LENA Scintillator Characterization Transregio 27 SFB-Tage in Heidelberg 9/10. Juli 2009 Michael Wurm

Outline Properties of Scintillation Signal Scattering Length Experiment Light Yield Time Resolution LENA Scintillator Characterization – Michael Wurm, TUM1

LENA SCIENTIFIC GOALS Low-Energy Neutrino Astrophysics SCIENTIFIC GOALS  Nucleondecay  Supernova neutrinos  Diffuse SN neutrinos  Geoneutrinos  Solar neutrinos  Atmosphericneutrinos  Neutrino propertiesby reactors/accelerators  Indirectdark matter search Liquid Scintillator ca. 50kt PXE/LAB Inner Nylon Vessel radius: 13m Buffer Region inactive, Dr = 2m Steel Tank, PMs r = 15m, h = 100m  high demands on the optical transparency of the scintillator Water Cherenkov Veto 1500 PMTs, Dr > 2m Egg-Shaped Cavern about 10 8 m 3 Overburden: 4000 mwe

Signal Energy and Timing Energy Resolution Light Yield (/MeV):10 4 Photoactive Coverage: 30% PMT Photoefficiency:20% + Light Absorption/Scattering Photoelectrons/MeV<600 e Light intensity in distance r: I 0 initial intensity Lattenuation length: LENA Scintillator Characterization – Michael Wurm, TUM3

Signal Energy and Timing Energy Resolution Light Yield (/MeV):10 4 Photoactive Coverage: 30% PMT Photoefficiency:20% + Light Absorption/Scattering Photoelectrons/MeV<600 Timing Resolution Fluorescence constants: fast componentca. 3ns slow component(s)>20ns Time of flight diff. O(100ns) Light Scattering Leading edge determines timing Trailing edge for particle ID Light scattering has impact on both light yield and pulse shape... LENA Scintillator Characterization – Michael Wurm, TUM4

Microscopic Processes Mie Scattering off small particulates (  m) in the liquid anisotropic emission increased forward scattering amplitude, depending on diameter removable by filtering θ θ Rayleigh Scattering off bound electrons in the scintillator anisotropic emission: fully polarized for orthogonal parallel to light direction Absorption/Reemission off organic molecules/impurities in the liquid isotropic re-emission: depends on wavelength/production process LENA Scintillator Characterization – Michael Wurm, TUM5

Experimental Setup measurement at several angles and for both polarizations determines contributions of Rayleigh scattering, absorption-reemission etc. =430±5nm x10 -5 monitors beam intensity measures scattered intensity LENA Scintillator Characterization – Michael Wurm, TUM6

Exemplary Measurement Result parallel to beam orthogonal to beam Sample: Dodecane Wavelength: 415nm Q=N s /N b is the (corrected) ratio of PM intensities  main contribution: Rayleigh scattering (large polarization difference)  no discernible increase in forward scattering: minor Mie-contribution  small orthogonal component at 90°: absorption/re-emission processes LENA Scintillator Characterization – Michael Wurm, TUM7

Scattering Length Results  no hints for Mie-scat.  anisotropic scattering in good agreement with Rayleigh expectation  correct wavelength- dependence found  literature values for PC, cyclohexane correctly reproduced Results for =430nm L S = 22±3 m after purification in Al 2 O 3 -column

Corrections and Uncertainties  unevenness of sample glass surface:4%(unc.)  beam reflection on glass, alignment, refractive index:0.3%(cor.)  background subtraction of glass scattering:diff.(unc.)  scattering solid angle (PM-S field of view):4%(unc.)  variation of PM-S efficiency with scattering angle:7%(unc.)  relative photoefficiency of the PMs:7%(cor.)  greyfilter transmission (wavelength-dependent):3.4%(cor.)

MC Simulation of Light Yield Input Parameters:  event in the center  10 4 photons/MeV  LENA radius: 15m  optical coverage: 0.3  photoefficiency: 0.2  attenuation length (from previous experi- ments at MPIK, TUM and SNO+ R&D)  overall range: photoelectrons/MeV (optimum: 600pe/MeV) corresponding energy resolution at 1MeV: 7.1% to 4.6%  yield could be increased by state-of-the-art photocathodes (  ->40%) LENA Scintillator Characterization – Michael Wurm, TUM10

Impact on Time Resolution Rise time determines resolution. General trends:  fast fluorescence component has largest impact on both rise time t s and decay flank  s  no effect of refractive index  lower scattering length smears out signal: t s larger  increase in attenuation length decreases t s LENA Scintillator Characterization – Michael Wurm, TUM11

Summary Scattering length of all current LENA scintillator candidates has been measured. Impact on both light yield and time resolution was tested. LAB provides larger light yield, while PXE (+C12) offers better time resolution. Scattering length of all current LENA scintillator candidates has been measured. Impact on both light yield and time resolution was tested. LAB provides larger light yield, while PXE (+C12) offers better time resolution. LENA Scintillator Characterization – Michael Wurm, TUM12