The lhcb pixel hybrid photon detectors
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The LHCb Pixel Hybrid Photon Detectors. Robert W. Lambert, University of Edinburgh On behalf of the LHCb RICH collaboration. Outline. Introduction: LHCb and Particle ID Hybrid Photon Detectors (HPDs) HPD Manufacture Testing and Results RICH Installation Progress Summary. LHCb.

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The LHCb Pixel Hybrid Photon Detectors

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The lhcb pixel hybrid photon detectors

The LHCb Pixel Hybrid Photon Detectors

Robert W. Lambert, University of Edinburgh

On behalf of the LHCb RICH collaboration

PD07, 28th June 2007


Outline

Outline

  • Introduction: LHCb and Particle ID

  • Hybrid Photon Detectors (HPDs)

  • HPD Manufacture

  • Testing and Results

  • RICH Installation Progress

  • Summary

PD07, 28th June 2007


The lhcb pixel hybrid photon detectors

LHCb

  • LHCb will examine CP-violation in B-mesons [1]

    • Why is there a matter-antimatter asymmetry in the universe?

    • What are the reasons for the parameters in the Standard Model?

    • Is there physics beyond the Standard Model?

PD07, 28th June 2007


Lhcb @ 100m

LHCb @-100m

RICH 2

Magnet

RICH 1

PD07, 28th June 2007


Rich 1 and rich 2

RICH 1 and RICH 2

  • Ring Imaging CHerenkov (RICH) detectors [2]

    • Relativistic charged particles in a medium radiate light

    • Characteristic cone angle, cos  = 1/bn

RICH 1

(Vertical)

RICH 2

(Horizontal)

TT

MAGNET

T1-T3

PD07, 28th June 2007


Cherenkov imaging

Cherenkov Imaging

  • Rings reconstructed

    • Velocity  Cone angle ≡ Ring radius

    • Combine with momentum to get Particle ID

RICH 1 for 1 < p < 60 GeV/c

RICH 2 for p < 100 GeV/c

~20 hits/ring

~4 hits/ring

~25 hits/ring

PD07, 28th June 2007


Requirements

Requirements

  • Stringent requirements for RICH photodetectors

    • 2.6 m2 detector plane

    • Single-photon sensitive

    • 65% active area overall

      • 80% for cylindrical devices

    • Cherenkov Spectrum

    • 2.5 mm x 2.5 mm granularity

    • 25 ns Clock <25ns response

    • 40 MHz Clock 40 MHz read out

    • Trigger decision 4ms data buffer

    • Photon yield  High Signal:Noise

    • 5-10 year lifetime

    • Radiation tolerant  30 krad

    • Fringe magnetic field

C4F10

200-600nm

PD07, 28th June 2007


Hybrid photon detectors

Photocathode (S20)

at -20kV

Si Sensor

8192 pixels

Ceramic

Carrier

8192

Vacuum

Photoelectrons

Photon

120 mm

Electrode

Solder

bump

bonds

87 mm

Binary

electronics

chip

Quartz

Window

Hybrid Photon Detectors

  • 484Hybrid Photon Detectors HPDs required [3]

    • Photocathode (S20)

    • Silicon sensor

    • Binary read-out chip

PD07, 28th June 2007


Hpd manufacture 1

HPD Manufacture (1)

  • Production at IBM, Canberra, Kyocera, VTT, HCM, DEP-Photonis

  • Full testing and gold plating by LHCb at CERN

Silicon sensor

Bump-bonding

Packaging

Readout chip

Ceramic carrier

Brazing and gold-plating

PD07, 28th June 2007


Hpd manufacture 2

HPD Manufacture (2)

  • Encapsulated by DEP-Photonis

  • Testing by LHCb

Photo-cathode deposition and vacuum sealing

Tube body assembly

Packaging

PD07, 28th June 2007


Hpd production

HPD Production

536 / 550

HPDs

Produced

519 / 536

HPDs

Tested

18th June 2007

PD07, 28th June 2007


The lhcb pixel hybrid photon detectors

PDTF

  • Photo-Detector Test Facilities

    • 2 centres (2 stations each)

    • Test 1 HPD/site/day

    • 506 of 519 HPDs pass  Failures Replaced.

PD07, 28th June 2007


Pdtf tests

PDTF Tests

  • Check out every function of the HPD, from the ground up

Photocathode

Dark Count

Response to light

Quantum Efficiency

Electron Optics

Image Size

Image Centre

HV Stability

Field Distortions

Readout Chip

Connections

Communications

DAQ

Readout

Dead Channels

Noisy Channels

Masking

Responses

Threshold

Noise

HPD Body

Dimensions

HV Stability

Vacuum Quality

Silicon Sensor

IV Curve

Efficiency (Backpulse)

PD07, 28th June 2007


Silicon sensor

Silicon Sensor

  • PDTF perform a bias scan of each sensor

    • Measures sensor quality

H527009, 0.46 mA leakage at 80V

Contract

Typical 1mA

Ramp-up

Operating

Point, 80V

Ramp-down

PD07, 28th June 2007


Readout chip

Readout Chip

  • Low number of faulty channels

    • Average 0.15% dead channels << 5% specification

    • Average 0.02% noisy channels << 5% specification

Specification

< 400

Specification

< 400

PD07, 28th June 2007


Sensor readout

Sensor + Readout

  • Thresholds and noise

    • Threshold scan performed on all 8192 pixels

    • ~85% sensor efficiency, Typical signal is 5000 e-

<T> = 1063 e-

<N> = 145 e-

PD07, 28th June 2007


Hv stability

HV Stability

  • PDTF perform a HV scan of each HPD

    • Measures HV stability

    • Pulsed LED used at each voltage step

H527009, a typical HPD

H527009, 200k events, LED run

Reflections

Operating

Point, 20kV

PD07, 28th June 2007

Backscatter


Vacuum quality

Vacuum Quality

  • Ion-feedback (IFB), afterpulse

    • Ionisation of residual gas atoms, particularly He, produces afterpulse

    • At 20 kV, IFB measures the vacuum quality

1

Residual Gas

Ionised

<IFB> = 0.03%

Specification

< 1%

Ion

liberates

many

secondary

electrons

2

3

Secondaries measured

after characteristic delay

PD07, 28th June 2007


Dark count

Dark Count

  • Thermionic emission, noise, and IR-sensitivity produce Dark Count

    • Specification 5 kHz cm-2

    • Average 2.6 kHz cm-2 ≡ 0.003 hit / event / HPD in LHCb

H520009, 5M events, 2.0 kHz cm-2

Specification < 5kHz cm-2

PD07, 28th June 2007


Quantum efficiency

Quantum Efficiency

  • QE is a function of wavelength, large improvement seen

    • Independent measurements: photocurrent from known light level

    • DEP improved the QE with each batch (i.e. with time)

Increased

over time

Agreement

across

measurements

Decreased

over time

Expectation

from preseries

PD07, 28th June 2007


S qe d e

SQE dE

  • S QE dE, integrate improvement in QE across energy

    • Cherenkov light has flat energy spectrum

    • 24% relative increase in S QE dE over expectations from preseries 

Expectation from

preseries

PD07, 28th June 2007


Hpds in use

HPDs in use

  • HPDs fulfil or exceed all requirements for the LHCb RICH

  • Excellent performance demonstrated in testbeam scenarios

Ring from Pions,

over 3 HPDs

124k events, with C4F10

Hit spectrum, 124k events

In agreement with

expected yields

PRELIMINARY

pedestal

and noise

Frequency, thousands of events

signal

Hit Count in expected region of ring for 1 HPD

PD07, 28th June 2007


Hpd integration

HPD Integration

  • HPDs -> Columns

    • Magnetic Sheilds

    • Level-0 Data Processing

    • LV power distribution

    • HV power distribution

HPD

L0

LV

HV

PD07, 28th June 2007


Rich 2 installation

RICH 2 Installation

PD07, 28th June 2007


Summary

Summary

  • 484 HPDs are required for the LHCb RICH

  • 536 HPDs have now been produced

    • 519 tested at PDTF with 506 passes

    • Excellent results overall

    • 24% relative improvement in QE will directly improve photon yields

  • RICH is now under installation and commissioning

    • RICH 2 fully populated with HPDs

  • LHCb is getting ready for data….

PD07, 28th June 2007


References

References

  • LHCb collaboration, LHCb Technical Proposal, CERN-LHCC-98-004 LHCb, 20th February 1998

  • LHCb collaboration, LHCb RICH, Technical Design Report 3, CERN-LHCC-2000-037 LHCb, 7th September 2000

  • T. Gys, LHCb RICH, “Production of 500 pixel hybrid photon detectors for the RICH counters of the LHCb,” NIM A 567 (2006), pp. 176-179

PD07, 28th June 2007


Backup

Backup

  • Additional slides hereafter

PD07, 28th June 2007


Physics and photons

Physics and Photons

  • RICH crucial to separate Kaons and Pions [1]

    • Similar hadrons, different in mass

    • Contribute to different physics

    • Important to separate

Signal Bd p+p-

PD07, 28th June 2007


Hpds realised

HPDs Realised

  • Hybrid Photon Detectors

Quartz window

thin metal

Photocathode (S20)

Photoelectric effect

produces electrons

120 mm

20kV accelerating

potential

Pixelated anode

8192 pixels

500 mm x 62.5 mm

Amplifier, Thresholder,

Buffer, Read out

87 mm

PD07, 28th June 2007


Hpd production1

HPD Production

536 / 550

HPDs

Produced

18th June 2007

PD07, 28th June 2007


Pdtf progress

PDTF Progress

519 / 550

HPDs

tested

15th May 2007

PD07, 28th June 2007


Qe at pdtf

Shutter/iris combination

bandpass filter (+- 10 nm FWHM)

Calibrated photodiode

(Newport 818-UV unbiased)

HPD

Quartz-tungsten halogen lamp

(6V, 50 W)

LOT Oriel

lamp

housing

ND filter (where required)

Fused silica lens

f = 50 mm,

diam. = 25.4 mm

Shutter/iris

combination

RL

IR-blocking filter

(Schott KG-5)

100V

q(HPD) = q(pd)* I(HPD)/ I(pd)

I HPD (pA)

I pd (pA)

QE at PDTF

  • Uses existing Darkbox

    • PC at -100V, focussing cathodes at -100V, Anode at ground

PD07, 28th June 2007


Results summary

Results Summary

  • HPD Quality Assurance

    • 506 of 519 tubes pass 

HPDs

with higher

darkcount

A+: Exceeds key specifications. A specifically recommended HPD

A: Pass all aspects of tests

B: Falls beneath contracted specifications, but still recommended for use in the RICH

E: HPD qualified for use in the RICH, but is flagged with an issue

F: Clear failure of HPD, such that it is unusable in the RICH. HPD returned to DEP if possible for replacement

HPDs with high

leakage current and

with >1% dead pixels

PD07, 28th June 2007


Hpd electron optics

HPD electron optics

  • Reliable manufacture

    • 73% of centres within 1 pixel of chip centre

    • standard deviation of image size ~ ¼ pixel

1 Pixel

PD07, 28th June 2007


Peak qe

Peak QE

  • QE peaks at ~270 nm

    • Consistent improvement of QE with batch,

    • All production HPDs are over specifications

<QE> = 30.9%

Contract

Minimum

20.0%

PD07, 28th June 2007


Backpulse

Backpulse

  • Efficiency of hit detection, hSi

    • Pixel chip efficiency important for reconstruction

    • Probability that the chip registers a hit, given a photoelectron has struck

    • Comparing the number of photoelectrons seen by the chip (via normal chip readout) to the number arriving at the backplane of the Si sensor.

  • We measure: hsi = (87±2)%.

3 electrons

2 electrons

4 electrons

5 electrons

1 electron

Fit to charge spectrum at backplane

PD07, 28th June 2007


Afterpulse

Afterpulse

  • Ion Feedback from Strobe Scan

    • Consistently low, indicating excellent vacuum in all tubes

    • Single HPD, H546002, displayed IFB and dark-count anomalies

<IFB> = 0.03%

Specification

< 1%

Very low IFB <<1%

PD07, 28th June 2007


Source sites

Source Sites

  • HPD sourced from around the world !

PD07, 28th June 2007


Qw reflections

QW Reflections

  • As predicted by naïve CAD approximations

    • 75% of light reflected off Chromium coating

    • TIR at QW-Air interface

    • ~20% reflection at QW-PC interface

PD07, 28th June 2007


Reflective effects

Reflective Effects

  • Activating QW reflections and Chromium reflections

    • 8.0% more hits (naïve estimate would predict ~11%)

Improved Geometrical Description

Reflections Activated

1.5 M events, 4,992,419 Hits

1.5 M events, 5,393,100 Hits

PD07, 28th June 2007


Backscatter

Backscatter

  • Only ~85% of all real photoelectrons produce digital hits

    • Thermal effects

    • Thresholding effects

    • Backscatter effects

-

- +

- +

+ -

+

-

+

- +

Si Sensor

+

-

Charge Sharing.

<5000 e-h pairs

per pixel

Thermal absorption

v. few e-h pairs,

Damage to lattice

Normal Case

~5000 e-h pairs

Backscatter.

Smaller amount

of energy

deposited

Electron “may”

Fall back onto

Si sensor

PD07, 28th June 2007


Rich in uv

RICH in UV

  • Below 200 nm photon yield is limited by absorption of air

PD07, 28th June 2007


Expected spectra

Expected Spectra

  • Folding in the expected QE

Cherenkov spectrum for RICH radiators

RICH 1, C4F10

RICH 2, CF4

RICH 1, Aerogel

Cherenkov Photons

Wavelength [nm]

PD07, 28th June 2007


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