1. Double Beta Decay With 20-ton Metal Loaded Scintillators A Detector for DUSEL? Frank Calaprice Princeton University Aldo Ianni LNGS

2. The Borexino Detector 14 C ~ 3 x 10 -18 U/Th <10 -17 85 Kr ~ 0.35 cpd/ton Cleanliness level 25 MIL-STD 1246C

3. General Idea (Similar to SNO+) Use radiopurity MEASURED in the Borexino detector Use preliminary data on Nd-loaded LS based on PC Goal: 1.Search for double beta decay with a 20ton- scale high purity LS detector 2.SNO+ proposal is for 1000 ton LS.

4. Basic working assumptions: 1.T  1/2 = 7 x 10 18 yr 2.50 meV neutrino mass (inverted hierarchy) T  1/2 = 1.2 x 10 25 yr 3.Photon yield = 12000 / MeV (PC liquid scintillator) 4.QE = 0.35 (new high QE PMTs) 5.Coverage = 0.85 6.Low radioactivity PMTs: ~ 30 mBq/PMT

5. The Detector: basic idea FM

6. Backgrounds: PMTs + Steel Sphere ~ 40 Bq 208 Tl from nylon (<1ppt in Th) : –0.861 MeV + 2.614 MeV  ’s 12% BR –need to define FM –Radiopurity of nylon can be measured in CTF at ppt level or below. Intrinsic Th in Scintillator: –Borexino 10 -17 g/g gives ~ 1 c/yr around peak Th coming with Nd ??? –Required ~ 10 -15 gTh/gNd

7. 1-kton SNO+ vs 20-ton scale detector: 1kton20ton Nd concentration0.1%*1%* Nd mass nat. [kg]1000195 150 Nd [kg]5612 Light yield [pe/MeV] ~400**~700** * Light absorption by Nd limits concentration **For comparison both detectors are assumed to have 50% PMT coverage.

8. Nd concentration10 g/l20 g/l32 g/l Relative light yield to pure LS 0.70.60.5 150 Nd mass [kg] 10.921.935.0 Resolution FWHM [%] 2.542.773.05 Rate 2 [Bq] 0.140.280.45 Rate 0 [c/yr] 2.55.18.1 S / B in [Q  -1 ,Q  +1  ] 1.42.54.0 Natural abundance, 50 meV neutrino, 20-ton FM: i)1 c/yr from nylon, ii) 1 c/yr from internal Th, iii) << 1 c/yr external ii)Muon-induced activities above 3 MeV are short-lived and vetoed

9. Nd concentration10 g/l20 g/l32 g/l 150 Nd mass [kg] 98195313 Rate 0 [c/yr] 123 S / B in [Q  -1 ,Q  +1  ] 0.40.51.2* 50% 150 Nd enrichment, 10 meV neutrino, 20-ton: In 5 years the uncertainty in the measurement is 35%

14. Breakdown of costs: ItemCost [$M]* Nd0.2 WT + SSS2.0 PMTs5.0 Nylon Vessel1.0 Electronics5.0 LS (solvent)0.1 solute0.1 Enrichment1.0 Total~15 Add $3M for new purification system if LNGS system is not used.

15. Roadmap: Measure radiopurity of nylon with present CTF Preliminary tests of light propagation and energy resolution in small test chamber (~5 m 3 ). Rebuild CTF with Stainless Steel Sphere –Study Nd-loaded LS Light propagation Radiopurity Energy resolution Search for double beta decay at 50 meV sensitivity with CTF system. Build larger (~50 ton LS?) system with optimum resolution/background for 10 meV at DUSEL?