ZEUSCentral Tracking Detector (CTD)

How does it work?

How is it used?

Mark Bell

ZEUS on HERA at DESY

ZEUSHERA

HERA accelerator: 6km long

920GeV protons &27.5GeV electrons

ZEUS Physics: Deep inelastic scattering, structure functions, electroweak, heavy flavours, exotics, QCD, diffraction.

Understanding proton & photon structure.

ZEUS Detector

CTD

Weighs 3600 tonnes = 1000 elephants

12m

19m

A multipurpose detector

Why does ZEUS need a CTD?

Charged particle detectionReconstruct final state by:

Identifying tracks and vertices

Measuring momentum

Measuring dE/dx

Trigger information

What properties must the CTD have?

CTD specifications

Good spatial and momentum resolution

Wide angular acceptance

Short drift time

Solution: Jet drift chamber in uniform magnetic field

Small individual cells

Separates close together tracks

Provides fast information for trigger

CTD design

2.05m

0.79m

1.4T magnetic field along beam axis provided by superconducting solenoid coil

9 superlayers

600 drift cells

5000 sense wires

20000 field wires

Covers polar angle from 15º to 164º

Gas Mixture

Ar:CO2:C2H6 in respective proportions 83:12:5.

Argon: Noble gas – good gain at low voltage, stable High specific ionisation, and cheaper than Kr and Xe

CO2: Reduces electron drift velocity

Stops whisker growth on wires

Ethane: Polyatomic molecule – quencherEnables CTD to operate at a higher voltage

CTD drift cell

Sense wireField wire

Spatial resolution ~ 0.1mm

Shaper wireGround wire

Field, ground and shaper wires provide uniform field.

Cell rotated to compensate for Lorentz angle.

CTD usesTracksMomentumdE/dxParticle ID

First level triggerZ-by-timingTracksVertex

Second level triggerFADC timingTrack parametersHigh pt tracks

Example event

Neutral currentHigh pt electron

Hadron jet

Identified by CTD

ZEUS Run 45923 Event 1349

SummaryHow does the CTD work?

Jet drift chamber (working reliably since 1992)Specific gas mixtureSmall cells with lots of wiresUniform electric and magnetic fields

What is the CTD used for?Particle identification and triggeringAllows interesting physics to be done!