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Fast Timing via Cerenkov Radiation

Earle Wilson,

Advisor: Hans Wenzel

Fermilab

CMS/ATLAS Fast Timing Simulation Meeting

July 17, 2009

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Overview

• Conducted simulations using a 6x6mm x 9cm Quartz bar and an incident beam of 7TeV protons:

Observed photons statistics: photon spectrum, prevalence of secondary photons etc.

Obtained arrival time and timing resolution using the quantum efficiency of the Hamamatsu MCP R3809U-65.

Studied effects of varying angle of incident proton beam. Compared results from Hamamatsu with Photek 240.

• Started simulations using aerogel: Observed Photon statistics. Studied effects of Rayleigh Scattering.

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Quartz Bar Geometry and Set-up

-Quartz bar: 6x6 mm x 9cm.

-6X6 mm sensitive detectors on each end.

-Incident beam of 7TeV protons perpendicular to bar.

-No air gap between detectors and quartz bar.

-Only Cerenkov radiation. Scintillation, Rayleigh scattering and dispersion were not added.

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Toolbox• Geant4: Simulates processes inside radiator, i.e.

Quartz bar and Aerogel. Includes Electro-magnetic physics Cerenkov radiation Rayleigh Scattering (only for Aerogel) Absorption Dispersion Reflection, refraction etc...

Outputs ROOT file for analysis

• ROOT: Simulates processes inside detector Quantum Efficiency Jitter

Outputs ROOT file for analysis.

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Quartz Bar Properties

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Comparing Geant4 to calculations

Geant 4

Calculation

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Photon Spectrum/Statistics

Geant 4 (primary photons)CalculationGeant 4 (Secondary photons)

Geant4 compares very well with standard calculations. Secondary photons radiate mostly in the blue/ultra-violet but there are significantly fewer secondary photons than primary photons. However, for a given event, there could be more secondary photons than primaries. This could have a major effect on timing and time resolution.

Refractive Index: 1.51000 EventsResults Taken at the moment of creation.

Primary PhotonsSecondary Photons

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Quantum Efficiency

Hamamatsu MCP R3809U-65Photek 240

The Hamamatsu has a better overall quantum efficiency, peaking at 40% at ~520nm.Photek 240 has a lower overall Q.E. but much better sensitivity in the blue/ultraviolet range.

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Average Number of Photons and Photoelectrons at Each Detector

vs. Angle of Incident Beam

-Jitter: 30 psec-Gain: 100-Cerenkov angle: 48.2-Each data point is the average of 1000 events.

Photons

Photoelectrons: Hamamatsu MCP R3809U-65

Photoelectrons: Photek 240

Cerenkov Angle

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Arrival Time and Timing-Resolution vs. Angle Incident

Beam

-Timing and timing resolution obtained using DCOG Method-Cerenkov Angle: 48.2-Jitter: 30 psec, Gain: 100-Each data point is taken over 1000 events.-Best timing resolution of ~2.8 psec at 65 degrees.

Photoelectrons: Hamamatsu MCP-PMT R3809U-65

Photoelectrons: Photek 240 Photoelectrons: Photek 240

Photoelectrons: Hamamatsu MCP-PMT R3809U-65

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Cerenkov AngleArrival time: ~0.24nsec

Cerenkov Angle:Timing resol. ~3.2 psec

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Aerogel (SiO2)Dimensions:

4cm X 4cm X 1cm

Silicon MCP-PMT dimensions:4cm X 4cm

Refractive Index: 1.0306

Incident protons @ 7TeV

Simulation of Aerogel Radiator

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Refractive Index: 1.0306

Material Properties of Aerogel

NOTE THE SCALES

Obtained values from a Geant4 example forRich Detector simulation for LHCb:http://www-geant4.kek.jp/lxr/source/examples/advanced/Rich/

1313Without Rayleigh Scattering With Rayleigh Scattering

Refractive Index: 1.0306

~10% loss of Photons

Simulation of Aerogel Radiator

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Simulation of the Aerogel Counter

Without Rayleigh Scattering Refractive Index: 1.0306

Aerogel (SiO2)Dimensions:

4cm X 4cm X 1cm

Silicon MCP-PMT dimensions:4cm X 4cm

Plane Mirror: 5cm * 5cm

Mirror Tilt: 45 degrees

Incident protons @ 7TeV

We plan to compare simulations with test beam results.

40 mm40mm

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•Create identical set-up of test beam experiment with Aerogel. Compare simulation results with experimental results. Explore ways to optimize experiment.

•For Quartz Bar Simulation: vary the position of the incident proton beam and observe changes in timing resolution.

•Vary length and thickness of Quartz Bar and observe changes in timing resolution.

• ...

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Upcoming Work