Time Projection Chamber Principles of operation and the ALICE - PowerPoint PPT Presentation

Time Projection Chamber Master seminar: Particle tracking and identification at high rates Physikalisches Institut Universität Heidelberg Time Projection Chamber Principles of operation and the ALICE example Max Lamparth, 18 th November 2016

Time Projection Chamber Outline - Concept of a TPC - Underlying theory - The ALICE TPC - Variations and outlook 2 Max Lamparth, 18 th November 2016

Time Projection Chamber Concept of a TPC 3 Max Lamparth, 18 th November 2016

Concept of a TPC Time Projection Chamber What is a TPC? TPC: 3D Reconstruction of charged particle trajectories Invented by David Nygren (1974) + / e - for 29 GeV -collisions at SLAC in PEP 4 e 4 a) LBL-SLAC, 1977, b) history.lbl.gov, c) wikipedia.com, d) Emanuel Pollacco, 2015 Max Lamparth, 18 th November 2016

Concept of a TPC Time Projection Chamber How does it work? Produced particles by collision propagate through gas/liquid → deposit energy and ionize gas → E-field to induce drift → detect electrons in end plates - ions e 5 a) O. Schäfer, lctpc.org Max Lamparth, 18 th November 2016

Concept of a TPC Time Projection Chamber How does it work? 6 a) Magnus Mager, Aug 2016 Max Lamparth, 18 th November 2016

Concept of a TPC Time Projection Chamber How does it work? 7 a) Magnus Mager, Aug 2016 Max Lamparth, 18 th November 2016

Concept of a TPC Time Projection Chamber How does it work? 8 a) Magnus Mager, Aug 2016 Max Lamparth, 18 th November 2016

Concept of a TPC Time Projection Chamber How does it work? 9 a) Magnus Mager, Aug 2016 Max Lamparth, 18 th November 2016

Concept of a TPC Time Projection Chamber How does it work? 10 a) Magnus Mager, Aug 2016 Max Lamparth, 18 th November 2016

Concept of a TPC Time Projection Chamber How does it work? 11 a) Magnus Mager, Aug 2016 Max Lamparth, 18 th November 2016

Concept of a TPC Time Projection Chamber How does it work? 12 a) Magnus Mager, Aug 2016 Max Lamparth, 18 th November 2016

Concept of a TPC Time Projection Chamber How does it work? 13 a) Magnus Mager, Aug 2016 Max Lamparth, 18 th November 2016

Concept of a TPC Time Projection Chamber How does it work? 14 a) Magnus Mager, Aug 2016 Max Lamparth, 18 th November 2016

Concept of a TPC Time Projection Chamber How does it work? 15 a) Magnus Mager, Aug 2016 Max Lamparth, 18 th November 2016

Concept of a TPC Time Projection Chamber How does it work? 16 a) Magnus Mager, Aug 2016 Max Lamparth, 18 th November 2016

Concept of a TPC Time Projection Chamber How does it work? Produced particles by collision propagate through gas/liquid → deposit energy and ionize gas → E-field to induce drift → detect electrons in endplates Detection: → Use principles of Multi-Wire-Proportional-Chamber - ions e Combine for full 3D reconstruction → xy-coordinates projected → z-coordinate via drift time ( ) ≈ 90 μ s Combinable with e.g. B-field for momentum measurement 17 a) O. Schäfer, lctpc.org Max Lamparth, 18 th November 2016

Time Projection Chamber Outline - Concept of a TPC - Underlying theory - The ALICE TPC - Variations and outlook 18 Max Lamparth, 18 th November 2016

Time Projection Chamber Underlying theory - Ionization mechanism - Wire grids - Motion in gas - Amplification and gain 19 Max Lamparth, 18 th November 2016

Underlying theory Time Projection Chamber Ionization mechanisms in gas - , ... Charged particles ( ) propagate through gas π , e → energy loss and ionization W ⟨ N I ⟩ = L ⟨ dE λ = 1 /( N σ I ) dx ⟩ W : energy, N I : average number of ionization electrons, N : particle density, λ : mean free flight path, σ I : ionization cross section per electron 20 a) b) “Particle Detection with Drift Chambers”, Blum et al., 2008 Max Lamparth, 18 th November 2016

Underlying theory Time Projection Chamber Ionization mechanisms in gas - , ... Charged particles ( ) propagate through gas π , e → energy loss and ionization W ⟨ N I ⟩ = L ⟨ dE λ = 1 /( N σ I ) dx ⟩ Different mechanisms: ● primary ionization: + e - , π A ++ e - e - ... π A → π A ● secondary ionization: - A → e - A - A + e - , e ++ e - e - ... e ● Intermediate: - A → e - A * or e * π A → π A * B → A B + e - A 21 a) b) “Particle Detection with Drift Chambers”, Blum et al., 2008 Max Lamparth, 18 th November 2016

Underlying theory Time Projection Chamber Ionization mechanisms in gas Total Energy loss determined by: ⟨ dx ⟩ total = ⟨ dx ⟩ collision + ⟨ dx ⟩ Bremsstr dE dE dE ⟨ dx ⟩ collision dE In TPC: Only measure without retarded ionization Adjusted Bethe-Bloch formula with cut-off at 95% Energy → ignore high energy electrons producing separable tracks (~1 cm restriction) 2 E max βγ 2 [ ln √ 2 mc 4 2 2 2 −δ(β) = 2 π N e −β ( dE z dx ) ] 2 I 2 β mc restricted z : charge of particle, N : number density of electrons in traversed matter, I : mean excitation energy, δ : correction term 22 a) Jens Wiechular, 2013 b) “Particle Detection with Drift Chambers”, Blum et al., 2008 Max Lamparth, 18 th November 2016

Underlying theory Time Projection Chamber Ionization mechanisms in gas Total Energy loss determined by: ⟨ dx ⟩ total = ⟨ dx ⟩ collision + ⟨ dx ⟩ Bremsstr dE dE dE ⟨ dx ⟩ collision dE In TPC: Only measure without retarded ionization Adjusted Bethe-Bloch formula with cut-off at 95% Energy → ignore high energy electrons producing separable tracks (~1 cm restriction) 2 E max βγ 2 [ ln √ 2 mc 4 2 2 2 −δ(β) = 2 π N e −β ( dE z dx ) ] 2 I 2 β mc restricted ● Average energy loss due to electromagnetic interaction ● For high energies Bethe-Bloch applicable to electrons 23 a) Jens Wiechular, 2013 b) “Particle Detection with Drift Chambers”, Blum et al., 2008 Max Lamparth, 18 th November 2016

Underlying theory Time Projection Chamber Ionization mechanisms in gas Fermi-Plat. 2 E max βγ 2 [ ln √ 2 mc 4 2 2 2 −δ(β) −β ( dE = 2 π N e z dx ) ] 2 I 2 β mc 24 restricted a) ALICE TPC, 2015 Max Lamparth, 18 th November 2016

Underlying theory Time Projection Chamber Ionization mechanisms in gas Fermi-Plat. More Detail in upcoming talk: “Signal creation, energy loss and dE/dx” 25 a) ALICE TPC, 2015 Max Lamparth, 18 th November 2016

Underlying theory Time Projection Chamber Wire grids and fields E-field of a wire & displaced wire in a tube 1 U 1 λ E r = r = 2 π ϵ o ln ( a / b ) r U d ( E 1 ) y = − ln ( a / b ) 2 b → sagitta due to drift field → affects gain λ : linear charge density, U : voltage, d : displacement from center 26 a) b) c) d) “Particle Detection with Drift Chambers”, Blum et al., 2008 Max Lamparth, 18 th November 2016

Underlying theory Time Projection Chamber Wire grids and fields E-field of a wire & displaced wire in a tube 1 U 1 λ E r = r = 2 π ϵ o ln ( a / b ) r U d ( E 1 ) y = − ln ( a / b ) 2 b → sagitta due to drift field → affects gain Use multiple wires to create grid: ● Similar to layer of charge with σ = λ/ s 27 a) b) c) d) “Particle Detection with Drift Chambers”, Blum et al., 2008 Max Lamparth, 18 th November 2016

Underlying theory Time Projection Chamber Wire grids and fields E-Field of a wire grid central electrode Drift region Sensor /acc. region 28 a) b) “Particle Detection with Drift Chambers”, Blum et al., 2008 Max Lamparth, 18 th November 2016

Underlying theory Time Projection Chamber Wire grids and fields E-Field of a wire grid Limited transparency (neutral wire): 29 a) b) “Particle Detection with Drift Chambers”, Blum et al., 2008 Max Lamparth, 18 th November 2016

Underlying theory Time Projection Chamber Wire grids and fields Gating grid: ● Additional layer of wires “open”: “closed”: → excludes ions/electrons → stops ion back-flow → no space charge → background measurement 30 a) b) c) “Particle Detection with Drift Chambers”, Blum et al., 2008 Max Lamparth, 18 th November 2016

Underlying theory Time Projection Chamber Motion in gas Ions and electrons propagate differently - : m e ≪ m p → leads to isotropic scattering e + : m A ≈ m p A → leads to preferred scattering direction In reality: E and B field → B field necessary for momentum measurement Langevin equation: m d u dt = e E + e [ u × B ] − K u u : velocity vector K : frictional force (due to interaction with gas) constant 31 a) “Particle Detection with Drift Chambers”, Blum et al., 2008 Max Lamparth, 18 th November 2016

Underlying theory Time Projection Chamber Motion in gas Solve Langevin equation: → Helix-like propagation Two Cases: (dominant in TPC) E ∥ B 2 τ 2 B y u y = ω τ B x +ω 2 τ u z 2 ) B z ( 1 +ω u i : velocity component, 2 τ 2 B x ω : electron cyclotron frequency, u x = −ω τ B y +ω τ= m / K 2 τ u z 2 ) B z ( 1 +ω Ψ : E field component in drift direction (dominant in TRD) E ⊥ B | u | = ( e / m ) τ 2 | E | = e m τ| E | cos (Ψ) 2 τ √ 1 +ω 32 a) b) c) “Particle Detection with Drift Chambers”, Blum et al., 2008 Max Lamparth, 18 th November 2016