R&D on Liquid-Scintillator Detectors

1. R&D on Liquid-Scintillator Detectors R&D and Astroparticle PhysicsLisbon, January 8th 2008Michael WurmTechnische Universität München

2. Organic Liquid Scintillators scintillator liquid organic → liquid-scintillator detectors are adapted for rare-event searches,such as low-energetic neutrinos, proton decay and 2b0n decay → detectors can be adjusted to the detection of individual particles

3. Upcoming liquid-scintillator detectors: NOvA30kt SNO+/++1kt Daya Bay, Angra … LENS>200t LENA, 50kt SuperNEMO HanoHano, 10kt or more

4. Borexino – a running LS experiment 300t of PC, Ø 13m, 2200 phototubes light yield:500 pe/MeV 210Poa‘s 7Ben‘s pulse shape discriminitation of a,b statistical at a level of ~10-3 high-level radiopurity:e.g. U/Th contamination <10-17 g/g 7Ben‘s already measured pep, CNOn‘s seem well feasible energy resolution:0.04 @ 1 MeV threshold:hardware: 40keV14C: ~200keV

5. SNO++ SNO+ • replacing the D2Oinside the acrylicsphere with liquidscintillator(LAB) • physicspotential: • solar n’s pep, CNO • reactor n’soscillation dip • terrestrial n’sfavourable S/B ratio • ~500 SN n events (10kpc) • loading the scintillatorwith 0.1% Neodynium → 50-500 kg 150Nd:2b0n@ 3.3 MeVphysicspotential: • large rates:spectral fit to2n/0n signals • predicted potential:n masses down to80 - 30 meV

6. solar neutrinos 5x1037Be ne events per day sign of time-dependent fluctuations? pep (210ev/d), 8B@13C (360/a) → test MSW transition region CNO contribution to fusion LENAa multi-purpose observatory proton decay into K+n favoured by SUSY, t < 1035 yrsefficiency ~67% as K+ is visible!1 background event in 10 yrs→ tp > 41034 yrs (90% C.L.) Supernova neutrinos 2x104 ev for SN@10kpc 8 different reaction channels → disentangle neutrino flavours, flux and spectral information n mass hierarchy,q13, MSW T. Marrodán Undagoitia et al., PRD 72 (2005) 075014 terrestrial anti-neutrinos ~103 events per year relative crust-abundancies of U/Thfavourable S/B conditionslook for a georeactor of >2TW Diffuse SN neutrinos 2-20 antineutrinos per year excellent background rejection: 1ev/yrspectroscopy possible: info on both SN rate (z<2) and SN models Hochmuth et al., Astrop.Phys 27, 21, hep-ph/0509136 _ Neutrino/Beta BeamsIndirect Dark Matter Search Wurm et al., PRD 75 (2007) 023007, astro-ph/0701305

7. Scintillator Components Solvent PC, PXE, LAB … target fp/p/n-ratiospurification, addition of oil energy transfer to fluor propagation of scint. light Wavelength Shifter (Fluor)PPO, bisMSB, PMP … signal decay timescombinations possiblelarge Stoke‘s shifts no self-absorption Additionsn/n catchers (Gd, In …) stability of the scintillatorbb candidates (Nd, …) absorption of scint. light all these properties have to be investigated …

8. Work @ TUM fluorescence time & spectra scattering length attenuation length light yield

9. Solvent Candidates LAB, C16-19H26-32 density: 0.86 kg/l light yield: ~100% fluorescence decay:t ~ 6ns attenuation length @ 430nm:~20m PXE, C16H18 density: 0.99 kg/l light yield:~10.000 ph/MeV fluorescence decay:t ~ 3ns attenuation length @ 430 nm: ≤12m (mostly scattering) +80% Dodecane, C12H26 density: ~0.80 kg/l light yield: ~85% fluorescence decay slower attenuation length increases! • effects and complexity of purification have to be considered. In terms ofsolvent transparency, a30m diameterdetectoris feasible.

10. Possible Wavelength Shifters • large detectors require Stoke‘s Shift to wavelength of 430 nm where scintillator is more transparent • a combination of a primary and a secondary shifter can be used→ might lead to self-absorption • fluors with large Stoke‘s Shifts like PMP have to be tested • other parameters like fluorescence time, solubility etc. have to be considered as well PPO, C15H11NO primary fluor absorption band:280-325nm emission band:350-400nm bisMSB, C24H22 secondary fluor absorption band:320-370nm emission band:380-450nm The Aim: A detailed MC study of light production and propagation in a large-volume detector like LENA.

11. Further R&D on liquid scintillators • Intrinsic Purity of the Scintillator:Production, Handling, Transport • Purification Methods, both Transparency and Radiopurity:Column-Chromotography (Silica Gel, Al2O3 etc.),Distillation, Water-Purging … • Scinitillation Light Production and Propagation:Wavelength-dependent emission, absorption and scattering of the lightExperiments and MC simulations for energy & time resolution • Investigation of New Materials:solvents: high transparency, short signal decay time …fluors: overlap of absorption with solvent emission, large Stoke‘s shifts (>430nm)

12. muon vetopanels of plastic scintillator LENA design target volume50kt of liquid scintillatorh 100m, Ø26m • detector location: • cavern or deep-sea • overburden of >4000 m.w.e. • for most purposes: far away from nuclear power plants • upright posititon favourable for buoyant forces, assembly etc. • detector dimensions adjusted to transparency of the scintillator • 30% optical coverage • light yield: >200 pe/MeV • buffer shields the target from external radioactivity • radiopurity as in Borexino (?) nylon vessel buffer volume solvent&quencherthickness: 2m steel tank~13k phototubes water tank>5mn shieldingactive m veto (?) egg-shaped cavernh 120m, Ø50m

13. R&D needs of the Detector • Construction of the Cavern:maximum depth, shape, maximum size,infrastructure for scintillator, (liquid) gases … • Materials of the Detector:treatment of the steel (inertness, low reflectivity),construction of nylon vessel, … • Photo-Detection:PMTs or alternative light detectors,optimization of optical coverage (light concentrators …) • Infrastructure of HV, Electronics

14. Outlook Liquid-Scintillator Detectors provide good energyresolution, particle identification and favourablebackground conditions at a relatively low price. • Large-volume detectors like LENA will be multi-purpose observatories and will address a widerange of interesting questions comprisingparticle, astro-particle and geophysics. • Purity and purification of materials, constructionof large & deep underground caverns andoptimization of photodetection are examplesfor possible synergies with other experiments(LAGUNA: Memphys, Glacier & Lena).