Highly Granular Scintillator-based Calorimetry with Novel Photodetectors

for Future Linear Collider

Michael Danilov ITEP(Moscow)

Representing CALICE Collaboration

ICHEP’04Beijing

LC Physics goals require EJ/√EJ~30%

This can be achieved with Particle Flow Method (PFM): Use calorimeter only for measurement of K,n, and Substitute charged track showers with measurements in tracker

LC detector architecture is based on PFM, which is tested mainly with MC

Experimental tests of PFM are extremely importantWe are building now a prototype of scintillator tile calorimeter to test PFM

Particle Flow Method

Ejet = Echarged + Ephotons + E neutr.hadr.

100% 65% 25% 10%

2Ejet = 2

Echarg. + 2Ephot + 2

Eneutr + 2Confusion

2Confusion - Dominant contribution

Shower separation and reconstruction are the main optimization parameters

3x3 cm2 granularity is highly desirable for shower separation. Is it possible?YES – with a novel photo detector Silicon Photomultiplier developed in Russia

SiPM main characteristics

R 50

h

pixel

Ubias

Al

Depletion Region2 m Substrate

ResistorRn=400 k

20m

42m

Pixel size ~20-30m Electrical inter-pixel cross-talk minimized by: - decoupling quenching resistor for each pixel - boundaries between pixels to decouple them reduction of sensitive area and geometrical efficiency• Optical inter-pixel cross -talk:-due to photons from Geiger discharge initiated by one electron and collected on adjacent pixel

Working point: VBias = Vbreakdown + V ~ 50-60 V V ~ 3V above breakdown voltage

Each pixel behaves as a Geiger counter withQpixel = V Cpixel

with Cpixel~50fmF Qpixel~150fmC=106e

Dynamic range ~ number of pixels (1024) saturation

SiPM Spectral Efficiency

Depletion region is very small ~ 2mstrong electric field (2-3) 105 V/cmcarrier drift velocity ~ 107 cm/svery short Geiger discharge development < 500 pspixel recovery time = (Cpixel Rpixel) ~ 20 ns

Photon detection efficiency (PDE):- for SiPM the QE (~90%) is multiplied by Geiger efficiency (~60%) and by geometrical efficiency (sensitive/total area ~30%) - highest efficiency for green light important when using with WLS fibers

Temperature and voltage dependence: -1 oC +4.2% in Gain * PDE*Xtalk+0.1 V +4.5% in Gain * PDE*Xtalk

WLS fiber emission

Photon detection efficiency = QEgeom

0

10

20

30

40

0 1 2 3 4 5 60

5

10

15

20

Ubreakdown=48V

operating voltage

one pixel gain (exp. data) one pixel gain (linear fit)

One

pix

el g

ain

M, 1

05

Overvoltage U=U-Ubreakdown

, V

detection efficiency ( =565nm)

Effi

cien

cyof

ligh

t reg

istr

atio

n

, %

1 10 100 1000 100001

10

100

1000

100 1

10 Energy Deposited, MIP

25

1

S

iPM

sig

na

l

Number of phe

Individual tile energy reconstruction using calibration curve SiPM signal vs energy deposited:

0 200 400 600 800 1000 12000

200

400

600

800

1000

1200

1400

1600

1ch = 50 ps

LED Tile

TDC channel

Co

un

ts

50

100

150

200

250

Co

un

ts

,pix

e ls

:

SiPM signal saturation due to finite number of SiPM pixels

Very fast pixel recovery time ~ 20ns

For large signals each pixel fires about 2 times during pulse from tile

Average number of photoelectrons for

central tiles for 6 GeV

SiPM Noise

random trigger

1p.e.2p.e.

3p.e.Ped.

noise rate vs. threshold

Optimization of operatingvoltage is subject of R&Dat the moment.

1p.e. noise rate ~2MHz.threshold 3.5p.e. ~10kHzthreshold 6p.e. ~1kHz

Experience with a small (108ch) prototype (MINICAL)

Tile with SiPM

cassette

3x3 tiles

SiPM

Moscow Hamburg

Light Yield from Minical tiles (5x5x0.5cm3)

Using triggered Sr source and LED at ITEP

Using electron beam at DESY(SiPM signals without amplification)

Good reproducibility after transportation from Moscow to Hamburg

N pixel

LED

Light Collection Uniformity, Y11 MC 1mm fiber, Vladimir Scintillator,mated sides, 3M foil on top and bottom Reduction in light yield near tile edges is due to finite size of a source

Sufficient uniformity for a hadron calorimeter even for large tilesAcceptable cross-talk between tiles of ~2% per sideSufficient light yield of 17, 28, 21 pixels/mip for 12x12, 6x6, and 3x3 cm2 tiles (quarter of a circle fiber in case of 3x3 cm2 tile)

5x5x0,5cm3

Light yield drop between tiles acceptable(Calorimeter geometry is not projective)Cross-talk between tiles ~2% - acceptable

Light collection efficiency

mm

Shower Shape

After single tile calibration and smearing MC describes well shower shape

3 GeV e+ Black – dataYellow -MC

Energy Resolution

Very good agreement between PM and SiPM on the whole range 1 - 6 GeV

Low sensitivity to constant term due to limited energy range

MC tuning still in progressinclude more effects: -beam energy spread-steal thickness tolerances

SiPM PM MC (SiPM)

Preliminary

Measurement of electron energy with HADRON CALORIMETER resolution modest

1 2 3 4 5 60,92

0,94

0,96

0,98

1,00

1,02

1,04

1,06

1,08

1 2 3 4 5 60,08

0,10

0,12

0,14

0,16

0,18

0,20

0,22

0,24

no

nlin

ea

rity

E[GeV]

centerindiv

side(0;+15) side(0;+25) side(+15;+15)

dE

/E

E[GeV]

centerindiv

side(0;+15) side(0;+25) side(+15;+15)

NON-LINEARITY and ENERGY RESOLUTION

for DIFFERENT BEAM POSITIONS

Beam position

SiPM

For all cases the same fit function is used !

)(

)(

i

i

EFIT

EAtynonlineari

Energy resolution

With universal SiPM calibration curve there is no differences in response for different beam positions (different SiPM saturation)

Cassette, Absorber and Support Structure

Cassette contains 220 tiles with SiPM and electronics

There are 40 cassettes between 2cm iron absorber

Altogether about 8000 tiles of 3x3, 6x6 and 12x12 cm2

with SiPM and individual readout

CONCLUSIONS

Particle Flow Method requires high granularity especially longitudinally

Scintillator tiles with WLS fiber light collection and SiPM mounted directly on tiles can be used to build highly segmented hadronic calorimeter, which can be used in analog or semidigital mode

Tests of 108 channel prototype (MINICAL) demonstrated effectiveness and robustness of this technique

Eight thousand channel calorimeter prototype with tiles in the core as small as 3x3 cm2 is being constructed now. It will be ready for tests next year.

Hcal prototype together with Ecal prototype will allow to to test experimentally the Particle Flow Method

Backup Slides

SiPM

Scheme of test bench for SiPM selection at ITEP

Steeringprogram

Remote control 16 channel

power supply

…….

Tested SiPM

.. X~100

16 ch amp

16 ch

12 bit ADC

16 ch

12 bit ADC

PC driven generatorLED driver

gate

DATA

BASE

SiPMs will be tested and calibrated with LED before installation into tiles (noise, amplification, efficiency, response curve, x-talk)

Test bench for tile tests at ITEP

16 sci tile plane-source

trigger counter

16 chan amps16 ch12 bitADC

movable frame

Steering program

stepmotor

DATA

BASE

discriminator

gate

16 ch remotecontrol powersupply

Tiles will be tested with a triggered β source and LED before installation into cassette

Emission Spectrum of Y11 WLS Fiber

Measured at distances 10cm, 30cm, 100cm and 300cm from source.

Longitudinalsegmentationmore important

Separation can be further improved by optimization of algorithm

LED signal ~150 pixels

A=f(G, , x)

Comparison of the SiPM characteristics in magnetic field of B=0Tand B=4T

(very prelimenary, DESY March 2004)

No Magnetic Field dependence at 1% level

(Experimental data accuracy)

Long term stability of SiPM

20 SiPMs worked during 1500 hours

Parameters under control:

•One pixel gain

•Efficiency of light registration

•Cross-talk

•Dark rate

•Dark current

•Saturation curve

•Breakdown voltageNo changes within experimental errors

5 SiPM were tested 24 hours at increased temperatures of 30, 40, 50, 60, 70, 80, and 90 degrees

No changes within experimental accuracy