INSTRUMENTATION & DETECTORS for HIGH ENERGY PHYSICS I - - PowerPoint PPT Presentation

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INSTRUMENTATION & DETECTORS for HIGH ENERGY PHYSICS I - - PowerPoint PPT Presentation

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INSTRUMENTATION & DETECTORS for HIGH ENERGY PHYSICS I 05-07.11.2014 Isabelle Wingerter-Seez (LAPP-CNRS) - AEPSHEP2014 - Puri (India) 1 WHAT IS A PARTICLE DETECTOR ? An apparatus able to detect the passage of a particle and/or

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05-07.11.2014 Isabelle Wingerter-Seez (LAPP-CNRS) - AEPSHEP2014 - Puri (India)

INSTRUMENTATION & DETECTORS for HIGH ENERGY PHYSICS I

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WHAT IS A PARTICLE DETECTOR ?

An apparatus able to

detect the passage of a particle and/or localise it and/or measure its momentum or energy and/or identify its nature and/or measure its time of arrival …..

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HOW ARE PARTICLES DETECTED ?

In order to detect a particle it must

interact with the material of the detector transfer energy in some recognisable way and leave a signal.

Detection of particles happens via their energy loss in the material they traverse.

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FOUR STEPS

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  • 1. Particles interact with matter

depends on particle and material

  • 2. Energy loss transfer to detectable signal

depends on the material

  • 3. Signal collection

depends on signal and type of detection

  • 4. BUILD a SYSTEM

depends on physics, experimental conditions,….

L e s s

  • n

1 L e s s

  • n

2 L e s s

  • n

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ELEMENTARY PARTICLES and FORCES

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PARTICLES

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H, + the ones we have not yet observed

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KNOWN PARTICLES

HOW CAN A PARTICLE DETECTOR

DISTINGUISH THE PARTICLES WE KNOW MEASURE PROPERTIES of PHYSICS PROCESSES IDENTIFY THE EXISTENCE OF A NEW PARTICLE

?

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+ the ones we have not yet observed

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LIMITED SIZE DETECTOR

A m o n g t h e s e 1 8 0 l i s t e d particles, 27 have a long enough lifetime such that, for GeV energies, they travel more than one micrometer Among these 27, 14 have c.τ <0.5 mm and leave a very short track in the detector

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THE 13 PARTICLES A DETECTOR MUST BE ABLE TO MEASURE AND IDENTIFY

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EXAMPLES OF INTERACTIONS

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HEP & SI UNITS

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MEASURING PARTICLES

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INTERACTION CROSS-SECTION

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FERMI GOLDEN RULE

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CROSS-SECTION: ORDER OF MAGNITUDE

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PROTON-PROTON SCATTERING CROSS-SECTION

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CROSS-SECTIONS AT THE LHC

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TRIGGER !

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ELECTROMAGNETIC INTERACTION PARTICLE - MATTER

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Interaction with the atomic electrons. The incoming particle loses energy and the atoms are exited or ionised. Interaction with the atomic nucleus. The incoming particle is deflected causing multiple scattering of the particle in the material. During this scattering a Bremsstrahlung photon can be emitted In case the particle’s velocity is larger than the velocity of light in the medium, the resulting EM shockwave manifests itself as Cherenkov radiation. When the particle crosses the boundary between two media, there is a probability of 1% to produce an Xray photon called Transition radiation.

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ENERGY LOSS BY IONISATION: BETHE-BLOCH FORMULA

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IONISATION & EXCITATION

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While the charged particle is passing another charged particle the Coulomb force is acting, resulting in momentum transfer. The relativistic form of the transverse electric field does not change the momentum transfer. The transverse field is stronger, but the time of action is shorter.

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IONISATION & EXCITATION

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The transferred energy The incoming particle transfers energy mainly/only to the atomic electrons.

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BETHE-BLOCH FORMULA - CLASSICAL DERIVATION

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BETHE-BLOCH FORMULA - CLASSICAL DERIVATION

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BETHE-BLOCH FORMULA

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ENERGY LOSS of PIONS in Cu

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UNDERSTANDING BETHE-BLOCH

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UNDERSTANDING BETHE-BLOCH

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CHARGED PARTICLE ENERGY LOSS in MATERIALS

Dependance on target element

Mass A Charge Z

Minimum Ionisation

  • dE/dx ~ 1-2 MeV g-1cm2

e.g. for Pb with ρ=11.35 g/cm3:

  • dE/dx ~ 13 MeV/cm

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MATERIAL PROPERTIES

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STOPPING POWER AT MINIMUM IONISATION

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dE/dX and PARTICLE IDENTIFICATION

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dE/dx FLUCTUATIONS

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dE/dx FLUCTUATIONS - LANDAU DISTRIBUTION

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MEAN PARTICLE RANGE

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ENERGY LOSS of ELECTRONS

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ELECTROMAGNETIC INTERACTION PARTICLE - MATTER

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Interaction with the atomic electrons. The incoming particle loses energy and the atoms are exited or ionised. Interaction with the atomic nucleus. The incoming particle is deflected causing multiple scattering of the particle in the material. During this scattering a Bremsstrahlung photon can be emitted In case the particle’s velocity is larger than the velocity of light in the medium, the resulting EM shockwave manifests itself as Cherenkov radiation. When the particle crosses the boundary between two media, there is a probability of 1% to produce an Xray photon called Transition radiation.

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BREMSSTRAHLUNG

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Real photon emission in the electromagnetic field of the atomic nucleus

where y=k/E and

For a given E, the average energy lost by radiation, dE, is obtained by integrating over y.

Electric field of the nucleus + of the electrons Z(Z+1) At large radius, electrons screen the nucleus ln(183Z-1/3) [D.F.]

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BREMSSTRAHLUNG & RADIATION LENGTH

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RADIATION LENGTH

The radiation length is a “universal” distance, very useful to describe electromagnetic showers (electrons & photons) X0 is the distance after which the incident electron has radiated (1-1/e) 63% of its incident energy

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Air Eau Al LAr Fe Pb PbWO4 LAr/Pb Z

  • 13

18 26 82

  • X0 (cm)

30420 36 8,9 14 1,76 0.56 0.89 1.9

dE/dx=E/X0 dE/E=dx/X0 E=E0e-x/X0

E0

1X0

0,37 E0

1 3 2

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RADIATION LENGTH

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Approximation (X0 in cm: divide by ρ [g/cm3]) Energy loss by radiation γ Absorption (e+ e- pair creation) For compound material wj being the relative density

: 1/ X0 = " wj / Xj

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CRITICAL ENERGY

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TOTAL ENERGY LOSS FOR ELECTRONS

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µ+ in COPPER

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INTERACTION OF PHOTONS WITH MATTER

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PHOTO-ELECTRIC EFFECT

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PHOTO-ELECTRIC EFFECT

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PAIR PRODUCTION

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COMPTON SCATTERING

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Process dominant at Eγ ≃ 100 keV - 5 GeV scattered e- Ee’=√me2c4+pe’2c2 Pe’=- pγ’ Atomic e- Ee=mec2 Pe~0

Incident Photon Eγ = h ν pγ =h ν/c Scattered photon Eγ’ = h ν’ pγ’=h ν’/c

θ φ

σcompton ∼ Z . ln(Eγ)/Eγ QED cross-section for γ-e scattering

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ANGULAR DISTRIBUTION

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INTERACTION OF PHOTONS WITH MATTER

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Mass absorption coefficient λ = 1/(µ/ρ) [g.cm2] with µ=ΝΑ.σ/A

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INTERACTION OF PHOTONS WITH MATTER

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ELECTROMAGNETIC INTERACTION PARTICLE - MATTER

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Interaction with the atomic electrons. The incoming particle loses energy and the atoms are exited or ionised. Interaction with the atomic nucleus. The incoming particle is deflected causing multiple scattering of the particle in the material. During this scattering a Bremsstrahlung photon can be emitted In case the particle’s velocity is larger than the velocity of light in the medium, the resulting EM shockwave manifests itself as Cherenkov radiation. When the particle crosses the boundary between two media, there is a probability of 1% to produce an Xray photon called Transition radiation.

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CERENKOV RADIATION

Particles moving in a medium with speed larger than speed of light in that medium loose energy by emitting electromagnetic radiation

Charged particles polarise the medium generating an electrical dipole varying with time Every point in the trajectory emits a spherical EM wave; waves constructively interfere

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CERENKOV RADIATION

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IDENTIFYING PARTICLES with CERENKOV RADIATION

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CERENKOV RADIATION: MOMENTUM DEPENDENCE

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mπ = 0.1395 GeV mK = 0.4937 GeV mp = 1 .007 GeV

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COSMIC RAYS

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HESS EXPERIMENT

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Transition radiation

Transition radiation occurs if a relativistic particle (large γ) passes the boundaries between two media with different refraction indices.

Intensity of radiation is logarithmically proportional to γ

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IDENTIFYING PARTICLES WITH TRANSITION RADIATION

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ATLAS TRANSITION RADIATION TRACKER

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IDENTIFYING PARTICLES WITH TRANSITION RADIATION

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MULTIPLE SCATTERING

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Example p=1 GeV, x=300µm, Si X0=9.4 cm ➝ θ0=0.8 mrad For a distance of 10 cm this corresponds to 80 µm, which is significantly larger than typical resolution of Si-strip detector. Scattering of charged particles off the atoms in the mdium causes a change of direction The statistical sum of many such small angle scattering results in a gaussian angular distribution with a width given by

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ELECTROMAGNETIC SHOWERS

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HADRONIC SHOWERS

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HADRONIC SHOWERS

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HADRONIC INTERACTION LENGTH

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For high energies incoming hadrons, the hedronic cross-section is ~constant as function of energy ~independant of the hadron type The material dependance of the total cross-sectionis given by σinel ≈ σ0A0.7, σ0 = 35 mb Characterize hadronic interactions by hadronic interaction length in g/cm2 (or in [cm] by normalising to the material density).

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INTERACTIONS OF PARTICLES WITH MATTER

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IONISATION AND EXCITATION Charged particles traversing material and exciting and ionising atoms. The average energy loss of the incoming particle by the process, is to a good approximation, described by the Bethe- Block formula. MULTIPLE SCATTERING AND BREMSSTRAHLUNG Incoming particles are scattering off the atomic nuclei which are partially shielded by the atomic electrons. This scattering imposes a lower level on the momentum resolution of the spectrometer, when measuring the particle momentum by deflection of the particle trajectory in the magnetic field. The deflection of the particle on the nucleus results in an acceleration that causes the emission of Bremsstrahlung photons. The photons in turn produce e+e- pairs in the vicinity of the nucleus, which causes the EM cascade. This effect depends on m-2: only relevant for electrons. CHERENKOV RADIATION If a particle propagates in a material with velocity > speed of light in this material, C radiation is emitted at a characteristic angle that depends on the particle velocity and the refractive index of the medium TRANSITION RADIATION If a charged particle is crossing the boundary between two materials of different dielectric permittivity, there is a certain probability for emission of an X- ray photon. HADRONIC INTERACTION Incoming hadrons on a material will interact with the nucleus and create a shower composed of hadrons, electrons, photon. A fraction of the energy is lost in the form of binding energy or neutrinos.

INTERACTIONS DETECTORS

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ELECTROMAGNETIC INTERACTIONS OF PARTICLES WITH MATTER

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Interaction with the atomic electrons. The incoming particle loses energy and the atoms are exited or ionised. Interaction with the atomic nucleus. The incoming particle is deflected causing multiple scattering of the particle in the material. During this scattering a Bremsstrahlung photon can be emitted In case the particle’s velocity is larger than the velocity of light in the medium, the resulting EM shockwave manifests itself as Cherenkov radiation. When the particle crosses the boundary between two media, there is a probability of 1% to produce an Xray photon called Transition radiation.

INTERACTIONS DETECTORS

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PARTICLE DETECTION: schematic

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INTERACTIONS DETECTORS

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PARTICLE DETECTION: schematic

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CREDIT and BIBLIOGRAPHY

A lot of material in these lectures are from:

Daniel Fournier @ EDIT2011 Marco Delmastro @ ESIPAP 2014 Weiner Raigler @ AEPSHEP2013 Hans Christian Schultz-Coulon’s lectures Carsten Niebuhr’s lectures [1][2][3] Georg Streinbrueck’s lecture Pippa Wells @ EDIT2011 Jérôme Baudot @ ESIPAP2014

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