1. Mo-92 EC/beta+ search with CaMoO4 crystal at Y2L
Jungil Lee
Sejong university
(KIMS)

2. Introduction 0ν double beta decay Double beta decay of 92Mo
Experimental setup at Y2L
E calibration & resolution(CaMoO4)
Multiplicity of CsI
Preliminary 0ν limit
U background for 100Mo

3. 0ν double beta decay β-β- β+β+
β-β β+β+
(A, Z) -> (A, Z+2) + e- + e (A, Z) -> (A, Z-2) + e+ + e+
EC/β EC/EC
(A, Z) + e- -> (A, Z-2 ) + e (A, Z) + e- + e--> (A, Z-2 )
Emitted in β-β-
E(2e-) = Q
Kinetic energy is equal to the Q-value.
Neutrino absolute mass can be studied by
48Ca, 76Ge, 82Se, 100Mo, 116Cd, 128,130Te, 136Xe, 150Nd

4. of 92Mo EC/EC Q-value=1,650keV, EC/β+ Q-value=628keV
92Mo nucleus is double EC and beta plus EC isotope.
511keV γ
Gamma detector
Active crystal
with 92Mo
Conceptual setup
EC/EC Q-value=1,650keV, EC/β+ Q-value=628keV
(A, Z) + e- -> (A, Z-2 ) + e keV(Q-value)
e+ stops in active(CaMoO4) Crystal.
(gamma can be also an active shielding detector for external gammas)
Abundance = 92Mo: 14.84%, 100Mo: 9.63%

5. Experimental setup at Y2L
pmt
CsI10
CsI9
CsI8
CsI7
CaMoO4
CsI11
CsI12
CsI1
CsI2
CsI3
CsI4
CsI5
CsI6 e+
511keV
628keV(Q-value)
PMTs & CsI crystals are crossly connected.
Lead shielding(10 cm)
CsI detectors surround the CaMoO4 crystal
511keV signal is a opposite direction for momentum conservation.
(back to back cut)
CaMoO4 is surrounded by 14 CsI crystals & 14 PMTs.
CsI CaMoO4
6.5x5.5x30cm(12) x2.2x6cm (2)
9x9x6cm(#13 & #14) g

6. Data taking & E calibration
starttime
Pedestal area
Signal region
CaMoO4
400MHz FADC module
2.5ns/bin(total 80us), 32000ch
(flash analog to digital converter)
CsI
64MHz FADC module
15.625ns/bin(60us), 4000ch
Area of signal is photoelectrons
Used sources of 22Na
(511keV, 1274keV) & 241Am(59keV)
Also from BG peaks of 137Cs
(662keV) & 40K(1460keV)
(keV)
22Na =>511, 1,274 keV peak for CsI # 8

7. E resolution of CaMoO4 w/ 22Na source
Charge spectrum
511 keV
for 22Na source
CaMoO4 resolution is 12.2%
Resolution of CsI 14 crystals are between ~4% and ~12%

8. Multiplicity of CsI hits
2sigma cut
CsI 2
Using 2sigma CsI cut for 511keV
energy threshold of ~50keV
2sigma cut

9. Background spectrum of CaMoO4 detector measured at Y2L
For CsI crystal
Included background
0 CsI hit
1 CsI hit
2 CsI hit (~50keV threshold)
+ CsI 511keV ±2*σ cut
+ b2b cut(triple coincident events)
Q-value region(2sigma)
0hit
1hit
2hit

10. Background spectrum by triple coincident
Q-value = 628+1,022 = 1,650keV
Energy of Camoo4+2CsI(keV)
Preliminary bg Limit is a comparable best!!!.
A.S Barabash paper(received : November 1996); 1.9×1020y (for the (0ν+2ν)β+EC)
Abundance efficiency

11. Simulation of k40(1460keV) from pmt
Q-value position
2gamma position
PMT
40K (in Quartz)
CsI E(keV)
CaMoO4
CaMoO4 E(keV)
40K contamination in the PMT measured with HPGe
504±72 mBq/PMT(~0.5Hz->~0.05 gammas/sec)

12. Data & Simulation of k40 Data
Q-value region
Data
G4 simulation
1460keV line
1460keV line
662keV line
100,000 events generation result with 1,460keV gamma
a ~4evt/100,000evt in the Q-value position
 59events are expected from simulation
 <10% of the background events

13. 40K backgrounds We used 1inch pmt in the middle of the experiment
662keV
1460keV
1inch + 3 inch pmt
3 inch pmt
We used 1inch pmt in the middle of the experiment
for the other SrCl2 crystal test
40K contamination increased by nearly 30%

14. U backgrounds for DBD U = ~ 28.7 ppt = 2.87X10-11 g/g :
CaMoO4 crystal have a Uranium internal background.
beta- alpha coincidence can be measured to measure U contamination.
The fit gives 229us with exponential shape.
This is consistent with the expected decay time of 231us.
U = ~ 28.7 ppt = 2.87X10-11 g/g :
we obtained U contamination as 0.37 mBq/kg
Ultimate goal for 100Mo DBD experiment = 0.05 mBq/kg

15. Summary Neutrino mass can be studied with 100Mo & 92Mo
We are installed by triple gamma coincidence of 92Mo and CsI
Now Preliminary BG Limit is a comparable best.
Our setup can be measured U contamination by beta-alpha coincidence

16. Thank you !

18. E resolution of CaMoO4 with 22Na source
Charge spectrum
511 keV
Cluster spectrum
This is the charge spectrum of camoo4. we got with Na-22 source. The energy resolution is 12.2%.
And this is the number of cluster distribution with the same source and we got a better energy resolution at 511keV gammas line, and it is 8.1%.
The higher energy peak is 1274keV from the source,
and we will use clustering spectrum for lower energy and charge sum for higher energy region. But for present analysis I will use only charge distribution for energy.
For high energy analysis
For low energy analysis
We observed nonlinearity in the case of clustering spectrum
since the clusters are overlapped.
But for present analysis I will use only charge distribution for energy.

19. Simulation for detection efficiency
CsI 511 keV
2gamma=1022keV
Next I will show the efficiency of 0 nu m0-92 decay events .
I studied detection efficiency with g4 simulation by producing mono energetic positron inside camoo4 crystal.
First spectrum is a total E deposited in CsI array.
Right spectrum is efficiency for CsI 2gamma,
and then Total efficiency is 15.09% for camoo4 628keV and CsI 2gammas.
The efficiency of 0 nu 92Mo
decay events.
CsI efficiency = 15.46%
Total efficiency = 15.09%
camoo4 628 keV
&2gamma 1022keV