水质契仑科夫探测器中的中子识别问题研究详解.ppt

水质契仑科夫探测器中的中子识别 张海兵 清华大学 2008.4.28, 南京 Neutrino Detection at Super-Kamiokande Neutrinos from Space Previous Searches for SRN Why Neutron Tagging? Methods of Tagging Neutron from Inverse βDecay Forced Trigger (FOG) Test with a Simulated Signal Experimental Setup Signal and Background in Forced Trigger Data Data Pre-process Distinctive Variables Neural Net Method Measurement of Neutron Capture Time Neutron Lifetime Tagging Efficiency Summary Neutron tagging in large water Cherenkov detector studied for the first time. Two methods tested at SK: * First Study of Neutron Tagging with a Water Cherenkov Detector ne Electron (e) nm Muon (m) The products are charged particles. The neutrino is observed by “seeing” the product of its interaction with water. Charged particles with β1/n emits Cherenkov light All 6 types of neutrino emitted when supernovae explode but only is most likely to observe. Detection of is the key step to see SRN at SK. Confirmed neutrinos from space Who’s next? Supernova relic neutrino (SRN)? Solar neutrino SN 1987A SK-I limit : 1.25 /cm2/s SK SRN Limits vs. Theoretical Predictions The result can be significantly improved if SK enhanced with neutron tagging capability. Neutron tagging plays a role in identifying inverse beta decay. A delayed coincidence technique can be used to identify reaction chain. Generate 500 additional “forced triggers” at the interval of 1us after primary trigger by e+. Search 2.2MeV candidates in the 500 us data pack. Threshold 5 cm Am/Be Am/Be neutron source embedded in BGO crystal n 5 cm Am/Be (1)Forced trigger case (2)Gadolinium case Source run (Am/Be+BGO) BG run (BGO only) – for neutron tagging efficiency study – Signal FOG: 500 BG events + one 2.2 MeV ? – for cross checking and background estimation – BG FOG: 500 BG events # of PMT hits time The main difficulty rests with how to extract the weak 2.2 MeV ? signal from heavy background, e.g. PMT noise and other low energy events . 2.2MeV ?