Drift Chambers Drift Chambers are MWPCs where the time it takes for the ions to reach the sense wire is recorded. This time info gives position info: t0= start time, ts=stop time=time electrons reach sense wire For some gases the drift velocity is ~constant (independent of E-field): x=v(ts-t0) A gas with almost constant drift velocity is 50-50 Argon-Ethane, drift velocity » 50mm/nsec By using the drift time information we can improve our spatial resolution by a factor of 10 over MWPCs (1mm ®100 mm). Hex-cell drift chamber drift times are circles around the sense wires 880.P20 Winter 2006 Richard Kass

Drift Chamber Spatial Resolution The spatial resolution of a drift chamber is limited by three effects: Statistics of primary ionization location of the primary ionizations (a few 100mm apart) Diffusion of the electrons as they drift to the wire magnetic field changes alters drift path: drift path depends on “lorentz angle”, ExB How well the electronics measures time must measure time to < 1nsec, must know start time (t0) N=# of primary ions D=gas diffusion constant m=mobility x=drift distance E=electric field Contributions to spatial resolution 880.P20 Winter 2006 Richard Kass

Drift Chambers Drift chambers come in all sizes, shapes and geometries: planar Þ fixed target cylindrical Þ colliding beam Time information gives a “circle” of constant distance around the sense wire (more complicated in B field) In almost all cases, wires in different layers are staggered to resolve the left-right ambiguity Typical cylindrical DC: Many wires in same gas volume. Use small angle stereo for z. Usually use single hit electronics. Sense (anode) and field wires. CLEO, CDF, BELLE, BABAR Tube Chamber: Single sense wire in a cylinder Can make out of very thin wall tubes. Þ very little material Small drift cell Þ single hit electronics Good cell isolation Þ broken wire only affects one tube CLEO’s PTL detector Jet chamber: optimized to resolve two tracks in a “jet”. Drift direction roughly perpendicular to wire plane. Single track gives multiple hits on several wires. Use multi-hit electronics so two tracks on a wire can be resolved. Lorentz angle must taken into account Þ wires are “slanted” 880.P20 Winter 2006 Richard Kass

A Real Life Drift Chamber-BaBar 40 layers total 10 “super layers” 100ns isochromes spatial resolution In B=1.5T the ions do not drift straight to the sense wire (anode) mom. resolution Time to distance relationship complicated! 7104 sense wires (20mm diameter) 30gm tension in each wire, sag~200mm In order to measure “z” (along wire) some wires are “slanted” at a slight angle AR/Isobutane gas (80/20%) HV=~1950V 880.P20 Winter 2006 Richard Kass

Time Projection Chamber TPC measures all 3 space coordinates sx=sy~0.1-0.2 mm (drift time), sz~0.2-1mm (readout pad size) Many hits per track (>100) Þ excellent dE/dx measurement Used at LEP, RHIC PEP4/9-TPC Drawbacks: Very complicated electric field shaping: E||B to reduce effects of diffusion Long drift times Þ complicated gas system Lots of electronic channels Þ complicated electronics 880.P20 Winter 2006 Richard Kass

Silicon Strip Detectors SSD’s are solid state proportional chambers Approximately 1000X more ionization in silicon compared to a gas. Not necessary to have charge multiplication to get useable signals. silicon strip detector measures position to ~10mm. silicon detector has many thin metal strips on top and (sometimes) bottom surface of silicon wafer charged particle ionizes the silicon as it passes through it takes ~3.6eV to create an electron-hole pair in silicon a minimum ionizing particle (one that passes through the silicon) deposits~390 eV/mm in a 300mm thick Si detector (typical) there are ~ 30,000 electron hole pairs created electric field in silicon guides ions to top/bottom ions are collected on one or or two (or 3) strips knowing which strip has signal gives position of charged track relative to silicon detector 880.P20 Winter 2006 Richard Kass

Silicon Strip Detectors Resolution is mainly determined by strip pitch: Dx=3.5s Þ need strips every 50mm to get 15 mm resolution Þ 200 strips per cm Strips can only be »5 cm long (technological limit) Modern silicon strip detectors have 105-106 strips! CLEO III hybrid (one of 122) Require custom electronics electronics must be small electronics must be radiation hard low power dissipation wire bond connections (105-106) Mechanical Structure must be rigid/strong must be low mass to minimize MS mechanical tolerances ~mm preamps Much more engineering involved with silicon detectors compared to drift chambers! Digital ADC capacitors 880.P20 Winter 2006 Richard Kass

Advanced Silicon Detectors Double sided silicon detector (CLEO, BaBar) Put orthogonal (x,y) strips on top and bottom surface. Allows 2 coordinate measurements per silicon wafer minimizes amount of material Þ less MS Problems in high rate environments Þ poor two track separation Pixel detector (ATLAS/CMS) Get position location (x,y) from hit pad (50mm x 50mm) minimizes amount of material Þ less MS Radiation hard(er) Quick response time Small detector capacitance Þ good s/n with thin detector Þ less MS Good two track resolution 880.P20 Winter 2006 Richard Kass

CLEO III Silicon Detector Installation of CLEO III silicon detector 1.25x105 strips Each strip has its own: RC, preamp, ADC Everything custom designed for this experiment. Readout cables Silicon wafers (layer 4) hybrids Drift chamber 880.P20 Winter 2006 Richard Kass

The ATLAS Pixel Detector ~380mm ~1850mm Inner most charged particle tracking Pixel size 50mm by 400 mm ~100 million pixels Barrel layers at r = 5.1 - 12.3 cm Disks at z = 50 - 65 cm Dosage after 10 years: optical link 17 Mrad or 3.7 x 1014 1-MeV neq/cm2 disks barrel layers 880.P20 Winter 2006 Richard Kass

The ATLAS Pixel Detector OSU! A pixel module contains: 1 sensor (2x6cm) ~40000 pixels 16 front end (FE) chips 2x8 array bump bonded to sensor Flex-hybrid 1 module control chip (MCC) There are ~1700 modules 880.P20 Winter 2006 Richard Kass

CLEO II.V Charged Particle Tracking System CLEO II.V had: 3 layer silicon detector 10 layer drift chamber (VD) 51 layer drift chamber (DR) All in a 1.5T B field DR Si VD 880.P20 Winter 2006 Richard Kass

The CLEO Vertex Detector Designed & built at OSU Part of the CLEO detector: 1984-1999 880.P20 Winter 2006 Richard Kass

PDG Summary of Tracking Detectors 880.P20 Winter 2006 Richard Kass