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

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

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

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+ + 628keV(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%

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) - 2.2x2.2x6cm (2) 9x9x6cm(#13 & #14) - 255g

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

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%

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

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

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

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)

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

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%

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

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

Thank you !

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.

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