detection methods in particle astrophysicscdeclerc/astroparticles/2010-11/exercises... · detection...

Detection Methods in Particle Astrophysics

Erik Strahler13/05/11

13/05/11 Erik Strahler - Particle Astrophysics 2

Outline

• Reminder of Energy Loss Mechanisms• General Detection Methods• Applications in Current Experiments• Dark Matter Detection Methods

– Accelerators– Direct Searches– Indirect Searches

• Exercises – due May 25th


Energy Loss Mechanisms and General Detector Methods


Radiation Energy Loss

• Photoelectric effect

3

5

EZCPE ⋅≈σ



• Compton Scattering

KNC Z σσ ⋅≈



• Pair Production

)ln(2 EZCPP ⋅⋅≈σ


Total Contribution

NaI Z Lead


Regions of Dominance


Charged Particle Energy Loss

• Ionization• Synchrotron

– Circular acceleration• Bremsstrahlung

– Linear acceleration


Proportional Counters• Volume of gas between 2 biased electrodes

– Ionization releases electrons (~30 eV threshold)– Drift to anode (wire)– Free more electrons on the way– Signal proportional to initial energy

• Semiconductor version– Much lower threshold (~3.5 eV)


Photomultipliers


Scintillation

• Convert deposited energy to emitted photons• Organic (crystals, plastics, liquids)

– Fast response, low yield– Wavelength shifters– Low Z (compton dominant)

• Inorganic (ionic crystals, glasses)– Slower response, very high yield– High Z


Cherenkov Counters

nc βθ 1cos =

Exercise!


Examples of Radiators


Detector Methods applied to Satellite-based Experiments


AMS• Antimatter• Dark matter• Large acceptance• Long mission (>10 yr)


AMS: Magnet

• Permanent– 0.15 T

• Superconducting– 0.75 T– 3 yrs


AMS: TRD

• Sensitive to E/m• Cross many layers

with sharp changes in index of refraction (plastic/felt and vacuum)

• Electrons emit x-rays, protons do not


AMS: ToF

• Triggering– 1.5x10-10 s resolution

• 4 Scintillator planes– Alternating directions


AMS: Silicon Tracker• Measure curvature

(rigidity), charge, direction, momentum


AMS: RICH

• 0.1% velocity measurement• Aerogel, NaF radiator plane• Cherenkov ring projected

onto PMT sensors


AMS: ECAL• e/p discrimination• ~500 kg of lead

interleaved with scintillating fibers

• 9 superlayers, criss-crossed

• electrons produce emshowers

• Protons produce hadronicshowers (wider)


AMS: Anti-coincidence


AMS: Current Status

• To be mounted on ISS• Launch eminent after long doubts


Fermi GST


GBM• NaI

– 8 keV to 1 MeV– Rate dependent on angle,

gives pointing

• BGO– 150 keV to 40 MeV– Dense to provide stopping

power at higher energy


GRB Skymap


LAT Performance


Gamma Ray Sky


Point Source Catalogue


Some Sources


Leptonic vs. Hadronic Source?

Leptonic Hadronic


From γ flux to ν prediction: pp

γγπ

ννννμπ

ννννμπ

μμμ

μμμ

+→+→

+++→+→+→

+++→+→+→+−−−

+++

0

X

eX

eXpp

e

e

3/pEE ≈π


From γ flux to ν prediction: pγ

γγπ

ννννμπγ μμμ

+→+→

+++→+→+→Δ→+ +++

0 p

enp e BR = 1/3

BR = 2/3

K = 4


Neutrino Event Rates at Earth

• Extremely long baseline (asymptotic) oscillations• Effective Area = size of an ideal detector with

100% efficiency– Function of energy,

declination– Convolve with flux

to get event rate

νν

νν dEtA

dEdNN eff ⋅= ∫

Exercise!


Dark Matter and how we could observe its properties


Dark Matter Candidates• Masses, cross sections over

many orders of magnitude

• 10-6 eV to 1015 GeV

• Non-interacting to strongly interacting

• Must not be part of the standard model sector


WIMPS as Dark Matter• Weakly Interacting Massive Particles

– In thermal equilibrium intially

– Freeze out at some time where Mχ << T– Can have correct relic density (explain missing mass) if the

annihilation cross-section is weak

– Many options (neutralino, lightest KK excitation, …)

XX +↔+ χχ

vscmh

Aσχ1103 13272 −−×≈Ω


Search Methods• Accelerator, Direct, Indirect

– Complementary!


Accelerator (LHC)

• Produce WIMPs, measure decay signatures


Direct Detection Principles• Elastic collisions lead to low

energy nuclear recoil– Need ULTRA-low backgrounds

)cos1(2

222

θμ

−==NN

R mv

mqE

cmsin angle scattering target torelative velocity mean WIMP

mass reduced

transfermomentum

==

+==

=

θ

μχ

χ

vmm

mmq

N

N


Expected Rates

• N = number of target nuclei in detector • ρχ = local density of WIMPs in the galaxy• <v> = mean WIMP velocity relative to the detector• mχ = WIMP mass• σχΝ = WIMP-nucleon elastic scattering cross section

– Spin-dependent and spin-independent contributions– Dependence on atomic number of the nucleon

vm

NR Nχχ

χ σρ

∝


Local Density and Flux at Earth• N-body simulations give

galactic DM density profile

• ρhalo= 0.1-0.7 GeV cm-3

• ρdisk= 2-7 GeV cm-3

• With 100 GeV WIMP, gives ~ 3000 m-3

• Flux at Earth is then ~105cm-2s-1

• MEASUREABLE!


Predicted Cross-Sections (SI)

MSUGRA CMSSM


Expected Interaction Rates

• Differential rate versus energy depends on masses of WIMP and of target


Techniques

• Very small signal (few keV)

• Very rare (~1 per ton per year)

• Background is millions of times higher


Cryogenic Phonon Detection

• Also measure charge from electron drift after excitation


CDMS-II


CDMS-II

5x6 Ge/Si Towers


CDMS-II

cryostat

Lead shield(γ’s from radioactivity)

Polyethylene shield(neutron moderation)

Active muonveto to reject cosmic rays


Calibration

• electron recoil from most backgrounds (e, μ, γ)• nuclear recoil from WIMPs, neutrons


Calibration

• electron recoil from most backgrounds (e, μ, γ)• nuclear recoil from WIMPs, neutrons• reduced ionization yield from particles near surface


Removing Surface Events


Result


CDMS-II SI Limit

• Background:

• p=0.23 to observe 2 or more events

(syst) 2.0 (stat) 1.08.0 ±±


Noble Liquids• Large, scalable,

homogeneous, and self-shielding

• 3D localization by segmentation of top PMT array, and measurement of drift time.

• Ratio of light and charge signals gives particle ID


Noble LiquidsIonization

Scintillation


Xenon 100


Xenon 100• Internal Background

– Move components outside shield

– Material screening– Kr distillation column

• External Background– Copper shield versus

polyethylene contribution– 105 kg LXe active veto,

with 65 kg target


Typical Signals

S1 S2


Background Rejection


Background Rejection• Factor 100 times lower than previous experiments

detection methods in particle astrophysicscdeclerc/astroparticles/2010-11/exercises... · detection...

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