09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan Tsinghau/CCAST TPC School January 2008 Experience with the Aleph TPC (and other things) Ron Settles MPI-Munich/Desy

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan Outline What physics do we want to do, where?What physics do we want to do, where? What is the best detector?What is the best detector? TPC and the Aleph TPCTPC and the Aleph TPC

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan International Linear Collider Where?: Technology decision: COLD superconducting à la TESLA chosen Baseline: 200 GeV < √s < 500 GeV Integrated luminosity ~ 500 fb -1 in 4 years 80 % e- beam polarisation Upgrade to 1TeV,  L = 1 ab -1 in 3 years 2 interaction regions Concurrent running with the LHC from 2015

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan The Global Design Effort Formal organization begun at LCWS 05 at Stanford in March 2005 when Barry became director of the GDE Technically Driven Schedule ACFA’07 Beijing: RDR(+cost), DCR

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan Physics we want to do? Physics we want to do? Keisuke gave a nice overview yesterdayKeisuke gave a nice overview yesterday For example,For example, from my talk at Arlington WS Jan.2003:

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan y y+SF 25

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan Where are we with the Higgs? CERN Courier, Nov 2005

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan Very latest electroweak combinations:

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan Why do we think these indirect, precision meas. are telling us anything??? CERN Courier, Nov 2005 :

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan The value of precision measurements…

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan Polarization Multipole expansion

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan …the Higgs? …the Higgs? Expt (GeV)Decay Channel (GeV/c 2 )ln(1+s/b) 115 GeV/c 2 1ALEPH jet ALEPH jet ALEPH jet L3206.4E-miss OPAL jet Delphi jet ALEPH205.0Lept ALEPH208.1Tau ALEPH jet OPAL jet And in addition we have LEP events… And in addition we have LEP events…

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan LCs But this all may be a fata morgana…

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan % Dark matter 25% Baryons Speed of light in the filaments is slower than in the voids. Take this into account, ‘dark energy’ is a fata morgana? And in reality…? Is this true??

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan What is the best detector?What is the best detector?

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan High precision tracking…

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan Highly efficient tracking, high granularity calorimetry…

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan LDC/GLD=ILD Concept or A TPC for a Linear Collider Detector

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan GLD LDC HCal ECal TPC

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan Now 2x10-5/(GeV/c) Now 0.25/  Zpeak Particle Flow

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan The Aleph Time Projection Chamber Ron Settles, MPI-Munich/DESY (talk at Mike Ronan’s TPC 2003)

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan TPC is a 3-D imaging chamber –Large volume, small amount of material. –Slow device (~50  s) –3-D ‘continuous’ tracking (  xy  170  m,  z  600  m for Aleph) Review some of the main ingredients History –First proposed in 1976 (Dave Nygren, PEP4-TPC) –Used in many experiments –Aleph as an example here –Now a well-established detection technique that is still in the process of evolution… Summary

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan Outline Examples TPC principles of operation –Drift velocity, Coordinates, dE/dx TPC hardware ingredients –Field cage, gas system, wire chambers, gating, laser calibration system, electronics The Aleph TPC From the drawing board to the gadget Performance Some ‘features’ (i.e. trouble shooting…) Conclusion

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan Some TPC examples Grand-daddy/mama of all TPCs STAR FTPC ALICE ILD (future) …

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan TPC principles of operation A TPC contains: –Gas E.g.: Ar % CH 4 –E-field E ~ few x 100 V/cm –B-field as large as possible to measure momentum, to limit electron diffusion –Wire chamber (those days) to detect projected tracks y z x E B electron drift charged track wire chamber to detect projected tracks gas volume with E & B fields Now trying out new techniques-- ►

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan TPC Characteristics –Only gas in active volume, small amount of material –Long drift ( > 2 m ) therefore slow detector (~50  s) want no impurities in gas uniform E-field strong & uniform B-field –Track points recorded in 3-D (x, y, z) –Particle Identification by dE/dx –Large track densities possible y z x E B drift charged track

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan Drift velocity Drift of electrons in E- and B-fields (Langevin) mean drift time between collisions particle mobility cyclotron frequency V d along E-field lines V d along B-field lines Typically ~5 cm/  s for gases like Ar(90%) + CH 4 (10%) Electrons tend to follow the magnetic field lines (  ) >> 1

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan D coordinates z x y wire plane track projected track –Z coordinate from drift time –X coordinate from wire number –Y coordinate? along wire direction need cathode pads

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan Coordinate from cathode Pads projected track pads drifting electron s avalanche y x y z –Measure A i –Invert equation to get y Amplitude on ith pad avalanche position position of center of ith pad pad response width

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan TPC Coordinates: Pad Response Width Normalized PRW: Distance between pads is a function of: –the pad crossing angle  spread in r  –the wire crossing angle  ExB effect, lorentz angle  –the drift distance diffusion

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan TPC coordinate resolution Same effects as for PRW are expected but statistics of drifting electrons must be considered electronics, calibration angular pad effect (dominant for small momentum tracks) angular wire effect forward tracks -> longer pulses - > degrades resolution “diffusion” term (…disappears with new technologies…)

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan Particle Identification by dE/dx –Energy loss (dE/dx) depends on the particle velocity. –The mass of the particle can be identified by measuring simultaneously momentum and dE/dx (ion pairs produced) –Particle identification possible in the non- relativistic region (large ionization differences) –Major problem is the large Landau fluctuations on a single dE/dx sample. 60% for 4 cm track 120% for 4 mm track Energy loss (Bethe-Bloch) mass of electron charge and velocity of incident particle mean ionization energy density effect term

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan TPC ingredients (Aleph example) Wire chambers –Gating –Cooling –Mechanics Field cage Gas system Laser system Electronics

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan Wire Chambers 3 planes of wires –gating grid –cathode plane (Frisch grid) –sense and field wire plane –cathode and field wires at zero potential pad size –various sizes & densities –typically few cm 2 gas gain –typically 3-5x10 3 pad plane field wire sense wire gating grid Drift region cathode plane V=0 x z

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan Wire Chambers: ALEPH 36 sectors, 3 types –no gaps extend full radius wires –gating spaced 2 mm –cathode spaced 1 mm –sense & field spaced 2 mm, interleaved pads –6.2 mm x 30 mm –~1200 per sector –total pads readout pads and wires

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan Gating Problem: Build-up of space charge in the drift region by ions. –Grid of wires to prevent positive ions from entering the drift region “Gating grid” is either in the open or closed state –Dipole fields render the gate opaque Operating modes: –Switching mode (Aleph) –Diode mode

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan Cooling, Mechanics Terribly mundane but terribly important (everything is important) Cooling: –Combined air and water cooling to completely insulate the gas volume Mechanics: –25% X_0 for sectors, preamps, cooling (but before cables)

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan E-field produced by Field Cage HV E wires at ground potential planar HV electrod e potential strips encircle gas volume –chain of precision resistors with small current flowing provides uniform voltage drop in z direction –non uniformity due to finite spacing of strips falls exponentially into active volume z y

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan Field cage: ALEPH example Dimensions cylinder 4.7 x 1.8 m Drift length 2x2.2 m Electric field 110 V/cm E-field tolerance  V < 6V Electrodes copper strips (35  m & 19  m thickness, 10.1 mm pitch, 1.5 mm gap) on Kapton Insulator wound Mylar foil (75  m) Resistor chains M  (  0.2%) Nucl. Instr. and Meth. A294 (1990) 121

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan Laser Calibration System Purpose Measurement of drift velocity Determination of E- and B-field distortions Drift velocity Laser system  ∂( v_drift) ~ 1‰ Hookup tracks to Vdet  ∂( v_drift)~a few times 0.01‰ …used after Vdet installation ExB Distortions Laser used only in early days to get firstcorrections. After, tracks (mostly μ pairs from Z decays) used exclusively (read on…) Laser tracks in the ALEPH TPC

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan Gas system Properties: Drift velocity (~5cm/  s) Gas amplification (~7000) Signal attenuation my electron attachment(<1%/m) Parameters to control and monitor: Mixture quality (change in amplification) O 2 (electron attachment, attenuation) H 2 O (change in drift velocity, attenuation) Other contaminants (attenuation) Typical mixtures: Ar91%+CH 4 9% Ar93%+CH 4 5%+CO 2 2% Ar93%+CF 4 3%+IsoB1% Operation at atmospheric pressure

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan Influence of Gas Parameters (*) (*) from ALEPH handbook (1995)

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan Electronics: from pad to storage TPC pad amp FADC zero suppression feature extraction DAQ Pre-amplifier charge sensitive, mounted on wire chamber Shaping amplifier: pole/zero compensation. Typical FWHM ~200ns Flash ADC: 8-9 bit resolution. 10 MHz. 512 time buckets Multi-event buffer Digital data processing: zero-suppression. Pulse charge and time estimates Data acquisition and recording system

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan Analog Electronics ALEPH analog electronics chain –Large number of channels O(10 5 ) –Large channel densities –Integration in wire chamber –Power dissipation –Low noise

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan More details about Aleph…

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan Wire Chambers: ALEPH Long pads for better coordinate precision

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan After 3 man-centuries (or more, depending on how you count) … From TPC90… ↑ …as usual, lots of meetings… ↓

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan From the drawing board to the gadget…

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan A Detector with TPC …where… you end up with ►

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan Thanks to many people… (and to Pere Mato and Werner Wiedenmann for help on these slides) …you need a few cables, cooling, etc…

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan It finally started working…

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan ALEPH Event, early days…

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan And towards the end…

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan Coordinate Resolution(1): ALEPH TPC

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan Coordinate Resolution(2): ALEPH TPC

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan dE/dx: Results Good dE/dx resolution requires long track length large number of samples/track good calibration, no noise,... ALEPH resolution up to 334 wire samples/track truncated (60%) mean of samples 4.5% (330 samples)

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan But, there were ‘FEATURES’… Werner’s talk contains many details, see alephwww.mppmu.mpg.de/~settles/tpc  here a few examples…

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan Historical Development (1) LEP start-up: –Failure of magnet compensating power supplies in 1989 required development of field-corrections methods derived from 2 special laser runs (B on/off) correction methods described in NIM A306(1991)446 –Later, high statistics Z->μμ events give main calibration sample LEP 1: –VDET 1 becomes operational in 1991 –Development of common alignment procedures for all three tracking detectors –Incidents affect large portions of collected statistics and require correction methods based directly on data , seven shorts on field cage affect 24% of data 1994, disconnected gating grids on 2 sectors affect 20% of data –All data finally recuperated with data-based correction methods

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan Historical Development (2) LEP 1/2: –Tracking-upgrade program (LEP 1 data reprocessed) Improved coordinate determination requires better understanding of systematic effects Combined calculations for field and alignment distortions, reevaluation of B-field map –All methods for distortion corrections now based directly on data –Development of “few”-parameter correction models to cope with drastically reduced calibration samples at LEP 2 LEP 2: –New VDET with larger acceptance at beginning of run periods have limited statistics –Frequent beam losses cause charge-up effects and new FC shorts Superimposed distortions Short-corrections with Z -> μμ;time-dep. effects tracked with hadrons

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan Examples from Werner’s slides…

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan e.g. (see Werner’s slides…)

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan e.g., non-linear F.C. potential

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan e.g., disconnected gating grids

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan e.g., field-cage shorts

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan (N.B., design your detector to be easily accessible…)

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan σ ~ 0.54E-03

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan the bottom line (e.g., momentum resolution)

09/01/2008Ron Settles MPI-Munich Tsinghua TPC School Jan Conclusion We’d better learn from these past lessons so that the new TPC will evolve to a much better main tracker for the future LC  its performance will then improve by an order of magnitude relative to that at Lep…