Status of 100Mo based DBD experiment J. H. So Kyungpook National University 2nd International Workshop on Double Beta Decay search at KRISS

Theory issues 1/T0n 1/2 = G0n(E0,Z) |M0n|2 <mbb>2, G0n(E0,Z) : phase space factor (~ Qbb5) : higher Q-value is better. M0n-Nuclear Matrix Element, hard to calculate Uncertain to factor 2-10, isotope dependent Motivation to measure several isotopes Experimental limits : T0n 1/2 = (ln2/1.64) x 6 x1026   (a/A)  (M T/B R) at @ 90% C.L. B = background index in cts/(keV kg y) R = FWHM energy resolution at Qbb in keV M = mass of detector in kg, A = mass number of candidate material e = detection efficiency at Qbb, a = bb isotope fraction (Enrichment), t = measured time in years

Experimental methods for 0n DBD (e factor) Source  Detector (calorimetric technique)  + high energy resolution +100% efficiency - no event topology + event shape reconstruction low energy resolution low efficiency e- source detector Source  Detector  If you use the calorimetric technique : Poor energy resolution can mask the peak of 0n. Signature: shape of the two electron sum energy spectrum two neutrino DBD continuum with maximum at ~1/3 Q R = 5% sum electron energy / Q neutrinoless DBD peak enlarged only by the detector energy resolution

Energy resolution issue (R factor) NIMA 584 (2008) 334 A.N. Annenkov et. al. At least, 4-5% of energy resolution will promise to separate the 0n energy peak with 2n energy spectrum for 0n DBD search with 100Mo based crystal.

Why 40Ca100MoO4 scintillator? (a, B factor) 100Mo is one of promising candidate material for 0n DBD search. (Natural Abundance : 9.63%) The enrichment of 100Mo is concerned with bb isotope fraction factor (a factor). The natural Ca have been composed by 40Ca (N.A : 97 %) and 48Ca (N.A : 0.187 %). 48Ca is also a candidate material of DBD. We need to use 48Ca distilled crystal to reduce the background (B factor in previous formula).

BG Spectrum of SB29 for 80 days Raw data Anti-coincidence with front and back of 4p detector for internal BG

New 40C100MO crystal from Russia SB35 SB28 CMO-3

Schematics CsI channel Preamp DAQ CsI channel FADC 400MHz CsI channel 10 times amplified for CMO Preamp DAQ FADC 64MHz CsI channel 10 times amplified for CsI 137Cs gamma ray source : 661-keV Trigger conditions - Threshold : 25 ADC (1V/1024 = 1ADC) - Pulse width : 200 ns - Photon number : 6

Light output / energy resolution of SB35 Resolution : 30% (FWHM) Mean : 2.88 x 105 SB35 Resolution : 16% (FWHM) Mean : 5.97 x 105 CMO_3 Resolution : 16% (FWHM) Mean : 6.79 x 105

Upgrade of 4p CsI tagging detector Previous setup Future setup CsI(Tl) CsI(Tl) CsI(Tl) CsI(Tl) CsI(Tl) CsI(Tl) CsI(Tl) CsI(Tl) 14 CsI channel + 14 PMT 12 CsI channels (side) were shared a PMT with neighbor channel. 14 CsI channel + 26 PMT 12 CsI channels (side) will be attached with 2 PMTs. 14 new PMTs (12 for upgrade and 2 extra) are prepared at KNU, and ready to test.

New DAQ machine DAQ machine for DBD at Y2L : kims10 Current DAQ machine has used for 4 years and data storage is not enough for our new experiment. New machine has been prepared at KNU, we are installing the software for data taking. SB35 is running with old kims10 machine. After this running, we will replace the DAQ machine to new one.

Upgrade of external shielding 12 cm CsI(Tl) Lead 15 cm for external shield Poly-ethylene 20 cm 40Ca100MoO4 N2 gas flowing 100 cm

Upgrade of external shielding CsI(Tl) Front side 23 cm 12 cm Upper View Lead 15 cm for external shield N2 gas flowing Poly-ethylene 20 cm 3 inch PMT : 13 cm + 7 cm 30 cm 3 inch PMT : 13 cm + 7 cm + CsI 6 cm Extra space : 14 cm 100 cm 160 cm

360 cm 90 cm 140 cm 4p Detector Rn Detector 110 cm HPGe New 4p Detector 100 cm 160 cm Ukraine CaMoO4 Setup 400 cm 220 cm 140 cm 80 cm

Summary and Future Plans SB35 has better performance than the previous crystals. (SB28, SB29) We took the background data for 3 weeks, it will be taken for 2 month with 4p CsI tagging detector. #14 of PMTs have been prepared at KNU to upgrade the 4p CsI tagging detector. The external shield will be required to upgrade for external background shielding. (lead and poly-ethylene) The DAQ machine already have been prepared to replace the old machine.