1. Efficiency Study of Prototype Scintillator for INGRID
2006/11/08
for the T2K Collaboration
H.Kawamuko
Kyoto University

2. Introduction 1 [Purpose of this experiment]
・We want to suppress the systematic errors under 2%.
The main causes are as follows :
- Uncertainty of tracker efficiency
- Uncertainty of background content rate and so on..
In MC simulation, this event rate against
the signal ＜ 0.1% ⇒ enough disregard.
・We find that more than 99.5% is necessary for the tracker efficiency from MC simulation.
We should measure whether the efficiency of prototype scintillator is satisfied with this requirement !

3. Previous Result 2
Same type scintillator has already examined by cosmic-ray.
・Scintillator design : 17cm × 17cm × 1cm
・Measure the efficiency & light yields at
each eight positions.
・Average efficiency : 99.5%
・Average light yields : 13.3 p.e
(at least 8.9 p.e can be obtained)
WLSF has an attenuation length. ~350cm ⇒ 1/e
We can predict that prototype status is ,
: 8.9 × exp(-100/350) = 6.7 p.e
: 8.9 × exp(-200/350) = 5.0 p.e
with same thickness
⇒ We expect to obtain at least 14 p.e (both ends sum)

4. Configuration of Prototype Scintillator3
・Two designs are being examined for INGRID counter.
Design-A
1cm
Fiber length = 200cm
10cm
Thickness : 1cm
100 cm
In this type, we use the WLSF to read out the signal and bend the fiber to embed in the groove.
We plan to read out the signal from one side and use PMT or MPPC as a read out device.
Design-B
Fiber length = 100cm
5cm
Thickness : 1.25cm
100 cm

5. Configuration of Prototype Scintillator4
・Two designs are being examined for INGRID counter.
Design-A
1cm
10cm
On the other hand , in design-B, we don't bend the fiber .
But the wideness is as half as design-A
→ # of channel is necessary as twice as above one.
Thickness : 1cm
100 cm
Design-B
We measured the efficiency & light yields of design-A
with cosmic-ray.
5cm
Thickness : 1.25cm
100 cm

6. Experimental setup 5 < setup > Trigger
cosmic ray
Trigger
Prototype Scinti
Trigger position
100cm
20cm
10cm 5 4 3 2 1
・The distance between trigger spots is 20cm.
Read out by PMT
・We measure ～2000events at each position.

7. Result with PMT 6 ◆light yields mean of ADC counts light yields(p.e) =
1 p.e peak counts
◆efficiency
# of events above 0.5p.e.
efficiency =
# of triggered events
#event
← For example
mean ADC counts = 265.7
efficiency = 99.8%
light yields = 9.6p.e.
At position1, efficiency is over 99.5%
⇒ O.K!
ADC counts

8. Efficiency is not OK (less than 99.5%) 7
position
Light position
Efficiency(%)
Light yields (p.e) 10
99.5 95 1 2 3 4 5
Efficiency is not OK (less than 99.5%)
But light yields are consistent with expected value. 1 2 3 4 5
position
position
◆average efficiency ⇒ 98%
◆average light yields ⇒ 6.7p.e. ( 14.6 p.e by both ends sum ) expected value is 14 p.e

9. Read out by MPPC 8
・We plan to use MPPC instead of PMT in the T2K experiment.(→ see photo-sensor discussion)
･MPPC is superior to PMT in terms of a quantum efficiency for green wave length. (emitted in WLSF)
assemble

10. Result with MPPC 9 MPPC has good efficiency & light yields.
Experimental setup is as same as one with PMT.
Raw
efficiency
light yields
Position 1
> 99.9%
24.5 p.e.
Mean ADC : 237.2
(10cm away)
Position 2
> 99.9%
20.3 p.e.
(30cm away)
Position 3
> 99.9%
Miss measure…
(50cm away)
・Measured ~2500 events.
→ Efficiency is more than 99.5% at all three position.
→ light yields are much larger than the one by PMT.
MPPC has good efficiency & light yields.

11. Summary & Future Plan MPPC has a good efficiency and light yields10
・Read out by PMT
We measure at the each 5 position with cosmic-ray.
→ The average efficiency is about 98%.(not reach 99.5%)
→ Light Yields are consistent with expected value.
・Read out by MPPC
→ Both efficiency & light yields are good value (satisfy the
requirement).
MPPC has a good efficiency and light yields
enough to be used in the T2K experiment.

12. That’s All! Thank You!

13. Back Up
Raw data of ADC hist with PMT
Raw data of ADC hist with MPPC

14. position1 position2 efficiency = 99.85% light yields = 9.58p.e.
mean = 265.7
position2
efficiency = 99.13%
light yields = 7.76p.e.
mean = 225.6

15. position3 position4 efficiency = 98.2% mean = 200
light yields = 6.40p.e.
mean = 200
position4
efficiency = 96.35%
light yields = 5.28p.e.
mean = 172.7

16. position5 efficiency = 96.55% light yields = 4.84p.e. mean = 169.4
← The picture of Prototype Scintillator

17. ※ This result isn’t satisfied with MC simulation requirements!!
efficiency
Light yields
Position 1
99.8%
9.6 p.e.
Position 2
99.1%
7.7 p.e.
Position 3
98.2%
6.4 p.e.
Position 4
96.3%
5.3 p.e.
Position 5
96.5%
4.8 p.e.
◆average efficiency ⇒ 98 %
◆average light yields ⇒ 6.7 p.e.
※ This result isn’t satisfied with
MC simulation requirements!!

18. Remember that MPPC is very sensitive to the change of H.V.
Raw
Raw
Remember that MPPC is very sensitive to the change of H.V.
→ further study will be done .