DØ Central Tracker Replaced with New Scintillating Fiber Tracker and Silicon Vertex Detector The DØ Central Detector Upgrade The 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 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 History In 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. +- Intrinsic Region Gain Region Drift Region Spacer Region Photon eh Substrate

VLPC Timeline Initial SSPM Publication Fermilab Approaches Rockwell About HEP Applications Experiments By Rockwell And Fermilab/UCLA Using Scintillating Fibers and SSPMs VLPCs Differentiated From SSPMs HiSTE Proposal Submitted VLPCs Successfully Demonstrated HiSTE I, HiSTE II, HiSTE III DØ Scintillating Fiber Tracker Proposed HiSTE IV Manufactured 3000 Channel Scintillating Fiber Test at Fermilab Large Scale Testing of HiSTE VI Begins 140,000 VLPC Pixels DØ Data Taking Commences The Hunt Is On!! HiSTE VI Wafers Grown Final VLPC Design DØ Scintillating Fiber Tracker Installed Commissioning Begins

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 ~ electrons per converted photon Low gain dispersion Highly suppressed infrared sensitivity 0123 Visible

Wafer VLPC Chip HISTE VI 7.62 cm (3”) 0.30 cm (0.12”) Each VLPC pixel is a 1 mm diameter detector, well suited for use in scintillating fiber applications. Each wafer is grown via vapor phase epitaxy and then masked for the desired configuration.

B A = VLPC die B = Aluminum Nitride substrate C = Solder preform A A B C