Prospects for 7 Be Solar Neutrino Detection with KamLAND Stanford University Department of Physics Kazumi Ishii

June 24, 2005INT Workshop2 KamLAND Collaborators

June 24, 2005INT Workshop3 Outline Neutrino Oscillation Measurement with Reactor Anti-neutrinos Solar Neutrinos Solar Neutrino Measurement and Background Liquid Scintillator Purification

June 24, 2005INT Workshop4 Neutrino Oscillations in Vacuum The weak interaction neutrino eigenstates may be expressed as superpositions of definite mass eigenstates The electron neutrino survival probability can be estimated as a two flavor oscillations:

June 24, 2005INT Workshop5 Reactor Anti-Neutrinos KamLAND was designed to measure reactor anti-neutrinos. 80% of total flux baseline km. KamLAND

June 24, 2005INT Workshop6 KamLAND Detector Electronics Hut Steel Sphere, 8.5m radius Water Cherenkov outer detector ” PMT’s 1 kton liquid- scintillator Inner detector ” PMT’s ” PMT’s 34% coverage 1km Overburden Buffer oil Transparent balloon, 6.5m radius

June 24, 2005INT Workshop7 Inside the Detector

June 24, 2005INT Workshop8 Determining Event Vertices Vertex determined using the photon arrival times at PMTs. Calibrated using sources deployed down the center of the detector. New vertex finding algorithm is under development to improve the performance for lower energy events.

June 24, 2005INT Workshop9 Determining Event Energies The “visible” energy is calculated from the amount of photo-electrons correcting for spatial detector response. The “real” energy is calculated from the visible energy correcting for Cherenkov photons and scintillation light quenching.

June 24, 2005INT Workshop10 4  Calibration 4  off-z-axis calibration device is under development.

June 24, 2005INT Workshop11 Detecting Anti-neutrinos with KamLAND KamLAND (Kamioka Liquid scintillator Anti- Neutrino Detector) d p e+e+ 0.5 MeV  2.2 MeV  n p 0.5 MeV  e e-e- Inverse beta decay e + p → e + + n E ~ T e + 1.8MeV The positron loses its energy then annihilates with an electron. The neutron first thermalizes then gets captured on a proton with a mean capture time of ~200  s. Prompt Delayed

June 24, 2005INT Workshop12 Selecting Reactor Anti-neutrino Events Δr < 2m 0.5μs < ΔT < 1000μs 2.6MeV < E p < 8.5MeV 1.8MeV < E d < 2.6MeV Veto after muons R p, R d < 5.5m e+e+ 0.5 MeV  2.2 MeV  0.5 MeV  Prompt Delayed

June 24, 2005INT Workshop13 Reactor Neutrino Oscillation Measurement Result KamLAND saw an anti-neutrino disappearance and a spectral distortion. KamLAND result combined with solar experiments precisely measured the oscillation parameters.

June 24, 2005INT Workshop14 Solar Neutrinos from the p-p Chain Reactions p + p  2 H + e + + e p + e - + p  2 H + e 99.75% 0.25% 2 H + p  3 He 86% 14% 3 He + 3 He   + 2p 3 He +   7 Be 99.89% 0.11% 7 Be + e -  7 Li + e 862keV & 383keV 7 Be + p  8 B 7 Li + p   +  8 B  8 Be + e + + e 8 Be   +  7 Be e flux is much greater than 8 B e flux!

June 24, 2005INT Workshop15 Solar Neutrino Spectrum Solar Neutrino Flux at the surface of the Earth with no neutrino oscillations. Uses the solar model, BS05(OP). We expect to see a few hundreds of events per day.

June 24, 2005INT Workshop16 MSW Effect  e ’s experience MSW effect in the Sun. For 7 Be e ’s, For E = 862keV &  m 2 =7.9x10 -5 eV 2 Possible sin 2 2 

June 24, 2005INT Workshop17 7 Be Solar Neutrino Detection Solar scatters off e -. The electron recoil energy is From e From  &  *Detection resolution is not included.

June 24, 2005INT Workshop18 Irreducible Radioactivity  ’s (1.46MeV) from 40 K in the balloon  ’s (2.6MeV) from 208 Tl decay in the surrounding rocks 14 C throughout the detector (less than ~200keV) 11 C from cosmic muons (more than 700keV) Most of the 40 K and 208 Tl background is removed with fiducial volume cut. Most of the 14 C and 11 C background is removed with energy cut.

June 24, 2005INT Workshop19 Current Reducible Radioactivity in KamLAND After fiducial volume cut is applied

June 24, 2005INT Workshop20 Current Radioactivity Levels in the Liquid Scintillator and Reduction Goals

June 24, 2005INT Workshop21 Removal of 222 Rn Distillation removed 222 Rn by a factor of 10 5 after dissolving 222 Rn in ~100ml of liquid scintillator. A detector that can measure very low amount of 222 Rn is under development.

June 24, 2005INT Workshop22 Removal of 210 Pb Since decay rate of 210 Pb is low, we study with 212 Pb. Most of Pb is ionic, but some is organic. Heating breaks the covalent bonds of organic Pb. Heating and distillation reduced the 212 Pb activity in a few liters of liquid scintillator by a factor of 10 4 to 10 5 after spiking it with 220 Rn increasing the 212 Pb activity by a factor of Adsorption by silica gel also reduced the 212 Pb concentration by a factor of 20.

June 24, 2005INT Workshop23 Removal of 40 K Distillation reduced the 40 K concentration in PPO by a factor of 10 2.

June 24, 2005INT Workshop24 Removal of 85 Kr 85 Kr is produced in nuclear reactors. Noble gas bubbling is under investigation. Distillation achieved nat Kr reduction by a factor of 10 6 after dissolving nat Kr in 80ml of liquid scintillator. A system to do inline monitoring of nat Kr levels during purification is under development.

June 24, 2005INT Workshop25 Test Distillation Tower Test distillation tower can run at a few L/hr. Actual distillation tower will purify the liquid scintillator at 2m 3 /hr.

June 24, 2005INT Workshop26 Purification System Construction

June 24, 2005INT Workshop27 Summary Neutrino oscillation parameters have been measured precisely by KamLAND with reactor anti- ’s and by solar experiments. 7 Be detection and testing the solar model is one of the KamLAND’s next goals. According to the best fit neutrino oscillation parameters, we expect that 7 Be ’s experience mainly just vacuum neutrino oscillations, and almost no MSW effect. KamLAND needs to reduce current background significantly. Background reduction studies are under way, and look promising.