Transcript 9-0783-danilov

ICHEP’04
Beijing
Highly Granular Scintillator-based
Calorimetry with Novel Photodetectors
for Future Linear Collider
Michael Danilov
ITEP(Moscow)
Representing CALICE Collaboration
LC Physics goals require DEJ/√EJ~30%
This can be achieved with Particle Flow Method (PFM):
Use calorimeter only for measurement of K,n, and g
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 important
We 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 = 2Echarg. + 2Ephot + 2Eneutr + 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
42m
20m
pixel
h
Resistor
Rn=400
k
Al
Depletion
Region
2 m
R 50
Substrate
Ubias
Pixel size ~20-30m

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 + DV ~ 50-60 V
DV ~ 3V above breakdown voltage
Each pixel behaves as a Geiger counter with
Qpixel = DV Cpixel
with Cpixel~50fmF  Qpixel~150fmC=106e
Dynamic range ~ number of pixels (1024)
 saturation
SiPM Spectral Efficiency
Depletion region is very small ~ 2m
strong electric field (2-3) 105 V/cm
carrier drift velocity ~ 107 cm/s
very short Geiger discharge development < 500 ps
pixel 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
40
One pixel gain M, 10
5
one pixel gain (exp. data)
one pixel gain (linear fit)
detection efficiency ( l =565nm)
15
30
10
20
5
10
operating voltage
0
0
0
1
Ubreakdown=48V
2
3
4
5
6
Overvoltage DU=U-Ubreakdown, V
Photon detection efficiency  = QEgeom
Efficiencyof light registration  , %
20
SiPM signal saturation due to finite number of SiPM pixels
Individual tile energy reconstruction using
calibration curve: SiPM signal vs energy deposited:
Average number of
photoelectrons for
central tiles for 6 GeV
1000
250
1400
1200
LED
Tile
1000
25
10
200
150
800
600
Counts
100
Counts
SiPM signal
1600
100
400
50
200
0
0
200
400
600
TDC channel
800
1000
1200
1ch = 50 ps
1
1
10
100
1000
Number of phe
1
10
1
10000
100 Energy Deposited, MIP
Very fast pixel recovery time ~ 20ns
For large signals each pixel fires about 2 times during pulse from tile
SiPM Noise
noise rate vs. threshold
random trigger
1p.e.
2p.e.
Ped.
3p.e.
1p.e. noise rate ~2MHz.
threshold 3.5p.e. ~10kHz
threshold 6p.e. ~1kHz
Optimization of operating
voltage is subject of R&D
at the moment.
Experience with a small (108ch) prototype (MINICAL)
Moscow
SiPM
cassette
3x3 tiles
Tile with SiPM
Hamburg
Light Yield from Minical tiles (5x5x0.5cm3)
Using triggered Sr source and LED at ITEP
LED
b
N pixel
Using electron beam at DESY
(SiPM signals without amplification)
Good reproducibility after transportation from Moscow to Hamburg
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 b source
Light yield drop between tiles acceptable
(Calorimeter geometry is not projective)
Cross-talk between tiles ~2% - acceptable
Light collection efficiency
5x5x0,5cm3
mm
Sufficient uniformity for a hadron calorimeter even for large tiles
Acceptable cross-talk between tiles of ~2% per side
Sufficient 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)
Shower Shape
3 GeV e+
Black – data
Yellow -MC
After single tile calibration and
smearing MC describes well
shower shape
Energy Resolution
Measurement of electron energy with HADRON CALORIMETER  resolution modest
Very good agreement
between PM and SiPM on the
whole range 1 - 6 GeV
Low sensitivity to constant
term due to limited energy
range
 SiPM
 PM
 MC (SiPM)
MC tuning still in progress
include more effects:
-beam energy spread
-steal thickness tolerances
NON-LINEARITY and ENERGY RESOLUTION
for DIFFERENT BEAM POSITIONS
1,08
centerindiv
side(0;+15)
side(0;+25)
side(+15;+15)
1,06
1,04
nonlinearity
nonlineari ty 
1,02
A( Ei )
FIT ( Ei )
For all cases the same fit function is used !
1,00
0,98
SiPM
0,96
0,94
0,92
1
2
3
4
5
6
EnergyE[GeV]
resolution
0,24
0,22
centerindiv
side(0;+15)
side(0;+25)
side(+15;+15)
0,20
dE/E
0,18
0,16
0,14
0,12
0,10
0,08
1
2
3
4
E[GeV]
5
6
Beam position
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
SiPMs will be tested and calibrated with LED before installation into tiles
(noise, amplification, efficiency, response curve, x-talk)
PC driven generator
LED driver
Steering
program
Remote control
16 channel
power supply
DATA
BASE
…….
gate
..
X~100
16 ch
12 bit ADC
Tested SiPM
16 ch amp
16 ch
12 bit ADC
Scheme of test bench for SiPM selection at ITEP
Tiles will be tested with a triggered β source and LED before installation into cassette
Test bench for tile tests at ITEP
16 ch
12 bit
ADC
16 chan amps
16 ch remote
control power
supply
b -source
Steering
program
16 sci tile plane
step
motor
trigger counter
movable frame
DATA
BASE
discriminator
gate
Emission Spectrum of Y11 WLS
Fiber
Measured at distances 10cm, 30cm, 100cm and 300cm from source.
Longitudinal
segmentation
more important
Separation can be further improved by optimization of algorithm
Comparison of the SiPM characteristics in magnetic field of B=0Tand B=4T
(very prelimenary, DESY March 2004)
LED signal ~150 pixels
A=f(G, , x)
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 voltage
No 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