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

The Borexino Detector 14 C ~ 3 x U/Th < Kr ~ 0.35 cpd/ton Cleanliness level 25 MIL-STD 1246C

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.

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

The Detector: basic idea FM

Backgrounds: PMTs + Steel Sphere ~ 40 Bq 208 Tl from nylon (<1ppt in Th) : –0.861 MeV 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 g/g gives ~ 1 c/yr around peak Th coming with Nd ??? –Required ~ gTh/gNd

1-kton SNO+ vs 20-ton scale detector: 1kton20ton Nd concentration0.1%*1%* Nd mass nat. [kg] 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.

Nd concentration10 g/l20 g/l32 g/l Relative light yield to pure LS Nd mass [kg] Resolution FWHM [%] Rate 2 [Bq] Rate 0 [c/yr] S / B in [Q  -1 ,Q  +1  ] 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

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

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.

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?