1. Rayleigh scattering measurement for Super-Kamiokande Gd project Ryosuke AKUTSU, Institute for Cosmic Ray Research, Univ. of Tokyo / NNN2015 Physics target : 1. Discovery supernova relic neutrinos 2. Improve pointing accuracy for galactic supernova. 3. Precursor of nearby supernova by Si burning neutrinos. 4. Reduce proton decay background. 5. Neutrino/anti-neutrino discrimination (Long-baseline and atmospheric) 6.Reactor neutrinos 200 m 3 tank with 240 PMTs 15 m 3 tank to dissolve Gd 2 (SO 4 ) 3 ● EGADS is a Gd 2 (SO 4 ) 3 loaded water Cherenkov detector for studying the effect of Gd 2 (SO 4 ) 3 on the water transparency, all the materials and the environmental neutron background. ● Loading EGADS with 0.2% Gd 2 (SO 4 ) 3 concentration caused about 8% decrease in the transparency from the pure water, which was measured by UDEAL. The performance of Super-K could be affected by the change of transparency for a given adding Gd 2 (SO 4 ) 3 concentration, depending on the variation of β and γ. 4. Measurement principle ● Since only the scattered photons are needed for the measurement, a device which can generate linearly polarized laser is used to observe redirected photons of the laser due to scattering as hits of PMTs inside EGADS. 8. Summary & future plan cosθ Wave length [nm] β 0.2% / β 0.1% Top Bottom Barrel ● Only the hits in the barrel part have been used for evaluating scattering coefficient to avoid a background contamination which is thought as the halo component of the laser. But, the effect of the contamination is not estimated yet. ● The measured change of β from 0.1% to 0.2% Gd 2 (SO 4 ) 3 concentration has been compared with a expected value which is calculated a spectrometer measurements and UDEAL with an absolute value of attenuation coefficient as the model used in Super-K. Model in Super-K Total, Absorption Rayleigh sct., Mie sct. ● A Rayleigh scattering measurement in EGADS was conducted. Preliminary Assumed negligible background contamination Assumed 100% sct. Assumed 20% sct. & 80% abs. Assumed 10% sct. & 90% abs. ● Data were compared between 0.1% and 0.2% Gd 2 (SO 4 ) 3 concentrations. ● Assuming that the contamination of the laser halo is negligible, the resulting relative change of scattering coefficient, while still consistent with zero, is at most 10%. ● Evaluation of the contamination for the halo component by MC and data. ● Using data and an reliable Monte Carlo simulation(MC), obtain the relative change of scattering coefficient from the pure water to the % Gd 2 (SO 4 ) 3 loaded water. The logo is not officialized yet Polarization vector of incident photon Incident direction Scattered direction Φ Ψ 3. Motivation Y ・Observe light originating from the laser by PMTs. ・The laser intensity was adjusted to be about 1% occupancy of PMTs. ・Data was taken by periodic trigger with 200 or 30 Hz. ・The laser injecting device was put at the center of EGADS. ・The scattered photon and laser intensity measurements were performed by turns. ・The observed laser intensity was stable with about 3%. Corrected hits/event Φ [rad] 6. Angular distributions ● Corrections : distance between each PMT and laser, PMTs acceptance, relative quantum efficiency of PMTs, dark hits subtracting ∝β∝β ● The observed hits patterns in the barrel of the tank were consistent with a expected curves which are derived by the differential cross section of Rayleigh scattering. Ryosu ke ● Super Kamiokande(Super-K) is an underground water Cherenkov detector and has operated since April 1996. ● The Gd project adds 0.2% Gd 2 (SO 4 ) 3 to the current Super-Kamiokande detector with ultra pure water. This will give a high neutron detectability by the large cross section of Gd for thermal neutron(about 1.5 billion times that of Hydrogen), so that we can distinguish between neutrinos and anti-neutrinos by a delayed coincidence technique. 1. Super-Kamioknade detector & Gd project 5. Set up Gd loaded water circulation system Water transparency measurement (UDEAL) 2. EGADS detector - E valuating G adolinium’s A ction on D etector S ystems - Clock (200Hz/30Hz) DAQ (ATM) LD(375,405nm) Gas laser(337nm) Optical fiber Z wire 4.7m Cables of PMTs Scattered photons measurement Laser intensity measurement 5.2m Emit the linearly polarized laser Absorb or reflect the laser ZOOM About 1m travel length 7. Relative variation of β Corrected Hits/event/PMT 337nm : USHO KEN1020 (600ps) 375nm : SCIENTEX OPG-NIM (1-5ns) 405 : SCIENTEX OPG-1000-NIM (70-80ps)