TORCH – a Cherenkov based Time-of-Flight DetectorEuan N. Cowieon behalf of the TORCH collaboration

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Outline

• TORCH Design and Principles.• Suitability for use in LHCb.

• MCP Requirements.• Results and simulation work.

• Electronics.• Test-Beam plans and Preparation.

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Time Of internally Reflected Cherenkov

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The basics of the TORCH design

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• TORCH aims to achieve 10-15ps timing over large areas.

• Utilises Cherenkov light for fast signal production.

• Focussing optics along edges couple light to photodetectors.

5m

6m

TORCH in LHCb

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pp

10 – 300 mrad

LHCb showing potential locations for TORCH [1]

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See:The RICH detector of the LHCb experimentAntonis PapanestisSession 2a) Experiments and Upgrades

Motivation

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π-K ToF difference as a function of particle momentum

• TORCH will be used in conjunction with RICH 1 & 2.

• Covers momentum region up to 10GeV/c.

• Pion-Kaon time-of-flight difference ~35ps over 9.5m.

• 3-σ separation 10-15 ps.

• ~30 photons detected per track gives requirement of 70ps per photon.

Focussing

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Schematic of focussing optics

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• Converts photon propagation angle into position on focal plane.

• Photodetector is split into 128 pixels, with resolution ~1mrad.

• Accounts for uncertainty in photon emission position through plate.

• Covers angles from 0.45rad to 0.85rad.

Photon Detection

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Required granularity of the final TORCH MCP.

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Development of MCP-PMTs underway.

Final device requires:

1. Stable gain performance up to least 5C/cm2.

2. Granularity equivalent to 8x128 pixels.• Proposed device has 64x64 pixels.

• Nearest neighbour charge sharing in fine granularity direction.

• Pixels ganged together in coarse granularity direction.

3. 60 mm pitch with 53x53mm2 active area.

Photon Detection

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Required granularity of the final TORCH MCP.

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Three phases of development by Photek:

1. Long lifetime ALD coated single channel.• Currently under study.

2. High granularity devices.• Pixel size and pitch matching

final device.

3. Full prototype.• Full size and pitch, high

granularity, long lifetime.

MCP-PMT Lifetime

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Photocathode response as a function of collected charge [2].

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Coated (improved) MCP-PMT Uncoated MCP-PMT

TORCH Minimum Requirement

MCP-PMT Simulation

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Simulated uncertainty on position using charge-sharing as a function of gain and electronics threshold.

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• Extra granularity achieved with charge sharing.

• Uncertainty in reconstructed position depends on gain and electronics threshold.

• For more information see poster: Simulation studies of a novel, charge sharing, multi-anode MCP detector. Thomas Conneely & James Milnes, Photek LTD.

Ele

ctro

nics

Thr

esho

ld (

fC)

Gain ( electrons)

Timing

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σpmt = 23ps

𝜎 𝑡𝑜𝑡𝑎𝑙=𝜎 𝑝𝑚𝑡=23𝑝𝑠Phase 1 MCP-PMT timing distribution.

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0 200 400 600 800 1000 1200 14001

10

100

1000

10000

Time [ps]

Co

un

ts

Timing smear divided into three categories:

1. Contributions arising from the PMT.

Timing

E N Cowie - TORCH - TIPP 2014

𝜎 𝑡𝑜𝑡𝑎𝑙=√𝜎𝑝𝑚𝑡2 +𝜎𝑜𝑝𝑡𝑖𝑐𝑠

2 60𝑝𝑠

σopt = 55ps

Simulated optics timing distribution.

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Timing smear divided into three categories:

1. Contributions arising from the PMT.

2. Contributions arising from the optics.

Timing

E N Cowie - TORCH - TIPP 2014

𝜎 𝑡𝑜𝑡𝑎𝑙=√𝜎2𝑝𝑚𝑡❑ +𝜎❑

2𝑜𝑝𝑡+𝜎❑

2𝑒𝑙𝑒𝑐 70𝑝𝑠

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Timing smear divided into three categories:

1. Contributions arising from the optics.

2. Contributions arising from the PMT.

3. Contributions arising from the Electronics.

NINO leading edge jitter [3].

HPTDC timing resolution [4].

Electronics

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• Initial tests of Nino8 and HPTDC show intrinsic resolution of 40ps [5].

• R&D into electronics using 32 Channel NINO chips with HPTDC underway.

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Nino8HPTDC

Nino32

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Fused Silica

MCP-PMTs

Test-Beam

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Focussing Surface

• Radiator plate measuring 350x120x10 mm3 joined to a focussing block.

• Read out by two MCP-PMTs on the focal plane.

• Aiming for December deployment at T9 beam on the PS at CERN.

Future Work• Phase 1 MCP-PMTs continue to be tested.

• Phase 2 MCP-PMTs delivered this year.• Phase 3 to follow next year.

• A prototype module will be developed to prove the full concept.

• Proposal will be submitted to LHCb upon successful completion of R&D phase.

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FinThanks for listening!

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References[1] The LHCb Collaboration, “Letter of Intent for the LHCb Upgrade”, CERN-LHCC-2011-001, 29 March 2011 (v2).

[2] T. M. Conneely, J. S. Milnes, J. Howorth, Nuclear Instruments and Methods in Physics Research A 732 (2013) 388-391.

[3] M. Despeisse et al. IEEE TRANSACTIONS ON NUCLEAR SCIENCE, VOL. 58, NO. 1, FEBRUARY 2011

[4] J. Christiansen, “High Performance Time to Digital Converter”, CERN/EP-MIC, 2002.

[5] R Gao et al, 2014 JINST 9 C02025.

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Extra Slides

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Start Time

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Example from PV of same event After removing outliers

ps

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Modular Design

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A modular design for TORCH

Effects of Modular Design

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Moduleconsidered

Without dispersion or

reflection off lower edge

Including dispersion and

reflection off lower edge

Dispersion

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𝑐𝑜𝑠𝜃𝑐=1

𝛽𝑛❑

𝑛❑=1

𝛽cos𝜃𝑐

Wavelength (nm)

n

𝑛𝑔𝑟𝑜𝑢𝑝=𝑛− 𝜆0𝑑𝑛𝑑𝜆

Photon production spectrumWavelength dependence of refractive indexes

Performance

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Correct ID

Mis-ID

Correct ID

Mis-ID

Kaon ID performancePion ID performance

Photon Detection

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Faceplate

Photocathode

Dual MCP

Anode

Gain ~ 106

photoelectron V ~ 200V

V ~ 200V

V ~ 2000V

photon

Faceplate

Photocathode

Dual MCP

Anode

Gain ~ 106

photoelectron V ~ 200V

V ~ 200V

V ~ 2000V

photon

Example of MCP internal layout

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• Photodetectors required to have precise single photoelectron time resolution and long lifetime

• MCP-PMTs chosen for lower intrinsic transit-time spread.

• Atomic Layer Deposition coating will be used to increase lifetime.