DØ Central TrackerReplaced with NewScintillating Fiber

Tracker andSilicon Vertex

Detector

The DØ Central Detector UpgradeThe DØ Detector is a 5000 ton multi-purpose detector. It is capable of inspecting 50,000 high-energy particle collisions per second, and recording 30 of them to magnetic media.

It is currently undergoing an extensive upgrade to improve its rate capabilities.

DØ Scintillating Fiber Tracker: Operational Principles

Scintillating Fiber Optical Connector

Waveguide Fiber

Mirror

Electrical Signal Out

Cryostat

Photodetector Cassette

• Charged particles cross a scintillating fiber, where it causes a ‘blink’ of light.

• The light is transported via optical fiber over a distance of 8-11 meters to a device called a VLPC which converts light into electricity.

• VLPC are solid state devices which run at cryogenic temperatures.

• A ‘cassette’ of VLPC devices contains 1024 channels and is housed in a cryostat, which carefully regulates the operating temperature.

VLPC HistoryIn 1987, a paper was published by Rockwell detailing the performance of Solid State PhotoMultipliers (SSPMs). These solid state devices detected both visible and infrared light. Infrared detection technology is regulated under international treaty so Fermilab proposed a device which maintained the visible light response, but reduced the infrared response. This device is called a Visible Light Photon Counter (VLPC).

With the successful demonstration of VLPC technology, the High-Resolution Scintillating Fiber Tracking Experiment (HiSTE) proposal detailed using scintillating fiber technology combined with VLPCs to track particles from high energy particle collisions. There have been six models of HiSTE chips, with HiSTE-VI being used in the DØ experiment.

D+ flow

E field

Undoped Silicon

(Blocking) Layer

Doped Silicon Layer

Gain Region

Drift Region

Top Contact (+)

Bottom Contact (-)

VLPC Operational Principles

Photon is converted in the intrinsic region, creating an electron-hole pair.

Hole drifts into the drift region, where it knocks an electron out from an atom.

Electron accelerates back through gain region, knocking electrons from atoms as it goes.

Spacer region and substrate are for mechanical support and field shaping.

Thus each photon generates a pulse of many electrons. Gains of ×20,000 – 60,000 are achievable.

•+ •-

IntrinsicRegion

GainRegion

DriftRegion

SpacerRegion

Photon

•e •h

Substrate

VLPC Timeline

200220001987

1988 1990 1992 1994 1996 19981989 1991 1993 1995 1997 1999 2001

Initial SSPMPublication

Fermilab ApproachesRockwell

About HEPApplications

ExperimentsBy Rockwell

And Fermilab/UCLA

Using Scintillating

Fibers and SSPMs

VLPCs DifferentiatedFrom SSPMs

HiSTEProposal Submitted

VLPCsSuccessfully

Demonstrated

HiSTE I, HiSTE II,HiSTE III

DØScintillating

Fiber Tracker Proposed

HiSTE IVManufactured

3000 ChannelScintillating

Fiber Test at

Fermilab

Large ScaleTesting ofHiSTE VI

Begins

140,000VLPC Pixels

DØ DataTaking

Commences

The HuntIs On!!

HiSTE VIWafersGrown

Final VLPCDesign

DØScintillating

Fiber Tracker Installed

CommissioningBegins

HiSTE Improvement History

HiSTE I

HiSTE II

HiSTE III

HiSTE IV

HiSTE V

• VLPC concept demonstrated• Visible light quantum efficiency ~85%• Noisy, couldn’t resolve individual photons• Further infrared suppression required

• Infrared suppression adequate• Visible light quantum efficiency ~40%• Narrow operating range (temperature and voltage bias)

• Good infrared suppression• Visible light quantum efficiency ~50%• Improved operating range• Bias Current a little high

• Visible light quantum efficiency ~60%• Good infrared suppression• Bias current 10× higher than HISTE III• Uniformity improvement needed

• Visible light quantum efficiency ~80%• Meets all specifications except for poor performance at high rates.

HiSTE VI

• Solid state photon detectors

• Operate at a few degrees Kelvin (~ -450° F)

• Bias voltage 6-8 Volts

• Detects single photons

• Can work in a high rate environment

• Quantum efficiency for visible light ~80%

• High gain ~50 000 electrons per converted photon

• Low gain dispersion

• Highly suppressed infrared sensitivity

0 1 2 3

Visible

Wafer VLPC Chip

HISTE VI

7.62 cm(3”)

0.30 cm(0.12”)

Each VLPC pixelis a 1 mm diameterdetector, well suited

for use in scintillatingfiber applications.

Each wafer is grownvia vapor phase epitaxy andthen masked for the desired

configuration.