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Principles of Charged Particle Tracking in Particle Physics - Maria Laach 2015

Join the Maria Laach Summer School Part 2 to explore Charged Particle Tracking in Particle Physics, focusing on gaseous detectors, ionization chambers, and drift chambers. Understand detection principles and operation regimes for accurate momentum and position measurements.

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Principles of Charged Particle Tracking in Particle Physics - Maria Laach 2015

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  1. Maria Laach Summer School Maria Laach Abbey 9-18 September, 2015 Principles of Detection for Particle PhysicsPart 2: Charged Particle Tracking Bruce A. Schumm Santa Cruz Institute for Particle Physics and the University of California, Santa Cruz

  2. Charged Particle Tracking: Introduction Basic idea: • Place as many layers in the way of energetic particles as you can afford (cost, material) • Each layer should measure the position of the through-going particle as precisely as possible • Exploit curvature in a magnetic field (typically solenoidal) to measure momentum • We will discuss tracking sensors (gaseous, solid-state) as well as generic aspects of kinematic reconstruction Maria Laach 2015, Part 2: Charged Particle Tracking

  3. Tracking in Cylindrical Geometry Typical application: cylindrical-geometry detector in colliding beam experiment (e.g., the DELPHI Detector at LEP, 1980s and 1990s) • Solenoidal magnetic field • Particles emerging from the collision point execute helical trajectories Maria Laach 2015, Part 2: Charged Particle Tracking

  4. Gaseous Detectors A little “old school”… but still many applications and R&D. Also, generic principles: F. Sauli, Principles of Operation of Multiwire Proportional Chambers, CERN Yellow Report 77-09 (1977) Ionization Recall that primary mode of charged-particle energy loss is ionization; for almost all gases <Eion> is between 20 and 40 GeV • ~5x104 e- per g/cm2 of material Argon STP: ~10 e- per mm Helium STP: ~1 e- per mm Maria Laach 2015, Part 2: Charged Particle Tracking

  5. Most Basic: Cylindrical Ionization Detectors V0 Rb a b Anode (sense) wire Typical dimensions: • b of order cm • a of order 10s of m (1.2 mil = 30 m typical) Different regimes of operation as a function of V0 Maria Laach 2015, Part 2: Charged Particle Tracking

  6. Ionization Detectors: Regimes of Operation I In order of increasing sense wire (“bias”) voltage V0 I. Recombination V0 = 0. No net motion of electrons relative to ion. II. Ionization Chamber For V0 high enough so that E  ~10V/cm over most of gaseous volume, each ionization will produce a 1e- signal.  Radiation detection (Accelerator PPS, diagnostics) Maria Laach 2015, Part 2: Charged Particle Tracking

  7. Ionization Detectors: Regimes of Operation II number of primary ions Maria Laach 2015, Part 2: Charged Particle Tracking

  8. Ionization Detectors: Regimes of Operation IV IV. Geiger-Muller Region For large voltage, avalanche is large, and creates significant UV light (electron-ion recombination) that creates ionization throughout gaseous volume (unless “quenched” by additive) • Complete discharge, large signal, large dead time • “Geiger counter” V. Discharge Tube For very large voltage, gas is unstable, leading to spontaneous discharge and emission of light, independent of passage of ionizing particle.  Fluorescent light Maria Laach 2015, Part 2: Charged Particle Tracking

  9. Regimes of Operation: Graphical Synopsis Signal (in equivalent electrons) as a function of bias voltage V0 for our “typical” ionization chamber Note that Geiger counter signals are of order 1010 electrons (sensitive electronics not required) From: A. Melissinos, Experiments in Modern Physics Maria Laach 2015, Part 2: Charged Particle Tracking

  10. Multiwire Proportional Chambers Charpak, 1968 “Brute-force” approach to achieving position resolution Wires spaced with ~2mm pitch ( ~1mm resolution) Exploits fact that avalanche is close to wire electron drift E E electron drift Maria Laach 2015, Part 2: Charged Particle Tracking

  11. Drift Chambers Exploit distance-time relationship between point of ionization and collection at anode wire. Multiple measurements along trajectory  reconstruct helical trajectory electron drift E Maria Laach 2015, Part 2: Charged Particle Tracking

  12. Opal Precision Drift Chamber Maria Laach 2015, Part 2: Charged Particle Tracking

  13. Drift Chamber Resolution Dominant phenomenon: Diffusion of ionization cloud as electrons drift through field •  proportional to square root of drift distance • Depends on mean time between collision: sensitive to T,P • Can achieve better than 100 m resolution Maria Laach 2015, Part 2: Charged Particle Tracking

  14. Mean Ionization Energy Loss In explicit form, the Bethe energy-loss form is • For incident particle, depends only on the velocity parameters , • If p is known independently (coming soon…) the mean ionization loss determines the mass of the incident particle via p/c = m  Since a drift chamber (or any tracker; true for solid-state tracking as well!) makes multiple measurements of the energy loss, a mean may be calculated  In principle, any tracker also provides particle ID Maria Laach 2015, Part 2: Charged Particle Tracking

  15. Truncated Mean However, recall Landau Distribution: well-defined mean but infinite RMS • An average of proportional-chamber pulse-heights over any number of depositions contains no information about the true mean! SOLUTION: Truncated Mean Remove (truncate) the highest n% of the pulse height, eliminating the pathological tail What should n be? Optimization issue… 20% typical Landau Distribution Truncate Maria Laach 2015, Part 2: Charged Particle Tracking

  16. DeDx and Particle ID Can be done for any repetitive tracking medium (e.g. solid-state) Distribution of truncated means for 45 Gev muons Opal Collaboration: The Opal Detector at LEP p K e Each point is the truncated mean for a single traversing particle , Maria Laach 2015, Part 2: Charged Particle Tracking

  17. Gaseous Tracking Pulse Development I V0 Rb a b +q dr Maria Laach 2015, Part 2: Charged Particle Tracking

  18. Gaseous Tracking Pulse Development II Maria Laach 2015, Part 2: Charged Particle Tracking

  19. Gaseous Tracking Pulse Development III Maria Laach 2015, Part 2: Charged Particle Tracking

  20. Opal Precision Drift Chamber (again) Here, we remind ourselves of the typical drift chamber geometry, so that we can contrast it with that of a more recent idea: The TPC… Maria Laach 2015, Part 2: Charged Particle Tracking

  21. The TPC David Nygren, Lawrence Berkeley National Laboratory The Time Projection Chamber (TPC) 3D gaseous tracking: Z coordinate from drift, r coordinate from anode pads Well-suited for dense tracking environ-ments, including heavy ion physics The ALICE tracker Maria Laach 2015, Part 2: Charged Particle Tracking

  22. Precision Micro-Patterned Gaseous Tracking High fields produced by micro-patterned arrays lead to local gas gain; precision provided by segmentation of anode GEM Detectors MicroMegas e.g., TPC end-plate readout Maria Laach 2015, Part 2: Charged Particle Tracking

  23. Helical Tracking Parameters Most prevalent application of charge-particle tracking is for cylindrical-geometry detectors with a solenoidal B-field  Helical trajectories with five defining “track parameters” Maria Laach 2015, Part 2: Charged Particle Tracking

  24. Helical Track Parameters: , d0, 0 Consider projection in plane transverse to magnetic field (x,y or r, plane): Collision point N.B.: For track with pT > ~1 GeV, only a small arc of the trajectory is visible in the tracking system Radius of curvature 2D point of closest approach J. Strube, PNNL Three of the five track parameters are: d0: 2D distance of closest approach 0:  angle at 2D distance of closest approach  = curvature = 1/R y x z Maria Laach 2015, Part 2: Charged Particle Tracking

  25. Helical Tracking Parameters: , z0 y x z z0  2D point of closest approach Collision point The two remaining track parameters are defined at the 2D point of closest approach: : polar angle z0: longitudinal displacement Maria Laach 2015, Part 2: Charged Particle Tracking

  26. Billoir Algorithms Track parameter resolution can be calculated (in Gaussian approximation) in closed form, e.g., Pierre Billoir, TRACK FITTING WITH MULTIPLE SCATTERING: A NEW METHOD, Nuclear Instruments and Methods in Physics Research 225 (1984) 352-366 There are several (rather dusty) packages available that implement the Billoir method with a convenient driver. For high-energy experiments (LHC, ILC), I have written LCDTRK; see http://scipp.ucsc.edu/~schumm/lcdtrk/lcdtrk20011204.tar.gz • Not a commercial-grade product, but documentation and some support available! NOTE: For Gaussian layer-by-layer measurement uncertainties, curvature () and not transverse momentum (pT) is the Gaussian-distributed track parameter Maria Laach 2015, Part 2: Charged Particle Tracking

  27. LCDTRK Example: Momentum Resolution Note: pT in GeV/c (not MeV/c) for this plot Maria Laach 2015, Part 2: Charged Particle Tracking

  28. Momentum Uncertainty Scaling Behavior I Track of radius of curvature R measured in chamber of radius b Not shown: N precision tracking layers filling tracking volume of radius b. Solenoidal magnetic field (into page) of strength B Typically, 0.5<B<5 Tesla R = 1/ b O x Maria Laach 2015, Part 2: Charged Particle Tracking

  29. Momentum Uncertainty Scaling Behavior II s b O Maria Laach 2015, Part 2: Charged Particle Tracking

  30. Momentum Uncertainty and MCS I 1/pT: Below some value of pT, MCS will dominate the momentum resolution, leading to a regime for which pT/pT2 is not constant. Example: For (proposed!) ultra-precise International Linear Collider tracking systems, break-point is between 50 and 100 GeV…  Low-mass tracking technology is major focus of ILC R&D. Note: pT in GeV/c (not MeV/c) for this plot MCS-dominated Geometry-dominated Maria Laach 2015, Part 2: Charged Particle Tracking

  31. A Modern Alternative: Solid State Tracking Consider adjoining two oppositely-doped semiconductors (circled charges fixed, uncircled are mobile) in a diode junction circled = fixed uncircled = free + + + + + - - - - - + + + + + - - - - - p-type n-type - - - - - - - - - - - - - - - - - - - - + + - - - + + + + + + + + + + + + + + + + + + + + + - - + + + + - - - + + + - - V -xp xn V0 x Depletion Zone Tradeoff between diffusion and energy minimization leads to finite junction potential V0, with associated capacitance C0. Maria Laach 2015, Part 2: Charged Particle Tracking

  32. The Depletion Zone Maximize signal (and minimize capacitance) by maximizing d Maria Laach 2015, Part 2: Charged Particle Tracking

  33. N- and P-Type Sensors Maria Laach 2015, Part 2: Charged Particle Tracking

  34. Bias Voltage and Full Depletion Even for high-resistivity Si (  104 -cm), d is only about 50 m. • At about 80 e/h pairs per micron, signal about 4000 e/h pairs, or about 2/3 fC • Small signal (compare to gas gain of 105 or greater, and multiple ionizations) Solution: Reverse bias voltage (e.g., N-type sensor) Metalization + - + - + - - + - + + - + - + - - + - + p n VB Maria Laach 2015, Part 2: Charged Particle Tracking

  35. Position-Sensitive Solid State Sensors Heavily-doped p-type “implant”; depletes N bulk. Heavily-doped n-type implant to reduce Schottky barrier Metallization N bulk To achieve position resolution, segment anode (N-type) or cathode (P-type) into strips (strip detector) or pixels (pixel detector) Typical “pitch” is around 50 m  point resolution of between 5 and 15 m 5-10 times better than gaseous tracking, but fewer layers. Which is “better”? I discuss in Nucl. Instrum. Meth. A579 (2007) 595-598. • Energy frontier: Si tends to show up more often. • Luminosity frontier (flavor physics): gaseous tracking if it can tolerate the radiation environment. Maria Laach 2015, Part 2: Charged Particle Tracking

  36. Silicon Diode Pulse Development I VB p p+ n+ - + x x0 d E Time scale =    Maria Laach 2015, Part 2: Charged Particle Tracking

  37. Silicon Diode Pulse Development II -Q/e total signal electrons holes t (units of ) For high-resistivity silicon,  =   1 nsec Maria Laach 2015, Part 2: Charged Particle Tracking

  38. Readout Noise Response Weighting Functions RB Id (t) RS ia,va CS where  is the amplifier rise time H. Spieler, Semiconductor Detector Systems, Oxford, 2005 For “lumped” elements, in electron-equivalent noise Maria Laach 2015, Part 2: Charged Particle Tracking

  39. Lumped Elements vs. Distributed Network K. Collier et al., Microstrip electrode readout noise for load-dominated long shaping-time systems, Nucl. Instr. & Meth. A729 (2013), 127. Expectation (dotted) and measurement (red dashed) suggest that distributed sensor RC network shunts significant noise to ground… Maria Laach 2015, Part 2: Charged Particle Tracking

  40. Monolithic Pixel Sensors (e.g. MAPS) Advanced microelectronic technology (sub 100-nm feature size) allows significant processing and data-flow architecture to be developed local to pixel, e.g., the MAPS (Monolithic Active Pixel Sensor) concept; now part of baseline designs. Maria Laach 2015, Part 2: Charged Particle Tracking

  41. Next Stop Next stop: High-energy caloimetry… Maria Laach 2015, Part 2: Charged Particle Tracking

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