R&D on Liquid-Scintillator Detectors R&D and Astroparticle Physics Lisbon, January 8th 2008 Michael Wurm Technische Universität München

Organic Liquid Scintillators high light yield fast fluorescence decay particle-dependent response good energy resolution time resolution of ns background discrimination solar, geo ‘s, 2  0 proton decay all handling of large volumes possible purification solubility of foreign atoms large target mass, self-shielding high radiopurity, low threshold doping of the target all solar ‘s 2  0, reactor ‘s target consists of Hydrogen and Carbon free protons high p/n ratio antineutrinos proton decay liquid scintillator organic → liquid-scintillator detectors are adapted for rare-event searches, such as low-energetic neutrinos, proton decay and 2  0 decay → detectors can be adjusted to the detection of individual particles

Upcoming liquid-scintillator detectors: SNO+/++ 1kt NOvA 30kt LENA, 50kt HanoHano, 10kt or more SuperNEMO LENS >200t Daya Bay, Angra …

Borexino – a running LS experiment 300t of PC, Ø 13m, 2200 phototubes light yield: 500 pe/MeV energy resolution: 1 MeV threshold: hardware: 40keV 14 C: ~200keV pulse shape discriminitation of ,  statistical at a level of ~10 -3 high-level radiopurity: e.g. U/Th contamination < g/g 7 Be ‘s already measured pep, CNO ‘s seem well feasible 210 Po  ‘ s 7 Be ‘ s

SNO+ SNO++ replacing the D 2 O inside the acrylic sphere with liquid scintillator (LAB) physics potential: solar ’s pep, CNO reactor ’s oscillation dip terrestrial ’s favourable S/B ratio ~500 SN events (10kpc) loading the scintillator with 0.1% Neodynium → kg 150 Nd: 2  3.3 MeV physics potential: large rates: spectral fit to 2 /0 signals predicted potential: masses down to meV

LENA a multi-purpose observatory solar neutrinos 5x Be e events per day sign of time-dependent fluctuations? pep (210ev/d), 8 13 C (360/a) → test MSW transition region CNO contribution to fusion Supernova neutrinos 2x10 4 ev for 8 different reaction channels → disentangle neutrino flavours, flux and spectral information mass hierarchy,  13, MSW terrestrial anti-neutrinos ~10 3 events per year relative crust-abundancies of U/Th favourable S/B conditions look for a georeactor of >2TW proton decay into K + favoured by SUSY,  4  yrs (90% C.L.) Wurm et al., PRD 75 (2007) , astro-ph/ Hochmuth et al., Astrop.Phys 27, 21, hep-ph/ T. Marrodán Undagoitia et al., PRD 72 (2005) _ Diffuse SN neutrinos 2-20 antineutrinos per year excellent background rejection: 1ev/yr spectroscopy possible: info on both SN rate (z<2) and SN models Neutrino/Beta Beams Indirect Dark Matter Search

Scintillator Components Solvent PC, PXE, LAB …target fp/p/n-ratios purification, addition of oilenergy transfer to fluor propagation of scint. light Wavelength Shifter (Fluor) PPO, bisMSB, PMP …signal decay times combinations possiblelarge Stoke‘s shifts no self-absorption Additions n/ catchers (Gd, In …)stability of the scintillator  candidates (Nd, …)absorption of scint. light all these properties have to be investigated …

TUM light yield attenuation length scattering length fluorescence time & spectra

Solvent Candidates LAB, C H density: 0.86 kg/l light yield: ~100% fluorescence decay:  ~ 6ns attenuation 430nm: ~20m PXE, C 16 H 18 density: 0.99 kg/l light yield: ~ ph/MeV fluorescence decay:  ~ 3ns attenuation 430 nm: ≤12m (mostly scattering) +80% Dodecane, C 12 H 26 density: ~0.80 kg/l light yield: ~ 85% fluorescence decay slower attenuation length increases! In terms of solvent transparency, a 30m diameter detector is feasible. effects and complexity of purification have to be considered.

PPO, C 15 H 11 NO primary fluor absorption band: nm emission band: nm bisMSB, C 24 H 22 secondary fluor absorption band: nm emission band: nm 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 The Aim: A detailed MC study of light production and propagation in a large-volume detector like LENA.

Further R&D on liquid scintillators Intrinsic Purity of the Scintillator: Production, Handling, Transport Purification Methods, both Transparency and Radiopurity: Column-Chromotography (Silica Gel, Al 2 O 3 etc.), Distillation, Water-Purging … Scinitillation Light Production and Propagation: Wavelength-dependent emission, absorption and scattering of the light Experiments 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)

LENA design 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 (?) target volume 50kt of liquid scintillator h 100m, Ø 26m buffer volume solvent&quencher thickness: 2m muon veto panels of plastic scintillator nylon vessel steel tank ~ 13k phototubes water tank >5m n shielding active  veto (?) egg-shaped cavern h 120m, Ø 50m

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

Liquid-Scintillator Detectors provide good energy resolution, particle identification and favourable background conditions at a relatively low price. Large-volume detectors like LENA will be multi- purpose observatories and will address a wide range of interesting questions comprising particle, astro-particle and geophysics. Purity and purification of materials, construction of large & deep underground caverns and optimization of photodetection are examples for possible synergies with other experiments (LAGUNA: Memphys, Glacier & Lena). Outlook