Cosmic Ray Detection

Cosmic Ray Detection Techniques

Juan Wu

For course “Experimental techeniques

for particle astrophysics”

Cosmic Rays

Balloon/Sattlite carried detectors

Ground-based experiments



Energetic particles incident on the Earth from outer space.



Present (Still) physics issues:

 Origin?

 Composition?

 Acceleration mechanism?

 Propagation mechanism?

 Is there an end to the CR spectrum?

……

How do we detect cosmic rays?



To detect primaries, observatories are put in space or in high-altitude balloons

 Good: it studies the original cosmic ray without interference from the atmosphere

 Bad: it is an expensive detector that is too small to “catch” a lot of CRs



To detect secondary

showers, observatories are put on the ground

 Good: they are cheaper, bigger, and detect a lot more!

 Bad: it takes some work to figure out what the primary is like. But it can be done to some extent!

Charged primaries identification

• spectrometer: determine whether the particles are charged, and in conjunction with a magnetic field, measure the sign of the charge and the momentum of the particles

• Calorimeters: measure the energy of particles, do a lepton- hadron discrimination.

• Cherenkov detector: measure the particle velocity

• Transition radiation detector: measure the cone opening angle thus the mass of particles

• Time of flight: measure the time difference and the velocity

Spectrometer

 Maganet:

 Tracking system eg:

MWPC (multiwire proportional chamber)

~30 eV for an e-ion pair

~ 1mm

silicon microstrips

3.6 eV for an e-hole pair

~10 µm

Iterative c²

minimization as a function of track state- vector components a Magnetic deflection

|η| = 1/R

R = pc/Ze  magnetic rigidity s_R/R = s_h/h

Maximum Detectable Rigidity (MDR)

def: @ R=MDR  s_R/R=1

MDR = 1/s

Spillover: high rigidity particles may be assigned wrong sign-of-charge due to finite spectrometer resolution.

Crucial to rare particles (antiprotons, positrons ) in CRs

MDR > 850 GV, no EM shower

Selected antiprotons

spillover protons From Adriani et al. Phys.

Rev. Lett., 102:051101,2009

Calorimeter



A destructive method



Calorimeter usually divided into active and passive parts:

Active: responsible for generation of signal (e.g. ionization, light) Passive: responsible for creating the “shower”

An example of shower development

Passive Material Properties

R_L(cm) E_c(MeV) l_a(cm)

Lead 0.56 7.4 17.2

Iron 1.76 20.7 16.8

Tungsten 0.35 8.0 9.6

l_a= nuclear absorption length

proton (R=19GV) electron (R=17GV)

Cherenkov detector



Produced in three dimensions, so the wave front forms a cone of light around the particle direction



Measuring the opening angle of

cone → particle velocity can be

determined

Ring imaging

• From a classic paper by J. Seguinot and T. Ypsilantis [NIM 142 (1977) 377]

the Cherenkov cone can be imaged into a ring, using a spherical mirror

• Measuring the ring radius r allows the Cherenkov angle q_C to be determined

Spherical mirror radius R

Detector plane radius R/2

Track Interaction point

 r

r ~ R q_C / 2

Photons

Radiator medium

Transition radiation

 Local speed of light in a medium with refractive index n is c_p = c/n

 If its relative velocity v/c_p changes, a particle will radiate photons:

1. Change of direction v (in magnetic field)  Synchrotron radiation

2. Change of |v| (passing through matter)  Bremsstrahlung radiation

3. Change of refractive index n of medium  Transition radiation

 Transition radiation is emitted whenever a relativistic charged particle traverses the border between two media with different dielectric constants (n ~ e)

 The energy emitted is proportional to the boost g of the particle

 Particularly useful for electron ID

Can also be used for hadrons at high energy

charged particle

Time Of Flight

 Simple concept: measure the time difference between two detector planes

b = d / c Dt

 At high energy, particle speeds are relativistic, closely approaching to c

 For a 10 GeV K, the time to travel 12 m is 40.05 ns, whereas for a p it would be

40.00 ns, so the difference is only 50 ps

 Organic scintillators provide light on a

timescale of ~ 100 ps (Inorganic are slower)

 TOF gives good ID at low momentum Very precise timing required for p > 5 GeV

Track

d Detectors

TOF difference for d = 12 m

p d

3He

4He

Li Be B , C

(track average)

e

•Energy loss –

Bethe Bloch formula

Particle ID with dE/dx and beta

• beta vs Rigidity consistent

Ⅱ PAMELA experiment

Installed in Resurs-DK1 satellite: multi- spectral imaging of the Earth’s surface

Quasi-polar and elliptical orbit (70.0°, 350 km - 600 km)

PAMELA detectors

GF: 21.5 cm²sr Mass: 470 kg

Size: 130x70x70 cm³ Power Budget: 360W

Spectrometer

microstrip silicon tracking system + permanent magnet It provides:

- Magnetic rigidity  R = pc/Ze - Charge sign

Time-Of-Flight

plastic scintillators + PMT:

-Trigger

-Albedo rejection;

-Mass identification up to 1 GeV;

- Charge identification from dE/dX.

Electromagnetic calorimeter W/Si sampling (16.3 X₀, 0.6 λI) -Discrimination e+ / p, anti-p / e^-

(shower topology)

-Direct E measurement for e^-

Neutron detector

3He tubes + polyethylene moderator:

-High-energy e/h discrimination

Main requirements  high-sensitivity antiparticle identification and precise momentum measure

+ -

AMS will be launched to ISS

Launch 19th April 2011, 7:48 pm EDT Mission duration through the lifetime of the

ISS, until 2020 or longer (it will not return back to Earth)

Ground-based experiment

 UHECRs with more than 10

eV are found only one per square km per century large shower and low flux require large apertures &

long exposure times

 Exploit the atmosphere as a giant calorimeter->

produce extensive air showers (EAS)

 Detect the shower properties primary species

The Greisen-Zatsepin-Kuzmin (GZK) effect Nucleons can produce pions on the cosmic microwave background

nucleon 

4 10 eV

4

2

th

   





m

m E m

0901.0254

“Primary” Cosmic Ray (Ion, for example a proton)

Atmospheric Nucleus







 

e

e

 e

Electromagnetic







m

n

neutrino

Hadronic Shower

“Secondary” Cosmic Rays...

(about 50 produced after first collision)

Cosmic Ray “Showers”

Space

Earth’s atmosphere

Plus some:

 

Creating:

Properties of EAS

 As the cascade develops in the atomosphere, the number of particles in the shower increases until the nergy of the secondary particles is degraded to the level where ionization losses

dominate.

 <X_max>=D_e ln (E/E₀)

X_max & D_e: can be determined from the longitudinal shower profile measured with a fluorescence detector

E₀: can be extracted after estimating E from the total fluorescence yield.

Properties of EAS



Primary particles:



nucleus/nucleon



gamma-ray

above the ~10

eV, a γ-shower produces < 20% muons as a proton shower with same E

 The muon content of the EAS depend on the composition of

the primary CR

Measurement techniques



Surface arrays: lateral profile (energy density, relative timing of hits E and direction of Primary particles)



Fluorescence eyes: excited nitrogen molecules fluoresce  ultraviolet radiation.



Radio detection: e- and e+ generated in CR EAS are accelerated

in the presence of the earth magnetic field and subsequently emit

short radio pulse Radio signal keeps information about the full

shower history

AGASA

(Akeno Giant Air Shower Array)

 at the Akeno Observatory (35

47' N, 138

30' E) start from 1990



111 surface detectors (2.2m2 scintillator) and 27 lead

shielded muon detectors spread over 100km



10

(embedded previous generation 1km

array) - 10

eV



-Method:

(1)S(600)

(2)Measure composition by

comparing muon and e

transverse profiles

High Resolution Fly's Eye



HiRes has two detectors 12.6 km apart located atop desert mountains in west- central Utah. Operated from May, 1997 to April, 2006.

22 and 46 “fly’s eye” modules



Collected data on moonless nights:

about 10% duty factor.



stereo detection allowed between stations improve angular resolution



Energy : 10

– 10

eV

mehod: energy of air shower fluorescence



Composition method:

independent shower depth and energy measurement



5 times exposure than AGASA

The Pierre Auger experiment

Pierre Auger Southern Observatory Total sky coverage:

Northern-hemisphereUSA

Southern-hemisphereArgentina

Lateral Distribution Function (LDF)

Super hybrid detector (+ radio)

Auger Engeering Radio Array



AERA is in the infill array, good sensitivity lg(E)>17.6



AERA is located near FD at

Cohuieco. Possibility to see super hybrid events.



>2000 events per year over 10

eV, also detected by AUGER infill array



AERA will provide a 20 km

array with good measurement of ari

shower parameters.

Experiments starting

date acceptance

in km²sr

angular resolution

energy resolution

AGASA

High – Res Fly’s Eye

since 1999 350-1000 few

degrees ~40% mono

~10% stereo Auger ground full size in

about 2004 >7000 < 2^o ~15%

Auger hybrid ~2004 >700 ~0.25^o ~8%

radio

detection ??? >1000 ? few

degrees ? ???

UHE Cosmic Ray Experiments

References

 Kleinknecht K., Detectors for particle radiation, Cambridge university press, 1998

 Anchordoqui L. et al., Unltrahigh energy cosmic rays: the state of the art before the auger observatory, arxiv: hep-ph/0206072, 2002

 Berezinsky V., Ultra high energy cosmic ray protons: signature and observations, arxiv:

0901.0254, 2009

 Kounine A., Status of the AMS experiment,, ISVHECRS 2010, 2010.

 Van den Berg A. M. et al. Radio detection of cosmic rays at the southern Auger Observatory, Proceedings of the 31^st ICRC, 2009

 Some lectures from http://joram.web.cern.ch/joram/lectures.htm

 Some presentations from http://ecrs2010.utu.fi/

 http://pamela.roma2.infn.it/index.php?option=com_content&task=view&id=22&Ite mid=206

 http://www.ams02.org/

 http://www-akeno.icrr.u-tokyo.ac.jp/AGASA/

 http://www.cosmic-ray.org/

 http://www.auger.org/