Basic of Detector Atsushi Taketani RIKEN Nishina Center

Basic of Detector Atsushi Taketani 竹谷篤 RIKEN Nishina Center Detector Team RIKEN Brookhaven Research Center

What I worked for detectors • Electron-Positron collider Experiment at 60 Ge. V – Trigger electronics, TRD, EMCAL, Si Sensor • Proton-Antiproton collider experiment at 1. 8 Te. V – Muon detector, Readout electrinics • Large scale Accelerator control at 8 Ge. V – Distributed computing system hardware/software • Polarize proton-proton/ Heavy Ion collider experiment at 200 Ge. V – Muon detector, Si detector Working higher energy • Start to work for Detectors for RIBF experiment 2

Index of this lecture 1. 2. 3. 4. 5. 6. Why/How we need detector? What do we want to measure? Gas Chamber basics Scintillator PHENIX experiment and Silicon Detector Summary 3

Importance of Detector Physics detector Human • We need detector to understand physics • Detector innovation can arise new physics • Telescope (1590) : Newton mechanics　(Late 1600’s) • Velocity of light measurement (1873): Relativity (1905, 1916) • High resolution hydrogen spectroscopy : Quantum mechanics ( 1925) 4

Discovery of Charm Quark On 1974 丁肇中 and B. Rchiter discovered independtly. 　　　Novel prize in Physic in 1976. Ting: Energetic proton was bombarded to nuclear target, measure the invariant mass of produced electron and positron e+ J/f e. Until Ting’s discovery, many experiments saw the sign of the similar phenomena, But their resolution of the mass measurement were not good as Ting’s experiment.

Major Detector Principle 1. 2. 3. 4. 5. 6. 7. Particle penetrates or stops at detector Particle interacts with material of detector Generating some signal Amplification mechanism Analog to Digital conversion Getting into computer Analyze at digital data ->physics PC Digital signal Amp. Analog to digital conversion Sensor Particle Scintillator Semiconductor Detectors electric signal (analog) Coaxial cable Data taking 6

Particle mass • Particle has its own mass. – electron 0. 511 Me. V – m 105 Me. V – p+, p- 140 Me. V, p 0 135 Me. V – Proton 928 Me. V – J/y 3069 Me. V (discovered by S. C. C. Ting and B. Richter) – Top quark 172 Ge. V (heaviest particle ever observed) • If we know the mass of particle, we can identify the particle species. 7

4 -momentum • Treating the mass at relativity P 2 = E 2 - | p|2 = m 2 Where P : 4 -momentum E : Energy p : 3 -momentum ( px, py, pz ) m : invariant mass 8

4 -momentum • (E, px, py, pz ) • Invariant mass : m 2 = E 2 - | p|2 • 3 -momentum (velocity) v/c = b = p/E Where c is light velocity • If we can measure 3 -momentum p, and Energy E or 3 -momentum b, m can be obtained -> identifying particle. 9

3 -momentum measurement • Momentum can be measured by using Lorentz force F: force, q: electric charge, E: electric field v: particle velocity = p/m, B: magnetic field Constant force -> Constant curvature -> particle track trajectory P [Me. V/c] = 3 * r[cm] * B[T] 10 r: curvature radius, B: magnetic field

Energy measurement • Particle stops at the material and measure all deposited energy by energy loss Calorimeter particle • Energy (value) b = p/E : particle velocity measure timing deference between 2 known location L b = V/c = L/(t 2 -t 1)/c particle t 1 t 2 11

Particle and material interaction • Particle will hit, penetrate, or stop at material, including gas, liquid, solid. • Particle has some interaction with material, then we can detect it. -> Detector • Energy Loss, Multiple Scattering and So. 12

5. 49 Me. V a particle in air Path length [cm] Energy loss [Me. V/cm] Energy Loss and stopping power electric nuclear Particle energy [Me. V] 13

Bethe-Bloch formula Particle charge Energy loss [Me. V cm 2/g] β =v/c v velocity of the particle E energy of the particle x distance travelled by the particle c Energy. Loss. bmpspeed of light particle charge of the electron me rest mass of the electron n electron density of the target I mean excitation potential of the target permittivity of free space Particle energy [Me. V] 14

Typical Energy Loss • d. E/d. X ~ 1 Me. V cm 2/g for Minimum ionizing particle • Energy loss / Unit length ~ 2 Me. V cm 2/g * Material density [g/cm 3] For example at Al d. E/d. X = 1. 615 Me. V cm 2/g Aluminum r=2. 70 g/cm 3 Energy loss =0. 60 Me. V/cm Minimum Ionizing Particle 15 Particle energy [Me. V]

Multiple Scattering for M. I. P. Z: particle charge x: material thickness X 0: radiation length 16

Atomic and Nuclear properties of materials 17

Example • Aluminum 1 cm thickness with electron 50 Me. V • Estimate the angle deviation at exit, ignore energy loss. • Radiation length X 0=24. 01 [g/cm 2] / 2. 699[g/cm 3]=8. 9[cm] x/X 0=0. 11 18

Typical Wire Chamber 19

Gas Chamber 1. Energetic particle passing through gas. 2. Gas molecules are ionized -> electrons and ions. 3. Electrons and ions are drifted to electro load with minus and plus voltage 4. Avalanche near by wire 5. Getting electrical signal 20

Ionization - + + - + - + Gas Chamber • Ionization happens along charged particle track • #Electorn-Ion pair/unit length = d. E/d. X / Pair creation energy • Pair creation Energy • H 2 37 e. V • Ar 26 e. V 21

Ionization Ar: d. E/d. X = 1. 519 Me. V cm 2/g electron-ion = 97 /cm density = 1. 662 g/L pair creation energy = 26 e. V #electron-ion = 1. 519 Me. V cm 2/g * 106 e. V/Me. V * 1. 662 g/l*1000 cm 3/l = 97 /cm /26 e. V 22

Drift drift velocity =50~100 mm/nsec Drift velocity　[mm/nsec] = 5 mm~10 mm / 100 nsec Electric field and potential Electric field [KV/cm] 23

Avalanche E: electric field r: distance from wire V 0: bias voltage a: radius of cylinder b: wire radius Electric filed electron gas molecule Gas multiplication 24

Multiplication a/Pressure Gas Gain Electric field/Pressure [V/cm /mm. Hg] Voltage [V] 25

Measurement of the momentum Magnetic filed P [Me. V/c] = 3 * r[cm] * B[T] r: curvature radius, B: magnetic field 26

Photo Multiplier Tube 27

Precise Time measurement detector Plastic scintillator 1. Charged particle is penetrating 2. Lower energy electron is exited to upper state 3. Upper state electron drops into lower state and emits a photon Charged particle 4. Propagate to P. M. T. Light guide 5. P. M. T. generates electric pulse. Photo Multiplier Tube Timing pulse 28

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Calorimeter Mass of electron is 511 Ke. V g->e++e- for Eg>1. 02 Me. V Electric pulse ~ particle energy electron/positron g Na. I Crystal P. M. T. 30

Typical Detector System Magnetic field L: length Calorimeter Energy =E Wire Chambers Scitillator Timing = t 1 b = V/c = L/(t 2 -t 1)/c Scitillator P [Me. V/c] = 3 * r[cm] * B[T] Timing =t 2 r: curvature radius, B: magnetic field E=P/b m 2=E 2+P 2 Determine 4 -momentum 31

Other Major Detectors (include past) Position sensitivity Timing sensitivity Detector dead time after a hit 32

Summary • We need to have detector to investigate nature since you can not feel particles. • You have to build and/or be familiar with detector for your own experiments. 33

PHENIX Where is VTX p, Au • Good particle ID • High resolution • High trigger rate p, Au VTX will be installed into inner most detector from beam pipe 34