal

Neutrino signature: an inclined shower with large electromagnetic component hadron

neutrino-like

old shower

flat front, muons

young shower electr.

and muons

(35)

- need composition data E> 40 EeV to understand the nature of the suppression - better understanding of hadronic interaction models

- isolate a light component pointing back to astrophysical sources

spectrum

features

ankle/suppression

heavier

c om po si tio n

with increasing energy

absence of

cosmogenic γ/υ

mismatch data vs

ha dr on ic m od el

large/intermediate scale

an iso tro py Open science case

at the highest energies sourc e

scen ario ?

(36)

FUTURE

Space

JEM-EUSO

Ground-based: CTA

(37)

Our Universe Our Universe

Cosmic microwave temperature fluctuations Red regions are warmer and blue regions are colder by about 0.0002 degrees.

Data from:

Wilkinson Microwave Anisotropy Probe (WMAP)

Only 5% is in fact accesible

(38)

Take home message Take home message

Cosmic Ray Physics is interdiscilinary Cosmic Ray Physics is interdiscilinary Several issues still open!

Several issues still open!

Origin and acceleration mechanism not fully unveiled Origin and acceleration mechanism not fully unveiled Chemical composition at the highest energy still unclear Chemical composition at the highest energy still unclear

Joint effort and complementary

techniques: multi-messenger

astronomy era!

(39)

What else?

“ That isn't dark matter, sir - You just forgot to take

off the lens cap.”

(40)

E < E

ankle

E > E

ankle

The combined Auger spectrum

Auger Collaboration @ ICRC 2017

No indication of dependence on declination

Exposure

6.7 104 km2 sr y

(41)

→ non constant composition large proton fraction at the ankle

increase of the mean mass above and below ~ 2 EeV

→ interpretation depends on hadronic interaction models

FD Syst uncertainty ~ 10 g cm-2 (20 g cm-2 at the lowest energies) FD Xmax resolution ~ 20 g cm-2 (30 g cm-2 at the lowest energies)

Auger Collaboration @ ICRC 2017

average of X

max

std. deviation of X

max

(42)

Search for photon primaries with AUGER Search for photon primaries with AUGER

Photon showers develop deeper in the atmosphere and have less muons

steeper LDF

steeper LDF longer rise-time longer rise-time

FD FD

deeper Xmaxdeeper Xmax

SD → SD

steeper LDF and longer rise-time signalssteeper LDF and longer rise-time signals

Higher fraction of muons (hadrons) flattens the LDF

Muons are produced higher in the atmosphere and arrive within a shorter time

Photon signature

(43)

Search for neutrinos with AUGER Search for neutrinos with AUGER

Important for neutrino detection: observable only if almost horizontal

Neutrino signature: an inclined shower with large electromagnetic component hadron

neutrino-like

old shower

flat front, muons

young shower electr.

and muons

(44)

4 photons candidate above 10 EeV (SD)

3 photons candidate between 1-2 EeV (Hybrid) Strictest limits at E> 1 EeV

- Top-down model strongly disfavored

- CR proton dominated scenario start to be disfavoured

No candidates dN/dE = k E-2

→ k ~ 5 x 10-9 GeV cm-2 s-1 sr-1 [0.1 – 25] EeV

Auger limits constrains models with pure proton primaries

Neutrinos

Photons

Search for photons and neutrinos

(45)

45 Greisen Zatsepin Kuz'min effect (1966):

Interaction with the cosmic microwave background (CMB)

nuclei: photo-disintegration and

pair production on CMB (RB IR) protons:

End to the cosmic ray spectrum?

End to the cosmic ray spectrum?

“horizon” (p and nuclei) ~ 100 Mpc ( ~1020 eV )

propagation scenario propagation scenario

The knowledge of composition at the highest energies and the detection of cosmogenic neutrino and/or photons is the main challenge for near future source scenario

source scenario

We may be observing the end of cosmic ray accelerators “fuel”.

Emax Z B R

]

E  7 1019 eV

figura

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