2007/10/15-20 6th International Workshop on Ring Imaging Cherenkov Counters

Development of TOP counterfor Super B factory

- Introduction- Design study

- PMT property- Focusing system

- Summary

K. Inami (Nagoya university)

2007/10/15-20 RICH07 2

Introduction

Side view of Super Belle detector

2.6m

1.2m

e-

8.0GeVe+

3.5GeV

1.5T

TOP (Time Of Propagation) counterDeveloping to upgrade the barrel PID detectorFor Super B factory

Lpeak~1035~36/cm2/s, 20~100 times higher than presentNeed to work with high beam BG

To improve K/π separation powerPhysics analysis

B ππ/Kπ, ργ, Kνν etc.Flavor tagFull reconstruction

Target; 4σ for 4 GeV/c

2007/10/15-20 RICH07 3

TOP counterCherenkov ring in quartz bar

Reconstruct ring image using ~20 photons on the screen reflected inside the quartz radiator as a DIRC.

Photons are detected with photon detectors.

πK

x

y

θc = cos (1/nβ)

Quartz : n = 1.471 (@λ=390nm)

Φ

Different ring image for the pion and kaon of the same momentum

Need large screen...

2007/10/15-20 RICH07 4

TOP counter2D position information Position+Time

Compact detector!~400mm

Linear-array type photon detector

LX

20mm

Quartz radiatorx

y

zLinear array PMT (~5mm)Time resolution σ~40ps

~2m

12000

14000

16000

18000

20000

22000

24000

26000

28000

30000

-20 -10 0 10 20

TD

C (

ps)

X (cm)

Kπ

Simulation2GeV/c, θ=90 deg.

~200ps

Different opening angle for the same momentumDifferent propagation length(= propagation time)

+ TOF from IP works additively.

2007/10/15-20 RICH07 5

Test counter

0

50

100

150

200

250

300

-100 -50 0 50 100x (mm)

TOP

(

ch/2

5ps)

2 3 4 5TDC (ns)

6 gaussian fit.

σcommon = 82.ps

TDC distribution (x=11.3mm)

Quartz bar spec. Quartz : sprasil P20 (Synthetic fuzed silica,

made by shin-etsu co.) size : 1000mm 200mm 20mm surface : 0.5nm(rms), figure < 2µm squrness : < 0.3mrad, edge radius < 5µm polished by Okamoto optics work,inc

1000mm

PMT HPK R5900-U-L16

200mm

Test counterBeam test@ KEK PS π2 line

3 GeV/c π− beamθin=φin=90 degree

• Clear ring image

• Reasonable time resolution

• Enough bar quality

1mm pitch readout

2007/10/15-20 RICH07 6

DesignQuartz: 255cmL x 40cmW x 2cmT

Cut at 47.8deg. to reduce chromatic dispersion

Multi-anode MCP-PMTGood time resolution (<~40ps), Linear array (5mm pitch)Three readout planes

IP

Forward BackwardPMT

32.8o~123.5o

47.8o 1180mm

z=1830mm z=1070mm z=-780mm

5mm

40cm

2cm

MCP-PMT

2007/10/15-20 RICH07 7

ChromaticityDetection time depending on the wavelength of Cherenkov photons

Worse time resolution→ Worse ring-image separation

Propagation velocity depending on λ in the quartz bar

12000

14000

16000

18000

20000

22000

24000

26000

28000

30000

-20 -10 0 10 20

TD

C (

ps)

X (cm)

300

400

500

600

16000 20000 24000 28000

TDC(ps)0

100

200

16000 20000 24000 28000

λ(nm

)

π, 2GeV/c, θ=90deg., ch=40

2007/10/15-20 RICH07 8

Chromatic dispersionVariation of propagation velocity depending on the wavelength of Cherenkov photons

0

5

10

15

20

25

30

35

40 Bi-alkali

GaAsP

photon lambda(nm)

QE

(%)

300 400 500 600 700

Multi-alkali

GaAsP photo-cathode ( alkali p.c.)Higher quantum-efficiency at longer wavelength → less chromatic error

0.19

0.2

0.21

300 400 500 600 700Wave length (nm)

Gro

up v

eloc

ity (m

/ns) Light propagation

velocity inside quartz

Photon sensitivity at longer wavelength shows the smaller velocity fluctuation.

2007/10/15-20 RICH07 9

GaAsP MCP-PMT developmentSquare-shape MCP-PMT with GaAsP photo-cathode is developed with Hamamatsu Photonics.

PrototypeGaAsP photo-cathode

Al protection layer

2 MCP layersφ10µm hole

4ch anodesSlightly large structure

Less effective area

Performance testTime resolution

22(effective area)27.5mm

1ch

2ch

3ch

4ch

Target structure

DISC

PLP PMT ATTN AMP DIV

TDC

ADCFILTER

BLACK BOXDISC

λ=407nmJitter～10ps

there 100mV

36dB

there 20mV

25ps/1bin

CAMAC

START

GATE

DISC

PLP PMT ATTN AMP DIV

TDC

ADCFILTER

BLACK BOXDISC

λ=407nmJitter～10ps

there 100mV

36dB

there 20mV

25ps/1bin

CAMAC

DISC

PLP PMT ATTN AMP DIV

TDC

ADCFILTER

BLACK BOXDISC

λ=407nmJitter～10ps

there 100mV

36dB

there 20mV

25ps/1bin

CAMAC

DISC

PLP PMT ATTN AMP DIV

TDC

ADCFILTER

BLACK BOXDISC

λ=407nmJitter～10ps

there 100mV

36dB

there 20mV

25ps/1bin

CAMAC

PLP PMT ATTN AMP DIV

TDC

ADCFILTER

BLACK BOXDISC

λ=407nmJitter～10ps

there 100mV

36dB

there 20mV

25ps/1bin

CAMAC

START

GATE

2007/10/15-20 RICH07 10

GaAsP MCP-PMT performanceWave form, ADC and TDC distributions for single photon

Enough gain to detect single photo-electronGood time resolution (TTS=35ps) for single p.e.

Single p.e.0.5ns/div20mV/div

ADC

0

100

200

300

400

500

600

100 120 140 160 180/0.25pc

cou

nt

pedestal

single photon peak

Gain～0.64×106

Time

0

1000

2000

3000

-20 -10 20/25ps

cou

nt

0 10

TTS~35ps

2007/10/15-20 RICH07 11

IP

Forward BackwardPMT

32.8o~123.5o

47.8o 1180mm

z=1830mm z=1070mm z=-780mm

0

2

4

6

8

10

12

14

16

40 60 80 100 120polar angle (deg.)

Sep

arat

ion

pow

er (

σ)

2GeV/c3GeV/c4GeV/c

90

92

94

96

98

100

40 50 60 70 80 90θ (deg.)

Effi

cien

cy (

%) 2.0GeV/c

3.0GeV/c

4.0GeV/c

0

2

4

6

8

10

40 50 60 70 80 90θ (deg.)

Fak

e ra

te (

%)

2.0GeV/c3.0GeV/c

4.0GeV/c

K/π separation powerGaAsP photo-cathode + >400µm filter, CE=36%

3.5σ K/π for 4 GeV/c, θ=70ﾟ

Performance with GaAsP

2007/10/15-20 RICH07 12

Focusing TOP

Focus Mirror

y

PM

T

Side view

Mirror image

Remaining chromatic effect makes ~100ps fluctuation for TOP.Use λ dependence of Cherenkov angle to correct chromaticityFocusing system to measure θc

λ θc y positionReconstruct ring image from 3D information (time, x and y).

))(1

(cos=)( 1

βλnλθ c

ー

Rotate PMT

Focus Mirror

2007/10/15-20 RICH07 13

Focusing TOP (2)∆θc~1.2mrad over sensitive λ range

∆y~20mm (~quartz thickness)We can measure λ dependence and obtaingood separation even with narrow mirror and readout plane, because of long propagation length.

Not need focusing blockNot need fine readout channels

1850mm

Virtual readout screen22mm x 5mm matrixFocusing

mirror

∆θc~1.2mrad

2007/10/15-20 RICH07 14

Performance of focusing TOPK/π separation power

GaAsP photo-cathode(+>400µm filter), CE=36%

40 50 60 70 80 90polar angle (deg.)

0

1

2

3

4

5

6

Sep

arat

ion

pow

er (

σ)

95

96

97

98

99

100

40 50 60 70 80 90

0

1

2

3

4

5

40 50 60 70 80 90polar angle (deg.)

Effi

cien

cy(%

)F

ake

Rat

e(%

)4

Separation power Efficiency,Fake rate@ 4GeV/c

4.3σ separation for 4GeV/c

2007/10/15-20 RICH07 15

Mirror test

Focusing mirror

2cm

40cm

Spherical mirror (R=5m)

Prototype by Okamoto-optics40x2x2cm, R=5mAttached at the end of quartz bar

Shape measurementNeed continuous mirror image

Found (4.9±0.2)mm shiftAdjusted by re-polishing flat planes

Focus Mirror

y

PM

T

Laser depth meter

2007/10/15-20 RICH07 16

SummaryR&D of TOP counter is in progress!

To install super B factoryDesign studies

To suppress the influence of chromaticityGaAsP photo-cathode MCP-PMT

Prototype shows the enough performanceGain = 0.64x106, TTS = 35ps for single photonHigh Q.E. (>40% at 500nm)

Focusing systemNarrow mirror and narrow readout planeForm large virtual readout screen

Not need focusing block and fine PMT channelsImproved performance (4.3σ for 4GeV/c)

Prototype production