KamLAND and Geoneutrinos Sanshiro Enomoto KamLAND Collaboration RCNS, Tohoku University 1. Review of Previous Results 2. Recent Improvements (Preliminary) 3. Future Prospects 4. Far Future Dreams Applied Antineutrino Physics 2007, APC Laboratory Paris, December

KamLAND Experiment observes low energy anti-neutrinos in the Kamioka Mine, Hida, Japan consists of 1000ton Liquid Scintillator, surrounded by 1845 PMT ’ s Reaction: 1000m Kamioka Mine 2002 Jan: Start data taking 2002 Dec: Evidence for reactor neutrino disappearance (145 days) 2005 Jan: Evidence of reactor neutrino spectral distortion (514 days) 2005 Jul: Investigation of geoneutrinos (749 days) 2007 Dec: 1491 day data accumulated

KamLAND Detector Yields light on ionization (8000 photons / MeV) Mainly consists of only C and H 20m Liquid Scintillator Liquid Scintillator 1000 ton Contained in plastic balloon 17-inch PMT inch 554 Detector Center Surrounded by (PMT : Photo Multiplier Tube, a photo sensor) PC: 20%dodecane: 20%PPO: 1.5 g/l

Antineutrino Detection Method time τ~210 μsec Two characteristic signals Clear event identification Great BG suppression

KamLAND Detector Japan Arc Kamioka Mine KamLAND Outer View KamLAND Inner View Photo Multiplier Tube Scintillator Container

Antineutrino Sources Nuclear Power ReactorsHPE (U/Th) in the Earth ~50% from surrounding crust ~25% from mantle

Reactor Neutrino Flux Calculation Example of Reactor Operation Data Neutrino Flux at KamLAND (no oscillation case) Japanese Reactors (95.5%): Operation data, including fuel burn-up, for each core are provided by operators. Korean Reactors (3.4%): Flux are calculated based on published electrical output Other Reactors (1.1%): Nominal power is assumed Total ~2% error (conservative)

Expected Geoneutrino Flux U-Series 2.3x10 6 [1/cm 2 /sec] Th-Series 2.0x10 6 [1/cm 2 /sec] Geoneutrino Flux Prediction BSE composition by [McDonough1999] Crustal composition by [Rudnick et al. 1995] Crustal thickness by CRUST 2.0 Uniform Mantle Model No U/Th in the Core With target protons, U-Series 32 events / year Th-Series ８ events / year Geoneutrino Origination Points Detectable at KamLAND (MC) South America Antarctic Australia KamLAND Greenland 50% within 500km 25% from Mantle [Earth.Plan.Sci.Lett, 258, 147 (2007)]

KamLAND Antineutrino Spectrum (expected) Neutrino Property Study Signature of Neutrino Oscillation Precision Measurement of Oscillation Parameters [Phys.Rev.Lett. 94, (2005)] Geoneutrinos: Neutrino Application Direct measurement of HPE in the Earth [Nature 436, 499 (2005)]

Geoneutrino Expected Rate and Spectrum Fiducial Volume: 408 ton Live-time: 749 days Efficiency: 68.7% Expected Geoneutrinos U-Series： 14.9 Th-Series：4.0 Backgrounds Reactor： 82.3±7.2 (α,n) ： 42.4±11.1 Accidental：2.38±0.01 BG total： 127.4±13.3

First Geoneutrino Result Fiducial Volume: 408 ton Live-time: 749 days Efficiency: 68.7% Expected Geoneutrinos U-Series： 14.9 Th-Series：4.0 Backgrounds Reactor： 82.3±7.2 (α,n) ： 42.4±11.1 Accidental：2.38±0.01 BG total： 127.4±13.3 Observed： 152 Number of Geoneutrinos: ＋19 －18 25 [Nature 436, 499 (2005)]

Spectrum Analysis Number of Geoneutrinos： % C.L. upper limit：70.7 events Significance 95.3% (1.99-sigmas) ＋15.6 －14.6 Parameters N U, N Th : Number of Geoneutrinos sin 2 2θ, Δm 2 : Neutrino Oscillation α 1, α 2 : Backgrounds Uncertainties KamLAND is insensitive to U/Th ratio → adopt U/Th ~ 3.9 from Earth science Discrimination of U and Th Total Number of U and Th Earth Model Prediction

Flux Prediction from Earth Models Scale Bulk Composition Fix Crustal Composition, Parameterize Mantle U+Th Mass [kg] Geoneutrino Flux [1/cm 2 /sec]

Comparison with Earth Model Predictions Consistent with BSE model predictions 99%C.L. upper limit too large to be converted to heat production (No Earth models applicable) U+Th Mass [kg] Geoneutrino Flux [1/cm 2 /sec] Earth Model Prediction KamLAND 1-σ Range KamLAND 99% Limit Total Terrestrial Heat Flow (44TW)

KamLAND Problem: Overwhelming Backgrounds Reactor Neutrino BG (α,n) BG 206 Pb 210 Bi 210 Po 210 Pb d 22.3 y stable d 222 Rn 3.8 d 13 C (α,n) 16 O n + p → n + p 210 Po decay rate error 14% Cross-section error: 20% Quenting factor error: 10%

Improvements New (α,n) Cross section data available Vertex reconstruction improved (for 210 Po decay rate) Proton quenching factor measured 210 Po- 13 C source calibration performed ⇒ (α,n) error reduced from ~26% to ~11% (α,n) Background error reduced Po-C Calibration (MC/Data)P quenching measurement

Improved Results (Preliminary) More statistics accumulated: 749 day to 1491 day (α,n) error reduced: ~26% to ~11% Reconstruction improved (off-axis calibration) Analysis improved: – Fiducial volume increased – Time variation included – Optimal event selection with figure-of-merit basis Preliminary

Geophysics with Improved Results (Preliminary) Earth Model Prediction KamLAND 1-σ Range KamLAND 99% Limit Error is reduced from 56% to 36% Consistent with BSE model predictions 99%C.L. upper limit is approaching to the total terrestrial heat Preliminary

Future Prospects LS Distillation in Progress ⇒ removes radioactivity by we remove these distilled scintillator Preliminary

Future Prospects If combined with the current 1491 day data, Error is reduced：from 36% to 25% (error is dominated by reactor neutrinos) Significance： % (3.96 sigmas) BEFORE AFTER we remove these Assuming: reduction of 210 Pb Enlarged fiducial volume (5.5m) Improved selection criteria 749 days livetime

Future Prospects 25% uncertainty 749 days after purification, combined with current 1491 day data Measurement error is comparable with Earth model predictions 99%C.L. limit can exclude some “ upper limit ” models 99% upper limit 1.6 times above BSE

Far Future Dreams: Directional Sensitivity Directional information provides: ・Rejection of backgrounds ・Separation of crust and mantle ・Earth tomography by multiple detectors Good News: ・Recoiled neutron remembers direction Bad News: ・Thermalization blurs the info ・Gamma diffusion spoils the info ・Reconstruction resolution is too poor Wish List: ・large neutron capture cross-section ・(heavy) charged particle emission and ・good resolution detector (~1cm)

Towards Directional Sensitivity 1 Neutron Capture Position (MC) Delayed Event Position (MC) 6 Li loading helps preserving directional information Large neutron capture cross-section: 940 barn 6 Li + n → α + T : no gamma-ray emission Natural abundance 7.59% Various chemical forms for Li loading are being tested …

Towards Directional Sensitivity 2 ~1M pixel imaging can achieve 1 cm resolution LS lends image intensifier 10cm CCD lens LS image intensifier CCD Fresnel lens Proper optics need to be implemented Sensitivity to 1 p.e. and high-speed readout required First step for LS imaging, just started … Muon Event ??? Isotope Decay Event ??? (Bis-MSB added)

Summary KamLAND, low-energy antineutrino detector, – determined oscillation parameters precisely – made first experimental investigation on geoneutrinos Recent updates with more stat. and less syst. err., – reduced geoneutrino measurement error from 54% to 36% – Upper limit is comparable with Earth model limits Further LS purification is in progress – will reduce error to ~25% – Measurement error will be comparable with Earth models R&D for directional sensitivity underway