1. A new tile calorimeter with Silicon Photomultipliers for the KLOE-2 experiment
Ivano Sarra
University of Tor Vergata
Laboratori Nazionali di Frascati
Young Researcher Program
@ Frascati Spring School 2008
LNF- Frascati ( )

2. Summary of the existing QCAL
Outline
The proposal of a new quadrupole calorimeter QCALT
A new kind of device: the SIPM
Test on SiPM (Hamamatsu MPPC)
Test on different fiber types
Tests on Tiles
Conclusions

3. Summary of the existing QCAL Summary of the existing QCAL
At KLOE the measurement of direct CP
violation is possible through the double ratio:
R = G(KL p+p) G(KS p0p0)
/ G(KS p+p) G(KLp0p0)
For the neutral decay of
KL ―› 2π0 ―› 4γ
To recover photons lost on the quadrupole region the area is covered by a Tile Calorimeter QCAL

4. Proposal of new QCAL Proposal of new QCAL
For the high precision measurement of KL20 decay rate
- Adapt a new calorimeter over new interaction region
- Improve granularity, time resolution & efficiency.
Barrel with 12 modules
- Each module has a thickness
of 5-6 cm and 1 m length.
It is made by 8 layers of
2 mm W /3 mm Scint. Z R
Along Z, each slab is divided in 20 tiles of 5x5 cm2
Tile dimension increases along R. Z

5. New tile design New tiles design MPPC = SIPM by Hamamatsu 1 mm^2 area
The R&D for Tesla/ILC made possible a very promising tile detector:
- Square tiles with fibers in circular grooves.
- Tile readout is possible with SiPM
SIPM =SILICON PHOTOMULTIPLIER
Array of Single Geiger Mode APD. It is a discrete detector for photon counting depending on the PIXEL size
MPPC = SIPM by Hamamatsu
1 mm^2 area
100 pixels --> 100 um
400 pixels --> 50 um

6. Test on SiPM

7. First study on SiPM First study on SiPM
To study SiPM characteristics we use:
Black box
Pulsed led to fire SiPM
Polaroid filter to change light intensity
We can measure:
Gain vs Vbias
Gain vs Temperature
Dark noise rate

8. SIPM signal with BLUE Led Pulser
From Scope:
Vbias 69.25Volt, T:24°C
Rise Time ~3ns,
Fall Time ~150ns
From Adc:
0pe
1pe
2pe
3pe
4pe
From ADC spectra, we get single photoelectron charge (Vbias 69.25, T:24°C):
Q = 0.36pC
Gain = 2.3E+06
Δcount=17.4
Q’=17.4*0.25pC=4.35pC
Q=4.35/11.8(ampl.)=0.36pC
G=Q/e

9. Gain vs T
ΔG = ΔT
Our result
Vbias=69.30V
Hamamatsu
ΔG=-0.12 ΔT

10. Dark Count vs Vbias
Dark-Count(kHz)
Our result
Hamamatsu

11. Test on fibers

12. Test of single Scintillating Fibers
We have studied the characteristics of 3 different types of fibers:
Kuraray SCSF 81 (Blue )
Saint Gobain BCF92 single cladding (Green)
Saint Gobain BCF92 multi cladding (Green)
The test is performed using SiPM and a beta source of Sr90.
The trigger is provided by a NE110 finger (1cm x 5cm) readout by 1” PM.
SiPM + electronics
fiber
Sr90
NE110 PM
Trigger

13. Selected Scintillating Fibers
After the test we
have selected:
Saint-Gobain Multi
Cladding fibers:
1) Best light yield
2) Fast emission time
(3-4 ns/p.e.)
3) High attenuation
length (3.5 m)
Q( ADC COUNTS)

14. Test on tiles

15. Test of tiles 3 possible solutions under study:
1) SIPM directly on tile
2) SIPM + amplifier + HV on tile
3) SIPM connected to fibers in a
far-away position from tile
At the moment we have tested
only the third solution:
Tiles: 3mm and 5 mm thickness
Without reflector at fiber end
Simple mylar around tile
SiPM placed outside tile in
optical contact (w grease)
with fiber.

16. Test of Tiles
Data taking with cosmic rays.
Trigger using 2 scintillator counters read at both ends.
Tested 2 tiles with different thickness and different SIPM.
To investigate the use of pixels (vs pixels) which has:
a gain reduction of 1/3 ( instead 2.4E10+6)
a reduced temperature dependence DG = -0.03DT (instead -0.12)
SiPM + electronics
NE110
Trigger
Tile
Fiber
Scintillator

17. Test of Tiles (MIP distribution)
ADC distributions
for two different thicknesses
The MIP values are compatible taking into account different
thicknesses and QE
of the two SIPMs.
N3mm = N5mm
x 3/5
x 0.40/0.45
N3mm ~ 14
3mm thick
400 Pixels SIPM
<MIP> = 14 pe
5mm thick
100 Pixels SIPM
<MIP> = 26 pe

18. Tile test (time resolution for MIP)
110 ps/counts
5 mm thick
3 mm thick
TDC ( Counts)
After correcting the pulse height dependence on the timing,
a Time Resolution of 750 (1000) ps is obtained for a MIP
on the 5 (3) mm thick tiles.
No correction applied to the trigger jitter.

19. Conclusions and plans
SiPM: our tests confirm Hamamatsu characteristics for 100 pixels MPPC:
- Gain vs HV
- Gain vs temperature
- Dark noise
Reduced temperature variation of gain and dark noise expected for a
400 pixels MPPC (50 m pixel).
Fibers: adopted solution is the Saint Gobain multi cladding.
Tile: Good results on light response and timing.
Light yield and time resolution sufficient for our purposes.
Solution with MPPC+amp directly on tile under development.

20. Spares

21. Set Up - HV stability 10 mV - Blue LED diode on SiPM
Temperature measured
on SiPM
CAMAC DAQ
ADC sensitivity
0.25 pC/cnt

22. Mppc: Multi Pixel Foton Counter
Mppc: Multi Pixel Foton Counter -100C N.370, characteristics at 25°C and λ=655 nm: Vop. 69,28V, Gain 2.41E+6

23. The KLOE experiment
The KLOE design was driven by the measurement of direct CP violation
through the double ratio: R = G(KL p+p) G(KS p0p0) / G(KS p+p) G(KLp0p0)
Collision at sqrt(s)=Mphi = 1.02GeV
(e-e+)―› Φ ―› (kS kL) (k- k+)
Electromagnetic Calorimeter
Measure charged particles
lead/scint. fibers
4880 PM
Drift Chamber
Measure charged particles
(4 m thick  3.4 m lenght)
 90% He; 10% iC4H10
52140 wires
Superconducting coil B=6kGauss

24. Dark Count shape vs Vbias
Vbias 68.90V
Vbias 68.97V
0.5pe 470kHz
1.5pe 34kHz
0.5pe 530kHz
1.5pe 40kHz
T = 24 °C
V=R*I=R*Q/τ,
Where:
τ = 35ns
R = 50Ω
Dark rate follows
specifications.
It becomes negligible
when triggering at
1.5 pe.
Vbias 69.03V
Vbias 69.09V
0.5pe 610kHz
1.5pe 58kHz
0.5pe 680kHz
1.5pe 85kHz

25. Tile test
Time resolution measured using different number of photoelectrons on tile.
Result compatible with 5mm tile.
No trigger jitter corrected.
Stochastic term roughly consistent with:

26. Fibers test Saint Gobain multi cladding Pedestal Cut @ 0.5 pe

27. Fibers test Saint Gobain single cladding Pedestal Cut @ 0.5 pe

28. Fibers test Kuraray Y11 Pedestal Cut @ 0.5 pe Cut @ 1.5 pe 0pe 1pe 2pe

29. Tile test
Entries
ADC distribution obtained using a 3mm tile optically coupled with a 400 pixels SiPM.
0pe
1pe
ADC counts

30. Tile test Using 3mm tile with 400 pixels MPPC. Slewing correction.
Fit function:
TDC Vs
ADC
The use of a fixed threshold TDC brings about a dependence of the threshold crossing time on the collected charge, the well-known time-slewing effect.
Charge of imput signal [ADC counts]

31. Apd operanti in Geiger Mode
Diodo a Vbias > Vbd
t < t0 ... i=0, non ci sono portatori
t = t0, inizia la valanga
t0 < t < t1, la valanga si diffonde
t > t1, la valanga si auto-sostiene ed è limitata ad Imax dalle resistenze in serie t t0 i
imax t1
Vbias
Vbd
Meccanismo di Quencing

32. Apd operanti in Geiger Mode
Gli Apd operanti in geiger mode possono essere modellati tramite il seguente circuito elettronico:
Switch Open: quando la valanga non è innescata Cd si carica a Vbias e non scorre corrente
Switch Close: quando la valanga si innesca Cd si scarica fino a Vbd con τ=Rs*Cd e la corrente va ad I=(Vbias-Vbd)/RQ
τQ=RQ*Cd=35ns

33. Gain vs Vbias.2
From Hamamatsu:
Our measurement:

34. Gain vs Vbias ADC spectra as a function of the applied HV. Gate: 350ns
T=24°C
Vbias 68.60V
Vbias 68.66V
Vbias 68.70V
Vbias 68.75V
Vbias 68.81V
Vbias 68.87V

35. Gain vs Vbias Increasing HV we increase dark rate Vbias 68.94V

36. Gain vs Vbias Our result Hamamatsu ΔG=2.24 ΔV ΔG=2.19ΔV ΔG=2.12ΔV