Properties Pr Detect ction o s of E of h high-energy Elementar ary y Par y par Particl artic icles f cle Fluxe s from t uxes s in Pr the Un Primar Univ iverse ary Co y Cosm se: smic c Rays Meas Rays bas asic co c concepts, asured wi s, methods, with the A s, an Alpha and ch a Mag chal allenges agnetic ic Spect ctrometer on the Internat atio ional al Sp Space ace Statio ion 6 th CNRS thematic School of Astroparticle Physics 26/11/2019 – OHP Saint Michel l’Observatorie, France Francesco Nozzoli INFN-TIFPA
HOW much does it cost? SpaceX: a revolution in spaceflight is ongoing... Past/current space experiments costs >10$/g The cost of the launch has implications in the detector performances/design HEAO3 AMS01 AMS02 NUCLEON 6T 45T 2 0.4T 2.4T 0.5T 0.8T 0.4T 7.5T 1.4T 0.4T HERD? AMS100? VOYAGER ULYSSES ALADINO? PAMELA DAMPE
Balloons? Not really cheaper now … was an option for past experiments Residual atmosphere is a passive target: the same of 5 cm of plastic - Fragmentation effects - Production of secondary particles (problem for antimatter search) by comparison Galaxy grammage for CR typ. path lenght is ~2 g/cm 2 3
your kinetic energy during a quiet walking (3km/h) … but the momentum of just 4 a single eyelash hair ...
GALACTIC SOURCES (some interesting PeVatron) EXTRA-GALACTIC 5
GALACTIC SOURCES Direct measurement of cosmic rays with a detector in space are feasible above this line (m 2 acceptance x year) EXTRA-GALACTIC Indirect measurements (next lectures … ) 6
Cosmic Ray composition: NUCLEI composition: - particle charge - particle “Energy” SubFe LiBeB “High” abundances of “secondary nuclei” Production by Fragmentation 7
Cosmic Ray composition: NUCLEI composition: - particle charge - particle “Energy” 8
Cosmic Ray composition: NUCLEI composition: - particle charge - particle “Energy” which “Energy”? Kinetic Energy: calorimeters (ATIC, JACEE, RUNJOB) E/nucleon: TRD, Cherenkov (CRN-Spacelab, HEAO, CREAM, TRACER, HESS) Rigidity (P/Z): Spectrometers (AMS02, Pamela, Bess) 9
Energy vs Energy/nucleon vs Rigidity: Measurement + Physics RIGIDITY: GV (Giga-Volt) MEASUREMENT: P/Z is the quantity related to the trajectory in magnetic field (easily converted to Momentum knowing the particle charge Z) PHYSICS: Different particles with same rigidity follow the same trajectory in magnetic fields (in the Galaxy, in the Heliosphere, in the Earth magnetic field, in the detector field) Main effects of propagation in the magnetic field (and the main time dependent solar modulation effects) would cancel out in <Flux Ratio> vs <Rigidity> Energy/nucleon: GeV/n (usually average isotopic composition is assumed) MEASUREMENT: is a quantity related to velocity (ToF, RICH, TRD) (they measure GeV/M and cannot be converted to Energy if mass is unknown) PHYSICS: Fragmentation of nuclei roughly conserve E/n in spallation processes (when a relativistic CR nuclei during propagation interacts on a proton of ISM) A + p => A 1 + A 2 + p E/A ~ E 1 /A 1 ~ E 2 /A 2 10
Flux ratio vs Rigidity: solar modulation Solar modulation => time variation Solar modulation (Voyager is now outside the magnetosphere) Flux ratio vs R “time-flat” 11
Particle identification - a summary: 1 AMS02: 7.5 Tons – 5x4x3m B=0.15T in space since 2011 able to identify few antinuclei TRD over 150G events (0.5m 2 sr) is shown for PID examples ToF U 2 MAGNET 3-4 - Absolute value of charge: VERY SIMPLE Trk 5-6 - Particle Mass: easy for E<M, very difficult for E>>M 7-8 (typically evaluated by “velocity” vs Energy) ToF L - Particle Velocity: “easy” at few % (but saturation to β=1) (TRD measuring γ = E/M to avoid saturation for E>>M) RICH 9 - Particle direction: VERY SIMPLE ECAL - Particle Momentum: hard to do better than few %, very difficult for P>TV - Charge sign: (up to now) impossible for R>TV - Particle Energy: feasible down to few %, but large systematics for E>>TeV 12
The “easy” measurement: particle CHARGE Vertices of electromagnetic interactions are proportional to particle charge z => detection processes are typically based on EM interaction, thus prop to z 2 Z 13
Energy loss: Bohr classical evaluation Momentum transferred to an electron: Gauss th. ze 2 dx Φ E = Q Δ P = ∫ F dt = ∫ eE ⊥ v = 2 πϵ 0 b v ϵ 0 Energy loss in dV = 2πb db dx : n e = ρ N A Z / A − dE =(Δ P ) 2 2 e 4 1 4 π z db n e dV = 2 n e b dx 2 2 m e ( 4 πϵ 0 ) m e v ze 2 1 Δ E max = 2 γ 2 m e v 2 b min = b min : head on collision (v e = 2 v) 2 4 πϵ 0 γ m e v b max : This approach assumes electrons “at rest” that is Tcollision << Trevolution Tcollision ≈ b/(γv) and Trevolution ≈ 1/ν => b max ≈ γv/ν (then integrate over b) Bohr formula: Full quantum mechanical: Bethe-Block 2 4 π N A A ln ( γ 2 m e v 3 2 2 − dE e z 2 ρ Z − dE dx =( ) ) 2 ν 4 πϵ 0 m e ρ dx v z e relativistic rise (E>>M) projectile “minor” corrections Target material 14 Z/A quite similar in all materials main material effect from density
Energy loss: Bethe Block – in different materials − dE ρ dx The main effect of target material (due to the density) can be factorized out. 15
Energy loss: Bethe Block – in different materials Z/A (mainly) MIPs: 1.1-1.8 MeVcm 2 /g for Z>2 targets − dE ρ dx The main effect of target material (due to the density) can be factorized out. 16 MIPs (Minimum Ionizing Particles) are “calibration sources” for detectors.
Energy loss: Bethe Block - the Charge measurement N particle detector: deposited Energy to detector a voltage ΔE ΔV Δx DAQ Data acquisition from ΔV to a number (ADC) (Analog to Digital Converter) (from the voltage to a number) Boron z=5 Neon z=5 x2 =10 Signal amplitude: 860 ADC channels Signal amplitude: 860 x4 = 3440 ADC channels − dE ρ dx to measure dE/dx also some tracking to measure dx is necessary… (and to get a good charge measurement also some value for velocity is needed) 17
Energy loss: Bethe Block - the Velocity measurement almost proton Momentum(GeV/c) − dE ρ dx If charge is known, the energy loss allows a reasonable velocity measurement for γ<1 (possible but hard to exploit the relativistic rise for γ measurement) 18 On the other hand correction for this effect is required for precise charge measurements.
Simple spectrometers ΔE/E (mass for sub-MIPs particles): Advanced Composition Explorer (1997) ACE-CRIS evidence for 60 Fe (τ ≈ 2.6My) 200<E<500 MeV/n => PRODUCED BY A NEARBY SN 19
mass above MIPs? (directly measured) Velocity vs Momentum ISOMAX: Balloon (1998) 10 Be (τ ≈ 1 .4My) is the clock of cosmic rays (propagation times) (expected) DETECTOR COMPLEXITY INCREASES Velocity direct measurement: Time of Flight spectrometers Cherenkov Detector Momentum measurement: (R = P/z) 20 Magnet + tracker
Velocity measurement using Time Of Flight c = 30cm/ns (speed of light) plastic scintillator: particle n ≈ 1.6 (plastic scint. refr. index) ≈ 10000 photons/MeV τ ≈ ns (but N photons) => σT ≈ ns/√N ≈ 50-100 ps L A1 L A1 t 1 = t A +L A1 n/c t A t 1 t 2 t 2 = t A +L A2 n/c t A = (t 1 +t 2 )/2 + L n/(2c) L A2 H t B = (t 3 +t 4 )/2 + L n/(2c) PhotoMultiplierTubes Δx t B ToF = t B – t A = (t 3 +t 4 -t 1 -t 2 )/2 t 3 t 4 β = Δx/(ToF c) L B3 L B4 some tracking is required L Some “self tracking” capability: Velocity resolution: Δβ/β ≈ ΔToF/ToF ≈ 100 ps c/H t 2 -t 1 =(L A2 -L A1 )n/c=ΔL A n/c H=1m => Δβ/β ≈ 3% t 4 -t 3 =(L B4 -L B3 )n/c=ΔL B n/c Energy up to ≈ GeV/n (Δx) 2 = H 2 + (ΔL A -ΔL B ) 2 /4 Position resolution (along the bar) from time difference ≈ few cm 21
Example: AMS02 - Deuteron flux ToF RICH-NaF 1GeV/n RICH-Agl 3GeV/n 9GeV/n 22
Velocity measurement using Cherenkov Ring Imaging Basic equations: 1) cos θ = 1/(n β ) [Cherenkov] 2) n sin θ = sin θv [Snell] 2 θ λ 2 −λ 1 2 sin 3) N ph ≃ϵ d 2 πα Z λ 2 λ 1 N ph ≃ϵ d K Z 2 sin 2 θ Typically K 500-1000 photons/cm: Typ. photon coll.eff. 0.01-0.3 radiator d Radiator “d” θ expansion expansion Refmector θv length: L vacuum Detectors L # photons => Z 2 PMT plane Example of AMS02 RICH: L = 45cm s = d tg θ AeroGel n = 1.05 β min = 0.95 sin θ ≈ 0.3 d=2.5cm ring average NaF: n = 1.33 β min = 0.75 sin θ ≈ 0.65 d=0.5cm ring radius thickness r = d sin 2 θ d β s d β dr ∼ d β 2 tg θ+ Ltg θ v ¯ σ β =σ r dr = L n √ 12 ( N ph − 2 ) √ 12 ( N ph − 2 ) some tracking helps a β ∼ 1.2 x 10 − 3 lot to find the ring σ β AMS02:<N ph > ≈ 3xz 2 ; 23 ⇒ 10 GeV / n center z
Momentum measurement: magnetic spectrometers Lorentz force 1 2 d P dt = z e v × B Helix trajectory: R=P/z ρ = P ⊥ 3 zeB ⇒ ρ [ m ]= R [ GV ] 0.3 B [ T ] 4 Rigidity resolution: 5 Sagitta: y 2 - (y 1 +y 3 )/2 MAGNET 6 0.3 B = 8 √ 3 / 2 σ y 2 )≃ L 2 σ 1 / R = σ 1 / ρ s = ρ ( 1 − cos θ 2 8 ρ 0.3 B L 7 8 R σ R R = R σ 1 / R = MDR 9 ρ Maximum Detectable Rigidity For a Tracker with N>>3 layers: 1 720 σ y MDR = σ 1 / R ≃ √ N + 4 2 0.3 B L AMS02: z=1 σ y =10um MDR (z=1) = 2 TV z=2 σ y = 5um (larger S/N) 24 s = y 2 - (y 1 +y 3 )/2
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