Particle Detectors An Introduction

Carl Haber Physics Division

LBNL

https://www.youtube.com/watch?v=0fKBhvDjuy0

Subatomic

Subatomic Physics • Below the level of the atom we encounter a

variety of high energy particle radiations. • Since the early 20th century we have tried to

understand these “rays” and used them to explore the structure of matter.

• “Particle Physics” is concerned with understanding matter and radiation at a fundamental level.

• Radiations is created naturally or in particle accelerators.

How do we detect particles?

• We can detect particles because they directly, or indirectly, interact with atoms in matter through electromagnetic forces.

• Electromagnetic interactions can lead to atomic excitation, or ionization – electrons are ejected from atoms resulting in an electron-ion pair.

• We can detect these effects in a variety of ways.

• When electromagnetic energy is transferred to atoms they may –Emit light –Create phase transitions in matter –Drift in an electric field

Fluorescence

Iconic Experiment #1

• 1909: under the direction of Ernest Rutherford, Geiger and Marsden perform an experiment on the scattering of radiation by a foil.

• 1911: Rutherford demonstrates that the radiation is scattered by small hard points within a much larger atom – discovers the atomic nucleus

• Scattered radiation is detected by fluorescence – localized flashes of light on a screen.

The Cloud Chamber invented 1911 by C.T.R. Wilson

Iconic Experiment #2

• 1928 Paul Dirac predicts a symmetry – all particles should have anti-particles with the opposite charge

• 1932: Carl Anderson observes positively charged “electrons” in a cloud chamber.

Ionization and Drift

High Energy Reactions

• Chemical reactions – # atoms in = # atoms out – Energy added to break

bonds, or released as heat or motion

• Relativity: Mass and energy can be interchanged

• At energies exceeding the equivalent “rest mass” of particles we observe this exchange

𝛾𝛾 → 𝑒𝑒− + 𝑒𝑒+

Iconic Experiment #3

• 1992-95: using a precisely segmented array of ionization detectors, the top quark was observed at Fermilab.

Developments • Over the course of the 20th century a large

variety of particle detectors were developed and put into use for research and for practical applications.

• Significant influence from the concurrent developments in electronics, materials, and computing.

Nov 16, 2005 UC Davis Physics Carl Haber LBNL

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770 microns15 microns

15 microns

n=1.59n=1.49

n=1.42

fiber

cladding

track

mirror

scintillating section clear section photon detector

Time Projection Chamber

• 1970’s: Invented at LBNL by David Nygren • Full 3-dimension imaging of complex patterns

Today’s Requirements

• Many important experiments today require detectors which can handle very high data rates, in order to search for rare phenomena. – Fast signals – Stable operation – Reliable – Precise – Able to withstand high radiation doses. – Compatible electronics for readout

Silicon Detectors • Today’s requirements can often be met with a technology

based upon silicon. • Silicon can be made to function as an ionization detector. • Ionization drifts fast in silicon • Silicon is a solid – large signals • Silicon can be very radiation resistant • Using micro-fabrication methods, silicon can be precisely

subdivided into many detecting elements. • Micro-electronic circuits (“chips”) can be designed and

fabricated to process the signals from silicon detectors

The Microstrip

Human hair

Sensor

Readout ASIC

Hybrid Module Control Chip

Power Control Circuit

Prototype multi-modular silicon strip stave for use at the High Luminosity LHC

Present generation ATLAS pixel module in use today at the LHC…Higgs discovery?

June 10, 2011 Silicon Detectors TIPP 2011 Carl Haber LBNL 24

2 m.

CERN ATLAS tracker (4th generation, beam in 2008)

Top quark 1992-95

What’s really involved? • Fundamental research on the properties of silicon and

its reaction to radiation. • Semiconductor materials engineering • Design of custom integrated circuits • Microelectronics packaging, interconnections, and

materials • Thermal engineering • Fast data acquisition and data processing • High performance materials for mechanical support • Precision optical metrology

Engineered Silicon • Microscopic

understanding of radiation damage mechanisms, defects, and kinetics – Modeling – Measurements – Time and temperature

dependence • Engineer the silicon for

greater radiation resistance by adding impurities.

Readout Electronics: IC’s

• Large channel count and complexity require custom readout chips (ASICs) • On-chip complexity increases with process evolution • Impact of powerful design and simulation tools • Mixed analog-digital signals on the same chip • Speed and noise performance have kept up with requirements but S/N often

remains an issue, particularly with longer strips and irradiation

complexity

Feature size FEI4 2011

FEI3 2003

7mm

Interconnections

• Bond aluminum wires of diameter 0.001 inch (25 microns) • Used to interconnect silicon detectors and readout electronics • Another technique utilizes arrays of solder or indium bumps. • More suitable for 2 dimensional arrays of detector elements

Human hair

Advanced Materials

• Processed carbons – Carbon-Carbon: CF reinforced C

by pyrolysis – Pyrolytic Graphite: TC>1000

• Graphite Foams: of varying density, conductivity – Pocofoam – Allcomp foam

• Boron Nitride: fillers – Varying particle size, shape

• Thermal adhesives: rigid, compliant, radiation hard

• Silicon Carbide: solid, foam, also an electrical material

LBNL Composites Facility

Metrology: Laser Displacement

….Partial Conclusion

• Particle detectors rely on the simple processes of ionization or excitation.

• Through substantial interplay with modern technology they give us a powerful window on the subatomic world.

• Lot’s of clever ideas have contributed and are still needed….from you!